Process for the preparation of lower alkyl esters of N-L-.alpha.-aspartyl-L-phenylalanine and of new intermediates for their preparation

Abstract

The invention relates to a selective process for the preparation of N-L-.alpha.-aspartyl-L-phenylalanine-1-lower alkyl ester which comprises: A. reacting an L-aspartic acid 4-arylmethyl ester with a (i) 1,3-diketone; or (ii) acylacetic ester; in the presence of a base to form the salt of (i') L-N-(1-alkyl-2-acyl-vinyl)-aspartic acid 4-arylmethyl ester; or (ii') L-N-(1-alkyl-2-alkoxycarbonyl-vinyl)-aspartic acid 4-arylmethyl ester, and then either: (1) reacting salt (i') or (ii') with an organic or inorganic acid halide having the formula X-A, wherein X represents a halogen and A has the meaning indicated hereinafter, or with an acid anhydride to form ##STR1## wherein R represents an alkyl radical with 1 to 6 carbon atoms; R' represents an alkyl or alkoxy radical with 1 to 6 carbon atoms; Ar represents the phenyl, nitrophenyl, halogenphenyl or alkylphenyl radical; and A represents an acyl with 2 to 12 carbon atoms, alkoxycarbonyl with 2 to 12 carbon atoms, or a phosphoric acid, phosphorous acid, sulfuric acid, sulfurous acid or sulfonic acid radical; and reacting ester (I) with an L-phenylalanine lower alkyl ester; or (2) reacting a salt of (i') or (ii') with a phosphorazo-L-phenyl lower alkyl ester; to form (i") N-L-.alpha.-N'-(1-alkyl-2-acyl-vinyl)-aspartyl-L-phenylalanine-1-lower alkyl-4-arylmethyl ester; or (ii") N-L-.alpha.-N'-(1-alkyl-2-alkoxycarbonyl)aspartyl-L-phenylalanine-1-lower alkyl-4-arylmethyl ester; B. reacting (i") or (ii") with a strong acid to split off the respective N-(1-alkyl-2-acyl-vinyl) or N-(1-alkyl-2-alkoxycarbonyl-vinyl) protective group and produce: (iii) N-L-.alpha.-aspartyl-L-phenylalanine-1-lower alkyl-4-(arylmethyl)ester; and C. subjecting ester (iii) to catalytic hydrogenation to selectively split off the 4-(arylmethyl)-ester group and leave the N-L-.alpha.-aspartyl-L-phenylalanine-1-lower alkyl ester product. Novel intermediates for the synthesis are also disclosed.

Dependencies are inferred from the claim text.