Steroids microbial

There are two principal biotechnological appHcations dealing with steroids. Microbial agents are used for processing raw materials into useful intermediates for general steroid production and for specific transformations of steroids to advanced intermediates or finished products (120,145). 

In Table 2 antibiotic and steroid biotransformations are only poorly represented compared to their actual frequency more than 50 examples of antibiotic transformations were already reported in 1975 [9, 38, 39] a hsting of steroid microbial transformations, published in 1981, covers 853 substrates [40], while more than 1000 examples have been hsted for the 1979-1992 period [41-44]. However, most of the examples reported in those areas have been essentially oriented towards the preparation of new active compounds rather than towards a study of detoxification metabohtes derived from drugs. Alkaloids represent another group of biologically active natural substances where microbial metabolism was explored relatively early and exhaustively [40,45-47]. 

Current trends in steroid microbial biotransformations, S.B. Mahato and I. 

Kieslich, K. 1976, Microbial Transformations of Non-Steroid Cyclic Compounds, Thieme Stuttgart Kim, B. M. Sharpless, K. B. 1990, Tetrahedron Lett. 1990, 3003... 

The preparation of estranes via 19-hydroxy steroids has also been accompHshed microbially. 19-Hydroxycholesterol, prepared chemically (39), is incubated with JS icardia restrictus to provide estrone (20) direcdy (44). Similarly, 19-hydroxyandrost-4-en-3,17-dione is converted to estrone (20) (45). 

Experimental procedures have been described in which the desired reactions have been carried out either by whole microbial cells or by enzymes (1—3). These involve carbohydrates (qv) (4,5) steroids (qv), sterols, and bile acids (6—11) nonsteroid cycHc compounds (12) ahcycHc and alkane hydroxylations (13—16) alkaloids (7,17,18) various pharmaceuticals (qv) (19—21), including antibiotics (19—24) and miscellaneous natural products (25—27). Reviews of the microbial oxidation of aUphatic and aromatic hydrocarbons (qv) (28), monoterpenes (29,30), pesticides (qv) (31,32), lignin (qv) (33,34), flavors and fragrances (35), and other organic molecules (8,12,36,37) have been pubflshed (see Enzyp applications, industrial Enzyt s in organic synthesis Elavors AND spices). 

Fig. 2. Oxidation and reduction reactions using microbial transformation for steroid synthesis.

Processing Raw Materials. Along with the aforementioned chemical methods of processing steroid raw materials, microbial transformations have been and are used in a number of commercial degradation processes. The microbial degradation of the C17 side chain of the two most common sterols, cholesterol (2) and P-sitosterol (41), is a principal commercial method for the preparation of starting materials in Japan and the... 

Besides the aforementioned chemical methods, microbial degradations have been used to remove the C19 angular methyl substituent of readily available steroid precursors. For example, 19-hydroxysterols, such as 3P-acetoxy-19-hydroxy-5-cholestene [750-59-4] (107), can be converted to estrone by Mocardia sp. in yields up to 70% (120,145,146). 

Sobering investigators uncovered a second significant breakthrough in microbial biotechnology of steroid production. They discovered that Corynebacterium simplex converted hydrocortisone (cortisol) (29) to prednisolone via a 1,2-dehydrogenation reaction. This A -3-ketosteroid is a highly active antiinflammatory commercial product (162). 

A third advancement in microbial biotechnology of steroid production was the abiUty to introduce a 16a-hydroxyl group microbiologicaHy (163). Modifications of the liP-hydroxylation, 16a-hydroxylation 1,2-dehydrogenation microbial processes are used for the synthesis of hydrocortisone, prednisolone, triamcinolone, and other steroid pharmaceuticals. A few microbial transformations that have been used to manufacture steroids are Hsted in Table 1 (164). 

Biotransformations are carried out by either whole cells (microbial, plant, or animal) or by isolated enzymes. Both methods have advantages and disadvantages. In general, multistep transformations, such as hydroxylations of steroids, or the synthesis of amino acids, riboflavin, vitamins, and alkaloids that require the presence of several enzymes and cofactors are carried out by whole cells. Simple one- or two-step transformations, on the other hand, are usually carried out by isolated enzymes. Compared to fermentations, enzymatic reactions have a number of advantages including simple instmmentation reduced side reactions, easy control, and product isolation. 

A. Capek, O. Hanc and M. Tadra, Microbial Transformations of Steroids, Academia, Prague, 1966. 

W. Charney and H. Herzog, Microbial Transformations of Steroids, Academic Press, New York, 1967. 

H. lizuka and A. Naito, Microbial Transformation of Steroids and Alkaloids, University Park Press, State College, Pa., 1967. 

In section 9.3, we discussed in general terms the use of microbial metabolism to selectively remove the side chain from sterols to produce steroids. This removal may also be accompanied by some modification to the ring structure. We did not, however, discuss in any detail any specific reactions. In this section we will focus on some specific reactions. 

Many examples of microbial hydroxylation of sterols/steroids have been reported. These hydroxylations usually involve mixed function oxidases which utilise molecular oxygen and cytochrome P-450. The reaction can be represented by ... 

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