Selectivity biocatalytic reaction

The highly selective biocatalytic reactions afford a substantial reduction in waste. The overall isolated yield is greater than 90%, and the product is more than 98% chemically pure with an enantiomeric excess of >99.9%. All three evolved enzymes are highly active and are used at such low loadings that counter-current extraction can be used to minimize solvent volumes. Moreover, the butyl acetate solvent is recycled with an efficiency of 85%.The E factor (kgs waste per kg product) for the overall process is 5.8 if process water is excluded (2.3 for the reduction and 3.5 for the cyanation) [47]. If process water is included, the E factor for the whole process is 18 (6.6 for the reduction and 11.4 for the cyanation). The main contributors to the E factor are solvent losses which accounted for 51% of the waste, sodium gluconate (25%), NaCl and Na2SO4 (combined circa. 22%). The three enzymes and the NADP cofactor account for <1% of the waste. The main waste streams are aqueous and directly biodegradable. 

The classic potentiometric enzyme electrode is a combination of an ion-selective electrode-based sensor and an immobilized (insolubilized) enzyme. Few of the many enzyme electrodes based on potentiometric ion- and gas-selective membrane electrode transducers have been included in commercially available instruments for routine measurements of biomolecules in complex samples such as blood, urine or bioreactor media. The main practical limitation of potentiometric enzyme electrodes for this purpose is their poor selectivity, which does not arise from the biocatalytic reaction, but from the response of the base ion or gas transducer to endogenous ionic and gaseous species in the sample. 

Figure 5.7 shows a typical application of gas-diffusion membranes isolation of the circulating sample from a voltammetric or potentiometric electrode for the electrochemical determination of gaseous species. The ion-selective electrode depicted in this Figure includes a polymer membrane containing nonactin that is used for the potentiometric determination of ammonia produced in biocatalytic reactions. Interferences from alkali metal ions are overcome by covering the nonactin membrane with an outer hydro-... 

Process integration with combining downstream operation and biocatalytic reaction and further enzyme engineering to improve the selectivity has been a challenge in... 

In recent years biotransformations have also shown their potential when applied to nucleoside chemistry [7]. This chapter will give several examples that cover the different possibiUties using biocatalysts, especially lipases, in order to synthesize new nucleoside analogs. The chapter will demonstrate some applications of enzymatic acylations and alkoxycarbonylations for the synthesis of new analogs. The utQity of these biocatalytic reactions for selective transformations in nucleosides is noteworthy. In addition, some of these biocatalytic processes can be used not only for protection or activation of hydroxyl groups, but also for enzymatic resolution of racemic mixtures of nucleosides. Moreover, some possibilities with other biocatalysts that can modify bases, such as deaminases [8] or enzymes that catalyze the synthesis of new nucleoside analogs via transglycosylation [9] are also discussed. 

Here, we will review the various issues related to biocatalytic reactions in ionic liquids. Biocatalyst tested in ionic liquids will be discussed firstly, and then the effect of ionic liquids on the activity, selectivity as well as on the stability of biocatalyst in ionic liquids will be surveyed. Finally, various applications of ionic liquids as reaction medium for biocatalytic transformations will be reviewed. 

In this report, the nse of ionic Uquids/supercritical carbon dioxide in biocatalytic reactions has been extensively reviewed. Properties of supercritical carbon dioxide, ionic liquids and ionic liqnids/supercritical carbon dioxide biphasic systems have been analysed. Representative examples of the enzyme catalytic reactions in IL/ scCOj biphasic systems have been included. Finally, the effect of the biphasic systems on activity, selectivity and stability of enzymes has been carefully analysed. 

Bioselective electrodes are a class of hybrid devices which combine the selective properties of biocatalytic reactions with ISE detection of liberated ions or gases. In contrast to the organic ion liquid membrane electrodes described above, the bioelectrodes can often possess extraordinary selectivity over molecules which are very similar in structure to the analyte. In addition, these devices can respond to nonionic species. Consequently, such electrodes can be used directly in biological samples to determine a wide variety of biochemicals accurately. 

A cost effective and easily scaled-up process has been developed for the synthesis of (S)-3-[2- (methylsulfonyl)oxy ethoxy]-4-(triphenylmethoxy)-1 -butanol methanesulfonate, a key intermediate used in the synthesis of a protein kinase C inhibitor drug through a combination of hetero-Diels-Alder and biocatalytic reactions. The Diels-Alder reaction between ethyl glyoxylate and butadiene was used to make racemic 2-ethoxycarbonyl-3,6-dihydro-2H-pyran. Treatment of the racemic ester with Bacillus lentus protease resulted in the selective hydrolysis of the (R)-enantiomer and yielded (S)-2-ethoxycarbonyl-3,6-dihydro-2H-pyran in excellent optical purity, which was reduced to (S)-3,6-dihydro-2H-pyran-2-yl methanol. Tritylation of this alcohol, followed by reductive ozonolysis and mesylation afforded the product in 10-15% overall yield with excellent optical and chemical purity. Details of the process development work done on each step are given. 

In a further example, a biocatalytic route for the production of optically pure 3-substituted cyclohexylamine derivatives from prochiral bicychc P-diketones was established by employing three biocatalytic reaction steps (Scheme 4.16) [53]. The sequence combined the stereoselective hydrolysis of a C-C bond catalyzed by a P-diketone hydrolase [54] (6-oxocamphor hydrolase (OCH) from Rhodococcus sp. [55]), followed by an Upase-catalyzed esterification [Candida antarctica lipase B (CAL-B), Novozyme 435], and a subsequent asymmetric amination by either an (S)-or (1 )-selective m-TA [V.fluvialis [27] or a variant of the Arthrobacter sp. TA [16a] (ArRmutll)]. 

Several biocatalytic reactions have been investigated in ILs or IL-based systems. From these studies, a significant amount of information has been accumulated regarding the physicochemical properties of ILs (viscosity, polarity, hydrophobicity, nucleophUicity, H-bond basicity, and kosmotropicity/chaotropicity) that affect the activity and selectivity of enzymes. However, one should keep in mind that physical and chemical characteristics of ILs can be affected by several factors, for instance, by the presence of impurities (halide ions, acids, residual solvents, etc.) [12], which can further affect the enzyme activity and ultimately the performance of biocatalytic transformations [13-15]. 

The potentiometric enzyme electrodes are made from a basic sensing electrode which is modified with a selective biocatalytic layer coating their measuring surface. The layer of their surface catalyzes a reaction of the analyte. The local concentration change resulted by the reaction is detected by the potentiometric sensor. The first potentiometric biosensor has been reported by Guilbault and coworkers [17, 30]. From that time very high numbers of enzyme electrodes or electrometric biosensors have been reported. Potentiometric detection, however, is less frequently employed in their case comparing to the amperomet-ric one. 

A database prototype featuring information on biocatalytic reactions and biodegradation pathways for selected chemicals. The goal of the UM-BBD is to provide information on microbial enzyme-catalyzed reactions that are important for biotechnology. ... 

Over the past three decades, an increasing concern was put on application of nonaqueous solvents to facilitate biocatalytic reactions where several industrially attractive advantages are presented, such as increased solubility of nonpolar substrates, reversal of hydrolysis reactions, alternation of enzyme selectivity, and suppression of water-dependent side reactions. However, there are some inherent problems and technical challenges, including inactivation of biocatalysts, potentially reduced protein stability and lowered reaction rates due to mass-transfer limitations, and/or the increased rigidity of protein structure. 

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