Urdamycin L: A Novel Metabolic Shunt Product that Provides Evidence for the Role of the urdM Gene in the Urdamycin A Biosynthetic Pathway of Streptomyces fradiae TÜ 2717

Sixes and sevens: The isolation and structure elucidation of urdamycin L, a novel shunt product from the Sreptomyces fradiae TÜ 2717 urdM− mutant, gives new insight into the mechanism of 12b-hydroxylation during urdamycin biosynthesis (see scheme). The lactone structure of urdamycin L suggests an initial Baeyer–Villiger oxygenation followed by a rearrangement of the seven-membered lactone ring to a six-membered carbocycle, a step that is probably base assisted.