Eight new squalene-derived triterpenes possessing a hitherto unknown framework have been isolated from the Red Sea sponge Siphonochalina siphonella. The novel skeleton, designated sipholane, consists of a cis-odahydroazulene linked via an ethylene bridge to a trans-decahydrobenzoxepine. The structure of the sipholane skeleton was established by an X-ray diffraction analysis of one of the natural compounds derivatives (16). The structure of ...
