Cacospongionolide F (4a), a new bioactive cacospongionolide-related sestert
erpene, has been isolated from the Northern Adriatic sponge Fasciospongia c
avernosa. The structure was proposed on the basis of spectroscopic data and
chemical transformations. The absolute configuration was established using
the modified Mosher's method. A molecular mechanics study of the dehydrode
calin ring explained the observed differences in dynamic behavior between c
acospongionolide F and mamanuthaquinone, a related compound. Antimicrobial
activity, brine shrimp and fish lethalities of this new compound are report
ed.