Cholestane derivatives

The calculated shift of C-3 is 39.1 ppm as compared to an observed value of 39.45 ppm. Prediction of carbon chemical shifts using the Grant-Paul relation (4.1) is a practical aid in assigning the carbon signals of larger alkyl groups, e.g. in cholestane derivatives (Section 5.2.2). - Other increment systems have been proposed [201, 202], as well as an absolute scale for carbon shielding [203],... 

There have been known many examples that the hydrogenation of 3p-substituted A5-steroids yields mainly or exclusively saturated steroids of 5a series.166 Lewis and Shoppee studied the influence of various 3 a substituents on the stereochemical course of the hydrogenation of A5-steroids, and found that the 3a substituents lead to the preferential and sometimes exclusive formation of 5P-cholestane derivatives.166 The hydrogenations over platinum oxide were effectuated in methanol or ethyl acetate in the presence of traces of strong acids such as perchloric acid, sulfuric acid or hydrobromic acid. The results summarized by Lewis and Shoppee (eq. 3.34), which also include those by Haworth et al.,167 suggest that the bulkier the axial 3a substituent, the larger is the proportion of 5P steroid formed. The hydrogenation of A4-steroids usually leads to a mixture of 5a and 5P compounds and the stereochemical influence of 3a and 3P substituents is less marked than in the cases of A5-steroids.168... 

The formation of cholest-14-ene derivatives by hydrochlorination-dehydrochlorination of A8(14)-olefins (282) is accompanied at low temperature by the formation of 17a-cholestane derivatives, which become the main products at —60 to —78 °c.229 230 It is suggested230 that an acid-catalysed contraction of ring C leads to a... 

X-Ray analysis of the cholestane derivative (3) has established the structure and configuration of synthetic (24R)-24,25-dihydroxy-vitamin D2 (4), which has been identified for the first time as a kidney metabolite from rats fed with vitamin... 

Chemical ionization (Cl) mass spectra for 34 cholestane derivatives show correlations with structure. Methane, isobutane, and ammonia were used as... 

By treatment of acyclic and cyclic alkenes with cyanamide and A-bromosuccinimide, the corresponding /3-bromoalkylcyanamides were obtained in moderate to good yield via anti addition to the double bond, as shown for cholestane derivatives, e.g., 367-68, and cyclic, e.g., 470, and acyclic alkenes, e.g., 5 and 670... 

A considerable effort is still devoted to the preparation of halogeno-steroids. A new family of electrophilic fluorinating reagents (hypofluorites) can now replace the less powerful and explosive perchloryl fluoride (C103F). A review of the fluorination of cholestane derivatives with CF3OF has appeared. ... 

With the manufacture and use of steroids in pharmaceutical and contraceptive preparations increasing steadily, the quantities appearing in rivers and other natural waters are beginning to be a cause for concern. A report has now appeared on the identification and estimation of steroids in water. With 500 references, it is a useful source of information on analytical methods. The extent of interference by various cholestane derivatives in cholesterol determinations has been evaluated. Of five methods examined, none is wholly specific to cholesterol. Poor reproducibility in steroid solubility determinations can result from adsorption by filter papers. The g.l.c. retention times of an extensive series of sterols have been measured on four different stationary phases, in order to devise methods for the separation of particular mixtures. Some mixtures of saturated compounds with the corresponding unsaturated A -, A -, A -, A -, or A -sterols could not be separated, but A -, A -, and some dienic derivatives are easily separable from their isomers. The results were applied in the examination of sterols in sunflower and other plant oils. The... 

SECTION B Partial Syntheses 9 Cholestane Derivatives and Analogues... 

The complementary application of film balance and electron spin resonance techniques has given information regarding molecular motion in monolayers. The molecules used, 3-nitroxide androstan 17fi-ol and 3-nitroxide cholestane, have the molecular geometry required for a test of the Cooper-Mann theory of surface viscosity. These ellipsoidal molecules show distinctly different surface behavior as shown by the complete collapse of the hyperfine lines in the case of the cholestane derivative and the apparent lack of exchange broadening for the androstane derivative. These results are modeled in terms of transitional surface regions. 

An example showing diastcrcosclcctivc allylation of a stereogenic nucleophile with an achiral allyl carbonate is depicted in the next diagram91. The carboxylic ester group is later transformed into the angular methyl group of a des-AB-cholestane derivative. 

A series of steroidal a-methylene-lactones, potential anti-tumour agents, has been synthesized and is exemplified by the cholestane derivative (204). 14/S,17Q -Cholest-5-en-3)8-ol (206) was synthesized from the A -compound (205), and syntheses of radiolabelled bile acids and fatty cholesteryl esters ... 

A reported diastereoselective synthesis of precursor A of vitamin D3 involved the use of 2-methylcyclopent-2-enone as starting material. The Mukaiyama-Michael conjugate addition of ketene acetal 269 in the presence of trityl hexachloroaniimonate afforded the adduct 270. The lateral chain was introduced, according the procedure of Tsuji, by the treatment of crude 270 with allyl carbonate and palladium dibenzylideneacetone " (Scheme 63). The expected product 271 was obtained in 63% yield from 269. Reduction of 271 with LAH afforded a mixture of diols that was selectively tosylated at the primary hydroxy group. The secondary hydroxy group was protected with the methoxymethyl group and further functional modifications afforded the lactone 272. The reaction of lithium dimethyl methylphosphonate with the lactone 272 completed the synthesis of the AB-des-cholestane derivative 273. 

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