Marilones A-C, phthalides from the sponge-derived fungus Stachylidium sp.

The marine-derived fungus Stachylidium sp. was isolated from the sponge Callyspongia sp. cf. C. flammea. Culture on a biomalt medium supplemented with sea salt led to the isolation of three new phthalide derivatives, i.e., marilones A-C (1-3), and the known compound silvaticol (4). The skeleton of marilones A and B is most unusual, and its biosynthesis is suggested to require unique biochemical reactions considering fungal secondary metabolism. Marilone A (1) was found to have antiplasmodial activity against Plasmodium berghei liver stages with an IC50 of 12.1 mu M. Marilone B (2) showed selective antagonistic activity towards the serotonin receptor 5-HT2B with a K-i value of 7.7 mu M.