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.