Studies of Unusual Amino Acids and Their Peptides. VI. The Syntheses and the Optical Resolutions of β-Methylphenylalanine and Its Dipeptide Present in Bottromycin

Abstract

Abstract β-Methyl-phenylalanine was prepared by the condensation of α-methylbenzyl bromide with acetaminomalonate, followed by the hydrolysis and decarboxylation of the condensate. The decarboxylation occurred diastereoselectively to some extent. The erythro and the threo isomers could be separated by the fractional crystallization of their benzoyl derivatives, and differentiated by means of their NMR spectra. The optical resolution of the respective isomers was attained by treating the benzyloxycarbonyl derivatives with qunine or quinidine; thus, the four isomers could be obtained in a pure state. A dipeptide present in the C-terminal of bottromycin was synthesized by coupling N-protected erythro-l-β-methyl-phenylalanine with either l-β-(2-thiazolyl)-β-alanine ester or, more conveniently, with the Dl-compound, and by separating thereafter.