(±)-Nigronetides A−D and Nigronetides E−H, Complex Polyketides Produced by the Marine-Derived Fungus Nigrograna sp. M13

Abstract (±)-Nigronetides A−D (1−4) and nigronetides E−H (5−8), polyketides with complex carbon skeletons, were isolated from cultures of the marine-derived fungus Nigrograna sp. M13, presenting three novel carbon skeletons. While the planar structures and relative configuration of (±)-nigronetides A−D (1−4) were established by analysis of spectroscopic data, the absolute configuration of nigronetides E−H (5−8) was assigned using a combination of analysis of NOESY data, quantum chemical NMR calculations, as well as by comparison between experimental and calculated electronic circular dichroism (ECD) spectra. (±)-Nigronetides A−D (1−4) were isolated as scalemic mixtures of an almost identical ratio between enantiomers. Compounds 1−8 were inactive in antiplasmodial assays against the Plasmodium falciparum 3D7 strain as well as in cytotoxicity assays against several cancer cell lines.