Plakortinic acids A and B: cytotoxic cycloperoxides with a unique bicyclo4.2.0octene unit from sponges of the genera Plakortis and Xestospongia

摘要

Plakortinic acids A (2) and B (3), two polyketide endoperoxides having an unprecedented bicyclo[4.2.0]octene unit, were isolated as minor constituents from the sponge-sponge symbiotic association Plakortis halichondrioides-Xestospongia deweerdtae from Puerto Rico, along with the known epiplakinic acid F (1). The molecular structures of 2 and 3 were determined mainly on the basis of NMR spectroscopy. Due to the structural similarities, 2 and 3 are thought to be biosynthetically related to 1. Biological screening for cytotoxic activity against two human tumor cell lines revealed that these novel metabolites are very active at low to sub-micro molar concentration.