Lanthionine chemistry. Part 5. Synthesis of cyclic non-symmetrical lanthionyl peptides

Abstract

The synthesis of a protected fragment of the antibiotic nisin, specifically N^α-benzyloxycarbonyl-D-hemilanthionyl-L-isoleucyldehydroalanyl-L-leucyl-L-hemilanthionine α′-methyl ester (B) and of its analogue N^α-benzyloxycarbonyl-L-hemilanthionyl-L-isoleucyl-L-seryl-L-leucyl-L-hemilanthionine α′-methyl ester (A) is described. For the synthesis of these unusual peptidic compounds, unsymmetrically substituted derivatives of L- or mesolanthionine were used. For the synthesis of compound (B), the O-diphenylphosphorylserine portion of the peptide (26) was transformed by a β-elimination reaction to the dehydroalanine group in peptide (27), which after partial deprotection was subjected to cyclization. Compound (A) is a precursor of the dehydroalanine-containing cyclo-L-lanthionyl peptide. The monomeric structures of the cyclo-peptides (A) and (B) were proved by molecular-weight determination and the presence of the amino-acrylic acid grouping in the molecule of (B) was ascertained by amino-acid analysis and its i.r, spectrum.