Biotransformations microbial transformation products

Earlier biotransformation studies with vindoline were reported from the Eli Lilly Laboratories (166-168), and microbial transformation products included N-demethylvindoline (48), deacetylvindoline (49), and a structurally novel com-... 

One of the main obstacles for whole-cell microbial transformation in an organic solvent is its biocompatibility, which has led to screening for organic-solvent-tolerant microorganisms. Numerous organic-solvent-tolerant microorganisms have been found and their tolerance mechanisms have been reviewed [14,33,34]. Two-phase biotransformation systems have been successfully implemented for the production of pharmaceutically relevant metabolites. 

In every case the information provided has been obtained by collating public domain sources of information, but unfortunately very often little data is available, particularly on commercial aspects, even for products that have proved to be big successes. Thus microbial biotransformations for steroid modification, particularly stereoselective hydroxylations, such as the use of Rhizopus arrhizus to convert progesterone into antiinflammatory and other dmgs via 11- -hydroxyprogestrone, have proved to be very successful. However, comparatively little useful information exists from public domain sources, despite (or perhaps because) a market of hundreds of millions /a exists for such microbially transformed steroids (cortisone, aldosterone, prednisolone and prednisone etc.) produced by microbial hydroxylation and dehydrogenation reactions coupled with complimentary chemical steps. 

Figure 17.1 Sequence of events in the overall process of biotrans-formations (1) bacterial cell containing enzymes takes up organic chemical, /, (2) i binds to suitable enzyme, (3) enzyme / complex reacts, producing the transformation product(s) of /, and (4) the product(s) is(are) released from the enzyme. Several additional processes may influence the overall rate such as (5) transport of / from forms that are unavailable (e.g., sorbed) to the microorganisms, (6) production of new or additional enzyme capacity [e.g., due to turning on genes (induction), due to removing materials which prevent enzyme operation (activation), or due to acquisition of new genetic capabilities via mutation or plasmid transfer], and (7) growth of the total microbial population carrying out the biotransformation of /. ...

Tissue Cultures, Microbial Transformations.—Little success has rewarded the search for cell cultures that effectively biosynthesize monoterpenes de novo. The most impressive studies utilize cultures from a variety of Mentha spp. yields of oil were some 60 % (w/v) of those in the parent plants, but the monoterpene products were generally more oxidized (i.e. ketones extra C=C bonds predominated). In vitro, oxidation at C-3 of the menthane skeleton was also restricted, apparently owing to an inhibition of the enzymic reduction of the 4(8) double bond in the intermediates formed.925 926 Colchicine stimulated synthesis of essential oil by Mentha cultures.927 Iridoid glucosides have been produced by cultured cells of Gardenia spp.673 Menthone was biotransformed to neomenthol by Mentha suspension cultures,928 and Nicotiana lines oxidized linalool and its derivatives at C-10 to aldehydes and alcohols,929 and also foreign substrates such as a-terpineol (at C-6 and C-7) and /raw.s-/ -menthan-9-en-l-ol (at C-4 and C-10).930... 

The initial biotransformation products may, in some cases, be incorporated into cellular material. For example, the carboxylic acids formed by the oxidation of long-chain n-alkyl chlorides were incorporated into cellular fatty adds by strains of Mycobacterium sp.(Murphy and Perry 1983), and metabolites of metolachlor that could only be extracted from the cells with acetone were apparently chemically bound to unidentified sulfur-containing cellular components (Liu et al. 1989). More extensive details of a wider range of microbial transformation reactions will be found throughout Chapter 6. 

The microbial transformation of humulene, a substrate showing a structure similar to that of germacrone, was studied by Abraham and Stumpf using a screen of about 300 strains1175 . This led the authors to select the fungi Diplodia gossypina and Chaetonium cochlioides for preparative scale experiments. It was thus observed that the main reaction path starts with the epoxidation of the 1,2-double bond, as shown by direct biotransformation of this monoepoxide obtained by chemical synthesis. This is then further oxidized to yield a multitude of products including diepoxides and hydroxy-epoxides (Fig. 16.1-28). 

The importance of bioconversions in the industrial production of steroids has been reviewed ° and other reviews on the applications of microbial transformations have appeared.Biotransformations by plant tissue cultures and the application of mathematical models to optimization of fermentation have been reviewed. 

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. 

Biotechnological transformation is powerful tool to effectively utilize a broad variety of plant oils, with the aim to modify their structure for the production of new lipid-based materials with demanded properties and functions. One method of plant oil transformation is based on the direct utilization by microorganisms. Employed oils can be converted to aimed compounds by submerged cultivation or oils, and/or oleaginous plant materials can be utilized during solid state fermentation to useful bioproducts enriched with demanded microbial products. Another biotransformation technique covers the enzymatic modification of oil components to structured lipids with biological properties. 

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