Cholestenones hydrogenation

Chloropentammine Ir (HI) complex, incomplete Ir (III) autoreduction, 39 151-152 Chloroplasts, quantum conversion in, 14 1 1 -Chloroprop-2-ene thermal decomposition, 41 80 Chlorpromazine, reactivity with EDA complexes, 20 333, 336 CH O, 32 374-375 CH3OH, oxidation, 38 21-23 Cholestenone, hydrogenation, 25 57, 58 Cholesterol, biosynthesis of, 25 382 Cholinesterases, stracture of active surface, 10 130... 

Dihydrocholesterol has been prepared by the reduction of cholestenone with sodium and amyl alcohoP and by the hydrogenation of cholesterol. In the presence of platinum black or platinum oxide, yields varying from 6.5 per cent to 40 per cent have been obtained in ether, acetone, ethyl acetate, and acetic acid. ... 

Table 3-1 illustrates the influence of solvent polarity on the amount of 6W-product e.g. 10) formed from hydrogenation of octalone (9), testo-sterone and cholestenone. The product composition is determined by the amount of 1,2 and 1,4 adsorption of the substrate. 

A solution of 0.2 g of cholestenone and 0.47 g of (< 3P)3RhCl in 150 ml of acetone is stirred under a hydrogen atmosphere for 3 days. The solvent is evaporated and the residue separated by thin layer chromatography to afford 5a-cholestan-3-one in 25-35% yield. ... 

The 5/ -isomer is also obtained in acidic medium but the rate is slower than the base promoted hydrogenation. A solution of 0.4 g of cholestenone in 30 ml of acetic acid containing 0.2 ml 3 N hydrobromic acid is hydrogenated over 0.1 g of prereduced palladium oxide. After work-up and recrystallization of the product, 0.36 g of 5/ -cholestanone is obtained.112... 

TABLE 3-1 Percent Cis Ring-fused Product Obtained on Hydrogenation of Octal-1 (9)-en-2-one (9), Testosterone and Cholestenone... 

Solvent Effect on 5fl-Product Formation in the Hydrogenation of Cholestenone and Testosterone... 

In aprotic solvents, an increase in solvent polarity resulted in an increase in the amount of ds-0-decalone formed. Similar results were also obtained in the hydrogenation of cholestenone and testosterone (see Table I). If, as suggested by McQuillin et al. (3), a more polar aprotic solvent will facilitate complexation of the carbonyl oxygen of an a,j3-unsaturated ketonic system in the same way that it increases its polarization (25), it can be assumed that what is occurring in these polar solvents is a 1,4-addition of hydrogen to the conjugated system. 

The differences noted in Table I in the hydrogenation of cholestenone and testosterone are probably due to differences in solvent acidity used in each case. This is difficult to check since the acid concentrations used were not always reported. It is further possible that with substrates such as A4-3-ketosteroids the acid concentrations corresponding to the two product distribution breakpoints shown in Fig. 6 are different from those found for octalone hydrogenation. Thus, the change in acidity between alcoholic HC1 and alcoholic HBr could correspond to a change analogous to that found between the two breakpoints in Fig. 6. 

The ease and the stereochemical course of hydrogenation of a,p-unsaturated ketones are particularly influenced by the nature of the solvent and the acidity or basicity of the reaction mixture. Some efforts have been made to rationalize the effect of the various parameters on the relative proportions of 1,2- to 1,4-addition, as well as on the stereochemistry of reduction. For example, the product distribution in -octalone hydrogenation in neutral media is related to the polarity of the solvent if the solvents are divided into aprotic and protic groups. The relative amount of cis- -decalone decreases steadily with decreasing dielectric constant in aprotic solvents, and increases with dielectric constant in protic solvents, as exemplified in Scheme 21 (dielectric constants of the solvents are indicated in parentheses). Similar results were observed in the hydrogenation of cholestenone and of testosterone. In polar aprotic solvents 1,4-addition predominates, whereas in a nonpolar aprotic solvent hydrogenation occurs mainly in the 1,2-addition mode. 

The oxidative cleavage of unsaturated ketones takes place under the same conditions as that of alkenes or other unsaturated derivatives. The fate of the primary fission product depends on the position of the double bond with respect to the carbonyl group and on the subsequent reactions. Ozonization of A -cholestenone in acetic acid and ethyl acetate, followed by treatment with 30% hydrogen peroxide, gives a keto acid, evidently resulting from the decomposition of the primarily formed diketo acid (equation 444) [1176]. 

Oppenauer oxidation The oxidation of cholesterol to cholestenone as described by Oppenauer is carried out by gentle refluxingfor 8 hrs. of a mixture of commercial chuleslerol, aluminum t-butoxide. acetone (hydrogen acceptor), and benzene. The... 

The basis for all enzymatic cholesterol assays is the hydrolysis of cholesterol esters by cholesterol esterase (CEH, EC 3.1.1.13) to free cholesterol and fatty acids and the oxidation of free cholesterol to cholestenone by cholesterol oxidase (COD, EC 1.1.3.6) with concomitant oxygen consumption and hydrogen peroxide formation ... 

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