Steroidal alkaloids biogenesis

Several reviews have appeared, on such topics as steroid and terpenoid biogenesis, hemiterpenoid alkaloids,indole alkaloids (monoterpenoids), ophiobolins (sesterterpenoids), sterols in Digitalis, oestrogens, plant tri-terpenoids, and carotenoids. ... 

The origin of the steroidal alkaloids of the Apocynaceae and some of the Buxaceae (Sarcococca and Pachysandra) appears to be linked with the biogenesis in these plants of steroidal derivatives of pregnanes, pregnenolone in particular. The Buxus alkaloids appear to be derived from 4,4,14a-trimethyl-9j3,19-cyclo-5a-pregnanes. 

Evidence has been accumulated that the biogenesis of plant steroids proceeds by the same scheme as in animals this sequence was proved up to squalene and recently squalene has been shown to be a precursor of, 8-sitosterol evidence was also adduced that this conversion includes lanosterol as an intermediate (233). Goutarel assumes that the sequence squalene, lanosterol, zymosterol, and desmosterol may be implied also in the biogenetic pathway of Apocynaceae alkaloids (205). It may be assumed that biogenetic intermediates from sterol or triterpene precursors of Apocynaceae or Buxaceae alkaloids, respectively, are 3-and/or 20-ketones which may give rise to mono- and diamines. 

No investigation dealing with the biogenesis of Pachysandra or Sar-cococca alkaloids has been reported. However, their close similarity to Holarrhena alkaloids permits the assumption of analogous biosynthetic pathways. It may be noted that important questions concerning the biogenesis of steroidal Apocynaceae and Buxaceae bases remain still open. 

The biogenesis of the eastern hemisphere of the molecule is derivable from a 12-hydroxy-A14-steroid skeleton as shown in Scheme 7. The isolation of closely related dimeric alkaloids from two different phyla (Hemichordata... 

The configuration 8(S-, 9a-, 12a-, 14a-hydrogen in veramarine was inferred from the analogy with the other alkaloids of the cevanine group and from the consideration of biogenesis of the G-nor-D-homo steroidal skeleton (56). 

The glyco-alkaloid a-tomatine has been the subject of a detailed review, which covers chemical, biochemical, and biological aspects. The synthesis and biogenesis of steroidal Solarium alkaloids has also been reviewed. ... 

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