Biotransformation microbial

Venisetty RK, Ciddi V (2003) Application of microbial biotransformation for the new drug discovery using natural drugs as substrate. Curr PharmaceutBiotechnol 4 153-167... 

Microbial Biotransformation. Microbial population growth and substrate utilization can be described via Monod s (35) analogy with Michaelis-Menten enzyme kinetics (36). The growth of a microbial population in an unlimiting environment is described by dN/dt = u N, where u is called the "specific growth rate and N is microbial biomass or population size. The Monod equation modifies this by recognizing that consumption of resources in a finite environment must at some point curtail the rate of increase (dN/dt) of the population ... 

In the 1970s, Smith and Rosazza introduced the concept of microbial models of mammalian metabolism [38,39]. Two reviews in this area were published in 1999 [40,41]. Since these, there have been numerous reports describing the use of microbial biotransformation in drug metabolism studies [42-54]. These reports demonstrated that microbial enzymes were able to... 

Initial scale-up of microbial biotransformation is conveniently run with multiple flasks without extensive reaction optimization. A typical flask fermentation is performed at 28 °C, 250 rpm with 100 mL culture in a 500 mL Erlenmeyer flask, although other settings will work fine too. Three parameters need to be investigated before scale-up the time for adding the substrate, the optimal substrate concentration and the time course of product formation. Optimization of other factors, such as medium composition and pH, growing cells versus resting cells [74], is helpful, if the timeline allows and if there is a sufficient amount of the substrate to support the screening. 

Biotransformation with flasks can be used to make gram quantities of a desired product, as shown for the 21 -hydroxylation of epothilone B [75]. In cases when greater quantities of a metabolite are needed, microbial biotransformations can be carried out in a fermentor, which will allow better monitoring and control of fermentation conditions (such as pH, oxygen and glucose levels, etc.) for reaction optimization [76]. 

The M20 metabolite is a major circulating metabolite of dasatinib (SPRY CEL) in humans [77]. A large quantity of M20 was needed to serve as an analytical standard, but was not readily accessible by mammalian bioreactors or chemical synthesis. Microbial biotransformation was used to make the metabolite to support the development of dasatinib [58]. 

Figure 9.8 Microbial biotransformation of dasatinib with Streptomyces sp. SC15761...

Figure 9.9 Microbial biotransformation of (S)-ketoprofen with Streptomyces sp. ATCC 55043...

Li, W., Josephs, J.L., Skiles, G. and Humphreys, W.G. (2008) Metabolite generation via microbial biotransformation with actinomycetes rapid screening methods and synthesis of important human metabolites of two development stage compounds, BMS-587101 and dasatinib. Drug Metabolism and Disposition The Biological Fate of Chemicals, 36, 721-730. 

Lacroix, I., Biton, J. and Azerad, R. (1997) Microbial biotransformation of a synthetic immunomodulating agent, HR325. Bioorganic and Medicinal Chemistry, 5, 1369-1380. 

Canned, R.J., Knaggs, A.R., Dawson, M.J. et al. (1995) Microbial biotransformation of the angiotensin II antagonist GR117289 by Streptomyces rimosus to identify a mammalian metabolite. Drug Metabolism and Disposition The Biological Fate of Chemicals, 23, 724—729. 

Drug metabolite production, microbial biotransformations for, 16 398-399 Drug Price Competition and Patent Term Restoration, 15 686 Drug products... 

Figure 12.3 Synthesis of 5- and 6-hydroxy fluvastatin by microbial biotransformation...

Dealkylations have been used in the regioselective conversion of methoxyaryl groups to phenols in natural products, particularly alkaloids 1471 such as papaverine (30), and in the production of mammalian metabolites by microbial biotransformation, as exemplified by the biotransformation of bisprolol (4). 

As the biofuels industry evolves to more complex processes (e.g., involving microbial biotransformations) PAT will become more important both in scale-up and process operation, specially to nondestructively assess process performance (e.g., oil content of microalgae in snbmerged cnltivation) and accomplish prodnct release cheaper and faster than today s one-CQA-at-a-time methods. 

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. 

A description of transdermal drug delivery has been produced which is based on the physicochemical properties of the permeant. At this time transdermal delivery is limited to the administration of potent drugs. Higher doses may be accessible if penetration enhancers are incorporated into the formulation. The kinetic model shows what properties these should have and that they are a function of the physico-chemical properties of the drug. Various loss processes, e.g. microbial biotransformation, skin enzyme metabolism can be identified but cannot, as yet, be quantified. 

Enantiomer-Specific Microbial Biotransformation of Chiral POPs... 

In laboratory microcosms, ira 5-permethrin was selectively degraded compared to the other diastereomer, cw-permethrin, by six bacterial strains [19]. These strains also preferentially biotransformed 15-cw-bifenthrin over their antipodal l/ -cw-enantiomers, which were more toxic to daphnids [19]. Enantioselectivity was more pronounced for cw-permethrin than for cw-bifenthrin, and was strain-dependent. The (—)-enantiomer of both pyrethroids was preferentially depleted in sediments adjacent to a plant nursery, suggesting that in situ microbial biotransformation was enantioselective [20]. Although all enantiomers of permethrin were hydrolyzed quickly in C-labeled experiments in soils and sediments, the degradates of both cis- and irara-permethrin s -enantiomers were mineralized more quickly than those of the 5-enantiomer, while degradation products of cA-permethrin were more persistent than those of the trans-isomex [185]. Enantioslective degradation of fenvalerate in soil slurries has also been reported [83]. These smdies underscore how enantiomer-specific biotransformation can affect pyrethroid environmental residues, the toxicity of which is also enantiomer-dependent [18-20]. 

Though microbial biotransformation is an important removal process, it is not complete in the sense that the biphenyl backbone is not broken. Moreover, recent studies [116-118] indicate PCBs that flow to terrestrial, fresh water, and ocean surfaces are returned to the atmosphere. So it is important to identify permanent PCB sinks that is, sinks that result in the complete removal of the PCB molecule from atmospheric cycling. Burial of PCBs in fresh water or marine sediments below the resuspension layer and transformation processes initiated by OH attack in the troposphere are identified as major permanent sinks. 

The discovery of compactin and lovastatin prompted efforts to develop derivatives with improved biological properties (163, 164). Modification of the methylbutyryl side chain of lovastatin led to a series of new ester derivatives with varying potency and, in particular, introduction of an additional methyl group a to the carbonyl gave a compound with 2.5 times the intrinsic enzyme activity of lovastatin (165). The new derivative, named simvastatin (124), was the second HMG-CoA reductase inhibitor to be marketed by Merck. Both lovastatin and simvastatin are prodrugs and are hydrolyzed to their active open-chain dihydroxy acid forms in the liver (166). A third compound, pravastatin (125), launched by Sankyo and Squibb in 1989, is the open hy-droxyacid form of compactin that was first identified as a urinary metabolite in dogs. Pravastatin is produced by microbial biotransformation of compactin. 

This key discovery prompted further efforts to develop improved cholesterol lowering agents. For example, chemical modifications of the methylbutyryl sidechain gave simvastatin (having twice the potency of lovastatin) (Figure 10) which is also marketed by Merck. Pravastatin, marketed by Sankyo and Bristol Myers Squibb, is the 6-hydroxy open hydroxyacid derivative produced by microbial biotransformation of mevastatin (Figure 10). ... 

Traditional fermentation using microbial activity is commonly used for the production of nonvolatile flavor compounds such as acidulants, amino acids, and nucleotides. The formation of volatile flavor compounds via microbial fermentation on an industrial scale is still in its infancy. Although more than 100 aroma compounds may be generated microbially, only a few of them are produced on an industrial scale. The reason is probably due to the transformation efficiency, cost of the processes used, and our ignorance to their biosynthetic pathways. Nevertheless, the exploitation of microbial production of food flavors has proved to be successful in some cases. For example, the production of y-decalactone by microbial biosynthetic pathways lead to a price decrease from 20,000/kg to l,200/kg U.S. Generally, the production of lactone could be performed from a precursor of hydroxy fatty acids, followed by p-oxidation from yeast bioconversion (Benedetti et al., 2001). Most of the hydroxy fatty acids are found in very small amounts in natural sources, and the only inexpensive natural precursor is ricinoleic acid, the major fatty acid of castor oil. Due to the few natural sources of these fatty acid precursors, the most common processes have been developed from fatty acids by microbial biotransformation (Hou, 1995). Another way to obtain hydroxy fatty acid is from the action of LOX. However, there has been only limited research on using LOX to produce lactone (Gill and Valivety, 1997). 

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

The intestinal microflora of man and animals can biotransform bile acids into a number of different metabolites. Normal human feces may contain more than 20 different bile acids which have been formed from the primary bile acids, cholic acid and chenodeoxycholic acid [1-5], Known microbial biotransformations of these bile acids include the hydrolysis of bile acid conjugates yielding free bile acids, oxidation of hydroxyl groups at C-3, C-6, C-7 and C-12 and reduction of oxo groups to give epimeric hydroxy bile acids. In addition, certain members of the intestinal microflora la- and 7j8-dehydroxylate primary bile acids yielding deoxycholic acid and lithocholic acid (Fig. 1). Moreover, 3-sulfated bile acids are converted into a variety of different metabolites by the intestinal microflora [6,7]. 

Wilson and McNabb (1) have suggested that the population density of microbiota below the root zone in North American probably exceeds the bacterial biomass in the rivers and lakes on the continent. Biochemical measures of the biomass and metabolic actmty of subsurface biota indicate that the biomass is largely bacterial (8). Microbial biotransformation potential has been demonstrated in the laboratory for compounds in a number of priority pollutant classes (9-101... 

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