Biosynthetic Origin of the Methoxyl Extender Unit in Bafilomycin and Concanamycin using Stereospecifically Labeled Precursors

The microbial macrolides bafilomycin A 1 , B 1 and concanamycin A from Streptomyces spp. are potent and specific inhibitors of V-ATPases. The question of the biosynthetic origin of the two uncommon “glycolate units” of each of the macrolide structures was addressed by feeding experiments with stereospecifically 13 C-labeled precursors. Our studies clearly indicate that glycerol is a source for the methoxylated C 2 -units and determines the orientation of the incorporation. Products from the carboxylic acid pool or TCA cycle are ruled out as key precursors. The data suggest the action of a glycerol kinase and point to phosphoglycerate as an intermediate in their biosynthesis. However, glycerate itself is not accepted as a precursor. We present the likely biosynthetic pathway and show the value of stereospecifically labeled presursors as an important tool for biosynthetic investigations.