Triterpene cyclases

Poralla K (1999) Cycloartenol and other triterpene cyclases. Comprehensive Natural Products Chemistry, Vol 2. Elsevier, Amsterdam, pp 299-319. 

Class 11 terpene cyclases are known for the cycUzation of di-, sester-, and triterpenoids. Prominent examples of triterpene cyclases are the human lanosterol synthase (oxidosqualene cyclase, OSC) and the squalene/hopene cyclase (SHC) firom A. acidocaldarius [1]. Both enzymes have a py-domain architecture (Fig. 87.15a). The p-domain exhibits a highly regular Oe-Oe barrel structure with six inner and six outer helices surrounding a central cavity (Fig. 87.15b) [198,199, 208]. The y-domains may have originated from the p-domains by gene duplicatimi... 

BUNTEL GRIFFIN Evolution of Sterol and Triterpene Cyclases... 

Despite the broad medical potentials reported so far, the total synthesis of triterpene QMs is yet to be reported. On the contrary, the biosynthesis of triterpene QMs has recently been validated as from the oxidosqualene 88 (Scheme 8.16) in the plants including Maytenus aquifolium and Salacia campestris.10S With the assistance of HPLC analysis and isotopic labeling, it was found that triterpene QMs 90 were formed only in the root of these plants from friedelin 89 and similar cyclized intermediates, which were synthesized in the leaves from oxidosqualene by cyclase. 

KUSHIRO, T., SHIBUYA, M., EBIZUKA, Y P-Amyrin synthase. Cloning of oxidosqualene cyclase that catalyzes the formation of the most popular triterpene among higher plants, Eur. J. Biochem., 1998,256,238-244. 

It did involve a lot of help from individuals, from botanists in Africa, who collected the latex for us, from curators of botanical gardens, from friends who sent us specimen plants. I collected some myself in Jamaica and in the French Indies. It would have had to be followed by a study of the structure of the enzymes producing the various triterpenes isolated, but this was too difficult at the time it is only very recently that the structures of the first cyclases of this family have been defined. 

B Formation of Tetracyclic and Pentacyclic Triterpenes from Squalene Epoxide. In most microorganisms and in plants and animals the cyclic triterpenes are derived from squalene-2,3-epoxide, which is formed from squalene by a monooxygenase (C 2.6.5). The action of different, squalene epoxide cyclases results in the formation of different types of cyclic triterpenes. 

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