Comparison of different chemoenzymatic process routes to enantiomerically pure amino acids

Five common biocatalytic process platforms for the production of enantiomer ically pure amino acids are compared along four different dimensions of mer it: i) enantioselectivity, ii) overall yield, iii) biocatalyst operating st ability, and iv) reactor space-time yield. All processes practiced on indus trial scale utilize biocatalysts of very high enantioselectivity. Short eff icient process routes are a necessity, giving an inherent advantage to rout es based on lyase reactions or reduction of prochiral keto acids. For proce sses based on the splitting of a racemate, recycling the unwanted enantiome r is crucial. The pKa value of abstracting the a-proton serves as a first i ndication of the difficulty of achieving overall yields far in excess of 50 % through dynamic resolution. High solubility of substrates and products wa s found to favor high reactor productivity (space-time-yield s.t.y. > 1 kg/ (l.d)) and high biocatalyst productivity (enzyme consumption number e.c.n. < 500-1000 U/kg of product).