Studies of Unusual Amino Acids and Their Peptides. V. The Synthesis and the Absolute Configuration of β(2-Thiazolyl)-β-alanine Present in Bottromycin

In order to obtain an optically-active β-(2-thiazolyl)-β-alanine, N-acyl-l-aspartic α-thionamide-β-methyl ester was condensed with diethyl bromoacetal, but the amino acid thus obtained showed no perceptible optical activity. The racemic amino acid, however, could be resolved into its antipodes by treating its phthalyl derivative with brucine. Thus, the (+)-amino acid, a constituent of bottromycin, was isolated in a pure state; it was determined to belong to the l-series by examining its optical behavior. This amino acid was proved to racemize easily under the conditions of the acid hydrolysis of bottromycin.