Communication pubs.acs.org/bc Facile and Stabile Linkages through Tyrosine: Bioconjugation Strategies with the Tyrosine-Click Reaction Hitoshi Ban,‡ Masanobu Nagano,‡ Julia Gavrilyuk, Wataru Hakamata, Tsubasa Inokuma, and Carlos F. Barbas, III* The Skaggs Institute for Chemical Biology and the Departments of Chemistry and Molecular Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, California 92037, United States S Supporting Information * ABSTRACT: The scope, chemoselectivity, and utility of the click-like tyrosine labeling reaction with 4-phenyl-3H-1,2,4triazoline-3,5(4H)-diones (PTADs) is reported. To study the utility and chemoselectivity of PTAD derivatives in peptide and protein chemistry, we synthesized PTAD derivatives possessing azide, alkyne, and ketone groups and studied their reactions with amino acid derivatives and peptides of increasing complexity. With proteins we studied the compatibility of the tyrosine click reaction with cysteine and lysine-targeted labeling approaches and demonstrate that chemoselective trifunctionalization of proteins is readily achieved. In particular cases, we noted that PTAD decomposition resulted in formation of a putative isocyanate byproduct that was promiscuous in labeling. This side reaction product, however, was readily scavenged by the addition of a small amount of 2-amino-2-hydroxymethyl-propane-1,3-diol (Tris) to the reaction medium. To study the potential of the tyrosine click reaction to introduce poly(ethylene glycol) chains onto proteins (PEGylation), we demonstrate that this novel reagent provides for the selective PEGylation of chymotrypsinogen, whereas traditional succinimide-based PEGylation targeting lysine residues provided a more diverse range of PEGylated products. Finally, we applied the tyrosine click reaction to create a novel antibody−drug conjugate. For this purpose, we synthesized a PTAD derivative linked to the HIV entry inhibitor aplaviroc. Labeling of the antibody trastuzumab with this reagent provided a labeled antibody conjugate that demonstrated potent HIV-1 neutralization activity demonstrating the potential of this reaction in creating protein conjugates with small molecules. The tyrosine click linkage demonstrated stability to extremes of pH, temperature, and exposure to human blood plasma indicating that this linkage is significantly more robust than maleimide-type linkages that are commonly employed in bioconjugations. These studies support the broad utility of this reaction in the chemoselective modification of small molecules, peptides, and proteins under mild aqueous conditions over a broad pH range using a wide variety of biologically acceptable buffers such as phosphate buffered saline (PBS) and 2-amino-2hydroxymethyl-propane-1,3-diol (Tris) buffers as well as others and mixed buffered compositions. ■ INTRODUCTION Bioconjugation reactions exploit either the intrinsic chemical reactivity of the biomolecule or introduce extrinsic functionalities that can then be subsequently reacted in a bio-orthogonal fashion. In recent years a wide range of extrinsic bioorthogonal reactions have been developed (Figure 1a).1−4 This two-step approach relies on the introduction of functionalities such as ketones, aldehydes, azides, alkenes, or alkynes into the target protein. In a second step, the introduced extrinsic functionalities are selectively reacted to form oximes/hydrazones,1−12 Staudinger ligation products, 1−4,13 triazole-Click products,1−4,14−18 or Diels−Alder,1−4,19−23 among others.1−4,24 In addition to chemical routes, extrinsic functional groups can be introduced into biomolecules via enzymatic modification1−5,11,12,19−23 or genetic encoding.1−4,25−33 Thus, extrinsic approaches involve a minimum of two modification steps of the biomolecule. In contrast, intrinsic approaches have the potential © XXXX American Chemical Society to be one-step (Figure 1b). Intrinsic approaches to bioconjugation are, however, limited to the development of chemistry compatible with the 20 naturally occurring amino acids and are challenged by the fact that any given amino acid is likely to occur more than once in a protein. Regardless of the approach, bioconjugation reactions ideally proceed rapidly, selectively, and in high yield under physiological conditions while preserving the target protein’s biological activity.1−4,29−31 Much of the chemistry developed to tap intrinsic amino acid reactivity is many decades old and is centered on the modification of lysine and cysteine side chains. The abundance of lysine residues on the protein surface, however, makes sitespecific modification difficult. In contrast, cysteine is rare and Received: December 17, 2012 Revised: March 13, 2013 A dx.doi.org/10.1021/bc300665t | Bioconjugate Chem. XXXX, XXX, XXX−XXX Bioconjugate Chemistry Communication Figure 1. Bioconjugation reactions: (a) two-step extrinsic; (b) one-step intrinsic approach. Scheme 1. Model Tyrosine Click Reaction electrophiles such as diazodicarboxylates in organic solvents in the presence of activating protic or Lewis acid additives.46−54 However, highly reactive diazodicarboxylate reagents decompose rapidly in aqueous media and stabile diazodicarboxyamide reagents do not react efficiently with phenols in aqueous media; thus most diazodicarboxyamides are not suitable as bioconjugation reagents.55 Although cyclic diazodicarboxylate reagents can be activated by interaction with cationic species such as protons or metals, cyclic diazodicarboxyamides like 4-phenyl3H-1,2,4-triazoline-3,5(4H)-dione (PTAD) are not activated by protic or Lewis acid additives.55 Our initial study involved a survey of the reactivities and stabilities of diazodicarboxylate and diazodicarboxyamide; these studies led us to develop the tyrosine-click reaction of PTAD with the phenolic side chain of tyrosine (Scheme 1). The tyrosine click reaction is illustrated in Scheme 1 involving the reaction in this case of N-acyl tyrosine methyl amide 1 with PTAD 2a in mixed organic solvent/aqueous media. In sodium phosphate buffer (pH 7)/acetonitrile (1:1), 1 reacted rapidly (reaction was complete in less than 5 min) with 1.1 equiv of PTAD 2a to provide 3a in quantitative yield. PTAD labeling was more efficient than 4-methyl-3H-1,2,4triazoline-3,5(4H)-dione (MTAD) labeling;56 reaction of MTAD 2b with amide 1 gave 3b in 57% isolated yield as electronic modulation of the triazolinedione system is key to controlling this reaction.45 Here we present a comprehensive study concerning the synthesis and characteristics of versatile triazolinedione-based labeling reagents, studying of the scope, stability, and chemoselectivity of these reagents, and examine their applications in bioconjugation reactions with small molecules, peptides, and proteins. most often found in disulfide-linked pairs in native proteins. For cysteine modification, pretreatment by reduction to cleave disulfide bonds is typically required; this is followed by reaction with a reagent like maleimide.34 Recently, novel mono- and dibromomaleimides have expanded the potential of cysteinetargeted labeling.35,36 Less developed are methods for the selective modification of the aromatic amino acid side chains of tryptophan37,38 and tyrosine,39−43 but a number of promising approaches have been recently reported. Among nucleophilic amino acids, tyrosine has unique reactivity due to the acidic proton of the phenol ring.44 The alkyation or acylation reaction of tyrosine under basic conditions proceeds at the oxygen. Under acidic conditions, an ene-like reaction occurs at a carbon atom on the aromatic ring. Bioconjugation at carbon in mild, biocompatible, metal-free conditions was reported using Mannich-type additions to imines or cerium(IV) ammonium nitrate (CAN) as an oxidation reagent.39,43 However, in the former, the modification of tyrosine with imines formed in situ is limited by the requirement of an excess of highly reactive formaldehyde. Tryptophan and amine containing side chains and reduced disulfides form formaldehyde adducts under these reaction conditions. The latter, oxidative coupling with electron-rich aniline derivatives, results in the coupling of both tyrosine and tryptophan. An alternative tyrosine modification with cyclic imines solves this problem but often reacts in an uncontrolled way with either one or two equivalents of cyclic imine. Recently, we discovered that we could exploit the reactivity of certain diazodicarboxylate-related molecules and the intrinsic reactivity of tyrosine to create a rapid aqueous ene-type reaction, the tyrosine-click reaction.45 As a background for the development of this reaction, it should be noted that substituted phenols react with highly reactive B dx.doi.org/10.1021/bc300665t | Bioconjugate Chem. XXXX, XXX, XXX−XXX Bioconjugate Chemistry ■ Communication EXPERIMENTAL PROCEDURES General. 1H NMR and C NMR spectra44 were recorded on Bruker DRX-600 (600 MHz) or Varian MER-300 (300 MHz) spectrometers in the stated solvents using tetramethylsilane as an internal standard. Chemical shifts were reported in parts per million (ppm) on the δ scale from an internal standard (NMR descriptions: s, singlet; d, doublet; t, triplet; q, quartet; m, multiplet; br, broad). Coupling constants, J, are reported in Hertz. Mass spectroscopy was performed by The Scripps Research Institute Mass Spectrometer Center. Analytical thinlayer chromatography and flash column chromatography were performed on Merck Kieselgel 60 F254 silica gel plates and Silica Gel ZEOprep 60 ECO 40−63 Micron, respectively. Visualization was accomplished with anisaldehyde or KMnO4. High performance liquid chromatography (HPLC) was performed on Shimadzu GC-8A using Vydac 218TP C18 GRACE Column (22 mm × 250 mm) for purification and Hewlett-Packard series 1100 using MCI GEL C18 Mitubishi Chemical Column (4.6 mm × 250 mm) for analysis. Unless otherwise noted, all the materials were obtained from commercial suppliers, and were used without further purification. All solvents were the commercially available grade. All reactions were carried out under argon atmosphere unless otherwise mentioned. Amide starting materials, tyrosine, histidine, tryptophan, serine, cysteine, lysine, and (Ile3)pressionoic acid, were commercially available compounds or prepared according to published procedures.1 A peptide, H2NVWSQKRHFGY-CO2H, was custom-synthesized by Abgent, Inc. Chymotrypsinogen A (MW 25 kDa) (ImmunO) was used as a model protein for PEGylation. Synthesis of 1,2,4-Triazolidine-3,5-diones 8. Method A: To a 0.2 M solution of ethyl hydrazinecarboxylate 4 (1.0 equiv) in THF was added 1,1′-carbonyldiimidazole (CDI, 1.0 equiv) at room temperature. The resulting solution was stirred at room temperature. After 2 h, aniline 5 (1.0 equiv) and Et3N (2.0 equiv) were added at room temperature and stirred overnight. Then, EtOAc and 10% HCl were added. The organic layer was separated and washed once with 10% HCl and water. The resulting aqueous layer was extracted once with EtOAc. The combined organic layer was dried over MgSO 4 , and concentrated in vacuo. The obtained crude solid was washed with EtOAc, dried, and dissolved in MeOH (0.2 M solution) followed by addition of K2CO3 (3.0 equiv). The calculation was done based on the crude material. The suspension was stirred under reflux for 3 h. The reaction mixture was acidified with 12 N HCl to pH 2 and then concentrated in vacuo. The generated white solids were washed with water and EtOAc to give 8. 4-(4Propargyloxyphenyl)-1,2,4-triazolidine-3,5-dione (8a). The title compound 8a was obtained as white solid (2 steps, 28%). 1H NMR (300 MHz, DMSO-d6): δ 10.6 (br, 2H), 7.60−7.57 (m, 2H), 7.54−7.50 (m, 2H), 4.27 (s, 1H). 13C NMR (75 MHz, DMSO-d6): δ 158.83, 133.36, 133.07, 126.67, 121.59, 83.81, 82.41. HRMS: calcd for C10H8N3O2 (MH+) 202.0611, found 202.0619. 4-(4-(2-Azidoethoxy)phenyl)-1,2,4-triazolidine-3,5dione (8b). The title compound 18b was obtained as white solid (2 steps, 28%). 1H NMR (300 MHz, DMSO-d6): δ 10.4 (br, 2H), 7.36−7.33 (m, 2H), 7.07−7.03 (m, 2H), 4.21 (t, J = 6 Hz, 2H), 3.66 (t, J = 6 Hz, 2H). 13C NMR (75 MHz, DMSOd6): δ 158.16, 154.63, 128.67, 125.85, 115.63, 68.03, 50.44. HRMS: calcd for C10H11N6O3 (MH+) 263.0887, found 263.0889. 4-(4-(2-Oxopropoxy)phenyl)-1,2,4-triazolidine-3,5dione (8c). The title compound 8c was obtained as white solid (2 steps, 12%). This compound was purified by short column chromatography (CHCl3/MeOH). 1H NMR (300 MHz, DMSO-d6): δ 10.4 (br, 2H), 7.31−7.27 (m, 2H), 7.02− 6.95 (m, 2H), 4.87 (s, 2H), 2.16 (s, 3H). 13C NMR (75 MHz, DMSO-d6): δ 204.81, 157.96, 154.67, 128.57, 125.75, 115.57, 73.13, 27.16. HRMS: calcd for C11H12N3O4 (MH+) 250.0822, found 250.0826. 4-(4-Azidophenyl)-1,2,4-triazolidine-3,5-dione (8d). The title compound 8d was prepared from 4-azidoaniline hydrochloride, and was obtained as white solid (2 steps, 35%). 1 H NMR (300 MHz, DMSO-d6): δ 10.5 (br, 2H), 7.50 (d, J = 9.0 Hz, 2H), 7.23 (d, J = 9.0 Hz, 2H). 13C NMR (75 MHz, DMSO-d6): δ 154.25, 139.59, 129.76, 128.53, 120.47. HRMS: calcd for C8H7N6O2 (MH+) 219.0625, found 219.0617. General procedure B: To a 0.5 M solution of compound 6 (1.0 equiv) and Et3N (1.8 equiv) in THF (5 mL) was added 4-nitrophenyl chloroformate (1.8 equiv) at 0 °C. The resulting solution was stirred at room temperature overnight. Ethyl hydrazinecarboxylate 4 (2.6 equiv) and Et3N (2.6 equiv) were added at room temperature and stirred at 40 °C for 4 h. Then, EtOAc and water were added. The organic layer was separated and washed once with water. The resulting aqueous layer was combined and extracted twice with EtOAc. The combined organic layer was dried over MgSO4, and concentrated in vacuo. The obtained crude solid was washed with EtOAc, dried, and dissolved in MeOH (0.2 M solution) followed by addition of K2CO3 (3.0 equiv). The calculation was done based on the crude material. The suspension was stirred under reflux for 3 h. The reaction mixture was acidified with 12 N HCl to pH 2 and then concentrated in vacuo. The generated white solids were washed with water and Et2O to give 8. 4-(4-Ethynylphenyl)-1,2,4triazolidine-3,5-dione (8e). The title compound 8e was prepared from 4-ethynylaniline hydrochloride, and was obtained as white solid (2 steps, 38%). 1H NMR (300 MHz, DMSO-d6): δ 10.6 (br, 2H), 7.60−7.57 (m, 2H), 7.54−7.50 (m, 2H), 4.27 (s, 1H). 13C NMR (75 MHz, DMSO-d6): δ 153.83, 133.36,1 33.07, 126.67, 121.59, 83.81, 82.41. HRMS: calcd for C10H8N3O2 (MH+) 202.0611, found 202.0619. 4-(4Acetylphenyl)-1,2,4-triazolidine-3,5-dione (8f). The title compound 8f was prepared from 4′-aminoacetophenone, and was obtained as white solid (2 steps, 15%). 1H NMR (300 MHz, DMSO-d6): δ 10.7 (br, 2H), 8.09−8.06 (m, 2H), 7.71−7.68 (m, 2H), 2.62 (s, 3H). 13C NMR (75 MHz, DMSO-d6): δ 198.18, 153.67, 137.09, 136.26, 129.74, 126.17, 27.76. HRMS: calcd for C10H10N3O3 (MH+) 220.0717, found 220.0713. Oxidation of 3H-1,2,4-Triazole-3,5(4H)-diones. To a 0.05 M solution of compound 8 (1.0 equiv) in CH2Cl2 was added 1,3-dibromo-5,5-dimethylhydantoin 10 (1.0 equiv) at room temperature. The resulting solution was stirred at room temperature. After 2 h, silica sulfuric acid57 (SiO2−OSO3H, 4 times weight to starting material) was added at room temperature and stirred at room temperature. After 30 min, the silica sulfuric acid was removed by filtration. Then, volatile materials were evaporated in vacuo to give 9. The obtained material was relatively unstabile against light and humidity in solution at room temperature. Therefore, it was used for next reaction without additional purification after confirmation of purity by 1H NMR (see SI). 4-(4-(Propargyloxy)phenyl)-3H1,2,4-triazole-3,5(4H)-dione (9a). The title compound 9a was prepared from 8a (50.0 mg, 0.216 mmol), and was obtained as a deep red solid (42.0 mg, 85%). 1H NMR (300 MHz, CDCl3): δ 7.41−7.37 (m, 2H), 7.15−7.12 (m, 2H), 4.75 (d, J = 3.0 Hz, 2H), 3.64 (t, J = 3.0 Hz, 1H). 4-(4-(2-Azidoethoxy)phenyl)3H-1,2,4-triazole-3,5(4H)-dione (9b). The title compound 9b C dx.doi.org/10.1021/bc300665t | Bioconjugate Chem. XXXX, XXX, XXX−XXX Bioconjugate Chemistry Communication at room temperature and stirred for 30 min. Then, chloroform was added and washed with sat. NaHCO3 aq. and brine. Combined organic layer was dried over Na2SO4, and concentrated in vacuo. The residue was purified by silica gel chromatography (EtOAc/MeOH = 4/1) to give 27 (43 mg, 52%) as thin yellow solid. 1H NMR (400 MHz, MeOD-d4): δ 7.82−7.80 (m, 3H), 7.45−7.43 (m, 2H), 7.26−7.24 (m, 2H), 7.03−7.01 (m, 4H), 6.97−6.95 (m, 2H), 4.74 (m, 2H), 4.48 (m, 2H), 4.13 (m, 1H), 3.95 (m, 2H), 3.68−3.60 (m, 10H), 3.54 (t, J = 4.8 Hz, 2H), 3.46−3.38 (m, 4H), 2.97−2.84 (m, 2H), 2.74−2.69 (m, 2H), 2.54−2.47 (m, 2H), 2.41−2.27 (m, 2H). 2.20−2.07 (m, 4H), 2.02 (t, J = 2.6, 1H), 1.98−1.89 (2H), 1.73−1.53 (m, 8H), 1.40−1.13 (m, 8H), 0.96−0.85 (t, J = 7.2, 4H). 13C NMR (125 MHz, MeOD-d4): δ 173.51, 171.84, 168.40, 165.80, 160.35, 158.03, 157.15, 155.25, 154.88, 52.16, 46.76, 132.64, 129.53, 128.05, 123.27, 119.67, 118.08, 115.07, 79.13, 70.53, 70.27, 70.13, 69.54, 69.47, 66.93, 56.87, 49.92, 49.88, 40.1221, 39.96, 39.13, 35.30, 31.49, 26.49, 25.96, 21.46, 20.41, 13.15. HRMS: calcd for C 56H 75 N 11 O 12 (MH+ ) 1094.5669, found 1094.5660. Synthesis of Model Compounds Used in Stability Studies. 1-(2-Hydroxy-5-methylphenyl)-4-phenyl-1,2,4-triazolidine-3,5-dione (29). To a solution of p-cresol (80 mg, 0.740 mmol) in THF (5 mL) was added NaH (35.5 mg, 0.885 mmol) at 0 °C. After 20 min, PTAD (127 mg, 0.725 mmol) was added at 0 °C and stirred at room temperature for 3 h. Then, EtOAc and 10% HCl were added. The organic layer was separated and washed once with brine. The resulting aqueous layer was extracted once with EtOAc. The combined organic layer was dried over MgSO4, and concentrated in vacuo. The residue was purified by silica gel chromatography (CHCl3/MeOH) to give 29 (158 mg, 75%) as a white solid. 1H NMR (600 MHz, DMSO-d6): δ 9.86 (br, 1H), 7.53−7.49 (m, 4H), 7.43−7.40 (m, 1H), 7.19 (d, J = 2.0 Hz, 1H), 7.10 (dd, J = 8.3, 2.0 Hz, 1H), 6.87 (d, J = 8.3 Hz, 1H), 2.24 (s, 3H). 13C NMR (150 MHz, DMSO-d6): δ 151.98, 151.64, 151.46, 131.86, 130.98, 129.56, 128.80, 127.91, 127.72, 126.03, 122.89, 116.57, 19.67. HRMS: calcd for C15H14N3O3 (MH+) 284.1030, found 284.1028. Benzyl-3-(N-phenylsuccinimide)-thioether (30). To a solution of N-phenylmaleimide (2 equiv, 279 mg, 1.610 mmol) in EtOH (2.85 mL)/pH7.0 HEPES buffer (2.85 mL) was added benzylthiol (1 equiv, 100 uL, 0.805 mmol) in MeCN (2.85 mL) at room temperature. After 12 h, EtOAc and H2O were added. The organic layer was separated and the resulting organic layer was extracted twice with EtOAc. The combined organic layer was dried over Na2SO4, and concentrated in vacuo. The residue was precipitated and washed by Et2O/ EtOAc to give 30 (140 mg, 58%) as white solids. 1H NMR (400 MHz, CDCl3): δ 7.51−7.26 (m, 10H), 4.29 (d, J = 13.6 Hz, 1H), 3.90 (d, J = 13.6 Hz, 1H), 3.64 (dd, J = 3.7, 9.3 Hz, 1H), 3.16 (dd, J = 9.3, 18.9 Hz, 1H), 2.58 (dd, J = 3.7, 18.9 Hz, 1H). Peptide Modification. Labeled peptide (11a). To a 2 mM solution of custom-synthesized peptide 10 (1.82 mL, 3.82 μmol) in 100 mM pH 7.0 NaH2PO4/Na2HPO4 buffer, 100 mM solution of PTAD 9a (114 μL, 11.5 μmol) in MeCN was added (9.55 μL × 12 times, interval 1 min.) at room temperature. The resulting solution was stirred at room temperature for 30 min. The crude reaction was analyzed directly by ESI-LC/MS at 254 nm UV absorption and corresponding MS. The reaction mixture was then diluted with MeCN (1.00 mL). The obtained crude material was purified by reversed phase HPLC (mobile phase; gradient of MeCN/0.1% TFA water, 30:70 to 50:50 over was prepared from 8b (49.0 mg, 0.187 mmol), and was obtained as deep red oil (39.6 mg, 81%). 1H NMR (300 MHz, CDCl3): δ 7.40−7.35 (m, 2H), 7.10−7.06 (m, 2H), 4.20 (t, J = 3.0 Hz, 2H), 3.64 (t, J = 3.0 Hz, 2H). 4-(4-(2-Oxopropoxy)phenyl)-3H-1,2,4-triazole-3,5(4H)-dione (9c). The title compound 9c was prepared from 8c (47.0 mg, 0.189 mmol), and was obtained as deep purple solid (34.9 mg, 81%).1H NMR (300 MHz, CDCl3): δ 7.42−7.38 (m, 2H), 7.05−7.02 (m, 2H), 4.61 (s, 2H), 2.31 (s, 3H). 4-(4-Azidophenyl)-3H-1,2,4triazole-3,5(4H)-dione (9d). The title compound 9d was prepared from 8d (40 mg, 0.183 mmol), and was obtained as deep red solid (34.1 mg, 86%). 1H NMR (300 MHz, CDCl3): δ 7.51−7.46 (m, 2H), 7.22−7.17 (m, 2H). 4-(4-Ethynylphenyl)3H-1,2,4-triazole-3,5(4H)-dione (9e). To a solution of compound 9e (4.43 mg, 0.022 mmol) in MeCN (44 μL) was added 1,3-dibromo-5,5-dimethylhydantoin (6.29 mg, 0.022 mmol) at room temperature. The resulting solution was stirred at room temperature for 10 min. Completion of the reaction was monitored by the change of reaction solution color to a characteristic deep red color. The obtained material decomposed quickly at room temperature. Therefore, the 0.5 M MeCN reaction solution was used for next step without purification. Synthesis of Aplaviroc-Urazole. Aplaviroc-alkyne (26): To a solution of Azido-alkyne (See SI) (200 mg, 0.670 mmol) in diethyl ether (2 mL) was added triphenylphosphine (264 mg, 1.00 mmol) at 0 °C and stirred at room temperature for 3 h. Then, deionized water 200 mL was added to reaction mixture and stirred for 12 h. 10 % HCl aq. was added, followed by wash with diethyl ether. The aqueous layer was basified to pH 10 with 5 N NaOH and extracted with dichloromethane/iPrOH (4:1) 5 times. The organic layer was dried over Na2SO4, and concentrated in vacuo. The crude amine 25 was used to the next reaction without further purification. To a solution of Aplaviroc 2458 prepared by the previously reported method (300 mg, 0.513 mmol) in DMF (10 mL) was added BOP (174 mg, 0.639 mmol), triethylamine (362 mL, 2.596 mmol), and amine-alkyne 25 (174 mg, 0.639 mmol) at room temperature and stirred for 12 h. Then, dichloromethane were added and was separated and washed sat. NaHCO3 aq. and brine. The organic solution was dried over Na2SO4, and concentrated in vacuo. The residue was purified by silica gel chromatography (Dichloromethane/MeOH = 9/1) to give 26 (181 mg, 42%) as thin yellow oil. 1H NMR (400 MHz, CDCl3): δ 7.83−7.79 (m, 2H), 7.34−7.28 (m, 2H), 7.02−6.96 (m, 5H), 6.47 (br t, 1H), 6.42 (br s, 1H), 4.01 (dd, J = 1.4, 5.7 Hz, 1H), 3.68−3.60 (m, 10H), 3.54 (t, J = 4.8 Hz, 2H), 3.46− 3.38 (m, 4H), 2.97−2.84 (m, 4H), 2.74−2.69 (m, 2H), 2.54− 2.47 (m, 2H), 2.41−2.27 (m, 2H). 2.20−2.07 (m, 4H), 2.02 (t, J = 2.6, 1H), 1.98−1.89 (2H), 1.73−1.53 (m, 8H), 1.40−1.13 (m, 8H), 0.96−0.85 (t, J = 7.2, 4H). 13C NMR (125 MHz, MeOD-d4): δ 173.02, 171.97, 168.41, 165.92, 160.57, 156.64, 132.35, 129.57, 119.81, 117.95, 82.69, 78.94, 70.50, 70.27, 70.23, 69.69, 69.64, 69.55, 61.42, 59.37, 56.98, 53.94, 49.77, 47.27, 42.87, 40.10, 39,98, 39.42, 36.09, 34.98, 32.17, 31.65, 31.54, 30.02, 29.63, 26.53, 26.02, 20.46, 14.75, 13.30. HRMS: calcd for C46H65N5O9 (MH+) 832.4855, found 832.4854. Aplaviroc-urazole (27): To a solution of 8b (20 mg, 0.763 mmol) and 27 (70 mg, 0.0839 mmol) in tert-BuOH/H2O (3 mL/1 mL) was added THPTA59 (458 mL, 0.0229 mmol, 50 mM solution in H2O), copper sulfate 5 hydrate (114 mL, 0.0229 mmol, 50 mg/mL solution in H2O), and sodium ascorbate (91 mL, 0.0229 mmol, 50 mg/mL solution in H2O) D dx.doi.org/10.1021/bc300665t | Bioconjugate Chem. XXXX, XXX, XXX−XXX Bioconjugate Chemistry Communication and 16c; or BSA: 17a, 17b, and 17c) were recorded by a Microplate spectrophotometer (Spectra Max Gemini; Molecular Devices) using wavelength of excitation 485 nm and emission 538 nm. Pegylation of Chymotrypsinogen A. Synthesis of PEGurazole (22): In the 1.5 mL Eppendorf tube were mixed 5k PEG-alkyne 21 (See SI) (15 μL of 48 mM solution in DMF, 0.72 μmol, 1 equiv) and 1,2,4-triazolidine-3,5-dione azide 2045 (30 μL of 24 mM solution in DMF, 0.72 μmol, 1 equiv) followed by addition of a small piece of copper wire and copper sulfate (0.72 μL, 100 mM solution in DI water). The reaction mixture was vortexed gently and kept at 37 °C for 2 h with intermittent vortexing. Copper wire was removed and copper ions were scavenged from the reaction mixture using “CupriSorb” resin (Seachem) overnight at room temperature. The Cuprisorb resin was filtered and product polymer was precipitated out with cold ether, centrifuged, and ether decanted. The resulting white solid as PEG-urazole (22) was washed with cold ether two times and dried. Isolated yield 4.0 mg, 95%. MALDI-TOF MWav = 5921. Pegylation of Chymotrypsinogen A with PTAD-PEG: To the 0.65 mL Eppendorf tube containing 5k PEG-PTAD precursor 22 (50 μL, 10 mM solution in DMF) was added 1,3-dibromo-5,5-dimethylimidazolidine-2,4-dione (0.49 μL, 100 mM solution in DMF). The reaction mixture was vortexed gently and formation of the light cranberry red color was observed, characteristic for the presence of desired PTAD reagent. The reagent was kept on ice and used for the protein modification immediately. To the 1.5 mL Eppendorf tube containing chymotrypsinogen A (MW 25 kDa purchased from ImmunO) (50 μL of 1 mg/mL solution; 2 nM, 1 equiv) was added freshly prepared 5k PEGPTAD solution (2 μL of 10 mM solution in DMF, 20 nM, 10 equiv). The reaction was vortexed briefly and kept at room temperature for 30 min. The product pegylated chymotrypsinogen A 23 was purified by gel filtration using 7k MWCO Zeba Spin Desalting column (Pierce) and characterized by MALDITOF and gel electrophoresis. Bioconjugation of Herceptin with Aplaviroc-PTAD. To the 0.65 mL Eppendorf tube containing urazole-Aplaviroc 27 (10 μL, 6 mM solution in DMF) was added 1,3-dibromo-5,5dimethylimidazolidine-2,4-dione (10 μL, 6 mM solution in DMF). The reaction mixture was vortexed gently and formation of the light cranberry red color was observed, characteristic for the presence of desired PTAD reagent. The reagent was kept on ice and used for the protein modification immediately. To the 0.65 mL Eppendorf tube containing 70 μL of 1.0 mg/mL Trastuzumab (herceptin) in 100 mM pH 7.4 Na phosphate buffer was added freshly prepared 3.92 μL of 3 mM PTAD-Aplaviroc in DMF in 5 aliquots at 2 s intervals (* use fresh pipet tip for each addition). After 15 min, the resulting solution was purified by gel filtration using 7k MWC Zeba Spin Desalting column (Pierce). The concentration of recovered protein was 0.75 mg/mL (NanoDrop, IgG mode). The increase of molecular weight of 1376 was observed by MALDI-TOF MS analysis, that corresponds to an average 1.3 aplaviroc molecules per molecule of herceptin. Herceptin−apraviroc conjugate (28) was used for HIV neutralization assay without additional purification. HIV Neutralization Assay. Replication-incompetent HIV-1 enveloped pseudovirus was generated by cotransfection of 293T cells with JR-FL HIV-1 Env-expressing plasmid and pSG3ΔEnv as previously described.60 Serial dilutions of samples (50 μL) along with wt b12, 2D7, 2G12, and an 30 min, Rt; 14.5 min, detection; UV 254 nm) to give 11a (4.40 mg, 61%) as white amorphous solid. HRMS: calcd for C73H93N21O17 (MH+) 1536.7131, found 1536.7125. Reversed phase HPLC purity 95.1% (mobile phase; gradient of MeCN/ 0.1% TFA water, 0:100 to 100:0 over 30 min, Rt; 15.8 min, detection; UV 254 nm). Labeled peptide (11b). The compound 11b was prepared from custom-synthesized peptide 10 (5 mg, 3.82 μmol) and 9b (2.99 mg, 11.5 μmol), and was obtained as white amorphous solid (4.40 mg, 60%). Reverse phase HPLC conditions for isolation: mobile phase: gradient of MeCN/0.1% TFA water, 30:70 to 50:50 over 30 min, Rt 15.6 min, detection at UV 254 nm). HRMS: calcd for C72H94N24O17 (MH+) 1567.7301, found 1567.7236. Reversed phase HPLC purity 91.3% (mobile phase: gradient of MeCN/0.1% TFA water, 0:100 to 100:0 over 30 min, Rt 15.9 min, detection at UV 254 nm). Labeled peptide (11c). The compound 11c was prepared from custom-synthesized peptide 10 (5 mg, 3.82 μmol) and 9c (2.84 mg, 11.5 μmol), and was obtained as white amorphous solid (4.60 mg, 63%). Reverse phase HPLC conditions for isolation: mobile phase: gradient of MeCN/ 0.1% TFA water, 30:70 to 50:50 over 30 min, Rt 14.8 min, detection at UV 254 nm). HRMS: calcd for C73H95N21O18 (MH+) 1554.7236, found 1554.7220. Reversed phase HPLC purity 93.6% (mobile phase: gradient of MeCN/0.1% TFA water, 0:100 to 100:0 over 30 min, Rt 15.2 min, detection at UV 254 nm). Sequential Bioconjugation of Albumin Using Three Orthogonal Chemistries. (Step 1) Reaction of albumin with dansyl derivative. To a 1.5 mL centrifuge tube were added 300 μL of filtered albumin solution in H2O (pH 6.0) containing 1.5 mg albumin followed by addition of 10 μL of 140 mM 1-ethyl3-(3-dimethylaminopropyl) carbodiimide hydrochloride in H2O (pH 6.0) and 5 μL of 136 mM 11-(dansylamino) undecanoic acid in DMSO. Reaction tubes were gently shaken at 250 rpm and incubated for 14.5 h at 37 °C. The reaction mixtures were applied to Micro Bio-Spin Chromatography Columns (Bio-Gel P6̅ Gel, Bio Rad) and exchanged into nanopure water. The purified albumin construct was characterized by MALDI-TOF MS. The fluorescence signal of the modified albumins 12 and 13 were recorded by a Microplate spectrophotometer (Spectra Max Gemini; Molecular Devices) using wavelength of excitation 320 nm and emission 555 nm. (Step 2) Reaction of dansyl-albumins with PTAD derivative. The dansyl-albumin solutions 150 μL were applied to Micro BioSpin Chromatography Columns (Bio-Gel P6̅ Gel, Bio Rad) to exchange the buffer to 100 mM Na Phosphate buffer pH 7.4. The resulting solutions were diluted to 30 μM concentration. To a 1.5 mL centrifuge tube was added 99 μL of 30 μM of dansyl-albumin solution followed by addition of 1 μL of 100 mM PTAD solution in MeCN. Reactions were gently shaken and incubated at 25 °C for 15 min. The reaction mixtures were applied to Micro Bio-Spin Chromatography Columns (Bio-Gel P6̅ Gel, Bio Rad) to exchange the buffer to SSC buffer pH 7.0. The purified albumin constructs (HSA: 14a, 14b, and 14c; or BSA: 15a, 15b, and 15c) were characterized by MALDI-TOF MS. (Step 3) Reaction of dual labeled albumins with f luorescein-5maleimide. Labeling with fluorescein-5-maleimide (Thermo Scientific, Catalog No. 46130) was performed according to manufacturer’s procedure. The reaction mixtures were applied to Micro Bio-Spin Chromatography Columns (Bio-Gel P6̅ Gel, Bio Rad) to exchange buffer to H2O. The purified albumin constructs was characterized by MALDI-TOF MS. The fluorescence signal of the modified albumins (HSA: 16a, 16b, E dx.doi.org/10.1021/bc300665t | Bioconjugate Chem. XXXX, XXX, XXX−XXX Bioconjugate Chemistry Communication Scheme 2. Synthesis of PTAD Derivatives added 100 μL of 1 mg/mL 29 or 30, followed by the incubation at 37 °C (final volume: 2 mL, final concentration: 50 mg/mL, DMSO content: 5%). 100 μL aliquots were withdrawn at the following time points: 3 min, 15 min, 30 min, 1 h, 4 h, 8 h, 24 h, 48 h, 120 h, and 168 h. Each 100 μL aliquot was precipitated by addition of 600 μL of MeCN. Samples were centrifuged and 600 μL of supernatant were transferred into a new 1.5 mL Eppendorf tube. The solution was centrifugally evaporated followed by addition of 100 μL of 2 mg/mL methyl 4hydroxybenzoate as a internal standard (IS) for the subsequent HPLC assay. 80 μL aliquots of supernatants were taken and 40 μL of each sample solution was injected and analyzed by reverse phase HPLC under optimized conditions [(Analysis time: 20 min, Flow rate: 1.0 mL/min, Column: Phenomenex (4.6 × 250), Detection wavelength: 254 nm, Isostatic: 40−80% MeCN in 1% TFA/H2O), TR = 14.70 min (30), TR = 6.23 min (IS), TR = 7.40 min (29)]. isotype control antibody, DEN3, were added to TZM-bl target cells (50 μL) and preincubated for 1 h at 37 °C. Following incubation 250TCID50 of pseudovirus (100 μL) was added to each well and incubated at 37 °C. Luciferase reporter gene expression was evaluated 48 h post infection. The percentage of virus neutralization at a given antibody concentration was determined by calculating the reduction in luciferase expression in the presence of antibody relative to virus-only wells. The antibody dilution causing 50% reduction (50% inhibitory concentration [IC50]) was calculated by regression analysis using GraphPad Prism. Chemical Stability Study. Acidic or Basic Conditions. The solution of compound 29 or 30 (0.0353 mmol) in 10% HCl (0.5 mL) in MeOH (1.5 mL) and in 10% NaOH (0.5 mL) in MeOH (1.5 mL) was stirred at room temperature for 12 h, respectively. Then, EtOAc and water were added. In the case of basic condition, EtOAc was added after acidification with 10% HCl up to pH 3. The organic layer was separated and washed once with water. The resulting aqueous layer was extracted once with EtOAc. The combined organic layer was dried over MgSO4, and concentrated in vacuo. The residue was purified by silica gel chromatography (EtOAc) to recover compounds as white solids. The recovery of 29 (8.9 mg, 89%) or 30 (9.0 mg, 86%) under acidic conditions and 29 (10.2 mg, quant.) under basic conditions. 30 decomposed under basic hydrolysis conditions within 15 min, as monitored by TLC. The decomposed compounds were purified and analyzed by 1H NMR and LC-MS. Hydrolysis products constituted the yield of 85% (see the structures above). Stability Study of a Modified p-Cresol in Thermal Condition. Compound 29 (4.00 mg, 0.0141 mmol) or 30 (4.00 mg, 0.0135 mmol) was heated at 120 °C for 1 h according to literature.56 The recovery amounts were both 4.00 mg (quant.). No decomposition has been detected by 1H NMR. 3 Physiological stability in human blood plasma:61 To the 2 mL Eppendorf tube containing 1900 μL of fresh whole human blood plasma (Normal Blood Donor Program at TSRI) was ■ RESULTS AND DISCUSSION In order to develop a versatile family of PTAD based conjugation chemistries, we have focused on the design, preparation, and utility of PTAD analogues possessing readily derivatizable linker arms compatible with widely used bioorthogonol coupling chemistries; click chemistry, Staudinger ligation chemistry, and oxime/hydrazone chemistry. The coupling reaction between ethyl hydrazinecarboxylate 4 and anilines 5 or 6 was performed by Method A or B (Scheme 2) depending on the nucleophilicity of aniline. The anilines used were commercially available or were synthesized from commercially available compounds by the methods detailed in Scheme 2. Method A was used in the reaction of 4 with aniline 5: After activation of 4 by treatment with CDI, aniline 5 was reacted with the activated ester in THF at room temperature to afford coupling intermediate 15. The reaction of the less nucleophilic aniline 6 was carried out via Method B. First, 6 was converted to the corresponding activated ester using 4-nitrophenyl chloroformate, then reacted with 4 to F dx.doi.org/10.1021/bc300665t | Bioconjugate Chem. XXXX, XXX, XXX−XXX Bioconjugate Chemistry Communication reaction with electronically poor reagent 9f. The reagents substituted with electronically rich moieties, 9a, 9b, and 9c, efficiently modified 1. These results suggest that an electron donating substitution on the phenyl ring provides stability in water without compromising reactivity toward the phenolic side chain of tyrosine. In order to explore the potential of the tyrosine click reaction using these reagents for labeling of more complicated targets, we synthesized dodecapeptide 10, H2N-VWSQKRHFGYCO2H, which has a tyrosine at the C-terminus and contains the potentially reactive amino acids Trp, Ser, Glu, Lys, Arg, and His (Scheme 3). Because this peptide is designed to present amino acids with potentially reactive and competing sidechains, it serves as a stringent test of the chemoselectivity of this reaction. The reaction was performed using 3.0 equiv of PTAD or PTAD derivative in 6% MeCN/phosphate buffer (pH 7) at room temperature. After purification using reversed-phase HPLC, labeled peptides were obtained in approximately 60% yield (Scheme 6). Significantly, a single Tyr modified compound was observed in each reaction by LC-MS (Supporting Information) and HRMS and MS/MS data indicated tyrosine-selective modification. In MS/MS analyses, products obtained using all tested PTAD analogues showed similar fragmentation patterns and all daughter ions contained the ions of modified tyrosine peptide (Supporting Information). In our initial report of this reaction,45 we had shown that both Trp and Lys can react, albeit inefficiently, with PTAD in 50% MeCN/phosphate buffer (pH 7) at room temperature when studied in isolation. However, when N-acyl tyrosine methyl amide 1 was mixed with the corresponding Trp and Lys amino acid derivatives and reacted with PTAD under these conditions, only Tyr modification was observed. Other competitive labeling studies provided the same outcome: selective Tyr labeling (see SI, ref 45). These studies, together with the study of labeling of peptide 10 (which bears potentially competing functional groups in the same molecule) demonstrate here that the highly selective reaction of Tyr with PTAD derivatives is significantly favored under aqueous buffered conditions. As we initially reported, labeling with PTAD derivatives is effective in PBS, 2-amino-2-hydroxymethyl-propane-1,3-diol (Tris), 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES), and a variety of other buffers. In some cases, for example, where tyrosines of the target compound or protein are less accessible or reactive, we have noted that an isocyanate decomposition product of the PTAD may be formed that is promiscuous in its labeling and that the products of this type of side reaction are observed. This is the case for chymotrypsinogen labeling with PTADs (see SI). This problem, however, is readily solved by using Tris buffer or by simply adding a small quantity of Tris to form a mixed buffered solution. The primary amine of the Tris buffer we believe then acts to scavenge the isocyanate decomposition product of PTADs to minimize production of the side-reaction product (see Supporting Information). In our earlier study, we established the efficiency of protein labeling using a PTAD-rhodamine dye derivative and found that bovine serum albumin (BSA) was efficiently labeled in buffered solutions containing minimal organic cosolvent at pH ranging from 2 to 10 with 37−98% labeling efficiency (see ref 45, SI). To explore the potential of the tyrosine click for protein multifunctionalizations, here we studied trifunctionalization at tyrosine, cysteine, and lysine residues of bovine serum albumin (BSA) and human serum albumin (HSA). BSA contains 60 afford coupling intermediate 7 in THF at room temperature. Obtained intermediate 7 was cyclized in the presence of K2CO3 in MeOH under reflux without isolation. Finally triazolidine 8 was converted to desired triazole 9 by oxidization of the N−N single bond to an N−N double bond with 1,3-diboromo-5,5dimethylhydantoin 10 according to a literature procedure.57 Side products derived from 10 and unreacted starting material were removed by scavenging with silica sulfuric acid (SiO2− OS3H), because PTAD products 9 were unstabile during silicagel column chromatography. The oxidation reaction was readily monitored by observing the change in the reaction mixture from colorless to deep red. Reagents, 9a, 9b, 9c, and 9d were obtained as solids or oils but solutions were relatively unstabile. The products 9e and 9f were unstabile to isolation at room temperature. Purity of products was confirmed by 1H NMR. The reactivity of the PTAD analogues was evaluated in reaction with N-acyl tyrosine methyl amide 1, and results are shown in Table 1. All reactions were complete in less than 5 min based on color change; however, the reaction products were characterized after a more extended reaction time of 30 min. Electronically neutral reagents 9d and 9e gave the same results as PTAD with comparable percent conversions and without generation of side products. In contrast, significant amounts of uncharacterized side products were generated in the Table 1. Reactivity of PTAD Derivatives with N-Acyl Tyrosine Methyl Amide 1 a Reactions were performed in 100 mM NaH2PO4−Na2HPO4 (pH 7)/ MeCN (1:1) at room temperature. bPercent conversion was determined by 1H NMR. c0.5 M PTAD in MeCN mixture solution. d Reaction conditions were 100 mM NaH2PO4−Na2HPO4 (pH 7)/ MeCN (1:1.5). G dx.doi.org/10.1021/bc300665t | Bioconjugate Chem. XXXX, XXX, XXX−XXX Bioconjugate Chemistry Communication Scheme 3. Tyrosine Click Reaction of Designed Decapeptide with PTAD Derivatives to Test the Chemoselectivity and Efficiency of the Reaction Scheme 4. Triple-Labeling of Albumins at Lysine, Cysteine, and Tyrosine lysines, 21 tyrosines, and 35 cysteines, whereas HSA has 55 lysines, 19 tyrosines, and 35 cysteines. Cysteine and lysine were modified with a fluorescein maleimide and 11-(dansylamino) undecanoic acid, respectively (Scheme 4). Labeling of albumins at lysine was performed using 50 equiv of 11-(dansylamino) undecanoic acid and 100 equiv of N-[3-(dimethylamino)propyl]-N′-ethylcarbodiimide hydrocholide (EDC HCl) in water at 37 °C for 14.5 h. After the gel filtration, MALDI TOF analysis revealed that the modified HSA (12) and modified BSA (13) had 3.8 and 4.1 dansyl residues, respectively (Table 2). Next, tyrosines were reacted in 1% MeCN/100 mM phosphate buffer (pH 7.4) using 30 equiv of PTAD derivatives 9a, 9b, and 9c gave products with 4 to 8 modified residues (Table 2). Final labeling at cysteine in SSC buffer (pH 7.0) was achieved using 1 mM fluorescein-5-maleimide in DMSO at room temperature for 2 h (Table 2). As noted in Table 2, each of the desired labels could be efficiently installed onto the target proteins. Fluorescence properties and molecular masses of the modified BSA and HSA are given in the Supporting Information. Thus, PTAD derived reagents bearing bioorthogonal alkyne, azide, and ketone groups were readily prepared and efficiently modified small molecules, peptides, and proteins that can subsequently be further functionalized using click H dx.doi.org/10.1021/bc300665t | Bioconjugate Chem. XXXX, XXX, XXX−XXX Bioconjugate Chemistry Communication precursor reagent 22 (Scheme 5, see details in Supporting Information). We used this reagent to study the modification of Chymotrypsinogen A, which contains four tyrosine and fourteen lysine residues. Reactions were performed in buffer (pH 7.4) with 10 equiv of freshly oxidized PEG-PTAD or freshly dissolved PEG-NHS. Reactions were kept at room temperature for one hour with intermittent mixing. Excess reagents were removed using 7-kDa MWCO Zeba Spin Desalting columns, and the products were characterized by gel electrophoresis and MALDI-TOF MS (Supporting Information). We observed formation of mono-, bis-, tri-, and tetra-PEG addition products upon NHS conjugation and predominant formation of mono-PEG addition products upon PTAD conjugation. We have noted low reactivity of the chymotrypsinogen tyrosine residues accounting for the limited labeling of this protein (Supporting Information). Starting material was not completely consumed in either reaction but could be recovered and recycled. Because of the significance of antibody−drug conjugates in cancer and other therapeutic applications,64−66 we studied the conjugation of the CCR5 antagonist aplaviroc (24) with a monoclonal antibody. As a model monoclonal antibody, we used the well-characterized antibody trastuzumab.67 Aplaviroc was prepared as we previously reported.58 The carboxylic acid moiety of aplaviroc was condensed with an alkyne linker (25) to give aplaviroc having alkyne moiety (26), and then the click reaction with azide-urazole (9c) gave the PTAD-aplaviroc precursor (27). This precursor was oxidized to produce the PTAD moiety, then immediately used for labeling of trastuzumab in 0.1 M phosphate buffer (pH 7) at room temperature. After the removal of the small molecule by gel Table 2. Triple-Labeling of BSA and HSA through Three Different Bioconjugation Chemistriesa protein HSA BSA estimated number of available AAs/total number of residues labeled by amidation Lys 30/55 Tyr 15/19 Cys 1/35 Lys 35/60 Tyr 15/21 Cys 20/35 4.1 6.7 4.6 3.8 7.4 3.9 (12) (14b) (14c) (13) (15b) (15c) number of residues labeled by tyrosine-click 6.5 1.2 1.6 8.3 2.3 2.7 (14a) (16b) (16c) (15a) (17b) (17c) number of residues labeled by Michael reaction 1.8 (16a) 1.3 (17a) a Compounds numbers are shown in parentheses. Estimated numbers of surface accessible amino acids (AAs) from ThermoScientific or estimated by PyMOL v 1.5. chemistries and other well established bioorthogonal reaction chemistries. One of the most important protein conjugation reactions in the pharmaceutical industry concerns the introduction of poly(ethylene glycol) chains onto proteins (PEGylation) to modify their pharmacokinetic properties.62,63 Protein PEGylation is most commonly employed using maleimide- or Nhydroxysuccinimide-based PEGylation reagents. The high abundance of the lysine moieties on protein surfaces often results in generation of multiple PEG addition products and necessitates complicated separation procedures. Conjugation at cysteine residues typically requires the introduction of surface accessible cysteine residues by mutation of the parental protein sequence. To explore the potential of the tyrosine click reaction for protein PEGylation we prepared a 5-kDa PEG-PTAD Scheme 5. Protein PEGylation with a Linear PEG5000 PTAD Reagent I dx.doi.org/10.1021/bc300665t | Bioconjugate Chem. XXXX, XXX, XXX−XXX Bioconjugate Chemistry Communication Scheme 6. Tyrosine Click Bioconjugation of Trastuzumab Antibody with a Small Molecule HIV Entry Inhibitor filtration, a product with a single aplaviroc was observed by MALDI-TOF MS spectrum (Supporting Information). In order to study the bioactivity of conjugated 28, HIV neutralization activity of the aplaviroc−trastuzumab conjugate (28) was tested in TZM-bl cells expressing CCR5 and clade B pseudovirus JR-FL as shown in Figure 2. The IC50 value of conjugates and supports a chemical approach to multispecific antibodies.68,69 Key to many bioconjugation chemistries is the stability of the designed linkage. To further stability of the tyrosine click reaction in bioconjugation chemistry, we studied the stability of C−N linkage installed using PTAD reagents in comparison with the more commonly utilized C−S linkage provided by maleimide coupling chemistry (Scheme 7). As noted in our original communication on the PTAD adduct to p-cresol (29), it is stabile to acidic or basic conditions at room temperature for 24 h or at 120 °C for 1 h. On the other hand, 30, containing an S−C bond, was stabile in acidic conditions, but was hydrolyzed within 5 min in basic condition, although the S−C bond was not cleaved. 30 demonstrated a thermal stability similar to that of 29 after heat treatment for 1 h. This study suggests that the 1,2,4-triazolidine-3,5-dione linkage is hydrolytically and thermally stabile, whereas the maleimide linkage is unstabile in basic conditions. Next, stability was evaluated in human blood plasma in anticipation of the use of the tyrosine click reaction in protein conjugates, specifically antibody−drug conjugates (ADCs).70 For this purpose, we studied the stability of 29 and 30 by incubation in fresh human blood plasma at 37 °C for one week (Figure 3). At various time points the reaction was quenched by precipitation with MeCN and analyzed by reversed-phase HPLC (Supporting Information). Compound 29 was found to be completely stabile over the course of the 7day experiment, while 30 decomposed after hours. This data demonstrates that the Tyr click linkage is significantly more Figure 2. JR-FL HIV-1 pseudovirus neutralization assay: aplaviroc 24 (•), trastuzumab (■) and aplaviroc−trastuzamab 28 (▲). aplaviroc−trastuzumab conjugate 28 was 11.3 nM; trastuzamab alone had no neutralization activity. Interestingly, this value was very close to that of aplaviroc (24) alone (5.6 nM) indicating that the tyrosine click conjugation chemistry did not negatively impact the activity of the drug. No significant loss in trastuzumab binding was noted as determined by ELISA. This study and our earlier study45 concerning the bioconjugation of a peptide to trastuzumab indicates that the tyrosine click reaction is applicable the preparation of antibody−drug Scheme 7. Linkage Stability Study J dx.doi.org/10.1021/bc300665t | Bioconjugate Chem. XXXX, XXX, XXX−XXX Bioconjugate Chemistry ■ Communication AUTHOR INFORMATION Corresponding Author *E-mail: carlos@scripps.edu. Author Contributions ‡ H.B. and M.N. contributed equally. Funding Notes The authors declare no competing financial interest. ■ ACKNOWLEDGMENTS This study was supported by National Institutes of Health grants Pioneer Award DP1 CA174426, RO1 AI095038, and The Skaggs Institute for Chemical Biology. We thank Prof. Dennis Burton and Angelica Cuevas for HIV-1 assays (The Scripps Research Institute). M.N. thanks The Uehara Memorial Foundation for a postdoctoral fellowship for research abroad. We thank Dr. Qi-Yang Hu for discussion. Figure 3. Stability in human plasma at various time points. Peak Area is from HPLC. IS: internal standard; Ethyl 4-hydroxy benzoate. ■ ■ stabile in human blood plasma than the maleimide linkage and is consistent with reports that protein conjugates prepared with maleimide undergo maleimide exchange with reactive thiols in albumin, free cysteine, or glutathione.71,72 Furthermore, thiolmaleimide is prone to oxidation, and this facilitates the retroMichael reaction and subsequent decomposition.73 In view of our studies here and reports concerning maleimide based linkages, the tyrosine click reaction provides a more robust linkage for bioconjugation than maleimide based connections. ABBREVIATIONS CCR5, CC chemokine receptor 5; PEG, poly(ethylene glycol) (1) Best, M. D. (2009) Click chemistry and bioorthogonal reactions: unprecedented selectivity in the labeling of biological molecules. Biochemistry (Mosc). 48, 6571−6584. (2) Sletten, E. M., and Bertozzi, C. R. (2009) Bioorthogonal chemistry: fishing for selectivity in a sea of functionality. Angew. Chem., Int. Ed. 48, 6974−6998. (3) Devaraj, N. K., and Weissleder, R. (2011) Biomedical applications of tetrazine cycloadditions. Acc. Chem. Res. 44, 816−827. (4) Aslam, M., and Dent, A. (1998) Bioconjugation, In Protein Coupling Techniques for Biomedical Sciences, Grove’s Dictionaries Inc., New York, NY. (5) Carrico, I. S., Carlson, B. L., and Bertozzi, C. R. (2007) Introducing genetically encoded aldehydes into proteins. Nat. Chem. Biol. 3, 321−322. (6) Cornish, V. W., Hahn, K. M., and Schultz, P. G. (1996) Sitespecific protein modification using a ketone handle. J. Am. Chem. Soc. 118, 8150−8151. (7) Rose, K., and Vizzavona, J. (1999) Stepwise solid-phase synthesis of polyamides as linkers. J. Am. Chem. Soc. 121, 7034−7038. (8) O’Shannessy, D. J., Dobersen, M. J., and Quarles, R. H. (1984) A novel procedure for labeling immunoglobulins by conjugation to oligosaccharide moieties. Immunol. Lett. 8, 273−277. (9) Mahal, L. K., Yarema, K. J., and Bertozzi, C. R. (1997) Engineering chemical reactivity on cell surfaces through oligosaccharide biosynthesis. Science 276, 1125−1128. (10) Hang, H. C., and Bertozzi, C. R. (2001) Ketone isosteres of 2N-acetamidosugars as substrates for metabolic cell surface engineering. J. Am. Chem. Soc. 123, 1242−1243. (11) Cohen, J. D., Zou, P., and Ting, A. Y. (2012) Site-specific protein modification using lipoic acid ligase and bis-aryl hydrazone formation. ChemBioChem 13, 888−894. (12) Rashidian, M., Song, J. M., Pricer, R. E., and Distefano, M. D. (2012) Chemoenzymatic reversible immobilization and labeling of proteins without prior purification. J. Am. Chem. Soc. 134, 8455−8467. (13) Saxon, E., and Bertozzi, C. R. (2000) Cell surface engineering by a modified Staudinger reaction. Science 287, 2007−2010. (14) Rostovtsev, V. V., Green, L. G., Fokin, V. V., and Sharpless, K. B. (2002) A stepwise Huisgen cycloaddition process: copper(I)-catalyzed regioselective “ligation” of azides and terminal alkynes. Angew. Chem., Int. Ed. 41, 2596−2599. (15) Wang, Q., Chan, T. R., Hilgraf, R., Fokin, V. V., Sharpless, K. B., and Finn, M. G. (2003) Bioconjugation by copper(I)-catalyzed azidealkyne [3 + 2] cycloaddition. J. Am. Chem. Soc. 125, 3192−3193. ■ CONCLUSIONS AND IMPLICATIONS The studies described herein indicate that the tyrosine click reaction of PTAD derivatives is a highly efficient and chemoselective strategy for small molecule, peptide, and protein conjugation. The reactions of PTAD and designed derivatives developed here were selective for the phenolic side chain of tyrosine residues and proceeded in buffered aqueous media over a broad pH range without the requirement of added heavy metals or other reagents. The C−N linkage that is the product of the tyrosine click reaction is stabile to extremes of pH, temperature, and in human serum for extended periods of time. The stability profile of this C−N linkage is significantly better than the stability profile we determined for a model maleimide linkage. While tyrosine residues are commonly found in proteins, surface accessible tyrosines are less common and provide attractive opportunities for minimal labeling using this approach. Because this reaction is highly chemoselective for phenols, it can be applied to couple small molecules, peptides, and poly(ethylene glycol) chains (PEGylation) onto proteins without issues of self-reaction provided that one coupling partner lacks free phenolic groups. This provides an attractive new strategy for the preparation of protein conjugates, including drug conjugates and PEGylated products. We expect that this new methodology and the reagents developed here will find broad utility in production of novel biomolecules, labeled peptides and proteins, and a new chemistry for protein immobilization. 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(1998) MaleimidocysteineamidoDOTA derivatives: new reagents for radiometal chelate conjugation to antibody sulfhydryl groups undergo pH-dependent cleavage reactions. Bioconjugate Chem. 9, 72−86. M dx.doi.org/10.1021/bc300665t | Bioconjugate Chem. XXXX, XXX, XXX−XXX Facile and Stabile Linkages through Tyrosine: Bioconjugation Strategies with the Tyrosine-Click Reaction Hitoshi Ban, ‡ Masanobu Nagano, ‡ Julia Gavrilyuk, Wataru Hakamata, Tsubasa Inokuma, and Carlos F. Barbas, III* The Skaggs Institute for Chemical Biology and the Departments of Chemistry and Molecular Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, California 92037 carlos@scripps.edu Supporting Information 1. Coupling of N-acyl tyrosine methylamide with PTAD or MTAD........................................... 2 2. Synthesis of the PTAD analogs ............................................................................................. 5 3. NMR-charts of the PTAD analogs ........................................................................................ 8 4. The reactions of tyrosine derivative with PTAD analogs .................................................... 27 5. Peptide modification with PTAD analogs........................................................................... 31 6. Albumin modification through three different orthogonal reactions.................................... 38 7. Chymotrypsinogen PTAD labeling PBS/Tris buffer study................................................... 47 8. PTAD mediated PEGylation reaction ................................................................................. 52 9. Trastuzumab (Herceptin) conjugation with Aplaviroc-PTAD ............................................. 56 10. Stability study in human plasma ....................................................................................... 57 Ban, Nagano, Gavrilyuk, Hakamata, Inokuma, and Barbas, III S2 1. Coupling of N-acyl tyrosine methylamide with PTAD or MTAD O R O OH O H N N H O 1 Compound (3a). N N R N N O O NH OH PTAD: R = Ph (2a) MTAD: R = Me (2b) 100 mM Na phosphate buffer (pH 7) MeCN (1:1), r.t., < 5 min N O N H H N O R = Ph (3a), up to >99 % R = Me (3b), 57 % To a solution of tyrosine 1 (14.2 mg, 0.060 mmol) in 100 mM pH 7.0 NaH2PO4/Na2HPO4 buffer (1.5 mL) - MeCN (1.5 mL) was added the 0.5 M solution of PTAD 2a (0.132 mL, 0.066 mmol) in MeCN at room temperature. The resulting solution was stirred at room temperature for 30 min. The reaction mixture was acidified with 12N HCl (0.249 mL) and then concentrated in vacuo. The obtained crude material was purified by flash column chromatography (CHCl3/MeOH) to give 3a (16.0 mg, 65%) as a white solid. 1 H NMR (300 MHz, DMSO-d6): δ 11.57 (br, 1H), 8.06 (d, J = 8.4 Hz, 1H), 7.90 (q, J = 4.3 Hz, 1H), 7.74 (d, J = 1.7 Hz, 1H), 7.63 – 7.51 (m, 2H), 7.43 (t, J = 7.8 Hz, 2H), 7.34 – 7.21 (m, 1H), 6.83 (dd, J = 8.2, 2.0 Hz, 1H), 6.68 (d, J = 8.2 Hz, 1H), 4.33 (m, 1H), 2.85 (dd, J = 13.5, 5.1 Hz, 1H), 2.63 (dd, J = 13.7, 9.2 Hz, 1H), 2.55 (d, J = 4.5 Hz, 3H), 1.78 (s, 3H). 13 C NMR (150 MHz, DMSO-d6): δ172.64, 170.02, 153.90, 150.86, 148.44, 135.37, 129.22, 129.02, 126.96, 126.48, 126.03, 122.72, 117.74, 55.47, 38.23, 26.51, 23.56. HRMS: calcd for C20H22N5O5 (MH+) 412.1615, found 412.1615. Compound (3b). The compound 3b was prepared from tyrosine 1 (14.2 mg, 0.060 mmol) and 0.5 M solution of MTAD 2b (0.438 mL, 0.132 mmol), and was obtained as white amorphous solid (11.9 mg, 57%). 1 H NMR (300 MHz, DMSO-d6): δ 10.51 (br, 1H), 8.05 (d, J = 8.4 Hz, 1H), 7.86 (q, J = 4.4 Hz, 1H), 7.21 (s, 1H), 7.02 (dd, J = 1.9, 8.4 Hz, 1H), 6.77 (d, J = 8.3 Hz, 1H), 4.28 (m, 1H), 2.92 (s, 3H), 2.82 (dd, J = 13.8, 4.8 Hz, 1H), 2.60 (dd, J = 13.5, 9.9 Hz, 1H), 2.53 (d, J = 4.5 Hz, 3H), 1.75 (s, 3H). 13C NMR (75 MHz, DMSO-d6): δ172.28, 169.81, 154.68, 153.39, 152.07, 150.78, 130.59, 129.42, 124.27, 117.14, 54.98, 37.38, 26.20, 25.44, 23.22. HRMS: calcd for C15H19N5O5 (MH+) 350.1459, found 350.1460. 2 Ban, Nagano, Gavrilyuk, Hakamata, Inokuma, and Barbas, III S3 O N O N NH OH O H N N H O 3a 3 Ban, Nagano, Gavrilyuk, Hakamata, Inokuma, and Barbas, III S4 O Me N O N NH OH O H N N H O 3b 4 Ban, Nagano, Gavrilyuk, Hakamata, Inokuma, and Barbas, III S5 2. Synthesis of the PTAD analogs 2-1. Synthesis of aniline derivatives. 4N H2SO4 O O H2SO4 H2N AcHN A 4a 4-Propargyloxy aniline sulfate (4a). A solution of N-(4-(propargyloxy)phenyl)acetamide A (650 mg, 3.44 mmol) in 4 M H2SO4 (10 mL) was stirred under reflux for 3 h. Obtained white crystals were filtered and washed with Et2O to give 4a (577 mg, 68%). 1 H NMR (300 MHz, DMSO-d6): δ 8.18 (br, 2H), 6.97-6.90 (m, 4H), 4.73 (d, J = 3.0 Hz, 2H), 3.55 (t, J = 3.0 Hz, 1H). 13 C NMR (75 MHz, DMSO-d6): δ153.92, 134.71, 120.94, 117.17, 80.61, 79.20, 57.06. HRMS: calcd for C9H10NO (MH+) 148.0757, found 148.0754. O Br 1) H2, Pd/C 2) (Boc)2O O2N B O BocHN Br O NaN3 BocHN C D N3 O 4N HCl HCl H2N N3 4b 5 Ban, Nagano, Gavrilyuk, Hakamata, Inokuma, and Barbas, III S6 4-N-Boc-(2-bromoethoxy)benzene (C). A suspension of 1-(2-bromoethoxy)-4-nitrobenzene B (1.00 g, 4.06 mmol) and 10% Pd/C (100 mg) in THF (20 mL) was stirred at room temperature for 3 h under a hydrogen atmosphere. Hydrogen was replaced with argon, and a solution of (Boc)2O (708 mg, 4.06 mmol) in THF (5 mL) was added. After overnight, the catalyst was removed by passing through Celite. After evaporation, the obtained solids were washed with Hexane/Et2O to give C (742 mg, 58%) as white solid. 1 H NMR (300 MHz, CDCl3): δ 7.28-7.25 (m, 2H), 6.87-6.84 (m, 2H), 6.41 (br, 1H), 4.25 (t, J = 6.0 Hz, 2H), 3.61 (t, J = 6.0 Hz, 2H), 1.51 (s, 9H). 13C NMR (75 MHz, CDCl3): δ154.36, 153.39, 132.52, 120.80, 115.66, 80.67, 68.65, 29.53, 28.69. HRMS: calcd for C13H18BrNNaO3 (MNa+) 338.0362, found 338.0366. 4-N-Boc-(2-azidoethoxy)benzene (D). A suspension of compound C (1.64 g, 5.19 mmol) and NaN3 (1.68 g, 25.9 mmol) in DMF (25 mL) was stirred at 50 0C for 3 h. Then, EtOAc and water were added. The organic layer was separated and washed once with water. The resulting aqueous layer was extracted once with EtOAc. The combined organic layer was dried over MgSO4, and concentrated in vacuo. The residue was purified by short silica gel chromatography (Hexane/EtOAc) and washing with Hexane/Et2O to give D (1.24 g, 86%) as white crystals. 1 H NMR (300 MHz, CDCl3): δ 7.29-7.26 (m, 2H), 6.87-6.84 (m, 2H), 6.43 (br, 1H), 4.11 (t, J = 6.0 Hz, 2H), 3.57 (t, J = 6.0 Hz, 2H), 1.51 (s, 9H). 13C NMR (75 MHz, CDCl3): δ154.51, 153.41, 132.42, 120.75, 115.36, 80.63, 67.64, 50.49, 28.67. HRMS: calcd for C13H18N4NaO3 (MNa+) 301.1271, found 301.1258. 4-Propargyloxy aniline sulfate (4a). A solution of N-(4-(propargyloxy)phenyl)acetamide A (650 mg, 3.44 mmol) in 4 M H2SO4 (10 mL) was stirred under reflux for 3 h. Obtained white crystals were filtered and washed with Et2O to give 4a (577 mg, 68%). 1 H NMR (300 MHz, DMSO-d6): δ 8.18 (br, 2H), 6.97-6.90 (m, 4H), 4.73 (d, J = 3.0 Hz, 2H), 3.55 (t, J = 3.0 Hz, 1H). 13 C NMR (75 MHz, DMSO-d6): δ153.92, 134.71, 120.94, 117.17, 80.61, 79.20, 57.06. HRMS: calcd for C9H10NO (MH+) 148.0757, found 148.0754. O OH K2CO3, KI BocHN E O Cl O O O 4N HCl HCl H2N BocHN F 4c 6 Ban, Nagano, Gavrilyuk, Hakamata, Inokuma, and Barbas, III S7 4-N-Boc-(2-oxopropoxy)benzene (F). To a suspension of 4-N-Boc-aminophenol E (4.00 g, 18.2 mmol), K2CO3 (3.05 g, 22.1 mmol) and KI (1.22 g, 7.36 mmol) in acetone (40 mL) was added chloroacetone (0.703 mL, 8.83 mmol) under reflux. After 2 h, additional chloroacetone (0.703 mL, 8.83 mmol) was added. The resulting suspension was stirred under reflux for 2 h. Then, EtOAc and water were added. The organic layer was separated and washed once with water. The resulting aqueous layer was extracted once with EtOAc. The combined organic layer was dried over MgSO4, and concentrated in vacuo. The generated white solids were washed with Hexane/Et2O to give F (1.63 g, 83%). 1 H NMR (300 MHz, DMSO-d6): δ 9.13 (br, 1H), 7.33-7.30 (m, 2H), 6.82-6.78 (m, 2H), 4.71 (s, 2H), 2.13 (s, 3H), 1.45 (s, 9H). 13 C NMR (75 MHz, CDCl3): δ206.25, 153.96, 153.37, 132.78, 120.81, 115.23, 80.65, 73.72, 28.65, 26.92. HRMS: calcd for C14H20NNaO4 (MNa+) 288.1206, found 288.1199. 4-(2-Oxopropoxy)aniline hydrochloride (4c). A solution of compound F (400 mg, 1.51 mmol) in 4 M HCl/dioxane (10 mL) was stirred at room temperature for 3 h. Solvent was removed in vacuo and resulting pale brown solids were washed with EtOAc to give 4c (303 mg, quant.). 1 H NMR (300 MHz, DMSO-d6): δ 10.3 (br, 2H), 7.35-7.32 (m, 2H), 7.02-6.99 (m, 2H), 4.87 (s, 2H), 2.16 (s, 3H). 13C NMR (75 MHz, DMSO-d6): δ204.68, 158.20, 125.42, 116.32, 73.17, 27.20. HRMS: calcd for C9H12NO2 (MH+) 166.0863, found 166.0867. 2-2. Synthesis of Aplaviroc derivatives O O O O H2N O 3 N O O O PPh3, H2O/Et2O O N H G 3 N3 N H I N H O 3 O O O O O N N H O 26 NH O H N3 O N HO NH N O OH N HN HN BOP, TEA, DMF O O O O O 3 9b HN HN N O OH NH2 N3 CuSO4, Na Ascorbate, THPTA, t-BuOH/ H2O (1:1), rt, 52 % O Aplaviroc (24) O 25 N N N N N H O 3 O 27 O N N H NH N O OH Compound I: 7 Ban, Nagano, Gavrilyuk, Hakamata, Inokuma, and Barbas, III S8 To a solution of azido-amine G (Aldrich, 468 mg, 2.391 mmol) in acetonitrile (5 mL) was added pentynoic acid succinimide ester H (474 mg, 2.391 mmol) at room tempareture and stirred for 12 hours. Then, dichloromethane were added and was separated and washed 0.5 M HCl, sat.NaHCO3 aq. and brine. Combined organic layer was dried over Na2SO4, and concentrated in vacuo. The residue was purified by silica gel chromatography (EtOAc) to give I (620 mg, 87%) as a white solid. 1 H NMR (400 MHz, CDCl3): δ 6.30 (br s, 1H), 3.75-3.57 (m, 10H), 3.60-3.57 (m, 2H), 3.52-3.47 (m, 2H), 3.49-3.41 (m, 2H), 2.57-2.53 (m, 2H), 2.45-2.41 (m, 2H), 2.04 (t, J = 5.3 Hz, 1H), 13 C NMR (125 MHz, MeOD-d4): δ173.09, 82.78, 72.70, 70.67, 70.65, 70.62, 70.60, 70.56, 70.52, 70.48, 70.42, 70.32, 70.12, 69.60, 61.26, 50.81, 48.19, 39.48, 35.47. HRMS: calcd for C13H22N4O4 (MH+) 299.1714, found 299.1715. 3. NMR-charts of the PTAD analogs O Br BocHN C 8 Ban, Nagano, Gavrilyuk, Hakamata, Inokuma, and Barbas, III S9 O N3 BocHN D 9 Ban, Nagano, Gavrilyuk, Hakamata, Inokuma, and Barbas, III S10 O H2SO4 H2N 4a 10 Ban, Nagano, Gavrilyuk, Hakamata, Inokuma, and Barbas, III S11 11 Ban, Nagano, Gavrilyuk, Hakamata, Inokuma, and Barbas, III S12 O HCl H2N N3 4b 12 Ban, Nagano, Gavrilyuk, Hakamata, Inokuma, and Barbas, III S13 O O BocHN F 13 Ban, Nagano, Gavrilyuk, Hakamata, Inokuma, and Barbas, III S14 O O HCl H2N 4c 14 Ban, Nagano, Gavrilyuk, Hakamata, Inokuma, and Barbas, III S15 N3 O N HN N H O 8d 15 Ban, Nagano, Gavrilyuk, Hakamata, Inokuma, and Barbas, III S16 O O N HN N H O 8a 16 Ban, Nagano, Gavrilyuk, Hakamata, Inokuma, and Barbas, III S17 O N3 O N HN N H O 8b 17 Ban, Nagano, Gavrilyuk, Hakamata, Inokuma, and Barbas, III S18 O O O N HN N H O 8c 18 Ban, Nagano, Gavrilyuk, Hakamata, Inokuma, and Barbas, III S19 O N HN N H O 8e 19 Ban, Nagano, Gavrilyuk, Hakamata, Inokuma, and Barbas, III S20 O O N HN N H O 8f 20 Ban, Nagano, Gavrilyuk, Hakamata, Inokuma, and Barbas, III S21 N3 O N HN N H O 8d 21 Ban, Nagano, Gavrilyuk, Hakamata, Inokuma, and Barbas, III S22 O O N N N O 9a O N3 O N N N O 9b 22 Ban, Nagano, Gavrilyuk, Hakamata, Inokuma, and Barbas, III S23 O O O N N N O 9c 23 Ban, Nagano, Gavrilyuk, Hakamata, Inokuma, and Barbas, III S24 O O N H 3 N3 I 24 Ban, Nagano, Gavrilyuk, Hakamata, Inokuma, and Barbas, III S25 O O N H O 3 O N N H O 26 NH N O OH 25 Ban, Nagano, Gavrilyuk, Hakamata, Inokuma, and Barbas, III S26 O O O O HN HN N O N N N N H O 3 O 27 O N N H NH N O OH 26 Ban, Nagano, Gavrilyuk, Hakamata, Inokuma, and Barbas, III S27 4. The reactions of tyrosine derivative with PTAD analogs 1 H NMR of the mixture of the reaction 2a 1 1 3a Effect of buffer concentration 27 Ban, Nagano, Gavrilyuk, Hakamata, Inokuma, and Barbas, III S28 N3 N3 O N O N N H O NH OH O 8d H N N H N HN OH O O O 100 mM Na phosphate buffer (pH 7) MeCN (1:1), r.t. N H N3 O H N O 1 O N3 O N O O N OH O H N N H O N HN N H OH O 8b 100 mM Na phosphate buffer (pH 7) MeCN (1:1), r.t. NH O N H H N O 1 28 Ban, Nagano, Gavrilyuk, Hakamata, Inokuma, and Barbas, III S29 O O O O N N OH O N H OH O H N N H 100 mM Na phosphate buffer (pH 7) MeCN (1:1), r.t. O N O 8a H N N H O HN NH O 1 O O O O O N O N OH O HN N H H N N H O OH O 8c O N 100 mM Na phosphate buffer (pH 7) MeCN (1:1), r.t. NH O N H H N O 1 29 Ban, Nagano, Gavrilyuk, Hakamata, Inokuma, and Barbas, III S30 O N O N OH O H N N H O O HN N H N 8e 100 mM Na phosphate buffer (pH 7) MeCN (1:1), r.t. NH OH O O N H H N O 1 30 Ban, Nagano, Gavrilyuk, Hakamata, Inokuma, and Barbas, III S31 5. Peptide modification with PTAD analogs 5-1 HPLC and MS chart O 3 eq. O O HN H N H2N O H2N N H H N O N H OH H N O O N H H N OH O H N N H O N O NH O O NH2 NH N N N O O HN N H 100 mM Na phospate bufer (pH 7) N H2N N NH O O OH O 9a OH O H N HN NH2 O H2N N H H N O O N H OH H N O O N H H N O H N N H O O O N H OH O NH N NH2 NH2 Dodecapeptide (10) 11a 11a HPLC Crude reaction LC/MS 10 peak 1 mod. compound peak 1307.7 1536.7 31 Ban, Nagano, Gavrilyuk, Hakamata, Inokuma, and Barbas, III S32 MS of peptide (10) MS of modified peptide (11a) 32 Ban, Nagano, Gavrilyuk, Hakamata, Inokuma, and Barbas, III S33 O 3 eq. O HN H N H2N O H2N N H H N O N H OH H N O O N H H N OH O H N N H O N O NH N H H N O H2N HN NH2 N NH O O OH 9b OH O HN N N N O N3 O O NH O O NH2 N3 O 100 mM Na phospate bufer (pH 7) N H2N N H H N O O N H OH H N O O N H H N O H N N H O O O N H OH O NH N NH2 Dodecapeptide (10) NH2 11b 11b HPLC Crude reaction LC/MS SM peak 1 mod. compound peak 1307.6 1567.8 33 Ban, Nagano, Gavrilyuk, Hakamata, Inokuma, and Barbas, III S34 MS of peptide (10) MS of modified peptide (11b) 34 Ban, Nagano, Gavrilyuk, Hakamata, Inokuma, and Barbas, III S35 O O O 3 eq. O HN H N H2N O H2N N H H N O N H OH H N O O N H H N OH O H N N H O O N O NH O O NH2 O N O N H OH O NH N HN N N H N H2N O 9c 100 mM Na phospate bufer (pH 7) O H2N N H H N O N H OH H N O NH2 N NH O O HN O N H H N O OH O H N N H O O O N H OH O NH N NH2 NH2 Dodecapeptide (10) 11c 11c HPLC Crude reaction LC/MS SM peak 1 mod. compound peak 1307. 4 1555. 6 35 Ban, Nagano, Gavrilyuk, Hakamata, Inokuma, and Barbas, III S36 MS of decapeptide (10) MS of 1 modified peptide (11c) 36 Ban, Nagano, Gavrilyuk, Hakamata, Inokuma, and Barbas, III S37 5-2. MS/MS analysis of labeling peptides YG Y-­‐ CO2H YGFHRKQS/2 YGFHRKQSW/2 11a YGFHRK Y YGFHR YG Y-­‐ CO2H YGFHRKQS/2 YGFHRKQSW/2 Y 11c YGFHRK YGFHR YG YGFHRKQS/2 3 YGFHRKQSW/2 11b 37 Ban, Nagano, Gavrilyuk, Hakamata, Inokuma, and Barbas, III S38 6. Albumin modification through three different orthogonal reactions 1) Reaction of albumins with dansyl derivative O R1 NH2 R N 2 N N 9 O NH R1-CO2H R1 NH OH N N H OH HS OH K-modified protein HSA (12) BSA (13) EDTA, SSC O buffer (pH7.0) NH O R2 O O N N N S N H OH O C, Y, K-modified protein HSA (16a, 16b, 16c) BSA (17a, 17b, 17c) O a H N 5 R3 O Y, K-modified protein HSA (14a, 14b, 14c) BSA (15a, 15b, 15c) O R1 = R2 O R1 R3 N Na Phosphate buffer (pH7.4) HS HSA or BSA O N EDC, H2O (pH6) HS O O O O S O O R2 = N b O N3 R3 = O O CO2H OH c Overlay of MALDI-TOF MS charts of HSA (red) and 12 (blue); molecular weight increase 1592. 38 Ban, Nagano, Gavrilyuk, Hakamata, Inokuma, and Barbas, III S39 Overlay of MALDI-TOF MS charts of BSA (red) and 13 (blue); molecular weight increase 1706. Fluorescence intensity of dansyl moiety of HSA, BSA, 12, and 13. 12 13 39 Ban, Nagano, Gavrilyuk, Hakamata, Inokuma, and Barbas, III S40 2) Reaction of dansyl-albumins with PTAD derivative. Overlay of MALDI-TOF MS charts of 12 (blue) and 14a (red). Molecular weight increase 1540. Overlay of MALDI-TOF MS charts of 12 (blue) and 14b (red). Molecular weight increase 1681. 40 Ban, Nagano, Gavrilyuk, Hakamata, Inokuma, and Barbas, III S41 Overlay of MALDI-TOF MS charts of 12 (blue) and 14c (red). Molecular weight increase 1130. Overlaid MALDI-TOF MS chart of 13 (blue) and 15a (red). Molecular weight increase 1708. 41 Ban, Nagano, Gavrilyuk, Hakamata, Inokuma, and Barbas, III S42 Overlay of MALDI-TOF MS charts of 13a (blue) and 15b (red). Molecular weight increase 1681. Overlay of MALDI-TOF MS charts of 13a (blue) and 15c (red). Molecular weight increase 969. 42 Ban, Nagano, Gavrilyuk, Hakamata, Inokuma, and Barbas, III S43 3) Reaction of dual labeled albumins with fluorescein-5-maleimide. Overlay of MALDI-TOF MS charts of 14a (blue) and 16a (red). Molecular weight increase 966. Overlay of MALDI-TOF MS charts of 14b (blue) and 16b (red). Molecular weight increase 568. 43 Ban, Nagano, Gavrilyuk, Hakamata, Inokuma, and Barbas, III S44 Overlay of MALDI-TOF MS charts of 14c (blue) and 16c (red). Molecular weight increase 1142. Overlay of MALDI-TOF MS charts of 15a (blue) and 17a (red). Molecular weight increase 492. 44 Ban, Nagano, Gavrilyuk, Hakamata, Inokuma, and Barbas, III S45 Overlay of MALDI-TOF MS charts of 15b (blue) and 17b (red). Molecular weight increase 755. Overlay of MALDI-TOF MS charts of 15c (blue) and 17c (red). Molecular weight increase 682. 45 Ban, Nagano, Gavrilyuk, Hakamata, Inokuma, and Barbas, III S46 Fluorescence intensity of fluorescein moiety of 14a-c, 15a-c, 16a-c and 17a-c. 14a 14b 14c 16a 16b 16c HSA Deriv. 15a 15b 15c 17a 17b 17c BSA Deriv. 46 Ban, Nagano, Gavrilyuk, Hakamata, Inokuma, and Barbas, III S47 7. Chymotrypsinogen PTAD labeling buffer study We noted an experimental artifact in our original PTAD labeling study of chymotrypsinogen (ref. 1, figure 3B), namely the addition of a mass of approximately 336 daltons to the protein. It is known that PTADs can decompose to form isocyanates2 and a mass addition of 336 is consistent with isocyanate formation of the PTAD azide derivative used in the original study and its subsequent reaction with various nucleophilic functionalities present on proteins like amines and hydroxyls. The simplest PTAD shown above is expected to decompose to an isocyanate of mass 119 (see above). Reaction of isocyanate derivatives with a protein is expected to be promiscuous whereas direct reaction with PTADs is highly selective for the phenolic side chain of tyrosine as we have proven in many cases.3 We suspect that with slow reacting proteins with no or poorly exposed/reactive tyrosine residues like chymotrypsinogen, decomposition of PTADs produces isocyanates that then promiscuously label the protein. In our initial disclosure of PTAD labeling1, we had documented that labeling is effective in a wide variety of buffered solutions, including 2-amino-2-hydroxymethyl-propane-1,3-diol or Tris buffered solution. Since Tris buffer contains a primary amine, we studied the potential of using Tris buffer as an isocyanate scavenger in PTAD labeling reactions of chymotrypsinogen. As shown in the ESI-MS charts that follow, chymotrypsinogen labeling in phosphate buffer revealed significant isocyanate labeling. Addition of as little as 5% volume Tris to the PBS solution, however, acted to significantly scavenge the isocyanate decomposition product, while addition of 25% volume Tris nearly completely removed detectable isocyanate-derived protein labeling as effectively as performing the reaction in Tris buffer itself. Thus for the PTAD labeling of particular proteins, an exploration of buffers, including mixed PBS/Tris buffered media is recommended to ensure tyrosine selective labeling when Tyr specificity is critical. PBS buffer is often fine. 47 Ban, Nagano, Gavrilyuk, Hakamata, Inokuma, and Barbas, III S48 Study of Chymotrypsinogen labeling with PTAD in PBS/Tris buffered conditions: To the 1.7 ml microcentrifuge tube was added chymotrypsinogen solution (60.6 µM protein in 98 µL mixed buffer prepared by volumetric mixing of PBS (10 mM, pH 7.4) and Tris (1.0 M, pH 7.4) buffers) followed by addition of PTAD (100 mM in DMF, 2 µL). The reaction mixture was allowed to stand at room temperature for 15 min before the unreacted small molecules were removed using Zeba spin desalting column (7k MWCO). ESI-MS was then obtained and are given below. 1. Ban, H., Gavrilyuk, J., and Barbas, C. F. (2010) Tyrosine Bioconjugation through Aqueous Ene-Type Reactions: A Click-Like Reaction for Tyrosine. Journal of the American Chemical Society 132, 1523-1525. 2. Wamhoff, H., and Wald, K. (1977) Zur Photolyse und Thermolyse von 4-Aryl-1,2,4-triazolin3,5-dionen. Chem. Ber., 110, 1699-1715. 3. We thank Drs Edmund Graziani and Qi-Yang Hu for also bringing the artifact at ref. 1, Fig. 3B to our attention and Qi-Yang Hu for additional discussion. ESI-MS charts for Chymotrysinogen labeling with PTAD Unmodified protein 48 Ban, Nagano, Gavrilyuk, Hakamata, Inokuma, and Barbas, III S49 Labeling in PBS Labeling in PBS/Tris (95/5) 49 Ban, Nagano, Gavrilyuk, Hakamata, Inokuma, and Barbas, III S50 Labeling in PBS/Tris (85/15) 50 Ban, Nagano, Gavrilyuk, Hakamata, Inokuma, and Barbas, III S51 Labeling in PBS/Tris (75/25) Labeling in Tris 51 Ban, Nagano, Gavrilyuk, Hakamata, Inokuma, and Barbas, III S52 8. PTAD mediated PEGylation reaction Preparation of PEG-PTAD O O O 5k PEG Propargyl amine, DMF, rt, 3h N O N H 5k PEG O In the 1.5 ml Eppendorf tube were mixed 5k PEG-NHS (NOF Corporation, 98% end group reactivity) (38 ul of 50 mM solution in DMF, 1.89 umoles, 1 eq) and propargyl amine (1.89 ul of 1M solution in DMF, 1.89 umoles, 1 eq). The reaction mixture was vortexed gently and kept at room temperature for 3 hours with intermittent vortexing. Methyl amine (5 ul, neat) was added to the reaction to make sure all the activated ester groups were consumed; reaction was vortexed and kept at room temperature for 30 min. The product polymer was precipitated out with cold ether, centrifuged and ether decanted. The resulting white solid was washed with cold ether two times and dried. Isolated yield 9.1 mg, 93%. MALDI-TOF MWav.= 5656. MALDI-TOF Method: PEPDNA2 Laser : 2100 Mode: Linear Scans Averaged: 256 Accelerating Voltage: 25000 Pressure: 6.04e-08 Grid Voltage: 95.500 % Low Mass Gate: 900.0 This File # 2 : D:\DATA\ROUTINE\2012\APRIL\040912\SMOOTH.MS Guide Wire Voltage: 0.200 % Timed Ion Selector: 25.2 OFF Comment: Delay: 100 ON Negative Ions: OFF Sample: 18 Collected: 4/10/12 9:55 AM Original Filename: d:\data\routine\2012\april\040912\9350s.ms Low Mass Gate: 900.0 This File # 2 : D:\DATA\ROUTINE\2012\APRIL\040912\SMOOTH.MS Guide Wire Voltage: 0.200 % Timed Ion Selector: 25.2 OFF Comment: Delay: 100 ON Negative Ions: OFF Sample: 28 Collected: 4/10/12 10:11 AM PEG-alkyne: Savitsky-Golay Order = 2 Points = 19 1800 5541 5585 5629 5673 1600 5717 3500 5656 5700 5744 Savitsky-Golay Order = 2 Points = 19 4000 Pressure: 5.82e-08 Grid Voltage: 95.500 % 5788 Method: PEPDNA2 Scans Averaged: 256 Accelerating Voltage: 25000 5832 PEG-NHS (starting material): MALDI-TOF Laser : 2400 Mode: Linear Original Filename: d:\data\routine\2012\april\040912\9351s.ms Counts MALDI-TOF Method: PEPDNA2 Laser : 2100 Mode: Linear 1400 2500 Scans Averaged: 256 Accelerating Voltage: 25000 Original Filename: d:\data\routine\2012\april\040912\9350s.ms Pressure: 6.04e-08 Grid Voltage: 95.500 % Low Mass Gate: 900.0 This File # 1 : D:\DATA\ROUTINE\2012\APRIL\040912\9350SM.MS Guide Wire Voltage: 0.200 % Timed Ion Selector: 25.2 OFF Comment: Delay: 100 ON Negative Ions: OFF Sample: 18 Collected: 4/10/12 9:55 AM 2000 Savitsky-Golay Order = 2 Points = 19 3500 BSJG9350 BSJG9351 1200 1500 3000 1000 4500 5000 5500 Mass (m/z) 6000 6500 7000 5000 5500 6000 6500 7000 Mass (m/z) 2500 Counts Counts 3000 2000 1500 52 1000 4500 5000 5500 6000 Mass (m/z) 6500 7000 Ban, Nagano, Gavrilyuk, Hakamata, Inokuma, and Barbas, III S53 Overlay of PEG-NHS starting material (red) with PEG-alkyne (blue): Synthesis of PEG-urazole (23): In the 1.5 ml Eppendorf tube were mixed 5k PEG-alkyne (NOF Corporation, 98% end group reactivity) (15 µl of 48 mM solution in DMF, 0.72 µmoles, 1 eq) and 1,2,4-triazolidine-3,5-dione azide 14 (30 µl of 24 mM solution in DMF, 0.72 µmoles, 1 eq) followed by addition of a small piece of copper wire and copper sulfate (0.72 µl, 100 mM solution in DI water). The reaction mixture was vortexed gently and kept at 37 oC for 2 hrs with intermittent vortexing. Copper wire was removed and copper ions were scavenged from the reaction mixture using “CupriSorb” resin (Seachem) over night at room temperature. The Cuprisorb resin was filtered and product polymer was precipitated out with cold ether, centrifuged and ether decanted. The resulting white solid (23) was washed with cold ether two times and dried. Isolated yield 4.0 mg, 95%. MALDI-TOF MWav.= 5921. MALDI-TOF PEG-alkyne: Original Filename: d:\data\routine\2012\april\040912\9352s2.ms This File # 1 : D:\DATA\ROUTINE\2012\APRIL\040912\SMOOTH.MS Comment: Method: PEPDNA2 Laser : 2100 Mode: Linear Scans Averaged: 256 Accelerating Voltage: 25000 Pressure: 5.89e-08 Grid Voltage: 95.500 % Low Mass Gate: 900.0 Guide Wire Voltage: 0.200 % Timed Ion Selector: 25.2 OFF Delay: 100 ON Negative Ions: OFF Sample: 38 Collected: 4/10/12 10:20 AM MALDI-TOF Method: PEPDNA2 Laser : 2100 Mode: Linear Scans Averaged: 256 Accelerating Voltage: 25000 Original Filename: d:\data\routine\2012\april\040912\9350s.ms Pressure: 6.04e-08 Overlay of PEG-NHS (red) with PEG-PTAD(green). Grid Voltage: 95.500 % Low Mass Gate: 900.0 This File # 1 : D:\DATA\ROUTINE\2012\APRIL\040912\9350SM.MS Guide Wire Voltage: 0.200 % Timed Ion Selector: 25.2 OFF Comment: Delay: 100 ON Negative Ions: OFF Sample: 18 Collected: 4/10/12 9:55 AM Savitsky-Golay Order = 2 Points = 19 Savitsky-Golay Order = 2 Points = 19 3500 BSJG9350 O BSJG9352 6000 N 5833 5877 5921 5965 O 5000 5k PEG 3000 N H N N N O O O 3 Counts Counts 2500 4000 2000 3000 2000 1500 1000 1000 4500 5000 5500 6000 Mass (m/z) 6500 7000 7500 4500 5000 5500 6000 6500 NH NH 7000 Mass (m/z) 53 Ban, Nagano, Gavrilyuk, Hakamata, Inokuma, and Barbas, III S54 MALDI-TOF Method: BSAK Laser : 2200 Mode: Linear Scans Averaged: 256 Accelerating Voltage: 25000 Original Filename: d:\data\routine\2012\april\040912\9353s2.ms MALDI-TOF: This File # 1 : D:\DATA\ROUTINE\2012\APRIL\040912\SMOOTH.MS Chymotrypsinogen A: Comment: Pressure: 1.64e-07 Grid Voltage: 94.000 % Low Mass Gate: 1000.0 Guide Wire Voltage: 0.300 % Timed Ion Selector: 26.9 OFF Delay: 50 ON Negative Ions: OFF Sample: 55 Collected: 4/10/12 6:18 AM Savitsky-Golay Order = 2 Points = 19 25691 3500 3000 2500 Counts 2000 1500 1000 500 0 20000 25000 30000 Mass (m/z) 35000 MALDI-TOF Chymotrypsinogen-PEG (PTAD) Method: BSAK Laser : 2700 Mode: Linear Scans Averaged: 256 Accelerating Voltage: 25000 Original Filename: d:\data\routine\2012\april\040912\9354s.ms 40000 Pressure: 1.42e-07 Grid Voltage: 94.000 % Low Mass Gate: 1000.0 This File # 2 : D:\DATA\ROUTINE\2012\APRIL\040912\SMOOTH.MS Guide Wire Voltage: 0.300 % Timed Ion Selector: 26.9 OFF Comment: Delay: 50 ON Negative Ions: OFF Sample: 77 Collected: 4/10/12 6:37 AM Savitsky-Golay Order = 2 Points = 19 800 700 Chymotrypsinogen A + 5k PEGPTAD 600 Counts SM and +1 PEG product 26765 500 400 300 +2 PEG product 200 54 100 20000 25000 30000 Mass (m/z) 35000 40000 Ban, Nagano, Gavrilyuk, Hakamata, Inokuma, and Barbas, III S55 MALDI-TOF Original Filename: d:\data\routine\2012\april\040912\9355s2.ms This File # 2 : D:\DATA\ROUTINE\2012\APRIL\040912\SMOOTH.MS Chymotrypsinogen-PEG(NHS): Comment: Method: BSAK Laser : 2700 Mode: Linear Scans Averaged: 256 Accelerating Voltage: 25000 Pressure: 1.25e-07 Grid Voltage: 94.000 % Low Mass Gate: 1000.0 Guide Wire Voltage: 0.300 % Timed Ion Selector: 26.9 OFF Delay: 50 ON Negative Ions: OFF Sample: 79 Collected: 4/10/12 6:56 AM Savitsky-Golay Order = 2 Points = 19 1000 Chymotrypsinogen A + 5k PEGNHS 800 Counts 600 + 2 + 3 42501 36931 + 1 31372 400 + 4 200 0 20000 30000 40000 50000 60000 Mass (m/z) 70000 80000 90000 100000 55 Counts Scheme 1. Synthesis of heterobifunctional linker 3. O HN HN 400 130000 O N N N N O N N H OH 135000 N H O 27 O O N N N N O 140000 3 O O O O characterized. Linker 3 was reacted with the aptamer and purified. Mouse cp38C2 and human 38C2 (hucp38C2) were then reacted with the lactam portion to yield an irreversible linkage. The antibody and ARC245-conjugated antibodies were analyzed by gel electrophoresis as shown in Figure 2. The reactive lysine is located on the heavy chain of 38C2; consistent with this, we observed that only the heavy chain band was shifted to a higher molecular weight under reducing conditions indicative of site-specific labeling as demonstrated previously for other conjugates.[1c,o,r] Labeling was complete as determined by loss of aldolase activity (Supporting Information). In order to evaluate the binding properties of the ARC245–cpAbs, we performed a previously described dis- O [11d] Scheme 2. Irreversible programming of aldolase antibody 38C2 with aptamer ARC245. N H N N H O 145000 NH N 3 H O O MALDI-TOF Original Filename: d:\data\routine\2012\010312\7050s3.ms 7049: herceptin Mw: 148,444 150000 Mass (m/z) Scheme 1. Synthesis of heterobifunctional linker 3. 6071 N Br OH N O 155000 N O DMF, r.t., 1 min 160000 O N Br OH 165000 62 Method: BSAK Laser : 2300 Mode: Linear Scans Averaged: 200 Accelerating Voltage: 25000 Pressure: 2.55e-07 Grid Voltage: 94.000 % Low Mass Gate: 1000.0 This File # 2 : D:\DATA\ROUTINE\2012\010312\SM7050.MS Guide Wire Voltage: 0.300 % Timed Ion Selector: 26.9 OFF Comment: Delay: 50 ON Negative Ions: OFF Sample: 66 Collected: 1/4/12 6:25 AM characterized.[11d] Linker 3 was reacted with the aptamer and purified. Mouse cp38C2 and human 38C2 (hucp38C2) were then reacted with the lactam portion to yield an irreversible linkage. The antibody and ARC245-conjugated antibodies were analyzed by gel electrophoresis as shown in Figure 2. The reactive lysine is located on the heavy chain of 38C2; consistent with this, we observed that only the heavy chain band was shifted to a higher molecular weight under reducing conditions indicative of site-specific labeling as demonstrated previously for other conjugates.[1c,o,r] Labeling was complete as determined by loss of aldolase activity (Supporting Informa- Scheme 2. Irreversible programming of aldolase antibody 38C2 with aptamer ARC245. cpAb were determined by the method of Oroz e experiment, the affinity of ARC245 was deter 1.8 nm and the aptamer–cpAb had a 30-fold high 66 pM (Supporting Information). This result sh effective affinity of the hucp38C2–ARC245 c increased significantly relative to the monoval ARC245. Other reports indicate that bivalent a a higher functional affinity than their monoval parts.[15] The therapeutic target of ARC245 is V angiogenic factor excreted by many tumors th blood vessel growth, helping to maintain a supp and nutrients to rapidly dividing tumor cells.[16] ARC245 is a potent anti-VEGF antagonist t Figure 3. Competitive ELISA with increasing amounts of unmodified ARC245 (*) or hucp38C2–ARC245 (&) incu 20 nm biotinylated ARC245. Biotinylated ARC245 was de streptavidin–horseradish peroxidase and percent displac plotted. placement ELISA.[14] In this assay, either th ARC245 or hucp38C2-ARC245 competed fo surface-coated VEGF165 with biotinylated A from this assay is shown in Figure 3. hucp38 showed a 60-fold lower EC50 value than the a (0.69 nm vs. 41 nm). The affinities of aptamer a Figure 2. Representative SDS acrylamide gel after conju body and aptamer. Lane 1, unmodified 38C2; lane 2, hu (hu38C2) after conjugation to aptamer; lane 3, mouse 3 after conjugation to ARC245; lanes 1’, 2’, and 3’, sample three lanes under reducing conditions. www.angewandte.de cpAb were determined by the method of Oroz et al.[14] In this experiment, the affinity of ARC245 was determined to be 1.8 nm and the aptamer–cpAb had a 30-fold higher affinity of 66 pM (Supporting Information). This result shows that the effective affinity of the hucp38C2–ARC245 conjugate was increased significantly relative to the monovalent aptamer ARC245. Other reports indicate that bivalent aptamers have a higher functional affinity than their monovalent counterparts.[15] The therapeutic target of ARC245 is VEGF, a proangiogenic factor excreted by many tumors that stimulates blood vessel growth, helping to maintain a supply of oxygen and nutrients to rapidly dividing tumor cells.[16] ARC245 is a potent anti-VEGF antagonist that prevents VEGF from binding to the VEGF receptor.[11d] To study the biological activity of cp38C2–ARC245, we performed cell migration assays using human umbilical cord endothelial cells Figure 3. Competitive ELISA with increasing amounts of either unmodified ARC245 (*) or hucp38C2–ARC245 (&) incubated with 20 nm biotinylated ARC245. Biotinylated ARC245 was detected with streptavidin–horseradish peroxidase and percent displacement was plotted. placement ELISA.[14] In this assay, either the unlabeled ARC245 or hucp38C2-ARC245 competed for binding to surface-coated VEGF165 with biotinylated ARC245. Data from this assay is shown in Figure 3. hucp38C2–ARC245 showed a 60-fold lower EC50 value than the aptamer alone (0.69 nm vs. 41 nm). The affinities of aptamer and aptamer– 9. Trastuzumab (Herceptin) conjugation with Aplaviroc-PTAD ! 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim O Angew. Chem. 2010, 122, 6070 –6073 Figure 2. Representative SDS acrylamide gel after conjugation of antibody and aptamer. Lane 1, unmodified 38C2; lane 2, human 38C2 (hu38C2) after conjugation to aptamer; lane 3, mouse 38C2 (38C2) after conjugation to ARC245; lanes 1’, 2’, and 3’, samples as in first three lanes under reducing conditions. Ban, Nagano, Gavrilyuk, Hakamata, Inokuma, and Barbas, III S56 Comparison of products of reaction of Chymotrypsinogen A with 5-kDa PEG-PTAD and 5-kDa PEGNHS. Products were separated on a NuPage 4-12% Bis-Tris gel (Invitrogen) and the gel was Coomassie stained: L, molecular weight ladder; lane 1, Chymotrypsinogen A; lane 2, reaction with 10 eq. PEG-PTAD; lane 3, reaction with 10 eq. PEG-NHS. Herceptin Na Phosphate Buffer (pH 7.4)/3 % DMF, rt, < 5 min O N NH OH Herceptin-Aplaviroc (28) 1.3 600 Savitsky-Golay Order = 2 Points = 19 7049 500 7050 7050: herceptin-Aplaviroc Mw: 149,820 300 200 100 170000 56 Ban, Nagano, Gavrilyuk, Hakamata, Inokuma, and Barbas, III S57 10. Stability study in human plasma HPLC charts of the analyzed compounds. 7.40 min O N O 6.23 min S 0h 14.7 min O 6.23 min IS IS 12.8 min 14.7 min N O N NH 0h OH 3min 3min 1h 1h Decomposed! 120h O H N HO S O 120h O N H OH S O LC-MS found 57