Enzyme Screening, Optimization, and Recycling of Undesired Enantiomer

Enzyme Screening, Optimization, and Recycling of Undesired Enantiomer 

A review of the literature, examining potential approaches to avoiding product inhibition, suggested the addition of agents that could form a complex or salt with carboxylic acid 13, thus minimizing its ability to deactivate the enzyme [19]. ton exchange resins were evaluated, but these did not suppress the inhibihon to any extent. The use of bases other than sodium hydroxide that could supply a different 

The effect of calcium acetate in the reaction medium at higher concentrations of 4 was rather surprising as the enzymatic reaction proceeded without any problem at substrate loads as high as 3M (765 gL ) with conversion values ranging from 42 to 48% after 24h (see Table 8.2, entries 1-4). Since the level of calcium acetate used in these experiments did not exceed 170 mM, which is well below a stoichiometric ratio between the carboxylate of 13 and Ca , a more complex mechanism that probably involves enzyme stabilization as well as com-plexation of product might be taking place. 

The investigation of methods for recycling the remaining enantiomer, (R)-4, revealed that sodium ethoxide in ethanol at 80 °C effected more than 98% racemization in 8-16 h. This chemistry has been further developed and implemented by Pfizer, and the environmental benefits of racemizing and recycling the wrong enantiomer are shown in Section 8.4. 

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