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 alpha-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 13 mu M. To our knowledge, marinopyrones A-C are only the second reported natural products from the rare halophilic genus Streptomonospora. (C) 2016 Elsevier Ltd. All rights reserved.