Steroid core structure

In later studies by various groups, the enyneallene motif was incorporated into more complex hydrocarbon structures, allowing not only a better understanding of the Myers cyclization but also the generation of polycyclic hydrocarbons, some of them resembling the steroid core unit. Conceptually, these latter cyclizations are reminiscent of Johnson s biomimetic cyclization reactions with the main difference that here radical intermediates are involved rather than carbocations. Typical starting materials in these studies are the allenes 221 [87], 222 [88] and 223 [89], their cyclization behavior being discussed in Chapter 20. 

Common to all of the steroids is a molecular core structure consisting of four saturated rings, known as gonane. At the end of the steroid core, many steroids also carry a side chain, as seen in cholestane, the basic component of the sterols (steroid alcohols). 

Fig. 3-21 The precursor of steroids is squaiene that ieads to the core structure of choiesteroi, with its four carbon rings, and testosterone.

The reasons are not understood. However, it has been suggested that the close structural similarity between testosterone and vecuronium, with respect to their common steroidal core, might mean that they share similar metabolic pathways. Chronic elevation of circulating testosterone may up-regulate the hepatic metabolism of steroidal molecules in general, and so enhance the hepatic elimination of vecuronium. ... 

Figure 1.4 The core structure and representatives of sterol lipids, (a) The core structure of the majority of the sterol species or from which the sterol species are resulted, (b) The representative structures of cholesterol (R = H) and cholesteryl esters (R = a fatty acyl), (c) A representative structure of the steroid subgroup species (i.e., estrogen), (d) A representative structure of the secosteroid subgroup (i.e., vitamin Dj). (e) A representative structure of the species among the bile acid subgroup of sterol (i.e., cholic acid).

Sterols are a class of lipids containing a common steroid core of a fused four-ring structure with a hydrocarbon side chain and an alcohol group. Cholesterol is the primary sterol lipid in mammals and is an important constituent of cellular membranes. Oxidization and/or metabolism of cholesterol yield numerous oxysterols, steroids, bile acids, etc., many of which are important signaling molecules in biological systems. Cholesteryl esters esterified with a variety of fatty acyls are enriched in... 

The same fused, four-ring core structure is present in the steroids, which have different biological roles as hormones and signaling molecules. The C18 steroids include the estrogen family, whereas the C19 steroids constitute the androgens, such as testosterone and androsterone. The C21 subclass includes the progestogens, the glucocorticoids, and mineralocorticoids. 

Steroids are a class of biologically active natural products that have a common tetracyclic structure. This core structure consists of three fused... 

Figure 6. Construction of steroid structural analogues based on the square pyramidal Re03+ core.

Steroidal alkaloids These alkaloids have a core steroidal skeleton as part of the molecule, e.g. solanine. There are a number of structural varieties that exist in steroidal alkaloids. Following discussion is just on a few selected steroidal alkaloids. 

Structurally, cholesterol contains the steroid nucleus that is the common core of all steroids. 

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