Nocapyrones A−D, γ-Pyrones from aNocardiopsisStrain Isolated from the Marine SpongeHalichondria panicea

Four new γ-pyrones, nocapyrones A−D (1−4), were isolated from an organic extract of the Nocardiopsis strain HB383, which was isolated from the marine sponge Halichondria panicea. These are the first γ-pyrones reported from a Nocardiopsis strain. The structures were elucidated on the basis of one- and two-dimensional NMR experiments and supported by HPLC-UV/MS and HRESIMS analyses. The biosynthesis of nocapyrone A was investigated by feeding experiments with 13C-labeled compounds. In addition, one diketopiperazine, which was only known as a synthetic compound before, was isolated. The bioactivies of 1, 2, and the diketopiperazine were evaluated in a panel of assays.