Highly efficient synthesis of chiral lactams by using a ω-transaminase from Bacillus megaterium and its mutant enzymes

Abstract

In this study, a series of chiral lactams were successfully prepared by one-pot two-step reactions. It included a transamination reaction catalyzed by a ω-transaminase from Bacillus megaterium (ω-TABm), and subsequent spontaneous cyclisation. The different amine donors were firstly screened with ethyl levulinate as an amine acceptor, and both the excellent conversion and enantiomeric excess (e.e.p) of >99% could be achieved with 4-bromophenylethylamine as an amine donor, however, the long reaction time of 24 h was unfavorable for its application. After the amino acid residue Thr120 situated in the small pocket was mutated to Ser, the T120S variant could exhibit 10.6-fold higher activity comparing to that of wild type, and achieve the reaction with both conversion and e.e.p of >99% within 3 h. The T120S variant could also be applied to prepare the other chiral γ- and δ-lactams with excellent conversion and e.e.p. Furthermore, the inclusion bodies of ω-TABm and its variants could be aggregated as “native-like structures” to continuously prepare the chiral lactam for 18 h. The aim of the study is to provide a simply and efficiently biocatalytic route for preparing chiral lactams.