Steroids biogenesis

Farnesol pyrophosphate is an immediate precursor of squalene, the key intermediate in steroid and triterpenoid biogenesis, which arises from the coupling of two farnesol pyrophosphate molecules or of C,s units derived therefrom. The numerous types of sesquiter-penoid carbon skeletons represent various modes of cyclization of farnesol (sometimes with rearrangement) and it is probable that farnesol pyrophosphate is also the source of these compounds. 

In the biogenesis of steroids, the enzyme-catalyzed polycyclization of squalene (225) produces the tetracyclic substance lanosterol (225) which is eventually converted into cholesterol (227) Eschenmoser, Stork, and their co-workers (80-82) have proposed that the squalene-1anosterol conversion can be rationalized on the basis of stereoelectronic effects. The stereochemical course of this biological cyclization (83, 84) can be illustrated by considering the transformation of squalene oxide (228) (an intermediate in the biosynthesis of cholesterol (83, 84)) into dammaradienol 229. This transfor-... 

Kimura, T. In A symposium on biogenesis and action of steroid hormones, Yonago, Japan, August, 1967, in press. 

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. ... 

These studies firmly establish the role of 2,3-epoxysqualene (32) as progenitor of the polycyclic triterpenoids and steroids. However, a number of triterpenoids lack an oxygen function at C(3). In these cases, it has been suggested that a plausible biogenesis mechanism would involve the proton-initiated cyclization of squalene rather than of the terminal epoxide. An alternative hypothesis... 

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 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. 

D9. Diczfalusy, E., Pion, R., and Schweis, J., Steroid biogenesis and metabolism in the human feto-placental unit at midpregnancy. Arch. Anal. Microscop. Morphol. Exptl. 64, 67-83 (1965). 

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 biogenesis of this complex and highly oxygenated steroids (8 rings) containing a minimum of nine oxygen atoms calls for an elaborate system on the part of the plant. These were mainly formed in Physalis species, not in the other Solanaceous plants. A hypothetical biogenetic scheme, (Chart IV) was proposed by Crombie et al. . ... 

R)- and (22S)-22-aminocholesterol were stereospecifically synthesized in order to study their action on the biogenesis of C21 steroids from cholesterol. Water-soluble steroids with catalytic substituents were prepared. The synthesis of amino-steroids bearing an imidazoyl nucleus, (54) and (55), has... 

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. ... 

In both men and women there is a continuous secretion of the hypothalamic releasing factors so that there is a continuous production of gonadal hormones. In addition, in the female alone, there is superimposed an explosive cyclical release of FSH-RF and LH-RF which are essential for the ovulatory process [5]. In its simplest form it is possible to equate the follicular phase of the menstrual cycle with the preovulatory FSH surge and subsequent rupture of the follicle with mid-cycle LH release. Steroid biogenesis in the testis, in contrast, follows a continuous pattern with no dramatic changes in hormone output. Both ovary and testis utilise cholesterol as raw material for... 

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