Calyculatine: a new dolabellane diterpenoid from the marine sponge Eunicea calyculata.

A new dolabellane diterpenoid, 7(S)-hydroperoxy-13-keto-(1S,11R)-dolabella-3(E),8(17),12(18)-triene (1), and two known compounds, 7(S),8(S)epoxy-13-keto-1(S),11(R)-dolabella-3(E),12 (18)-diene (2) and 13-keto-1(S),11(R)-dolabella-3(E),7(E),12(18)-triene (3), were isolated from the marine sponge Eunicea calyculata. The structure of 1 was elucidated by 1D (1)H- and (13)C-NMR spectra and 2D HMQC, HMBC, and the relative stereochemistry was established by analysis of coupling constants and NOESY spectra. In addition, an X-ray crystallographic analysis on a single crystal of 2 was carried out. Compounds 1 and 2 were inactive in the hyphae formation inhibition assay (HFI) in Streptomyces 85E while compound 3 showed inhibitory activity at a concentration of 20 microg/20 microL in the HFI assay.