N-Methylamino Acids in Peptide Synthesis. II. A New Synthesis of N-Benzyloxycarbonyl, N-Methylamino Acids

Reaction of N-benzyloxycarbonyl derivatives of aliphatic amino acids, and threonine, aspartic, and glutamic acids whose side-chains were protected with the t-butyl group, gave the corresponding N-methylamino acid derivatives in good yields. The methionine derivative could be obtained by using only one mol of methyl iodide. Derivatives of threonine, and aspartic and glutamic acids whose side-chains were not protected could not be methylated. Analysis of the crude products of methylation in three cases showed that they contained 0–1% of racemized material.