Studies on the biosynthesis of 16-membered macrolide antibiotics using carbon-13 nuclear magnetic resonance spectroscopy.

The origin of the skeletal carbons in the lactone ring of 16-membered macrolide antiobiotics has been studied. 13C-labeled antibiotics leucomycin and tylosin, have been obtained from the culture broth of Streptomyces kitasatoensis 66-14-3 and Streptomyces fradiae C-373, respectively in the presence of appropriate 13C-labeled precursors, and 13C NMR spectra of the antibiotics thus obtained have been measured. It was shown that the aglycone of leucomycin A3 is derived from five acetates, one propionate, one butyrate, and an unknown precursor corresponding to two carbons. The formyl carbon which is characteristic of the basic 16-membered macrolides orginates from C-4 butyrate. On the other hand, the aglycone of tylosin is formed from two acetates, five propionates and one butyrate. Butyric acid and ethylmalonic acid are metabolized to propionyl-CoA or methylmolonyl-CoA through a pathway involving methylmalonyl-CoA mutase, and subsequently incorporated into the lactone ring of tylosin.