Sapogenins biosynthesis

Steroidal and Terpenoid Alkaloids.—Following upon earlier work on the biosynthesis of steroidal alkaloids it has been shown that (255)-5a -cholestan-3/8,26-diol (159), but not the corresponding furostan derivative (160), is a precursor for tomatidine (162) in Lycopersicon pimpinellifolium [This contrasts with the observation that the (255)-sapogenin, neotigogenin (163), was labelled by both precursors in these experiments.] If these results are taken together with the observation that... 

The above-mentioned types of Solanum alkaloids are derived from the same pathways as most other steroids in plants. For more information on the formation of the various precursors involved, see Chapters 23 and 24. The biosynthesis and metabolism of the C27 sapogenins and alkaloids are closely related (Ripperger and Schreiber, 1981 Gross et al, 1985). Acetate and mevalonate are incorporated into all types of steroid alkaloids. 

C. is biosynthesized from acetyl-CoA via the tri-terpene lanosterol (see Steroids, Figs. 7 8) and zymosterol. In turn, it is a key intermediate in the biosynthesis of many other steroids, including steroid hormones, steroid sapogenins and steroid alkaloids. 

Mevalonate kinase [E.C.2.7.1.36 (5) -> (6)] preparations from several plants are inhibited by geranyl, geranylgeranyl, farnesyl, and phytyl pyrophosphates, the most potent inhibitors being the latter two compounds.This enzyme may, therefore, be a control point of isoprenoid biosynthesis in plants. A cell-free system for conversion of mevalonic acid (5) into mevalonic acid S-pyro-phosphate (7) has been prepared from the sapogenin-producing plant Agave americana. ... 

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