Development of a Continuously Operating Process for the Enantioselective Synthesis of a β‐Amino Acid Ester via a Solvent‐Free Chemoenzymatic Reaction Sequence

Abstract

A sequential, chemoenzymatic process for a continuously operating production of the chiral b-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 b-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 0.4 kg L À1 d À1 was calculated for the total reactor system and 1.8 kg L À1 d À1 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)-b-amino acid ester starting from cheap substrates.Abbreviations: CALB = Candida antarctica lipase B; CSTR = continuously stirred tank reactor; d i = inner diameter [mm]; ee = enantiomeric excess; e = porosity; k cat,obs = apparent turnover number [h ].

Chemoenzymatic synthesis of amino-esters as precursors of ammonium salt-based surfactants from 5-hydroxymethylfurfural (HMF)

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Applied biocatalysis beyond just buffers – from aqueous to unconventional media. Options and guidelines

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