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Zhou and Mei
was added to the mixture. The white solid was obtained by filtering and
the organic layer was separated, dried over anhydrous MgSO4, and
evaporated to furnish other solid. The solid was combined and recrystal-
lized from ethanol to afford 5 (8.52 g, 75%). M.p. 223–224ꢀC. IR (KBr) ꢀ:
3380, 3260, 3180, 1665, 1625, 1525, 1495, 1345, 1215, 1125 cmꢁ1
.
1H NMR (DMSO-d6) ꢁ: 3.8–4.6 (br, 1H), 4.21 (dd, J ¼ 6.9, 3.4 Hz, 1H),
5.35 (dd, J ¼ 8.4, 3.6 Hz, 1H), 7.09–7.51 (m, 10H), 7.83–7.86 (m, 2H),
8.64 (d, J ¼ 8.4 Hz, 1H). Anal. calcd. for C16H16N2O3: C, 65.52;
H, 5.84; N, 9.55. Found: C, 65.57; H, 5.49; N, 9.43.
Erythro N-Benzoyl-3-phenylisoserine methyl ester (6): Erythro
N-benzoyl-3-phenylisoserineamide (6.0 g, 21.1 mmol) and TsOH (7.3 g,
42.2 mmol) were combined with methanol (150 mL) and the mixture was
heated at reflux for 40 h. The solvent was evaporated and NaHCO3 (3.54 g,
42.2 mmol) in water (50 mL) was added to the residue. The mixture was
extracted with chloroform (3 ꢂ 50 mL). The combined organic extracts
were dried (MgSO4), filtered and evaporated to afford a white solid.
Recrystallization (from chloroform) of the solid afforded 6 (4.3 g, 67%).
M.p. 131–132ꢀC. IR (KBr) ꢀ: 3500, 3350, 1725, 1635, 1510, 1435, 1320,
1220, 1100 cmꢁ1. 1H NMR (CDCl3) ꢁ: 2.60 (br, 1H), 3.73 (s, 3H), 4.71 (d,
J ¼ 3.6 Hz, 1H), 5.62 (dd, J ¼ 8.5, 3.5 Hz, 1H), 7.18 (br d, J ¼ 8.5 Hz, 1H),
7.25–7.52 (m, 8H), 7.80–7.83 (m, 2H). 13C NMR (CDCl3) ꢁ: 52.6, 55.5,
73.2, 127.3, 127.6, 128.5, 128.7, 131.9, 134.3, 136.7, 167.0, 172.7. Anal.
calcd. for C17H17NO4: C, 68.22; H, 5.72; N, 4.68. Found: C, 68.21;
H, 5.65; N, 4.69.
Threo N-Benzoyl-3-phenylisoserine methyl ester (7): Thionyl chloride
(9.4 g, 77.5 mmol) in chloroform (10 mL) was added dropwise to a
solution of 6 (9.5 g, 31 mmol) in chloroform (40 mL). The resulting
mixture was stirred at 45ꢀC for 5 h. The solution was concentrated,
dissolved in chloroform (50 mL), and refluxed for 48 h. The solution
was washed with water, dried (MgSO4), and concentrated. The residue
was hydrolyzed by refluxing with 1 N HCl (20 mL) in methanol (60 mL)
for 2 h. Sodium hydrogen carbonate (1.68 g, 20 mmol) was then cautiously
added to the mixture in portions. The resulting solution was stirred at
room temperature for 48 h and subsequently extracted with dichloro-
methane (4 ꢂ 80 mL). The combined organic extracts were then dried
(MgSO4), filtered, and evaporated. Recrystallization (from chloroform)
of the residue afforded pure compound 7 (4.6 g, 49%). M.p. 157–158ꢀC.
IR (KBr) ꢀ: 3360, 1720, 1640, 1525, 1435, 1320, 1230, 1090 cmꢁ1
.
1H NMR (CDCl3) ꢁ: 2.20 (br, 1H), 3.84 (s, 3H), 4.64 (d, J ¼ 1.8 Hz,
1H), 5.75 (dd, J ¼ 7.8, 1.8 Hz, 1H), 6.98 (d, J ¼ 8.1 Hz, 1H), 7.26–7.52
(m, 8H), 7.76–7.78 (m, 2H). 13C NMR (CDCl3) ꢁ: 53.3, 54.7, 73.1, 126.7,
127.0, 128.1, 128.8, 128.9, 131.7, 134.2, 138.7, 166.8, 173.3. Anal. calcd.