Triterpenoids biogenesis

Farnesol pyrophosphate is an immediate precursor of squalene, the key intermediate in steroid and triterpenoid biogenesis, which arises from the coupling of two farnesol pyrophosphate molecules or of C,s units derived therefrom. The numerous types of sesquiter-penoid carbon skeletons represent various modes of cyclization of farnesol (sometimes with rearrangement) and it is probable that farnesol pyrophosphate is also the source of these compounds. 

These studies firmly establish the role of 2,3-epoxysqualene (32) as progenitor of the polycyclic triterpenoids and steroids. However, a number of triterpenoids lack an oxygen function at C(3). In these cases, it has been suggested that a plausible biogenesis mechanism would involve the proton-initiated cyclization of squalene rather than of the terminal epoxide. An alternative hypothesis... 

Some resonances in the ursene series have been reassigned.The labelling pattern in ursolic acid and 2a-hydroxyursolic acid isolated from tissue cultures of Isodon japonicus fed with sodium [l,2- C]acetate conforms with the original Ruzicka hypothesis for the biogenesis of pentacyclic triterpenoids. 

Zeylasterone (154) is a novel phenolic 24-norfriedelane from K. zeylanica.108 Isoiquesterin (155) from Salaciamadagascariensis109 and (156) from S. macrosperma are new quinone methides.110 The biogenesis of triterpenoid quinone methides has been discussed.111... 

Goodwin, T. W., Recent developments in the biosynthesis of plant triterpenoids, in Terpenoids Stmcture, Biogenesis and Distribution, Vol. 6 (V. C. Runeckles and T. J. Mabry, eds.), 97-115, Academic Press, London, 1973. 

Cycloartane triterpenoids are interesting not only because of the fundamental biogenesis issues. The wide variety of structures makes them attractive as subjects for chemical modification and is also responsible for the broad spectrum of biological activity. These aspects also assured the furious pace of research on this class of compounds. As a result, the number of described compounds is currently approaching 900. Their biological properties are also under active investigatiOTi. 

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