4-Methylmorpholine → (-)-methyl(S)-2-[(2-amino-3-nitrobenzoyl)amino]propanoate

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To a stirred and cooled (−12° C.) mixture of 9.10 parts of 2-amino-3-nitrobenzoic acid, 6.95 parts of methyl L-α-alanine monohydrochloride, 13.50 parts of 1-hydroxy-1H-1,2,4-benzotriazole monohydrate and 178 parts of tetrahydrofuran there were added portionwise 5.05 parts of N-methylmorpholine and, after 5 min, 10.3 parts of N,N′-methanetetraylbis[cyclohexanamine] under an argon atmosphere. Stirring was continued for 5½ hours at −12° C. and for 15 hours at room temperature. After cooling to 0° C. for ½ hour, the reaction mixture was filtered and the filtrate was evaporated. The residue was partitioned between ethyl acetate and a saturated sodium hydrogen carbonate solution. The organic layer was separated, washed with NaHCO3 (sat.), dried, filtered and evaporated. The residue was triturated with hexane. The product was filtered off and dried, yielding 13.08 parts (97.9%) of (−)-methyl(S)-2-[(2-amino-3-nitrobenzoyl)amino]propanoate; mp. 132.9° C. (interm. 24).

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