Further evidence for the presence of a thiazoline ring in the isoleucylcysteine dipeptide intermediate in bacitracin biosynthesis

Abstract
Isoleucylcysteine dipeptide, a first intermediate peptide in bacitracin biosynthesis, was liberated from the enzyme protein and oxidized with manganese dioxide in dimethylsulfoxide. The resulting oxidation product was identified by thin‐layer chromatography as 2‐(2‐methyl‐l‐oxobutyl)‐thiazole‐4‐carboxylic acid which has been isolated from the hydrolysate of bacitracin F. This result shows that the intermediate dipeptide contains a thiazoline ring, and that the thiazoline ring is synthesized at the dipeptide stage in the process of peptide chain elongation in bacitracin biosynthesis. Improbability of non‐enzymatic dehydrative cyclization of the dipeptide is discussed.