Membrane reactor development for the kinetic resolution of ethyl 2-hydroxy-4-phenylbutyrate

(R)-Ethyl 2-hydroxy-4-phenylbutyrate is an important intermediate for the synthesis of several ACE-inhibitors (ACE = angiotensin-converting enzyme). A possible preparation of this intermediate is the kinetic resolution of the racemic 2-hydroxy compound. The enantioselective hydrolysis is catalyzed by the lipase from Pseudomonas cepacia in a two-phase system consisting of aqueous buffer and in organic solvent solubilized substrate. Production was carried out in a diafiltration reactor. A ceramic ultrafiltration membrane retained both the organic phase and the lipase that was solubilized in the aqueous phase. The aqueous phase was pumped continuously through the reactor, removing the inhibiting product 2-hydroxy-4-phenylbutyrate. Due to the use of this membrane reactor a kinetic resolution, which is limited by a strong product inhibition, can be carried out efficiently. By operating this membrane reactor in a repetitive batch mode, enzyme consumption could be greatly reduced. The remaining (R)-2-hydroxy ester could be produced with enantiomeric excess > 99.5% and a space-time yield of 275 g L−1 d−1.