Biotransformation Process

In the following sections we will explain some applications of enzymes (and cells) in the transformation of sterols and steroids. You should realise, however, that for each process a decision has to be made whether to use an enzyme-mediated transformation or to use a chemical reaction. In many instances the biotransformation process is foe most attractive but, as we will see later, this is not always the case. 

Table 5.13 Mass changes associated with common biotransformation processes...

The growth of industrial scale biotransformation processes has increased significantly over recent years with more than 130 reported in 2002 [1]. Major activity is focussed on the production of chiral pharmaceuticals although a number of large scale industrial processes have been developed for the food and agricultural industries. 

The advantages of such biotransformation processes are (1) the relatively high yields which can be achieved with specific enzymes, (2) the formation of chiral compounds suitable for biopharmaceuticals, and (3) the relatively mild reaction conditions. Key issues in industrial-scale process development are achieving high product concentrations, yields and productivities by maintaining enzyme activity and stability under reaction conditions while reducing enzyme production costs. 

In current industrial practice, benzaldehyde is added to fermenting baker s yeast Saccharomyces cerevisiae) with resultant PAC production occurring from the yeast-derived pyruvate. Typically PAC concentrations of 12-15 g F are produced at yields of 65-70% theoretical in a 10-12 h biotransformation process. [2], Appreciable concentrations of benzyl alcohol are produced as by-product due to oxidoreductase activity in the fermentative yeast. 

Prediction of benzaldehyde pulse feeding profile to optimize the production of PAC in fed batch PAC biotransformation process at 6°C. A molar ratio of 1.2 1 pyruvate to benzaldehyde was used, with AR grade benzaldehyde and a 1.4 M solution of pyruvate used in the simulated feeding. 

It was confirmed that much less of the reactants needs to be consumed for testing, which will be important if expensive compounds are used such as enantiomerically and isomerically pure products [84], Hence the feasibility of mini-scale biotransformation processing was demonstrated using a model reaction and now allows this testing procedure to be extended to other more important reactions. 

Garcia, E., Ferrari, F., Garcia, T, Martinez, M., Aracil, J., Use of microreactors in biotransformation processes study of the synthesis of diflycerd mono-laurate ester, in Proceedings of the 4th... 

Table 1 shows examples of some of the microorganisms involved in different biotransformation processes [11]. The following sections cite some more recent examples of microbial transformation of biologically important compounds, especially alkaloids and nitrogen-containing compounds. 

Table 1 Some examples of the microorganisms involved in different biotransformation processes (modified from [11])... 

The biotransformation process has been improved by significant advances in biochemical engineering advances in genetic and protein engineering, microbiological manipulations for the production of enzymes, and the use of biocatalysts in immobilized form and large-scale purification methods. 

General rules need to be adapted for different biotransformation processes because they are not based on the specific study of all systems. Biocatalysis conditions are optimized when carrying out experiments designed to increase knowledge of the process. 

Ecologically, copper is a trace element essential to many plants and animals. However, high levels of copper in soil can be directly toxic to certain soil microorganisms and can disrupt important microbial processes in soil, such as nitrogen and phosphorus cycling. Copper is typically found in the environment as a solid metal in soils and soil sediment in surface water. There is no evidence that biotransformation processes have a significant bearing on the fate and transport of copper in water. 

Law J Microbiology Path Parasito, Raleigh, NC Continued development of the isolated skin flap model for study of the transport and biotransformation processes of toxic substances and drugs through the skin U. S. Department of Agriculture, Cooperative State Research... 

Whole-Cell Biotransformation Processes Used in Commercial... 

Whole-cell biotransformation processes have been successfully applied for commercial production of pharmaceuticals, either as the drug substance itself or as an intermediate for the synthesis of the final drug substance. Some examples of the whole-cell biotransformation processes used by pharmaceutical industry are shown in Table 10.1. The structures of the biotransformation products are shown in Figure 10.1. 

Application of Whole-Cell Biotransformation Process in the Synthesis of Chiral Pharmaceutical Intermediates... 

Table 10.1 Commercial whole-cell biotransformation processes for the preparation of pharmaceuticals and pharmaceutical intermediates... 

Whole-cell biotransformations frequently showed insufficient stereoselectivities and/or undesired side reactions because of competing enzymatic activities present in the cells. These side reactions can modify the substrates and/or products. Furthermore, whole-cell biotransformations are limited due to the intrinsic need to grow biomass, which generates its own metabolites that are not related to the biotransformation reactions and, therefore, which need to be removed during the downstream process. Both the cells themselves and the unrelated metabolites produced are impurities that need to be removed after the biotransformation reaction. With isolated enzymes, there are no organism and unrelated metabolites to remove after the biotransformation processes. 

In this section, the advantages of the use of whole cells over the use of isolated enzymes in biotransformation processes are presented. 

Vanillin (4-hydroxy-3-methoxybenzaldehyde) is widely used in foods, beverages, perfumes and the pharmaceuticals industries. Biotransformation of isoeugenol from essential oil to vanillin represents an economic route for the supply of vanillin, which has a limited supply due to the availability of vanilli pod plants. The conversion yield of isoeugenol to vanillin by the whole-cell biotransformation process of Bacillus fusiformis was low due to the product inhibition effect. Adding resin HD-8 to the whole-cell biotransformation eliminated the product inhibition effect, yielding 8 gL 1 of vanillin in the final reaction mixture [27]. The resin HD-8 also facilitated the separation of vanillin from the used substrate. The recovered isoeugenol can be used for the subsequent biotransformation reaction. 

In order to extend the biocatalytic activities of the biotransformation processes and reduce the frequency of producing cell mass and undesirable side products, immobilized-cell technology has been successfully applied to the whole-cell biotransformation processes. In addition to the three commercial immobilized whole-cell biotransformation processes shown in Table 10.1, examples of immobilization of three different microorganisms for whole-cell biotransformations are shown below to demonstrate the broad application of the immobilized whole-cell biotransformation processes. 

Developing a New Whole-Cell Biotransformation Process for the Synthesis of Simvastatin... 

Leonov, A. V., Stygar, O. V. (2001). Mathematical modeling of organogenic material biotransformation processes for studying the conditions of water eutrophication in the Caspian Sea surface layer. Water Resources, 28(5), 532-555... 

With respect to drug-metabolizing enzymes, the majority of the CYPs responsible for phase I metabolism are concentrated in liver. The CYPs considered here are all found in the endoplasmic reticulum (isolated as microsomes ). Of the 18 human CYP families known, the bulk of xenobiotic biotransformation processes are carried out by enzymes from the CYP1, CYP2 and CYP3 families. In humans, realistically,... 

The formation of polar metabolites from nonpolar materials may actually facilitate monitoring programs—in many cases the polar chemicals are highly concentrated in certain body fluids such as bile and urine. On the other hand, materials such as certain cyclodienes and polychlorinated biphenyls, which are very lipid soluble and resistant to metabolism, may accumulate and these chemicals may persist in the environment and may be transferred via the food chain to man. There is also interest in these biotransformation processes in lower organisms since the simplicity of these systems may lead to a better understanding of the phylogenetic development of xenobiotic metabolism. 

These studies with aldrin and antipyrine are sufficient to document the in vivo oxidative metabolic capability of mussels. Limits of activity have not been established, but they will be explored by further varying dose and the duration of the test period. With these limits established, the influence of environmental stressors such as salinity, and dissolved and/or suspended particulate matter in water on biotransformation will be assessed. If biotransformation processes are affected by these conditions, their measurement may provide results which can be diagnostically used as indicators of environmental quality. 

---