Biomimetic Total Synthesis and Paired Omics Identify an Intermolecular Diels–Alder Reaction as the Key Step in Lugdunomycin Biosynthesis

Abstract

Microbial natural products are the basis of the majority of clinical drugs, where the discovery of truly novel structural scaffolds to fill the discovery pipelines is a prerequisite. Lugdunomycin is a highly rearranged angucycline polyketide produced by Streptomyces sp. QL37, with an enigmatic biosynthetic pathway. Here we show that lugdunomycin is formed by a rare intermolecular Diels-Alder reaction, with elmonin as a masked diene and iso-maleimycin as a dienophile. Genomics, mutational analysis, and heterologous expression revealed that the biosynthesis of the substrates is encoded by distinct biosynthetic gene clusters (BGCs), whereby elmonin is specified by an angucycline BGC, while the biosynthesis of iso-maleimycin is encoded by a BGC for a β-lactone-like compound. Biomimetic total synthesis of lugdunomycin showed that the Diels-Alder reaction leads to the production of a diastereomer of lugdunomycin as the main product in vitro. The diastereomeric ratio of the in vitro Diels-Alder reaction shifted toward lugdunomycin in the presence of proteinaceous material, suggesting that the in vivo Diels-Alder reaction is templated. Alphafold modeling and experimental data suggest that GarL could potentially function as a Diels-Alder template in lugdunomycin biosynthesis. The requirement of distinct biosynthetic pathways and complex chemical reactions indicates the challenges we face in discovering new chemical space.

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