17 3 - Hydroxy-16 -oxosteroid

The application of Westphalen and backbone rearrangement reaction conditions (MeN02, Bi(0Tf)3xH20 catalyst) [118] to 16a,17a-epoxy-20-oxosteroids has also been studied [124]. At room temperature and 0.05 eq. of catalyst, low conversion of 16a,17a-epoxy-20-oxopregn-5-en-3p-yl acetate was observed. However, on increasing the temperature to 50 °C, 16a- and 16p-hydroxy-17p-methyl-A13-18-nor pregnane derivatives were formed in near similar amounts from 16a,17a-epoxy-20-oxosteroids (Scheme 33). 

In 3-oxosteroid A4-steroid 5)3-reductase deficiency, key intermediates for cholic and chenodeoxycholic synthesis, 7a-hydroxy-4-cholesten-3-one and 7a,12a-dihy-droxy-4-cholesten-3-one undergo side-chain oxidation and conjugation to produce... 

Oxygen may be added by means of peracids to the double bond of enamines prepared from 20-oxosteroids. The 17,20-epoxides obtained may be readily hydrolyzed to 17a-hydroxy-20-oxosteroids.88 Schiff bases afford oxaziranes on treatment with peracids.285 By means... 

Henbest [ 4] has discussed a variety of reactions where the stereochemistry of the product is apparently controlled or influenced by the electrostatic effects of remote substituents. As an example, the isomer ratio of the steroid alcohols produced by reduction of a 12-keto function is sensitive to both the nature and configuration of a substituent at C(s) (p. 141). We may also cite the conversion of A -3-oxosteroids into their 4,5-epoxy-derivatives by alkaline hydrogen peroxide, where the proportion of /3-epoxy derivatives varies, according to substitution at C(iv>, from ca. 100% in the unsubstituted androst"4-en-3-one to 70% (- - 30% of a-epoxide) in the 17/ -hydroxy derivative. 

Defective Bile Acid Synthesis. Specific defects in bile acid synthesis have long been postulated. Two inborn errors of bile acid synthesis, both associated with idiopathic neonatal hepatitis, A -3-oxosteroid 5-P-reductase deficiency and 3-p-hydroxy-dehydrogenase isomerase deficiency, have been described. A third disorder associated with defective bile... 

In the presence of 100000 X g supernatant fraction of liver homogenate, 7 -hy-droxy-4-cholesten-3-one as well as 7a,12a-dihydroxy-4-cholesten-3-one are efficiently converted into the corresponding 3a-hydroxy-5 8-steroids via the 3-oxo-5/8-steriods [27,28] (cf. Fig. 3). The NADPH-dependent A -3-oxosteroid 5/S-reductase active on 7a-hydroxy-4-cholesten-3-one and 7a,12 -dihydroxy-4-cholesten-3-one has been partially purified by Bersdus [112,113]. The preparation was also active towards 3-oxo-A -steroids of the C19, Cj, and C24 series. The results of some inhibition experiments indicated that there were different A -3-oxosteroid 5j8-reductases with different substrate specificities in the preparation. 

The quantitative importance of the pathway involving 7a-hydroxy-4-cholesten-3-one and 7a,12a-dihydroxy-4-cholesten-3-one as intermediates in formation of alio bile acids is not known. At least in the rat, the capacity of the microsomal A" -3-oxosteroid 5a-reductase is high, and thus it is surprising that such small amounts of alio bile acids are formed under normal conditions in mammals. It seems probable that this enzyme is inhibited under in vivo conditions. Hoshita et al. found an efficient conversion of 7a,12a-dihydroxy-4-cholesten-3-one into 7a,12a-dihy-droxy-5a-cholestan-3-one in the microsomal fraction of liver from Iguana iguana [170], Alio bile acids are predominant in this species of iguana and it was suggested that the microsomal A -3-oxosteroid 5a-reductase is of major importance for their formation. 

Although cholesterol is the major source of 5)9-bile acids, an unsaturated acid, 3)8-hydroxy-5-cholenic acid [174] has been found in meconium, mainly as the sulfate [175], in bile of a boy with a deficiency of 3)8-hydroxysteroid dehydrogenase [176], and in urine of healthy persons and individuals with liver disease [164]. The details of metabolism of 3)8-hydroxy-5-cholenic acid to lithocholate have not been entirely elucidated, but the mechanism for conversion of the 3/8-hydroxy-A to the 3-oxo-A derivative has been formulated in the C27 series (cf. Chapter 9). Briefly, the 3)8-ol is dehydrogenated by a microsomal enzyme fortified with NAD to provide the 3-oxo-A system [177,178]. Whether a A - A" isomerase is essential is not known, since there is no direct evidence for the formation of the intermediary 3-oxo-A system the rate-limiting step is the dehydrogenation of the 3)8-ol which may prevent accumulation of the 3-oxo-A system [177]. The reduction of the double bond at 4-5 to the 5)8- or 5a-bile acid is catalyzed by the respective A -3-oxosteroid 5)8- or 5 -reductase obtained from liver cytosol [170], and has been purified about 10-fold [178]. The formation of the 3-oxo-5/9 derivative requires the enzyme and NADPH the proton from the A side (4A-NADPH) appeared in the product as the 5)8-H, whereas the proton at C-4 is derived from the aqueous medium. Formation of the 5a derivative requires (4B-NADPH) in a similar mechanism (Fig. 4) [179], Reduction of the 3-0X0 product is then catalyzed by 3a-hydroxysteroid dehydrogenase as discussed above. 

Fig. 44.22. Biosynthesis of the adrenocorticoids from cholesterol. The enzymes involved are (a) side chain cleavage, b) 17a-hydroxylase, (c) 5-ene-3p-hydroxy-steroid dehydrogenase, (cf) 3-oxosteroid-4,5-isomerase, (e) 21-hydroxylase, (f) 11 p-hydroxylase, and (g)...

The reduction of a 3-oxosteroid, catalyzed by 3a-hydroxysteroid dehydrogenase from rat liver, has been shown to involve transfer of a hydride ion from the A-side of NADPH to the 3j -position of the steroid (44,52). The oxidation of 4-cholestene-3a,7a-diol into 7a-hydroxy-4-cholesten-3-one, catalyzed by the same enzyme preparation, has also been shown to involve the A-side of NADPH (52). It remains to be established whether or not Zl -3a-hydroxysteroid dehydrogenase activity is due to enzyme(s) different from 3a-hydroxysteroid dehydrogenase(s). 

Figure 6 LC separation (A) and diode-array UV spectra (B) of Nestorone (1) and its impurities, 6a-hydroxy (2), 6 -hydroxy (3), 6-0X0 (4), 6-ene (5) derivatives. Column Nova PackC-18, 4 pm, 150 x 3.9 mm. Eluent A acetonitrile-water 1 9 v/v, B acetonitrile. Linear gradient, 0 min 25% B, 14 min 45% B, 20 min 75% B. Flow rate 1 ml min k UV detector 254 nm. (Reproduced with permission from Gorog S, Babjak M, Balogh G, et al. (1998) Estimation of impurity profiles of drugs and related materials Part 19. Theme with variations. Identification of impurities in 3-oxosteroids. Journal of Pharmaceutical and Biomedical Analysis 18 511-525.)...

Qualitative and Quantitative Analysis of Urinary 17-Oxosteroids and 20-Hydroxy-21-deoxysteroids by Gas-Liquid Cgromatography and Mass Spectroscopy... 

Hydroxy-A -C27-steroid dehydrogenase (3/ -HSDH) deficiency A -3-Oxosteroid 5/ -reductase deficiency (5//-reduclase deficiency) Fibroblasts 16pl 1.2-12 231100... 

Fig. 32.1. The classical ( neutral ) pathway for the synthesis of bile acids from cholesterol, where the modification of the steroid nucleus occurs prior to side-chain modification. Also illustrated are the inborn errors of bile acid synthesis and the resulting abnormal metabolites. 32.1, 3) -hydroxy-A -C27-steroid dehydrogenase (3) -HSDH) deficiency 32.2, A -3-oxosteroid 5 -reductase deficiency 32.3, sterol 27-hydroxylase deficiency (cerebrotendinous xanthomatosis, CTX) PD, peroxisomal disorders (defects of peroxisome biogenesis and peroxisomal j -oxidation). The abnormal metabolites that are readily detected by analysis of urine by LSI-MS are shown in boxes. Cholic acid can also be synthesised from 5 -cholestane-3a,7a,12a,25-tetrol this is the so-called microsomal or 25-hydroxylase pathway of cholic acid synthesis, which provides an alternative route for side-chain modification other than peroxisomal j -oxidation...

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