The C-Glycosyltransferase UrdGT2 is unselective toward d- and l-configured nucleotide-bound rhodinoses

UrdGT2 is a d-olivosyltransferase from the metabolic pathway of urdamycin A, an angucycline antitumor and antimicrobial drug. The remarkable feature of this biocatalyst is its ability to set up C-glycosidic bonds. Using an in vivo system suitable to deliver the trideoxysugar rhodinose in both d- and l- configuration we could verify that both have been accepted as substrates and attached to the urdamycin polyketide backbone via a C-glycosidic bond. Regardless of the stereochemistry, these C-glycosides served as acceptor for a subsequent glycosylation step to yield the novel urdamycins R and S with di-rhodinosyl side chains at C-9 of the polyketide moiety.