Metabolites of three marine sponges of the genus Plakortis

One sample of Plakortis halichondrioides contained the cyclic peroxides 3-epiplakortin (9) and 9,10-dihydro-3-epiplakortin (10). A second sample of P. halichondrioides that had been stored in ethanol gave anα,β-unsaturated ester 16 as the major secondary metabolite. A portion of the same sponge that had been frozen and then lyophilized contained the ester 16 and the lactone 19 together with the two peroxides 20 and 21 having a different, but closely related, carbon skeleton. A sample identified as Plakortis sp. contained two unstable peroxides (26 and 27) and a related aromatic hydrocarbon (25). All structures were elucidated by interpretation of spectral data and limited chemical-degradation reactions. The chemotaxonomic implications of these results are discussed.