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.