Non-enzymatic pyridine ring formation in the biosynthesis of the rubrolone tropolone alkaloids.

Nat Commun

State Key Laboratory of Phytochemistry and Plant Resources in West China, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming 650201, China.

Published: October 2016

The pyridine ring is a potent pharmacophore in alkaloid natural products. Nonetheless, its biosynthetic pathways are poorly understood. Rubrolones A and B are tropolone alkaloid natural products possessing a unique tetra-substituted pyridine moiety. Here, we report the gene cluster and propose a biosynthetic pathway for rubrolones, identifying a key intermediate that accumulates upon inactivation of sugar biosynthetic genes. Critically, this intermediate was converted to the aglycones of rubrolones by non-enzymatic condensation and cyclization with either ammonia or anthranilic acid to generate the respective pyridine rings. We propose that this non-enzymatic reaction occurs via hydrolysis of the key intermediate, which possesses a 1,5-dione moiety as an amine acceptor capable of cyclization. This study suggests that 1,5-dione moieties may represent a general strategy for pyridine ring biosynthesis, and more broadly highlights the utility of non-enzymatic diversification for exploring and expanding natural product chemical space.

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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5059770PMC
http://dx.doi.org/10.1038/ncomms13083DOI Listing

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