Gracilioethers E-J, new oxygenated polyketides from the marine sponge Plakinastrella mamillaris

Purification of the apolar extracts of the marine sponge Plakinastrella mamillaris afforded the isolation of six new oxygenated polyketides, gracilioethers E-J, featuring an unprecedented oxidation pattern of the polycyclic core. On a common tricyclic core, gracilioethers E, G, and feature the furanyliden methyl ester substructure and gracilioethers F, H, and I display a gamma-lactone substructure. The new structures were elucidated on the basis of extensive spectroscopic (H-1 and C-13 NMR, COSY, HSQC, HMBC, and ROESY), MS, computational and chemical methods. Pharmacological analysis demonstrated that gracilioether H is endowed with in vitro antiplasmodial activity against a chloroquine resistant strain. (C) 2012 Elsevier Ltd. All rights reserved.