Peniterretonins A-D, terretonin-type meroterpenoids from the marine-derived fungus Penicillium simplicissimum.

Four previously undescribed terretonin-type meroterpenoids, peniterretonins A-D (1-4), possessing unprecedented 6/6/6/6/6 pentacyclic systems, were isolated from the marine-derived fungus Penicillium simplicissimum. Peniterretonins B-D (2-4) represent the first examples of 21-nor-terretonin meroterpenoids, of which 2 and 3 bear a 10-hydroperoxyl group. Their structures were established by detailed analyses of the spectroscopic data, as well as by single-crystal X-ray diffraction analysis (Cu Kα), DP4+ probability analyses, and ECD quantum chemistry calculations. In the bioassays, compounds 1, 3, 4 exhibited significant inhibitory activity against LPS-induced NO release with IC50 values ranging from 2.51 to 3.98 μM.