Triterpenoids triterpene cyclase

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... 

A comprehensive rationale for structural and stereochemical outcome of squalene cyclization in terms of conformation dictated by the cyclase has been build up by the Zurich school. It provides a convenient basis for discussing various triterpene structures (263, 323). These conformations are described in terms of section-wise folding of the squalene chain into a chair (C), or boat (B) conformation or a part remaining unfolded (U). The following discussion of triterpenoids relevant to wood chemistry is based on these considerations. 

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