Triterpenes, structures

Table 51.3 and formula D show that the methyl connectivities of the CH COLOC plot are sufficient to indicate essential parts of the triterpene structure. 

Triterpenes, structural chemistry, 136 Tropopause, emissions model, 605 Troposphere ozone analysis, 605 trifluoromethyl peroxynitrate, 743 Tryptophan... 

Cyclization of squalene is via the intermediate squalene-2,3-oxide (Figure 5.55), produced in a reaction catalysed by a flavoprotein requiring O2 and NADPH cofactors. If squalene oxide is suitably positioned and folded on the enzyme surface, the polycyclic triterpene structures formed can be rationalized in terms of a series of cycliza-tions, followed by a sequence of concerted Wag-ner-Meerwein migrations of methyls and hydrides... 

From the same L. viridis algae, Norte s research group was able to isolate five new polyether triterpenes structurally related to both thyrsiferol (1) and venustatriol (2) [10]. These new compounds include dehydrovenustatriol (14), 15,16-dehydro venustatriol (15), predehydrovenustatriol acetate (16), 16-hydroxydehydrothyrsiferol (17) and 10-e/>/-15,16-dehydrothyrsiferol [18, Fig. (4)]. 

Triterpene saponins have an aglycone with a triterpene structure (e.g. primulagenin and quillajic acid). These saponins are used therapeutically as expectorants others are antiinflammatory and others are beheved to have adaptogenic properties. 

Triterpenes are C30 compounds, produced from two molecules of famesyl pyrophosphate (FPP) condensed head-to-head. Representative structures are shown in Fig. 20. The compounds shown represent only a few of the many triterpenes found in plants. They are chosen to suggest the great variety of structures and to illustrate specifically some of the compounds that have played, or are playing, key roles in studies of triterpene chemistry and biochemistry. For a detailed survey of triterpene structures the reader is referred to Connolly and Overton (1972) and Ourisson et al. (1964), as well as Devon and Scott (1972). Analytical techniques for triterpenoids, and the distribution of triterpenoids in plants, have been reviewed by Rastogi and co-workers (Kulsh-reshtha et al., 1972 Pant and Rastogi, 1979). Chandler and Hooper (1979) have recently reviewed the literature on fiiedelin and associated triterpenes. 

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. 

Nozawa, D., Takikawa, H., and Mori, K. (2000) Triterpenoid total synthesis. Part 5. Synthetic disproof of the triterpene structure proposed for naurol A, a cytotoxic metabolite of a Pacific sponge. J. Chem. Soc. Perkin Trans. I, 2043-2046. 

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