Abstract
Naphthoquinone-based meroterpenoids are hybrid polyketide-terpenoid natural products with chemical diversity and a broad range of biological activities. Here, we report the isolation of a group of naphthoquinone-containing compounds from Streptomyces sp. B9173, and their structures were elucidated by using a combination of spectroscopic techniques, including 1D, 2D NMR, and high-resolution mass (HRMS) analysis. Seven flaviogeranin congeners or intermediates, three of which were new, have been derived from common naphthoquinone backbone and subsequent oxidation, methylation, prenylation, and amino group incorporation. Both flaviogeranin B1 (1) and B (2) contain an amino group which was incorporated into the C8 of 1,3,6,8-terhydroxynaphthalene (THN). Flaviogeranin D (3) contains an intact C-geranylgeranyl residue attached to the C2 of THN, while the O-geranylgeranyl group of 2 links with the hydroxyl on the C2 site of THN. Four compounds were selected and tested for antibacterial activity and cytotoxicity, with 3 and flaviogeranin C2 (5) displaying potent activity against selected bacteria and cancer cell lines. In light of the structure features of isolated compounds and the biosynthetic genes, a biosynthetic pathway of naphthoquinone-based flaviogeranins has been proposed. These isolated compounds not only extend the structural diversity but also represent new insights into the biosynthesis of naphthoquinone-based meroterpenoids.
Highlights
Marine-derived microbial natural products are great sources for the discovery and development of pharmaceutical agents [1,2,3]
Marine microbial metabolites are a prevalent source of bioactive natural products and a number of entities have been identified with promising therapeutic potential [1,28]
We have achieved the isolation of seven flaviogeranin congeners, including three new compounds, from marine-derived Streptomyces sp
Summary
Marine-derived microbial natural products are great sources for the discovery and development of pharmaceutical agents [1,2,3]. Marine Streptomyces continue to be the predominant producers, accounting for up to 69% of new secondary metabolites isolated from marine bacteria in 2018 [4]. The genome of each Actinomycetes indicates genetic potential to produce 20–30 secondary metabolites. The rapidly accumulating microbial genomic information and developing bioinformatics platforms are further stimulating the revolution for natural product discovery [5]. The biosynthetic potential of microbial natural products is significantly underestimated based on the isolated compounds. It is hampered by the laboratorial cultivation methods, since many of these “cryptic” gene clusters are only expressed under certain culture conditions. Metabolite production is strongly influenced by growth conditions, including production media, pH, temperature, etc. [6,7]
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