NMR Confirmation That Tryptophan Dehydrogenation Occurs with Syn Stereochemistry during the Biosynthesis of CDA in Streptomyces coelicolor

Doubly labeled (2'S,3'R)-[3'-2H1,13C1]-tryptophan was fed to the Trp-His auxotrophic Streptomyces coelicolor strain WH101. Mass spectrometry showed single and double incorporation of the labeled Trp into the calcium-dependent lipopeptide antibiotic (CDA4a). From 13C NMR spectroscopy, it was apparent that the C3'-signal of the (Z)-2',3'-dehydrotryptophan (position 11 in CDA4) was a 1:1:1 triplet indicating that the deuterium atom in the pro-R position of the methylene group is retained during Trp-oxidation. This provides definitive proof that Trp dehydrogenation occurs through the loss of the 2' and pro-3'S hydrogen atoms with overall syn stereochemistry.