Nocapyrones A-D, γ-Pyrones from a Nocardiopsis Strain Isolated from the Marine Sponge Halichondria panicea

Four new gamma-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 gamma-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 (13)C-labeled compounds. In addition, one dikeopiperazine, 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.