to give 15 (135 mg, 93%) as a colorless viscous oil. The optical purity was 99% ee based on HPLC using
a chiral column (SUMIPAX OA-4600 n-hexane : i-PrOH : AcOH = 100 : 20 : 1). [α]21 -6.0° (c= 2.75,
D
CHCl3). IR (KBr) cm-1: 3281, 1744, 1655. 1H-NMR (CDCl3) δ: 1.93 (3H, s), 2.35 (3H, s), 3.32 (1H, dd, J
= 15.0, 8.0 Hz), 3.61 (1H, dd, J = 15.0, 6.0 Hz), 3.70 (3H, s), 5.01 (1H, ddd, J = 8.0, 8.0, 6.0 Hz), 6.04
(1H, d, J = 8.0 Hz), 7.13 (1H, dd, J = 8.0, 8.0 Hz), 7.24 (2H, d, J = 8.0 Hz), 7.39 (1H, d, J = 8.0 Hz), 7.47
(1H, s), 7.72 (2H, d, J = 8.0 Hz), 7.95 (1H, d, J = 8.0 Hz). EI-MS m/z: 494 (M++2, 4.0), 492 (M+, 3.8), 91
(100). Anal. Calcd for C21H21N2O5BrS: C, 51.12; H, 4.29; N, 5.68. Found: C, 51.08; H, 4.40; N, 5.51.
N-Acetyl-4-bromo-N-Boc-1-tosyl-D-tryptophan Methyl Ester (16)
To a stirred solution of N-acetyl-4-bromo-1-tosyl-D-tryptophan methyl ester (15) (59.0 mg, 0.120 mmol)
in THF (2.00 mL) were added 4-dimethylaminopyridine (8.20 mg, 0.07 mmol) and di-tert-butyl
dicarbonate (0.40 mL, 1.74 mmol).
The reaction mixture was stirred for 3 h at rt, diluted with water,
and then extracted with AcOEt. The combined organic extracts were washed with brine, dried over
MgSO4. After evaporation of the solvent, the resultant yellow viscous oil was purified by silica gel
column chromatography (benzene : AcOEt = 30 : 1) to give 16 (67.6 mg, 95%) as a colorless viscous oil.
[α]20D +94.3° (c= 0.40, CHCl3). IR (neat) cm-1: 2980, 1731, 1695. 1H-NMR (CDCl3) δ: 1.17 (9H, s), 2.34
(3H, s), 2.36 (3H, s), 3.29 (1H, dd, J = 15.1, 10.7 Hz), 3.76 (3H, s), 4.00 (1H, dd, J = 15.1, 3.9 Hz), 5.59
(1H, dd, J = 10.7, 3.9 Hz), 7.12 (1H, dd, J = 8.3, 8.3 Hz), 7.23-7.30 (3H, m), 7.39 (1H, d, J = 8.3 Hz),
7.71 (2H, d, J = 8.3 Hz), 7.93 (1H, d, J = 8.3 Hz). MS m/z: (FAB) 595 (M++2, 1.7), 593 (M+, 2.0), 57
(100). Anal. Calcd for C26H29N2O7BrS: C, 52.62; H, 4.93; N, 4.72. Found: C, 52.74; H, 5.09; N, 4.48.
N-Boc-4-bromo-1-tosyl-D-tryptophan Methyl Ester (17)
To a stirred solution of N-acetyl-4-bromo-N-Boc-1-tosyl-D-tryptophan methyl ester (16) (137 mg,
0.231 mmol) in 1,2-dichloroethane (3.60 mL) and methanol (0.90 mL) was added NH2NH2•H2O (0.035
mL, 0.72 mmol). The reaction mixture was stirred for 48 h at rt and then diluted with water, and extracted
with AcOEt. The combined organic extract was washed with brine, dried over (MgSO4), and evaporated
in vacuo to give a colorless viscous oil. The resultant residue was purified by silica gel column
chromatography (benzene : AcOEt = 10 : 1) to give 17 (125 mg, 98%) as a white powder. The optical
purity was 99% ee based on HPLC using a chiral column (Daicel Chiralcel OD n-hexane : i-PrOH = 9 : 1).
The powder was recrystallized from benzene-hexane to yield sharp white needles. mp 145 ~ 146 °C.
[α]25D +13° (c= 2.47, CHCl3). IR (KBr) cm-1: 3381, 1744, 1689. 1H-NMR (CDCl3) δ: 1.38 (9H, s), 2.35
(3H, s), 3.20 ~ 3.31 (1H, m), 3.58 (1H, dd, J = 14.6, 5.4 Hz), 3.70 (3H, s), 4.69 (1H, ddd, J = 8.8, 8.8, 5.4
Hz), 5.00 ~ 5.10 (1H, m), 7.12 (1H, dd, J = 7.8, 7.8 Hz), 7.24 (2H, d, J = 8.3 Hz), 7.38 (1H, d, J = 7.8 Hz),
7.48 (1H, s), 7.73 (2H, d, J = 8.3 Hz), 7.93 (1H, d, J = 7.8 Hz). EI-MS m/z: 553 (M++2, 0.67), 551 (M+,
0.74), 91 (100). Anal. Calcd for C24H27N2O6BrS: C, 52.27; H, 4.93; N, 5.08. Found: C, 52.27; H, 4.93;
N, 5.10.
N-Boc-4-bromo-N-methyl-1-tosyl-D-tryptophan Methyl Ester (D-4]
To a solution of N-Boc-4-bromo-1-tosyl-D-tryptophan methyl ester (17) (56.1 mg, 0.102 mmol) in 1,4-
dioxane (5.00 mL) and H2O (2.50 mL) was added a solution of 5% aqueous KOH (0.30 mL, 0.267 mmol)
at 0°C. The resulting mixture was stirred at rt for 30 min, allowed to acidify with 5% aqueous AcOH at