Biosynthesis of Gabosines A, B, and C, Carba Sugars fromStreptomyces cellulosae

Abstract

The biosynthesis of the gabosines A−C (3−5) was studied by feeding cultures of Streptomyces cellulosae subsp. griseorubiginosus (strain S 1096) with 13C-labeled precursors. Although the carba sugars are structurally related to shikimic acid, the biosynthetic origin was found to be different to the shikimate pathway. The results revealed that the gabosines are formed via a pentose phosphate pathway by cyclization of a heptulose phosphate intermediate. This intermediate arises from a triose phosphate by successive transfer of two C2 fragments by transketolases. This pathway is identical as that described for valienamine (7), the aminocarba sugar moiety of validamycin, and acarbose (2). The results from biosynthetic studies are discussed on the background of the variety of gabosines found in nature.