Incorporation of carbon-14 in the biosynthesis of the macrolide antibiotic, LL-F28249-alpha.

A total of 76 mCi of 14C LL-F28249-alpha, nemadectin (1), having a specific activity of 35.2 microCi/mg was isolated from a fermentation using a mixture of approximately 600 mCi of 14C carboxyl labeled acetate, propionate and isobutyrate. Nemadectin was used to synthesize carbon-14 labeled moxidectin which is being developed as a highly efficient ectoparasitic anthelminth. The labeled positions were determined by 13C NMR analysis of 13C nemadectin which was obtained by similar incorporation of 13C carboxyl labeled acetate, propionate and isobutyrate.