Synthesis of D-amino acid-containing dipeptides using the adenylation domains of nonribosomal peptide synthetase

Recent papers have reported dipeptides containing D-amino acids to have novel effects that cannot be observed with LL-dipeptides, and such dipeptides are expected to be novel functional compounds for pharmaceuticals and food additives. Although the functions of D-amino acid-containing dipeptides are gaining more attention, there are few reports on the synthetic enzymes that can accept D-amino acids as substrates, and synthetic methods for D-amino acid-containing dipeptides have not yet been constructed. Previously, we developed a chemoenzymatic system for amide synthesis that comprised enzymatic activation and a subsequent nucleophilic substitution reaction. In this study, we demonstrated the application of the system for D-amino acid-containing-dipeptide synthesis. We chose six adenylation domains as targets according to our newly constructed hypothesis, i.e., an adenylation domain located upstream from the epimerization domain may activate D-amino acid as well as L-amino acid. We successfully synthesized over 40 kinds of D-amino acid-containing dipeptides, including LD-, DL-, and DD-dipeptides, using only two adenylation domains, TycA-A from tyrocidine synthetase and BacB2-A from bacitracin synthetase. Furthermore, this study offered the possibility that the epimerization domain could be a clue to the activity of the adenylation domains toward D-amino acid. This paper provides additional information regarding D-amino acid-containing-dipeptide synthesis through the combination of enzymatic adenylation and chemical nucleophilic reaction, and this system will be a useful tool for dipeptide synthesis.