Alternative Method C.--A cold ( 0 ' ) mixture of 5.6 g (0.022 mole) of D-phenylalanine methyl ester hydrochloride and 2.2 g (0.022 mole) of Et3N in i 5 ml of DMF was filtered, and to the filtrate was added 9 g (0.022 mole) of 0-acet,yl-N-carbobenzoxyserine p-nitrophenyl ester.lO The solution was kept 2 days at, 23' aiid evaporated to an oil which was taken up in EtOAc. This solution was washed wit'h HZO, 5%, NaHCOs solution, and dilute HC1, then dried and evaporated to a solid. The product, 0-acet yl-N-carbobeiI~ox~ser~l-o-phe~i~lala~iiiie methyl ester was recrystallized from EtOA4c-petroleum ether, 7.3 g (77% j) mp Anal. Calcd for C?3H&\;20i: C, 62.43; H, 3.93; S, 6.33.Found: C, 62.44; H, 5.96; S , 6.32.The methyl ester and 0-acetj-1 groiips were removed using an excess of 2 A\-SaOH in JIeOH affording carbobenzoxyser?-l-Dphenylalanine in 725; ?-ield, mp 137-139".Method D.-To a cold ( 5 " ) solution of 7.9 g (0.03 mole) of carbobenzosyhydrox~proliiie in 150 ml of MeCN was added 3 g of Et3X and 7.5 g (0.03 mole) of Woodward's5 reagent K. The mixture was stirred 1 hr at 3', and 5 g (0.03 mole) of D-valine methyl eater hydrochloride and 3 g of Et3S were added. The mixture was stirred 48 hr at 2.7'. The solvent was evaporated, the residue was taken up in EtOAc, and the solution was washed with H20, 5cI; SaHC03 solution, and dilute €IC1 and dried.
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