Hydroxylation of steroid substrates

Recently, Breslow19 reported a regioselective and stereoselective hydroxylation of steroid substrates catalyzed by manganese porphyrin... 

Further examples of l/ -hydroxylation of steroid substrates with various microorganisms are listed in Table 4. 

Hydroxylation of progesterone has been reported with Phycomyces blakesleeanus M and Spicariu simplicissima2bb, while deoxycorticosterone139 and 3/ -hydroxyandrost-5-en-17-one 267 have been 15/J-hydroxylated with Lenzites abietina and Gibberella baccata (see Table 16 for these and further examples of microbial 15//-hydroxylation of steroid substrates). 

Microbiological Hydroxylations.—Microbiological hydroxylations of steroid substrates are too numerous for general inclusion in this report, but two results are of particular interest, d- And d/-19-nortestosterone, incubated with Curvularia lunata, both afforded the d-lO/9-hydroxy-derivative as major product, implying enzyme specificity for the d-form. Several minor products, however, resulted from non-specific attack upon the two antipodes. The 11 - and 6/ -hydroxylated derivatives, for example, were obtained as d/-mixtures from the dZ-steroid. ... 

The greatest contribution towards understanding the structural features in the substrate that effect, or indeed control, the selectivity in microbial hydroxylation of steroids was carried out by Jones and Meakins and their work is recorded in a series of papers entitled Microbiological Hydroxylation . Their last report was published in 1980, and serves as a source of references to earlier material. ... 

The value of microbial hydroxylation of steroids has long been that they allow functionalization of positions not easily accessible by normal chemical methods. For this reason yields of a few percent have often been tolerated, but yields approaching quantitative can be achieved in many instances. The objective of much current work is to improve the selectivity of microbial hydroxylations. This can be achieved in a number of ways, for example by structural modifications of the substrate, optimization of fermentation conditions and by strain improvement. The latter is most likely to yield the most significant improvements in selectivity, and has previously been discussed at length. ... 

In addition, a variety of steroidal substrates have been hydroxylated in the 15 -position by a number of microorganisms selected examples are given in Table 15. 

The distribution of 0 between the hydroxyl and hydroxymethylene functions of 19a and 19b, determined by the fragmentation pattern of these two species during mass spectrometry, could only result from addition of the carboxyl of the enzyme to the a face of the steroid. Had the carboxyl added to the spiro carbon from the jS face, the 0 would have been located in the hydroxymethylene function of 19a. Clearly, if the binding of the oxiranyl steroids is analogous to that of steroid substrates, Asp-38 could not be involved in the normal intramolecular proton transfer associated with the isomerization reaction. However, as recently emphasized by Pollack ei al., the oxiranyl steroids could conceivably bind to the active site in an upsidedown orientation in comparison to that of the substrate steroids (133). In this case, Asp-38 would still be the most probable base involved in the intramolecular proton transfer reaction. Perhaps upsidedown binding accounts for the report that the C-4a hydrogen of 5-androstene-3,17-dione undergoes slow labilization in the presence of the isomerase (134, 135). 

R. Breslow, J. Yan, S. Belvedere, Catalytic hydroxylation of steroids by cytochrome P-450 mimics. Hydroxylation at C-9 with novel catalysts and steroid substrates, Tetrahedron Lett., 2002, 43, 363-365. 

Mucorales on a variety of steroidal substrates, observii 6/3-hydr oxylation as a frequent occurrence (M-601). From our own experience, corticosteroids and their analogs (e.g., prednisone) are 6/3-hydroxylated efficiently by Chaetomium sp. (C-108). 

Heme-coupled monooxygenases contain cytochrome P-450. They are present in microsomes and are responsible for many hydroxylation reactions, e.g. llp-hydroxylation of steroids in the adrenal cortex, 2-hydroxylation of estrc ens in the liver the liver system is especially important in the hydroxylation of drugs and xenobiotics, thus rendering them water soluble, capable of conjugation and easily excreiable. A cytochrome P-450 system responsible for the hydroxylation of camphor (a 5-exo-hydroxylase) has been purified from Pseudomonas putida, and named putidaredoxin it contains FAD, an Fc2S2CyS4 center, and a P-4S0 cytochrome substrate hydroxylation is coupled to the oxidation of NADPH. 

The co-hydroxylation of fatty acids, which involves the addition of a hydroxyl group at or near the co-terminal carbon, was first shown to be catalyzed by the liver microsomal enzyme system in the 1960s [38], In particular, the CO pigment of CYP was recognized as a constituent of the microsomal mixed function oxidase system that contributes to the co-hydroxylation of steroids [39], Substrates that are susceptible to co-hydroxylation include laurate and AA [38], Early reports showed that CYP enzymes catalyze the CO (C-20) and co-1 (C-19) hydroxy lation of AA [40], In 1990, Faick et al. demonstrated that CYP enzymes also hydroxy late the C-16 (co-4), C-17 (co-3), and C-18 (co-2) carbons of A A [41], Thus, in the presence of nicotinamide adenine dinucleotide phosphate (NADPH) and molecular oxygen, CYPs mediate the hydroxylation of AA to generate a variety of co-terminal HETEs including 16-, 17-, 18-, 19-, and 20-HETR (Fig. 13.2). 

Sulfotransferases catalyze the transfer of sulfate from PAPS to wide-range xenobiotics that possess hydroxyl groups. Steroid alcohols are among the endogenous substrates. The sulfotransferases exist in different forms. 

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