Synthetic Studies of Bacitracin. IV. Synthesis of Thiazoline Peptides by Iminoether Coupling Method

Abstract

Abstract For the purpose of a total synthesis of bacitracin A, a synthetic method of the thiazoline peptide was investigated. A benzyloxycarbonylaminoalkylimino ethyl ether derived from glycine, l-alanine, l-valine, l-leucine or l-isoleucine was coupled with ethyl l-cysteinate hydrochloride to afford the corresponding thiazoline peptide, that is, a dehydrated form of cysteine peptide. While l-cystine was obtained from acid hydrolyzates of those thiazoline peptides, hydrolysis of them after treatment with alkali or ammonia gave Dl-cystine. Furthermore, alkaline treatment caused a racemization of the amino acid residue adjacent to the thiazoline ring too.