Cassanes, Cleistanthanes, Isocopalanes

Cassane is the basic skeleton of cassaic acid, the parent diterpenoid of alkaloids from the bark of Erythrophleum guinese and other Erythrophleum species (Fa-baceae). These act as local anaesthetics, cardiotonics, antihypertonics, and also induce cardiac arrest. Erythrophleum alkaloids such as cassaidine, cassain and cassamine are 2-(iV,iV-dimethylamino)ethyl esters of cassaic acid derivatives. 

Representatives of naturally occurring cleistanthanes include (+)-13(17),15-clei-stanthadiene from Amphibolis antarctica, (+)-auricularic acid from Pogostemon auricularis (Labiatae), the antineoplastic (-)-spruceanol from Cunurea spruceana and (-)-cleistanthol from Cleistanthus schlechteri (Euphorbiaceae). 

Isocopalane and its tetracyclic furan derivatives, referred to as spongianes, are found in various sponges such as Spongia officinalis, and in the naked snails eating these sponges. Such compounds include (+)-isocopalene-15,16-dial, the cyclohe-miacetal (-)-spongiane-15,16-diol, the lactone (+)-l ip-hydroxy-12-spongiene-16- 

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