Sesterterpenes tetracyclic

Corey, E.J. Luo, G. Lin, L.S. (1997A) A simple enantioselective synthesis of the biologically active tetracyclic marine sesterterpene scalarenedial. J. Am. Chem. Soc., 119,9927-8. 

A unique tetracyclic furanosesterterpene, wistarin (195), has been discovered in Ircinia wistarii in addition to the previously known isomer ircinianin (196) 131). 196 decomposed readily, whereas 195 was relatively stable. As wistarin (195) was not detected among the decomposition products of 196 and 196 did not undergo cyclization to 195 on treatment with dilute acid, base or Lewis acids, it was proposed that 195 was a natural product and not an artifact. The biosynthesis of these sesterterpenes must involve a different folding of the acyclic 25-precursor. 

Soetjipto, H., Furuichi, N., Hata, T., and Katsumara, S. (2000) StereocontroHed synthesis of a tetracyclic sesterterpene, (-L)-scalar-enediaL Chem. Lett., 11,1302—1303. 

Deoxoscalarin, a further sesterterpene with the unusual tetracyclic carbon... 

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