Stereochemical course of tryptophan dehydrogenation during biosynthesis of the calcium-dependent lipopeptide antibiotics.

[reaction: see text] Hydrogen atoms are abstracted from the C2' and C3'-pro-S positions of an (S)-tryptophanyl precursor, with overall syn stereochemistry, during the biosynthesis of the C-terminal Z-2',3'-dehydrotryptophan residue of the calcium-dependent lipopeptide antibiotics (CDAs) in Streptomyces coelicolor. The absence of beta-hydroxytryptophanyl, or other possible intermediates, further suggests a direct dehydrogenation mechanism similar to that proposed for the l-tryptophan 2',3'-oxidase from Chromobacterium violaceum.