Sterane structure

Corticosteroids are the most effective drugs in the treatment of acute and chronic inflammatory diseases. They were introduced in 1949, since when they have enjoyed a remarkable career . Numerous synthetic corticosteroids have been developed by modifying the chemical structure of cortisone and hydrocortisone. Indeed, the scientific literature shows that there is not one of the carbon atoms of the sterane structure that has remained unmodified in an endeavor to achieve a favorable biological effect. 

Ginsenosides with a few exceptions share a similar basic structure, consisting of a saturated 1,2-cyclopentanoperhydrophenanthrene (sterane or gonane) steroid nucleus. They are classified into two groups by the skeleton of aglycones, namely dammarane-type and oleanane-type. Ginsenosides... 

More than 1500 triterpenoids have been discovered based on 40 skeletal types. Some examples include amyrin (produced by terrestrial plants), cephalosporin (synthesized by marine bacteria), and the steranes. The skeletal structure of the last contains three six-membered carbon rings and one five-membered ring (Figure 22.19a). 

Minor changes in the stereochemistry and substitution pattern of the steran skeleton result in vastly different yet specific physiological and pharmacological effects, which in turn influence developmental, metabolic, and behavioral phenomena. The organic chemistry and biochemistry of steroids is the subject of many excellent books and an enormous amount of research and patent literature. This chapter compares and contrasts the structure and mode of action of various steroids, their role in regulating hormonal secretion, and the timing of this regulatory action. 

Advances in petroleum characterization at the molecular structure level by GC-MS methods renewed interest in OSC. Within the past few years, at least one-thousand new and novel OSC that previously were not known to be present in petroleum and bitumens have been reported. Tentative molecular structures inferred from GC-MS and other techniques have been confirmed in many cases by synthesis of authentic reference-compounds. The difficult and time-consuming synthetic work has been crucial in validating many of the novel structures. Another key finding has been that immature bitumens and crude oils (samples that have not received significant thermal stress) differ markedly from the previously known OSC in that they have carbon-skeletons resembling ubiquitous biomarker hydrocarbons (e.g., n-alkanes, isoprenoid alkanes, steranes, and hopanes). This similarity, of course, suggests that the hydrocarbons and OSC have common biogenic precursors. 

Figure 7 The concentrations of individual biomarkers in a crude oil are relatively low but the complex nature of their structures means their information content is high. This diagram provides an indication of the approximate concentrations of individual steranes and terpanes in a t)fpical cmde oil.

C30 structures. The steranes are characteristic of eukaryotes, and the 2a-methylhopanes are geolipids, the degradation product of the biolipids 2-methyl bacteriohopanepolyols, synthesized only by cyanobacteria. Hence the oldest biomarker molecules indicate that the Eucarya and cyanobacteria were present at ca. 2.7 Ga. 

Wingert W.S., Pomerantz M. (1986) Structure and significance of some twenty-one and twenty-two carbon petroleum steranes. Geochim. Cosmochim. Acta 50, 2763-9. 

The long-term stability of natural polymers can be assessed from geological samples (Table 3). Besides aromatic ring structures of lignin and tannin, the polyaromatic systems of steranes... 

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