Supporting information
A Family of Single-Isomer, Dicationic Cyclodextrin Chiral
Selectors for Capillary Electrophoresis:
Mono-6A-ammonium-6C-butylimidazolium-β-cyclodextrin
chlorides
Yun Dai, Shuye Wang, Jie Zhou, Jian Tang*, Weihua Tang*
Key Laboratory of Soft Chemistry and Functional Materials, Nanjing University of
Science and Technology, Nanjing 210094, P.R. China
Email: whtang@mail.njust.edu.cn
Content
1. Materials, Characterization and Methods……………………...………….…..S2
2. Experimental Procedures……………………………………………………..…S2
3.
1H
and 13C NMR spectra ....…………………………………………….…….....S6
4. CE operating procedure………………………………………………...………S10
S1
1. Materials, Characterization and CE Methods
Materials. All chemical reagents and solvents were purchased from Sigma (St.
Louis, MO, USA). Pyridine, ethanol and N,N-dimethylformamide (DMF) were
freshly distilled over CaH 2 prior to use. All racemic analytes (Structure in Figure S1)
were purchased either from Aldrich (Steinheim, Germany) or from Sigma (St. Louis,
MO, USA).
Characterization. All synthetic intermediate compounds were routinely checked
by infrared (IR) spectra (Shimadzu FT-IR 8101 M, Shimadzu Corporation, Kyoto,
Japan). 1H and
13
C nuclear magnetic resonance (NMR) spectra were obtained on a
Bruker AVANCE 500 (Bruker Bio-Spin Corporation, Europe) working at 500 and 125
MHz, respectively; δ in ppm relative to SiMe4 as internal standard; coupling constants
J in Hz; 13CNMR spectra were fully decoupled. The mass spectra of CD-cation were
collected in positive modes in a single run from a Finniga/AM TSQ Quantum
(Thermal, USA).
CE methods. Beckman P/ACE MDQ CE unit (Fullerton, CA, USA) was used for
all CE separations. 50 μm ID, 375 μm OD fused silica capillary was used with a total
length of 59.2 cm (49 cm to the detector). Detection of analytes was carried out
simultaneously at 214 nm, 254 nm and 280nm by using variable-wavelength PDA
(Photodiode Array, 190-300 nm) detector. The electrosmotic flow (EOF) was
measured
with
methanol
as
neutral
marker.
Samples
were
introduced
hydrodynamically into the capillary at 0.5 psi for 5 s. All experiments were performed
under normal polarity with 15 kV applied voltage.
2. Experimental Procedures
Synthesis of 6A-azido-6C-mesitylenesulfonyl-β-cyclodextrin (Mess-N3-CD, 2)
Starting from 6A-azido-β-cyclodextrin (N3-CD) 1 [1], disubstituted CDs at
primary ring were prepared via nucleophilic substitution of 6-hydroxy group with
2-mesitylenesulfonyl chloride. A typical synthesis is described as follows. Towards a
vigorously stirred solution of 1 (5 g, 4.3 mmol) in freshly distilled pyridine (25 mL)
was added with and 2-mesitylenesulfonyl chloride (4.3 g, 19.4 mmol). The reaction
mixture was stirred at 25oC for 9 h. The crude product was obtained by precipitating
the reaction mixture out of vigorously stirred acetone (200 mL). The precipitate was
S2
collected by filtration and washed with acetone to give
a mixture of three
regio-isomers, 6A-azido-6X-mesitylene-sulfonyl--cyclodextrin (X=B, C or D) as
white solid (5.32 g, yield 82%). The mixture was further subjected to a reversed phase
column
chromatography
to
afford
the
regio-isomer
(Figure
S1),
6A-azido-6C-mesitylene-sulfonyl- -cyclodextrin (Mess-N3-CD) 2 with a yield of 42%
[2]. Most characteristic for Mess-N3-CD in
13
C NMR is: 101.68 (C1), 81.53 (C4),
strong peak centered at 71.82 (C2, C3, C5), and 59.67 (C6 adjacent to hydroxyl),
which agrees well with the literature [3].
Figure S1. Reversed phase column chromatography of Mess-N3-CD 2. A linear
gradient elution of ethanol was applied according to ref. [2].
Characterization data for 2: decompose temperature (dp): 203.5oC; IR(cm-1,
KBr): 3387 (O-H str), 2928 (C-H str), 2104 (N≡N str), 1644, 1637 (C=C str),
1157(S=O str), 1080,1030 (C-O-C str); 1HNMR (500 MHz, DMSO-d6) δ: 7.11 (m, 2H,
aromatic), 5.83-5.70 (m, 14H, OH-2 and OH-3), 4.88-4.82 (m, 7H, H-1), 4.51-4.45 (m,
5H, OH-6), 4.21 (br, 1H, H-3’CD), 4.09 (s, 1H, H-5’CD), 3.64-3.55 (m, 26H, H-5CD,
H-3CD and H-6CD), 3.36-3.26 (m, 14H, H-2CD and H-4CD), 2.29 (s, 6H, Ar-o-CH3),
2.17 (s, 3H, Ar-p-CH3);
13
CNMR (125 MHz, DMSO-d6) δ: 142.99 (Cipso), 138.92
(Cortho), 131.25 (Cpara), 129.53 (Cmeta), 101.68 (C1), 81.53 (C4), 71.92-70.27
(C2,C3,C5), 68.79 (C5’), 59.67 (C6), 59.29(C6’), 21.75 (CH3-ortho), 20.24 (CH3-para);
Anal. Calcd. for C44H79N3O36S: C, 42.00; H, 6.33. Found: C, 41.84; H, 6.72; ESI-MS
(m/z): 1342.42 (calcd.), 1342.26 (found) for [M+].
S3
Synthesis of butylimidazole, 3
Towards a degassed and N2-filled flask was subsequently added with imidazole
(4 g, 58.8 mmol), sodium ethoxide (4.4 g, 64.6 mmol) and anhydrous ethanol (20 mL).
Afterwards, excessive 1-bromobutane (8.85 g, 64.6 mmol) was added dropwise. The
reaction mixture was refluxed at 50oC for 4 h before cooling down to room
temperature. The insoluble solid was filtered off and washed with dichloromethane.
The collected filtrate was concentrated and further distilled under reduced pressure to
afford the title product as yellowish liquid (5.84 g, 80% yield). 1HNMR (500 MHz,
CDCl3) δ: 7.38 (s, 1H, CH-2im), 7.01 (s, 1H, CH-4im), 6.83 (s, 1H, CH-5im), 3.85 (t,
2H, CH2-im), 1.64-1.70 (m, 2H, CH2), 1.22-1.26 (m, 2H, CH2), 0.86 (t, 3H, CH3).
Synthesis of 6A-azido-6C-butylimidazolium-β-cyclodextrin mesitylene sulfonate, 4
Towards a degassed and N2-filled two-necked, round-bottomed flask, was added
with mess-N3-CD 2 (3.0 mmol, 4.02 g), 1-butylimidazole 3 (9.0 mmol, 1.12 g) and
freshly distilled N,N-dimethylformamide (DMF, 15 mL). The reaction mixture was
stirred at 90oC for 48 h under N2 atmosphere. Cooling down to room temperature, the
reaction solution was precipitated using acetone (100 mL). The precipitate was
collected by filtration and washed with acetone (50 mL×2) before dry in vacco at
60oC under vacuum overnight. The crude product was recrystallized from water to
obtain the title product 4 (3.34 g, 76% yield) as a white solid. dp: 221.8oC; IR (cm-1,
KBr): 3396(O-H str), 2928 (C-H str), 2106 (N≡N str), 1644, 1636(C=C str), 1155
(S=O str), 1084, 1030 (C-O-C str); 1HNMR (500 MHz, DMSO-d6) δ： 9.03 (s, 1H,
CH-2im), 8.32 (s, 1H, CH-4im), 8.13 (m, 1H, CH-5im), 7.54 (m, 2H, aromatic),
5.60-5.92 (m,14H, OH-2 and OH-3), 4.86 (s, 1H, H-1), 4.84 (s, 6H, H-1), 4.27-4.63
(m, 5H, OH-6), 4.11 (t, 2H, CH2-im), 3.90 (m, 1H, H-3’CD), 3.83 (m, 1H, H-5’CD),
3.49-3.74 (m, 26H, H-5CD, H-3CD and H-6CD), 3.20-3.48 (m, 14H, H-2CD and H-4CD),
2.32(s, 6H, Ar-o-CH3), 2.16 (s, 3H, Ar-p-CH3), 1.71-1.78 (m, 2H, CH2), 1.20-1.25 (m,
2H, CH2), 0.88 (t, 3H, CH3);
13
C NMR (125 MHz, D2O): 149.10 (Cipso), 144.53
(Cortho), 143.03 (Cpara), 135.53 (Cmeta), 132.32 (=C2im), 128.41 (=C4im), 126.24 (=C5im),
102.39 (C1), 83.41 (C4), 82.30 (C4), 73.52-72.47 (C2,C3,C5), 70.67 (C5’), 60.41
(C6), 51.54 (CH2-im), 45.66 (CH2-im), 36.28 (CH2-im),31.27 (CH3-im), 24.13 (CH3-ortho),
19.94 (CH3-para); ESI-MS (m/z): 1267.25 (calcd.), 1268.69 (found) for [M+].
S4
Synthesis of 6A-amino-6C-butylimidazolium-β-cyclodextrin mesitylene sulfonate, 5
Towards a 50 mL two-necked round-bottomed flask was added with
6A-azido-6C-alkylimidazolium-β-cyclodextrin mesitylene sulfonate 4 (2.0 mmol, 2.93
g), triphenylphosphine (2.2 mmol, 0.52 g) and DMF (10 mL). The reaction was stirred
to proceed at room temperature for 2 h before the addition of deionized water (1.0
mL). The reaction mixture was then heated at 90oC for 3 h. Cooling down the reaction
mixture to room temperature, the reaction solution was precipitated out with acetone
(60 mL). Collected by filtration and washed with acetone (50 mL × 2), the crude
product was dried in vacco at 60oC overnight. After recrystallizaztion from water, the
title product 5 (2.19 g, 76% yield) was obtained as white solid. dp: 214.7oC; IR(cm-1,
KBr): 3383 (O-H str), 2928 (C-H str), 1667, 1658(C=C str), 1155 (S=O str), 1078,
1032 (C-O-C str); 1HNMR (500 MHz, DMSO-d6) δ: 9.03 (s, 1H, CH-2im), 8.62 (s, 1H,
CH-4im), 8.33 (m, 1H, CH-5im), 7.85 (m, 2H, aromatic), 5.52-6.10 (m,14H, OH-2 and
OH-3), 4.96 (s, 1H, H-1), 4.84 (s, 6H, H-1), 4.27 -4.63 (m, 5H, OH-6), 3.91 (t, 2H,
CH2-im), 3.82 (m, 1H, H-3’CD), 3.53-3.79 (m, 27H, H-5CD, H-3CD and H-6CD),
3.18-3.53 (m, 14H, H-2CD and H-4CD), 3.05 (m, 1H, H-4’CD), 2.88(s, 6H, Ar-o-CH3),
2.73 (s, 3H, Ar-p-CH3), 1.59 (m, 2H, CH2), 1.22 (m, 2H, CH2), 0.85 (t, 3H, CH3).
CNMR (125 MHz, DMSO-d6) δ: 145.95 (Cipso), 139.29 (Cortho), 137.83 (Cpara),
13
133.48 (Cmeta), 131.98 (=C2im), 129.20 (=C4im), 128.44 (=C5im), 102.42 (C1), 83.38
(C4’), 82.02 (C4), 73.50-72.55 (C2,C3,C5), 71.29 (C5’), 60.43 (C6), 36.27 (CH2-im),
35.02 (CH2-im) 31.30 (CH2-im), 29.57 (CH3-im), 21.83 (CH3-ortho), 19.30. (CH3-para);
ESI-MS (m/z): 1241.25 (calcd.), 1241.47 (found) for [M+].
Synthesis of 6A-amino-6C-butylimidazolium-β-cyclodextrin chloride, 6
6A-Amino-6C-alkylimidazolium-β-cyclodextrin mesitylene sulfonate 5 (1.4 mmol,
2.02 g) was dissolved in deionized water (50 mL). Amberlite IRA-900 ion-exchange
resin was packed into an addition funnel (100 mL) to half height. The
above-mentioned solution 5 was transferred into the addition funnel and left to stand
for 5 h. The eluent was then collected. Water was distilled off under reduced pressure
to obtain the crude compound. After drying at 60oC in vacco overnight, the title
compound 6 (1.49 g, 75% yield) was obtained as a white solid.
Synthesis of 6A-ammonium-6C-butylimidazolium-β-cyclodextrin chloride, 7
S5
6A-Amino-6C-butylimidazolium-β-cyclodextrin chloride 6 (1.0 mmol, 1.31 g) was
dissolved into deionized water (30 mL). Towards the above vigorously stirred solution
was added dropwise with freshly prepared dilute hydrochloric acid solution (0.1 M,
15 mL) over 1 h. The solution was concentrated to ~10 mL and precipitated from
acetone (100 mL). The solid was obtained by filtration and washed with acetone (50
mL × 2). After drying in vacco at 60oC overnight, the final product 7 (1.18 g, 88%
yield) was obtained by further recrystallization from deionized water as awhite solid.
IR (cm-1, KBr): 3387(O-H str), 2928 (C-H str), 1084, 1030 (C-O-C str); 1HNMR (500
MHz, DMSO-d6) δ: 8.93 (s, 1H, CH-2im), 8.22 (s, 1H, CH-4im), 8.13 (m, 1H, CH-5im),
5.50-6.14 (m,14H, OH-2 and OH-3), 4.96 (s, 1H, H-1), 4.88 (s, 6H, H-1), 4.53-4.27
(m, 5H, OH-6), 4.13 (m, 2H, NH2), 3.90 (t, 2H, CH2-im), 3.84 (m, 1H, H-3’CD),
3.50-3.72 (m, 27H, H-5CD, H-3CD and H-6CD), 3.28-3.50 (m, 14H, H-2CD and H-4CD),
3.15 (m, 1H, H-4’CD), 1.58 (m, 2H, CH2), 1.32 (m, 2H, CH2), 0.91 (t, 3H, CH3).
CNMR (125 MHz, DMSO-d6) δ: 132.81 (=C2im), 130.52 (=C4im), 128.45 (=C5im),
13
102.92 (C1), 83.98 (C4), 73.22 (C2), 72.57-71.92 (C3, C5), 68.12 (C5’), 60.54 (C6),
44.67 (CH2-im), 30.42 (CH2-im), 20.71 (CH2-im), 19.46 (CH2-im); ESI-MS (m/z):
1242.25 (calcd.), 1242.59 (found) for [M+].
3. 1H and 13C NMR spectra of intermediate and final compounds
Figure S2. 1H NMR spectrum of 6A-azido-6C-mesitylenesulfonyl-β-cyclodextrin
(Mess-N3-CD, 2).
S6
Figure S3. 1H NMR and 13 CNMR spectra of 6A-azido-6C-butylimidazoliumβ-cyclodextrin mesitylene sulfonate 4.
S7
Figure S4. 1H NMR and 13 CNMR spectra of 6A-amino-6C-butylimidazoliumβ-cyclodextrin mesitylene sulfonate 5.
S8
Figure S5. 1H NMR and 13 CNMR spectra of 6A-ammonium-6C-butylimidazoliumβ-cyclodextrin chlorides 7.
S9
4. CE operating procedure
Background electrolytes (BGEs) were prepared with 50 mM acetate buffer (pH
5.5, 6.0) and sodium phosphate buffer (pH 6.5, 7.0). The stock racemates (structure
shown in Figure S1) solution (50 μg ml-1) was prepared with methanol/water (50:50,
v/v) mixture solution, filtered with 0.45 μm syringe type Millipore membrane and
sonicated prior to use. Acetate buffer was prepared by dissolving a desirable amount
of sodium acetate in water, with its pH (5.5, 6.0) adjusted with acetic acid while
sodium phosphate buffer was prepared with sodium phosphate and sodium hydroxide
to get the required pH 6.5 and 7.0.
The effect of buffer pH on chiral separation of different types enantiomers was
assessed by gradually increasing the pH from 5.5 to 7.0. BAMIMCD demonstrated
outstanding enantioseparation towards both Dns-Aca and acidic racemates at
concentration low as 1 mM.
5. pI value of dansyl α-aminocarproic acid
S10
Figure S6. The charge vs. pH curve for Dns-α-aminocaproic acid, with pI value
calculated by SPARC [4].
References
(1)
(2)
(3)
(4)
W. H. Tang, S. C. Ng, Nat. Protocols 3 (2008) 691.
K. Fujita, A. Matsunaga, T. Imoto, Tetrahedron Lett. 25 (1984) 5533.
L. Tabushi, Y. Kuroda, K. Yokota, L. C. Yuan, J. Am. Chem. Soc. 103 (1981) 711.
S. H. Hilal, Y. El-Shabrawy, L. A. Carreira, S.W. Karickhoff, S. S. Toubar, M.,
Rizk, Talanta 43 (1996) 607.
S11