Supplementary Material
Chemical
synthesis
of
the
β-mercaptoethanol
adducts
of
(E)-
and
(Z)-p-
hydroxyphenylacetaldoxime
A mixture of (E)- and (Z)-S-(2-hydroxyethyl)-N-hydroxy-2-phenylethanimidothionate (2) was
synthesized from commercially available trans-β-nitrostyrene (1) as previously reported
(Bourderioux et al., 2005). Similarly, the corresponding (E)- and (Z)-S-(2-hydroxyethyl)-Nhydroxy-2-(4-hydroxyphenyl)ethanimidothionate (6) was chemically synthesized from the
commercially available trans-4-hydroxy-β-nitrostyrene (3) in 3 steps as shown in Scheme 1. In this
work, the phenolic OH-group of commercially obtained 3 was protected with a tertbutyldiphenylsilyl (TBDPSi) group via silylation with tert-butyldiphenylchlorosilane using DMAP
(4-dimethylaminopyridine)-TEA (triethylamine) (Chauhary and Hernadez 1979) to afford 4 in a
quantitative yield. Compound 4 was converted into the corresponding arylacethydroximoyl chloride
(Kumaran and Kulkarni 1997). Treatment of the crude product obtained with TEA and 2-mercaptoethanol (Bourderioux et al., 2005) afforded the protected-hydroxyethyl-ethanimidothionate
derivative 5. Removal of the TBDPSi-protecting group of 5 from the phenolic OH-group was
achieved by treatment with tetrabutylammonium fluoride (TBAF) (Hanessian and Lavellee 1975)
and gave rise to the target molecule 6 in 76 % yield as a mixture of E- and Z-isomer. Based on 1HNMR, the E/Z ratios for compounds 2 and 6 were 1:4 and 5:2, respectively. The chemically
synthesized compounds were characterized using electrospray ionization mass spectrometry and 1Hand 13C-NMR spectra (Materials and Methods).
Materials and Methods
Chemical synthesis
Oximes: (Z)-p-hydroxyphenylacetaldoxime and a mixture of (E)- and (Z)-phydroxyphenylacetaldoxime were chemically synthesized as previously reported (Moller 1977;
Moller 1978; Moller and Conn 1979). TLC plates were developed in ethyl acetate:toluene (1:5
vol/vol).
S-alkyl-thiohydroximates:
General: Column chromatography was carried out using silica gel 60 (particle size 0.040-0.063
mm, 230-400 mesh ASTM, E. Merck). Solvent extracts were dried with anhydrous MgSO4 unless
otherwise specified. The 1H and
13
C NMR spectra were recorded on a Bruker Avance 400
spectrometer at 400 and 101 MHz, respectively. CDCl3 was used as solvent (unless otherwise
indicated), δH and δC values are relative to internal added TMS.
S-(2-Hydroxyethyl)-N-hydroxy-phenylethanimidothionate (2): Compound 2 was synthesized
according to literature (Bourderioux et al., 2005). After silica gel chromatographic purification
using the eluent gradient 0-10 % ethyl acetate in dichloromethane, compound 2 was obtained as a
mixture of E- and Z- in the ratio 1:4 based on 1H-NMR-data. For the Z- isomer: 1H- and 13C-NMR
data are in agreement with as reported (Bourderioux et al., 2005). For E-isomer: 1H-NMR (400
MHz, CDCl3): δ = 2.88 (t, 2 H, CH2S), 3.85 (s, 2 H, PhCH2) 3.90 (t, 2H, CH2O), 7.36-7.18 (m, 5 H,
H-arom.);
13
C-NMR (100 MHz, CDCl3): δ = 32.6 (CH2S), 41.2 (PhCH2), 60.5 (CH2O), 136.0,
128.8, 128.8, 128.4, 128.4 and 127.2 (6 x C, arom-C), 154.0 (C=N).
trans-4-[(tert-Butyldiphenylsilyl)oxy]-β-nitrostyrene (4): tert-Butyldiphenylchlorosilane (3.4
mL, 13.2 mmol, 1.1eq) was added to a stirred solution of trans-4-hydroxy-β-nitrostyrene (3) (2.0 g,
12.0 mmol), TEA (2.0 mL, 14.4 mmol, 1.2 eq) and DMAP (1.6 g, 13.2 mmol) in CH 2Cl2 (30 mL)
at room temperature under argon. The reaction mixture was stirred at room temperature for 3h,
diluted with excess ethyl acetate (200 mL) and the organic phase was washed with ice-cold 1 N HCl
(3 x 100 mL), water (3 x 50 mL), sodium hydrogen carbonate aq.sat solution (3 x 50 mL), brine (50
mL), dried over anhydrous magnesium sulphate (MgSO4) and evaporated to dryness. The obtained
residue was chromatographed on silica (150 g) with 0-10 % diethyl ether in n-pentane to afford a
yellow solid of pure 4 (4.6 g, 95 %). 1H-NMR (400 MHz, CD3COCD3): δ = 1.13 (s, 9 H, C(CH3)3),
6.90 (d, 2H, arom-H), 7.54-740 (m, 7 H, arom-H and olefinic-H), 7.63 (d, 2H, arom-H), 7.78 (m,
4H, arom-H), 7.98 (d, 1 H, olefinic-H);
13
C-NMR (100 MHz, CD3COCD3): δ = 19.9 (C(CH3)3),
26.7 (3 x CH3), 160.0, 139.4, 136.9, 136.2, 132.9, 132.2, 131.2, 128.9, 124.6 and 121.4 (20 x C,
arom-C and olefinic-C).
S-(2-hydroxyethyl)-N-hydroxy-2-[4-(tert-Butyldiphenylsilyl)oxyphenyl]ethanimidothionate
(5): Triethylsilylsilane (3.5 mL, 22.0 mmol, 2.2 eq) was added to a stirred solution of 4 (4.1 g, 10
mmol) in dry CH2Cl2 (50 mL) under argon. The reaction mixture was cooled in an ice bath and
TiCl4 (2.8 mL, 24.3 mmol, 2.4 eq) was added dropwise to the reaction mixture and stirring was
continued at room temperature for 2h followed by aqueous work-up (Kumaran and Kulkarni 1997).
The mixture was hydrolyzed with ice, extracted with dichloromethane, dried over MgSO4 and
evaporated to dryness. Et3N (4.2 mL, 30 mmol, 3 eq.) was added to a stirred solution of the
obtained crude residue in dry CH2Cl2 (50 mL) followed by addition of 2-mercaptoethanol (0.85 mL,
12.1 mmol, 1.2 eq). The reaction mixture was stirred at room temperature for 3h, diluted with
excess ethyl acetate (200 mL) and the organic phase was washed with ice-cold 1 N HCl (3 x 100
mL), water (3 x 50 mL), sodium hydrogen carbonate aq.sat solution (3 x 50 mL), brine (50 mL),
dried over anhydrous magnesium sulphate (MgSO4) and evaporated to dryness. The obtained
residue was chromatographed on silica (150 g) with 50-80 % diethyl ether in n-pentane to afford
pure 5 (3.8 g, 82 %) which was solidified as a white solid by trituration with n-pentane. 1H-NMR
(400 MHz, CD3COCD3): δ = 1.10 (s, 9 H, C(CH3)3), 2.83 (t, 2 H, CH2S), 3.53 (t, 2 H, CH2O), 3.73
(s, 2 H, PhCH2), 6.77 (d, 2 H, arom-HAB), 7.07 (d, 2H, arom-HAB), 7.47 (m, 6 H, arom-H), 7.77 (m,
4H, H-arom-H);
13
C-NMR (100 MHz, CD3COCD3): δ = 19.9 (C(CH3)3), 26.9 (3 x CH3),32.4
(CH2S), 38.4 (PhCH2) 62.4 and 62.3 (CH2O), 152.8, 136.3, 136.3, 136.3, 136.3, 133.6, 133.6,
130.9, 130.9, 130.9, 10.0, 130.0, 128.8, 128.8, 128.8, 128.8, 120.5 and 120.5 (18 x C, arom-C),
155.2 (C=N).
S-(2-hydroxyethyl)-N-hydroxy-2-(4-hydroxyphenyl)ethanimidothionate (6): TBAHF (1M in
THF: 15.0 mL, 15.0 mmol) was added to a stirred solution of 5 (3.5 g, 7.5 mmol) in tetrahydrofuran
(THF: 20.0 mL) at room temperature and stirring continued for 30 min. The reaction mixture was
diluted with CH2Cl2 and filtered over silica gel, washed with CH2Cl2 till no UV active products
were detected. Then the silica was washed several times with CH3OH-CH2Cl2 (1:1 v/v), the
collected filtrate was concentrated and chromatographed on silica (150 g) with 5% CH3OH in
CH2Cl2 as eluent to obtain pure 6 as a white solid (1.3 g, 76 %). For Z-isomer: 1H-NMR (400 MHz,
CD3OD): δ = 2.85 (t, 2 H, CH2S), 3.53 (t, 2 H, CH2O), 3.78 (s, 2 H, PhCH2), 6.73 (d, 2 H, aromHAB), 7.10 (d, 2 H, arom-HAB); 13C-NMR (100 MHz, CD3OD): δ = 32.6 (CH2S), 38.8 (PhCH2), 62.6
(CH2O), 155.3, 130.3, 130.3, 128.8, 116.5 and 116.5 (6 x C, arom-C), 157.5 (C=N). For E-isomer:
1
H-NMR (400 MHz, CD3OD): δ = 2.98 (t, 2 H, CH2S), 3.68 (t, 2 H, CH2O), 3.69 (s, 2 H, PhCH2),
6.68 (d, 2 H, arom-HAB), 7.07 (d, 2 H, arom-HAB); 13C-NMR (100 MHz, CD3OD): δ = 33.1 (CH2S),
35.9 (PhCH2), 62.0 (CH2O), 155.2, 131.4, 131.4, 128.4, 116.1 and 116.1 (6 x C, arom-C), 157.4
(C=N).
Scheme 1: Chemical synthesis of a mixture of (E)- and (Z)-2-hydroxyethyl -N-hydroxy-2-(4hydroxyphenyl)ethaneimidothionate (6).
Reagents and conditions: a) TEA, DMAP, TBDPSi-Cl, CH2Cl2, r.t., 3 h, 97 %; b) TiCl4, Et3SiH,
CH2Cl2, r.t.; c) TEA, HS-CH2CH2OH, CH2Cl2, 2h, r.t.; d) TBAF, THF, 1h, r.t.
List of references
Bourderioux, A., Lefoix, M., Gueyrard, D., Tatibouet, A., Cottaz, S., Arzt, S., Burmeister, W.P. and Rollin, P.
(2005) The glucosinolate-myrosinase system. New insights into enzyme-substrate interactions by
use of simplified inhibitors. Organic & biomolecular chemistry, 3, 1872-1879.
Chauhary, S.K. and Hernadez, O. (1979) 4-Dimethylaminopyride: An efficient and selective catalyst for
silylation of alcohols. Tetrahedron Letters, No. 2, 99-102.
Hanessian, S. and Lavellee, P. (1975) The preparation and synthetic utility of tertbutyldiphenylsilyl ethers.
Can. J. Chem., 53, 2975-2977.
Kumaran, G. and Kulkarni, G.H. (1997) Synthesis of α-functionalized and nonfunctionalized hydroxyimoyl
chlorides from conjugated nitroalkenes and nitroalkanes. J. Org. Chem., 62, 1516-1520.
Moller, B.L. (1977) Intermediates in the biosynthesis of cyanogenic glucosides determined by use of a gas
chromatograph coupled with a gas proportional counter. Anal. Biochem., 81, 292-304.
Moller, B.L. (1978) Chemical synthesis of labelled intermediates in cyanogenic glucoside biosynthesis.
Journal of labelled Compounds and Radiopharmaceuticals, 14, 663-671.
Moller, B.L. and Conn, E.E. (1979) The biosynthesis of cyanogenic glucosides in higher plants. NHydroxytyrosine as an intermediate in the biosynthesis of dhurrin by Sorghum bicolor (Linn)
Moench. The Journal of biological chemistry, 254, 8575-8583.