accompanied the loss of each one of the carboxyl carbons via path A or B, as shown in Fig. 3. The site of decarboxylation in the nonaketide was. evidenced from the appearance of two enriched singlet signals assignable to the methyl groups (C-12 and C-12) of acetate unit in the NMR spectrum of [1,2-13C2]acetate-labeled setomi mycin. Appearance of triplet signals due to 13 C-13C couplings for all carbons except for the above mentioned methyl groups implies that setomimycin is derived from two nonaketide metabolites via decarboxylation at the terminals, as demonstrated in path A18)