To a mixture of 5.0 g (12.68 mmol) of methyl 2-[(2-aminobenzyl)-(4-methoxybenzenesulfonyl)amino]-3-hydroxypropionate and 17.7 ml (26.8 mmol) of triethylamine in 50 ml of CH2Cl2 chilled to 0° C. was added 9.05 ml (63.4 mmol) of benzyl chloroformate. The mixture was stirred overnight and then cooled to 0° C. and 0.8 ml of triethylamine and 9.05 ml (63.4 mmol) of benzyl chloroformate were added thereto. The mixture was stirred overnight and then washed with H2O, 2 N citric acid, brine and dried with Na2SO4. The solvent was removed under vacuum to give 6.95 g of solid. The solid was chromatographed on silica gel with hexane-ethyl acetate (1:1) to give 2.7 g of product as a viscous yellow oil. From a similar 0.5 g run, there was obtained 0.178 g of an oil. Anal. for C18H20N2O5S: Calc'd: C, 57.4; H, 5.4; N, 7.4; S, 8.5; Found: C, 57.9; H, 5.4; N, 6.7; S, 7.9;
