Stereoselective Synthesis of Structurally Diverse (S)-Lactams via an Engineered Amine Dehydrogenase

Optically pure lactams have a wide diversity of applications, one of which is serving as important intermediates in the synthesis of agricultural bioactive compounds or pharmaceuticals. Efficient stereoselective synthesis of chiral lactams with low-cost amine donors under mild conditions is desired for manufacturing of these important chemicals. Herein, a two-step chemo-enzymatic strategy has been designed to produce (S)-lactams by engineering a natural amine dehydrogenase from Thermoanaerobacter thermohydrosulfuricus (TtherAmDH). TtherAmDH was subjected to eight cycles of directed evolution to enhance its reductive amination activity toward keto acid substrates. The variants showed improved specific activity toward 6 tested substrates and gave high stereoselectivities of up to 99% in the asymmetric synthesis of gamma- and delta- lactams. In particular, TtherAmDH(V8) showed a 237-fold higher specific activity toward the model substrate levulinic acid and gave (S)-5-methyl-2-pyrrolidone in 99% ee with a space-time yield of 75.3 g L-1 d(-1). These results indicate that the engineered amine dehydrogenase TtherAmDH can serve as an efficient biocatalyst for the manufacture of highly valued chiral lactams.

Automated summary

Optically pure lactams have a wide range of applications, including the synthesis of agricultural bioactive compounds and pharmaceuticals. This study presents a two-step chemo-enzymatic strategy for the efficient stereoselective synthesis of chiral lactams using a natural amine dehydrogenase that has been engineered through directed evolution. The engineered enzyme showed improved activity and high stereoselectivity in the synthesis of gamma- and delta- lactams, indicating its potential as an efficient biocatalyst for the production of valuable chiral lactams.