Testosterone, conformation

Testosterone, conformation of, 129 molecular model of, 129 structure and function of, 1082 Tetracaine, structure of, 967 Tetrahedral geometry, conventions for drawing. 8... 

Polycyclic compounds are common in nature, and many valuable substances have fused-ring structures. For example, steroids, such as the male hormone testosterone, have 3 six-membered rings and 1 five-membered ring fused together. Although steroids look complicated compared with cyclohexane or decalin, the same principles that apply to the conformational analysis of simple cyclohexane lings apply equally well (and often better) to steroids. 

Within the prostate gland, the steroid hormone testosterone is irreversibly converted to 5a-dihydrotestosterone (DHT), the active androgen in the prostate. Binding of DHT to the AR triggers conformational changes which unmasks the... 

Ligand-induced conformational changes in the protein can result in both cooperative and antagonistic binding effects on other ligands binding to the same protein. An example of a cooperative interaction is the enhancement of the interactions of progesterone and testosterone with human serum albumin (HSA) by the palmitate ion. 

The stereoselectivity of the hydride reduction of conjugated cyclohexenones has also been subjected to close examination from both experimental and theoretical viewpoints. Much of the work has involved polycyclic systems, e.g.. steroids which have little conformational flexibility and in which axial and equatorial directions of approach can be clearly defined. With small" hydride donors, these substrates show an even clearer preference for axial attack than the corresponding cyclohexanones. For examples involving reductions with lithium aluminum hydride and sodium borohydride, see Table 10. 3/(-Acetylcholest-5-en-7-one and cholest-2-en-l-one are notable in that the analogous saturated substrates are attacked from the equatorial direction115 l16. The reduction of 17/i-hydroxy-4-androsten-3-one (testosterone) to 4-androstene-3/1,17/j-diol with d.r. 90 10 can be compared with the sodium borohydride reduction of 17/i-hy-droxyandrostan-3-one (dihydrotestosterone) to androstane-3/ ,17/ -diol with d.r. 81 19 (see p 4030). 

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