Terpenes, isoprenoid formulas

Although the term terpene once referred only to hydrocarbons current usage includes functionally substituted derivatives as well grouped together under the general term isoprenoids Figure 26 6 (page 1086) presents the structural formulas for a number of representative examples The isoprene units m some of these are relatively easy to identify The three isoprene units m the sesquiterpene farnesol, for example are mdi cated as follows m color They are joined m a head to tail fashion... 

FIGURE 26.6 Some representative terpenes and related natural products. Structures are customarily depicted as carbon skeleton formulas when describing compounds of isoprenoid origin. 

Although the term terpene once referred only to hydrocarbons, its use expanded to include functionally substituted derivatives as well, grouped together under the general term isoprenoids. Figure 24.7 presents the structural formulas for a number of... 

The structures of many of the naturally occurring flavonoids, isoflavonoids and neoflavonoids contain Cj units which are apparently derived from mevalonate the precursor of the isoprenoid units of terpenes and steroids. The biosynthetic processes in which the additional units are incorporated into the structures of these compounds presumably involved the intervention of yy-dimethyl-allylpyrophosphate or isopentenylpyrophosphate as intermediates . An additional, and rather unusual structural variation, which has recently been encountered is that of the flavonolignan class in which a flavonoid (taxifolin) is apparently condensed with a pbenylpropanoid intermediate (coniferyl alcohol) . Typical examples of the various classes and the considerable structural diversity which is to be found within them are shown in the accompanying formulae (13-33). 

---