The Sipholanes: A Novel Group of Triterpenes from the Marine Sponge Siphonochalina siphonella

Article abstract of DOI:10.1021/jo00168a029

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-octahydroazulene 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 the latter made possible the NMR and mass spectral interpretations and, hence, the structure elucidation of the additional seven new compounds.The structural determination were also assisted by various chemical correlations as well as transformations to compounds with well-defined functionalities.Of special interest is the suggested biogenesis of the sipholanes starting from 2,3:6,7:18,19-triepoxysqualene.In contrast to the single cyclization process that takes place in the biosynthesis of tetra- and pentacyclic triterpenes, the suggested route leading to the sipholanes involves two consecutive cyclizations.