PUB - Publikationen an der Universität Bielefeld

A sequential, chemoenzymatic process for a continuously operating production of the chiral -amino acid ester ethyl (S)-3-(benzylamino)butanoate was developed. The reactor set-up combined a plug-flow reactor for the thermal aza-Michael addition of benzylamine to trans-ethyl crotonate coupled to a subsequent packed-bed reactor for the lipase (Novozym 435)-catalyzed kinetic resolution of the racemic intermediate product, which was formed in the initial step. The coupled reactors were operated continuously for a time period of 4 days without significant loss of enzyme activity. The target -amino acid ester was obtained with 92% conversion in the plug-flow reactor and 59% conversion in the packed bed reactor at high enantiomeric excess of >98%. A space-time yield of 0.4kgL(-1)d(-1) was calculated for the total reactor system and 1.8kgL(-1)d(-1) based solely on the volume of the packed bed reactor. A total turnover number of 158,000 was calculated for the biocatalyst assuming the same deactivation rate as observed in batch experiments. The continuously operating, solvent-free process thus represents an efficient method for the enantioselective production of a value added (S)âamino acid ester starting from cheap substrates.