Biocatalysts, availability

As each BVMO is limited in substrate specificity, it is crucial to have a large collection of these oxidative biocatalysts available. Except for expanding the scope of possible reactions, a large toolbox of BVMOs would also increase the chance of being able to perform any wanted specific chemo-, regio- and/or enantioselective reaction. This contrasts with the present situation as only a relatively small number of BVMOs can be exploited for biocatalytic purposes. Therefore, it is still crucial to discover or engineer BVMOs with novel biocatalytic properties. 

Table 9.4 Metabolite production of selected drugs using human cytochrome biocatalysts available from Codexis, Inc"... 

Horseradish peroxidase is one of the most versatile biocatalysts available to the biotechnology industry, with applications that continue to be... 

Currently, resolution of racemates is a valuable strategy for the production of enantiopure P-amino acids [26]. The classical method of resolving amino acids is through transformation of the racemate into diastereomeric salts via complexation of the carboxylic acids with a chiral base, usually followed by multistep fractional recrystallization [25]. An alternative method is to resolve the enantiomers by applying the high stereoselectivity of enzymes, and there are a number of suitable biocatalysts available. 

The tools of modem molecular biology have led to an explosion in the number and range of biocatalysts available for use in the pharmaceutical industry. 

When starting our first experiments with available ionic liquids, in screening programs to identify suitable systems, we encountered several difficulties such as pH shifts or precipitation. More generally, the following aspects should be taken into account when ionic liquids are used with biocatalysts ... 

The industrial development of biotransfonmations is hampered currently by lack of commercial availability of biocatalysts at a reasonable price, insufficient operational stability of most biocatalysts and the practical problems associated with the exploitation of cofactor-dependent biocatalysts. 

Despite the still growing number of available methods for the preparation of enantiopure compounds by the use ofasymmetric catalysis, kinetic resolution (KR) is still the most employed method in the industry [4], and in most cases biocatalysts (enzymes) are used. 

This suite of BVMOs is available via whole-cell expression systems and represents a complementary platform of biocatalysts for diverse applications in chiral synthesis. Representatives of this collection were utilized in the enantiodivergent synthesis of the indole alkaloids alloyohimbane and antirhine from a fused bicyclic precursor (Scheme 9.19) [151]. 

In particular, the availability of such bacterial biocatalysts in the form of recombinant expression systems [136] in combination with simplified purification protocols opened up this methodology for large-scale applications [204]. 

A prochiral bis(cyanomethyl) sulfoxide was converted into the corresponding mono-acid with enantiomeric excesses as high as 99% using a nitrilase-NHase biocatalyst. The whole-cell biocatalyst Rhodococcus erythropolis NCIMB 11540 and a series of commercially available nitrilases NIT-101 to NIT-107 were evaluated in this study. As outlined in Figure 8.18, the prochiral sulfoxide may be transformed into five different products (plus enantiomeric isoforms), of which, three are chiral (A, B, and C) and two achiral (D and E). Only products A, B, and E were observed with the biocatalysts employed in this investigation. Both enantiomerically enriched forms of both A and C could be obtained with one of the catalysts used. The best selectivities are as follows (S)-A 99% ee, (R)-A 33% ee, (S)-C 66% ee, and (R)-C 99% ee, using NIT-104, NIT-103, NIT-108, and NIT-107 respectively. Each of these catalysts produced more... 

The biocatalyst used in this invention is a microorganism such as that available from Finnerty Enterprises Inc., Athens, Ga. Two different conversion reactions occur, one exhibited by organic sulfides and another by organic thiophenes, namely ... 

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