Reductive Amination of Biobased Levulinic Acid to Unnatural Chiral γ-Amino Acid Using an Engineered Amine Dehydrogenase

Optically pure (S)-4-aminopentanoic acid is a pivotal precursor in the synthesis of therapeutic molecules and pyrrolidinone derivatives. Enantioselective reductive amination of levulinic acid catalyzed by amine dehydrogenases, a readily sustainable material from biobased lignocellulosic waste, represents an attractive approach for the synthesis of (S)-4-aminopentanoic acid. However, the natural amine dehydrogenases reported so far showed insufficient activity toward levulinic acid. Herein, we engineered a naturally occurring amine dehydrogenase from a thermophilic bacterium Petrotoga mobilis (PmAmDH) by directed evolution. The catalytic efficiency of the most active mutant PmAmDHI80T/P224S/E296G was elevated by 18 folds in comparison to the wild-type enzyme. Using PmAmDHI80T/P224S/E296G coupled with formate dehydrogenase for reduced nicotinamide adenine dinucleotide regeneration, 0.5 M of levulinic acid was reductively aminated in more than 97% conversion at 40 °C, generating the corresponding product (S)-4-aminopentanoic acid with >99% ee and 90% yield. Furthermore, we also successfully developed a chemoenzymatic cascade route for the synthesis of (S)-4-aminopentanoic acid from renewable starch. These results indicated that the engineered amine dehydrogenase PmAmDHI80T/P224S/E296G can serve as an efficient biocatalyst for the manufacture of highly valued chiral unnatural amino acids using renewable feedstocks.