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Tropolone Ring Construction in the Biosynthesis of Rubrolone B, a Cationic Tropolone Alkaloid from Endophytic Streptomyces
- Yan, Yijun, Ma, Ya-Tuan, Yang, Jing, Horsman, Geoff
P., Luo, Dan, Ji, Xu, Huang, Sheng-Xiong
- Organic letters 2016 v.18 no.6 pp. 1254-1257
- Streptomyces, alkaloids, biosynthesis, carbon, chemical reactions, endophytes, fungi, moieties, secondary metabolites, stable isotopes, tropolone, zwitterions
- 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 [¹³C]-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.