To a solution of piperazinone acetic acid 5a (0.45 g, 1.0×10-3 mole) and dry THF (3 ml) at -10° C. under argon is added in turn Et3N (0.16 ml, 1.1×10-3 mole) and isobutylchloroformate (0.15 ml, 1.1×10-3 mole). After stirring 10 minutes at -10° C., a freshly neutralized solution of glycyl-L-phenylalanine methyl amide 9a hydrochloride (0.30 g, 1.1×10-3 mole), Et3N (0.28 ml, 2.0×10-3 mole), THF (3 ml), and H2O (1.5 ml) is added in one portion. The cooling bath is then removed and the reaction allowed to warm to room temperature. After stirring overnight the reaction is quenched into 0.5 M aqueous HCl. The aqueous mixture is extracted with Et2O (2 times) and CH2Cl2 (2 times). The ethereal extracts are combined and washed with saturated aqueous NaHCO3 as are the CH2Cl2 extracts. The ethereal and CH2Cl2 extracts are then combined and dried over Na2SO4. Filtration of the drying agent and evaporation of the filtrate give 10a which is purified by chromatography, and the structure corroborated by NMR. NMR (CDCl3) δ1.26 (S, 9, t-boc), 2.64 (d, 3, methylamide), 3.08, 3.90 (m, 12, methylenes), 4.68 (m, 2, C3 -H and phenylala-CH), 4.98 (S, 2, benzyloxy methylene), 6.6-7.8 (m, 17, aromatic and amide NH's).
