Gravel et al.
172
518.176 30. Anal. calcd for C24H27N3O10: C 55.70, H 5.26,
N 8.12; found: C 55.03, H 5.33, N 8.04.
and 5 Hz), 5.10 (1H, m), 5.16 (2H, s), 5.8 (1H, d, J = 9 Hz),
7.31 (5H, m), 7.95 (1H, t, J = 5 Hz). 13C NMR (CDCl3,
75 MHz, ppm) δ: 27.90, 41.93, 46.04, 55.10, 67.15, 81.98,
127.50, 127.97, 128.37, 136.30, 156.87, 168.27, 170.02.
HRMS calcd. for C34H46N4O10S2 + H: 735.272 81; found:
735.272 07.
N-Benzyloxycarbonyl-O-(p-nitrophenoxycarbonyl)-L-
serinylglycine (2)
To a solution of N-Cbz-O-(p-nitrophenoxycarbonyl)-L-
serinylglycine tert-butyl ester (9) (0.4 mmol) in 2.5 mL of
anhydrous dichloromethane, 500 µL (6.5 mmol) of
trifluoroacetic acid (TFA) was added dropwise at 0 °C under
nitrogen atmosphere. The solution was stirred at 0 °C for 1 h
and then an additional portion (300 µL, 4.0 mmol) of TFA
was added and the solution was stirred for an additional 3 h
while the solution was allowed to warm to RT. A final por-
tion of 150 µL of TFA (2.0 mmol) was then added and the
solution was stirred at RT for 1 h before the solvent was re-
moved in vacuo to provide 0.165 g (92%) of product as a
yellow solid. Rf 0.28 (99:1 EtOAc–HOAc), mp 59–61 °C.
[α]d20 +11.0° (c 0.96, CHCl3). IR (KBr) ν: 3747–2633, 3086,
2968, 1772, 1740, 1734, 1640, 1595, 1351, 1526, 1493,
N-Benzyloxycarbonyl-L-cysteinylglycine tert-butyl ester
(12)
A 100-mg (0.136 mmol) portion of N-benzyloxycarbonyl-
L-cystinylglycine tert-butyl ester (11) and 100 mg
(2.6 mmol) of sodium borohydride were dissolved in a mix-
ture of 2 mL of ethanol and 2 mL of CHCl3. The mixture
was shaken for 30 min at RT. Then, 5 mL of CHCl3 was
added and the organic phase was washed with HCl (10 mL,
1 mol/L) and then concentrated in vacuo. If necessary, the
product can then be purified by silica gel chromatography
using 30:70 EtOAc–hexanes as eluant. To avoid oxidation,
the last step was carried out immediately. Rf 0.50 (50:50
1
1
1455, 1279, 1049. H NMR (CDCl3, 300 MHz, ppm) δ: 4.12
EtOAc–hexanes). H NMR (CDCl3, 300 MHz, ppm) δ: 1.17
(2H, d, J ≈ 17 Hz), 4.50 (1H, dd, J = 4.5 (3.8) and 10.7 Hz),
4.60 (1H, dd, J = 6.5 (5.8) and 10.9 Hz), 4.82 (1H, m), 5.15
(2H, d, J = 11.8 Hz), 5.84 (1H, s), 7.10 (1H, s), 7.29–7.39
(7H, m), 8.26 (2H, d, J = 9.2 Hz). 13C NMR (CDCl3,
75 MHz, ppm) δ: 41.81, 53.80, 68.17, 68.63, 122.19, 125.72,
128.50, 128.93, 129.05, 135.91, 145.90, 152.69, 155.53,
157.07, 169.74, 172.68. HRMS calcd. for C20H19N3O10:
462.114 87; found: 462.116 50. Anal. calcd. for
C20H19N3O10: C 52.06, H 4.15, N 9.11; found: C 50.33, H
4.20, N 8.41.
(3H, s), 1.42 (1H, dd, J = 8.4 and 11.4 Hz), 2.58 (1H, ddd,
J = 15.2, 11.4, and 6.6 Hz), 2.97 (1H, ddd, J = 15.2, 8.4, and
5.1 Hz), 3.87 (2H, d, J = 6.2 Hz), 4.50 (1H, m), 5.19 (2H, s),
6.04 (1H, d, J = 9.2 Hz), 7.11 (1H, t, J = 6.2 Hz), 7.61
(5H, m). 13C NMR (CDCl3, 75 MHz, ppm) δ: 27.91, 41.92,
46.14, 55.12, 67.02, 81.95, 127.80, 127.92, 128.74, 136.25,
156.92, 168.32, 170.06.
N-Benzyloxycarbonyl-S-(p-nitrophenyloxycarbonyl)-L-
cysteinylglycine tert-butyl ester (13)
First, 110 mg (0.3 mmol) of N-benzyloxycarbonyl-L-
cysteinylglycine tert-butyl ester (12) and 104 µL of DIEA
were dissolved in 0.5 mL of CHCl3 at 0 °C. Then, 60 mg
(0.3 mmol) of p-nitrophenyl chloroformate dissolved in
0.5 mL of CHCl3 was added at 0 °C and the mixture was
shaken for 15 min. The mixture was then purified by silica
gel chromatography using 1:2 EtOAc–hexanes. The product
was obtained as 68 mg (68%) of a yellow solid. Rf 0.50 (1:1
N-Benzyloxycarbonyl-L-cystine (10)
To 1.44 g (5.94 mmol) of L-cystine in 175 mL of water
was added 5 g (60 mmol) of NaHCO3 and the mixture was
cooled to 0 °C. A 1.70 mL volume (13.0 mmol) of benzyl
chloroformate was added dropwise and the biphasic solution
was stirred vigorously overnight. After acidification to pH 3
using 6N HCl, the aqueous phase was extracted with 3 ×
150 mL EtOAc and the extract was concentrated in vacuo to
give 3.38 g (99%) of a clear oil. Rf 0.05 (50:50 EtOAc–
hexanes). 1H NMR (CD3OD, 300 MHz, ppm) δ: 2.98 (1H, dd,
J = 9.1 and 13.9 Hz), 3.25 (1H, dd, J = 4.3 and 13.9 Hz),
4.51 (1H, dd, J = 4.3 and 9.1 Hz), 5.07 (2H, s), 7.27
(5H, m). 13C NMR (CD3OD, 75 MHz, ppm) δ: 41.18, 54.71,
67.81, 128.84, 129.03, 129.51, 139.09, 158.54, 174.02.
1
EtOAc–hexanes). H NMR (CHCl3, 300 MHz, ppm) δ: 1.18
(3H, s), 3.19 (1H, dd, J = 6.4 and 13.5 Hz), 3.37 (1H, dd,
J = 4.1 and 13.5 Hz), 3.88 (2H, d, J = 4.0 Hz), 4.70 (1H, dd,
J = 4.1 and 6.4 Hz), 5.23 (1H, d, J = 13.2 Hz), 5.27 (1H, d,
J = 13.2 Hz), 5.80 (1H, d), 6.95 (1H, t), 7.56 (2H, d, J =
10.5 Hz), 7.62 (5H, m), 8.58 (2H, d, J = 10.5). 13C NMR
(CDCl3, 75 MHz, ppm) δ: 28.2, 28.5, 43.3, 53.2, 65.2, 122.2,
124.8, 127.2, 127.3, 127.8, 136.6, 145.1, 155.1, 155.4,
167.3, 168.0, 169.9.
N-Benzyloxycarbonyl-L-cystinylglycine tert-butyl ester (11)
A 3.38-g (6.6 mmol) portion of N-benzyloxycarbonyl-L-
cystine (10) and 5.76 mL (33 mmol) of DIEA were dis-
solved in 120 mL of anhydrous acetonitrile. To this solution
was added 2.76 g (17 mmol) of glycine tert-butyl ester hy-
drochloride and 6.36 g (20 mmol) of TBTU. The mixture
was stirred overnight. The next day, 120 mL of EtOAc was
added and the organic phase was washed with 3 × 120 mL
satd. NaCl, 100 mL 1N NaOH, and 100 mL H2O. After con-
centration in vacuo and purification by silica gel chromatog-
raphy (15 cm × 2.5 cm, 33% EtOAc–toluene), 2.91g (60%)
of a white solid was obtained. Rf 0.43 (50:50 EtOAc–hex-
N-Benzyloxycarbonyl-S-(p-nitrophenyloxycarbonyl)-L-
cysteinylglycine (3)
To 34 mg (64 µmol) of N-benzyloxycarbonyl-S-(p-
nitrophenoxycarbonyl)-L-cysteinylglycine tert-butyl ester
(13) dissolved in 2 mL of chloroform was added 500 µL
(6.5 mmol) of TFA at 0 °C. The solution was stirred for 1 h
and then evaporated in vacuo. The product thus obtained was
used without further purification. Rf 0.12 (50:50 EtOAc–hex-
anes). 1H NMR (CHCl3, 400 MHz, ppm) δ: 3.10 (1H, dd, J =
6.3 and 13.6 Hz), 3.26 (1H, dd, J = 4.1 and 13.6 Hz), 4.05
(2H, d, J = 3.8 Hz), 4.82 (1H, dd, J = 4.1 and 6.3 Hz), 5.23
(1H, d, J = 13.1 Hz), 5.27 (1H, d, J = 13.1 Hz), 6.30 (1H, d,
J = 8.1 Hz), 7.56 (2H, d, J = 10.5 Hz), 7.62 (5H, m), 7.87
1
anes). H NMR (CDCl3, 300 MHz, ppm) δ: 1.42 (9H, s),
2.87 (1H, dd, J = 11 and 15 Hz), 3.10 (1H, dd, J = 15 and
4 Hz), 3.77 (1H, dd, J = 18 and 5 Hz), 4.00 (1H, dd, J = 18
© 2007 NRC Canada