Napyradiomycin A1

The biosynthetic route to the napyradiomycin family of bacterial meroterpenoids has been fully described 32 years following their original isolation and 11 years after their gene cluster discovery. The antimicrobial and cytotoxic natural products napyradiomycins A1 and B1 are produced using three organic substrates (1,3,6,8-tetrahydroxynaphthalene, dimethylallyl pyrophosphate, and geranyl pyrophosphate), and catalysis via five enzymes: two aromatic prenyltransferases (NapT8 and T9); and three vanadium dependent haloperoxidase (VHPO) homologues (NapH1, H3, and H4). Building upon the previous characterization of NapH1, H3, and T8, we herein describe the initial (NapT9, H1) and final (NapH4) steps required for napyradiomycin construction. This remarkably streamlined biosynthesis highlights the utility of VHPO enzymology in complex natural product generation, as NapH4 efficiently performs a unique chloronium-induced terpenoid cyclization to establish two stereocenters and a new carbon-carbon bond, and dual-acting NapH1 catalyzes chlorination and etherification reactions at two distinct stages of the pathway. Moreover, we employed recombinant napyradiomycin biosynthetic enzymes to chemoenzymatically synthesize milligram quantities in one pot in 1 day. This method represents a viable enantioselective approach to produce complex halogenated metabolites, like napyradiomycin B1, that have yet to be chemically synthesized.

Natural products with antioxidant and anti-inflammatory properties are important sources of therapeutic agents. The nuclear factor E2-related factor 2 (Nrf2)/antioxidant response element (ARE) pathway is a well-known defense system against oxidative stress. In this study, a panel of extracts of plants, fungi, and bacteria were screened for Nrf2 activation in a cell-based assay and a crude extract of cultured marine Streptomyces sp. YP127 was found to activate Nrf2. Chemical investigation of the extracts led to isolation of a series of napyradiomycins that activate Nrf2. Among them, napyradiomycin, 16Z-19-hydroxynapyradiomycin A1 (1) exhibited the highest Nrf2-activating efficacy. Compound 1 was further confirmed to induce both mRNA and protein levels of Nrf2-dependent antioxidant enzyme genes in BV-2 microglial cells and suppress inflammatory mediators and intracellular reactive oxygen species. Our findings confirm the antioxidant and anti-inflammatory properties of compound 1, making it a promising therapeutic natural compound for various diseases associated with oxidative stress and inflammation.

Vanadium-dependent haloperoxidases (VHPOs) are fascinating enzymes that facilitate electrophilic halogen incorporation into electron-rich substrates, simply requiring vanadate, a halide source, and cosubstrate hydrogen peroxide for activity. Initially characterized in fungi and red algae, VHPOs were long believed to have limited regio-, chemo-, and enantioselectivity in the production of halogenated metabolites. However, the recent discovery of homologues in the biosynthetic gene clusters of the stereoselectively halogenated meroterpenoids from marine-derived Streptomyces bacteria has revised this paradigm. Their intriguing transformations have both enhanced and contributed to the fields of synthetic organic and natural product chemistry. We, herein, describe the expression, purification, and chemical assays of two characterized vanadium-dependent chloroperoxidase enzymes (NapH1 and Mcl24), and one homologue devoid of chlorination activity (NapH3), involved in the biosyntheses of halogenated meroterpenoid products.