Tropolone Ring Construction in the Biosynthesis of Rubrolone B, a Cationic Tropolone Alkaloid from Endophytic Streptomyces

摘要

Rubrolones are tropolonoid natural products with a unique carbon skeleton. Extensive secondary metabolite analysis of the endophytic Streptomyces sp. KIB-H033 revealed a new class of rubrolone analogue possessing a rare benzoic acid pyridine inner salt moiety. Precursor feeding with [C-13] -acetate revealed a labeling pattern consistent with tropolone moiety construction via type-II PKS chemistry followed by complex oxidative rearrangements. This bacterial biosynthetic route represents a surprising departure from fungal tropolone assembly during stipitatic acid biosynthesis.