Marinopyrones A–D, α-pyrones from marine-derived actinomycetes of the family Nocardiopsaceae

[Display omitted] •The rare halophilic strain, Streptomonospora sp. was isolated from a marine sediment.•HPLC-UV guided fractionations of the extracts yielded marinopyrones A–D.•Marinopyrones A–C are only the second reported natural products from this strain. Two actinomycetes, a member of the rare halophilic genus Streptomonospora and a Nocardiopsis sp. (Nocardiopsaceae), strains CNQ-082 and CNQ-675, respectively, were isolated from marine sediments collected off shore near La Jolla, California. HPLC-UV guided fractionations of the extracts of these strains yielded marinopyrones A–D (1–4), the structures of which were elucidated by interpretation of 1D and 2D NMR and HRMS spectroscopic data. Oxidative ozonation, followed by conversion of the acid product to an α-naphthyl amide, provided the absolute configuration at the chiral center on the side-chain. Marinopyrones A–D were examined for the inhibitory activity on nitric oxide production in LPS-activated mouse macrophage cells (RAW 264.7); marinopyrone D (4) was inhibitory with an IC50 value of 13μM. To our knowledge, marinopyrones A–C are only the second reported natural products from the rare halophilic genus Streptomonospora.