Studies on the continuous production of (R)-(-)-phenylacetylcarbinol in anenzyme-membrane reactor

The optimization of a continuous enzymatic reaction yielding (R)-(-)-phenyl acetylcarbinol ((R)-PAC), a key intermediate of the (1R,2S)-(-)-ephedrine s ynthesis, is presented. We compare the suitability of different mutants of the pyruvate decarboxylase (PDC) from Zymomonas mobilis with respect to the ir application in biotransformation using pyruvate or acetaldehyde and benz aldehyde as substrates, respectively. Starting from 90 mM pyruvate and 30 m M benzaldehyde, (R)-PAC was obtained with a space time yield of 27.4 g/(L d ay) using purified PDCW392I in an enzyme-membrane reactor. Due to the high stability of the mutant enzymes PDCW392I and PDCW392M towards acetaldehyde, a continuous procedure using acetaldehyde instead of pyruvate was develope d. The kinetic results of the enzymatic synthesis starting from acetaldehyd e and benzaldehyde demonstrate that the carboligation to (R)-PAC is most ef ficiently performed using a continuous reaction system and feeding both ald ehydes in equimolar concentration. Starting from an inlet concentration of 50 mM of both aldehydes, (R)-PAC was obtained with a space-time yield of 81 g/(L day) using the mutant enzyme PDCW392M. The new reaction strategy allo ws the enzymatic synthesis of (R)-PAC from cheap substrates free of unwante d by-products with potent mutants of PDC from Z. mobilis in an aqueous reac tion system. (C) 2001 Elsevier Science B.V. All rights reserved.