Asymmetric synthesis of l-6-hydroxynorleucine from 2-keto-6-hydroxyhexanoic acid using a branched-chain aminotransferase

Abstract

l-6-Hydroxynorleucine was synthesized from 2-keto-6-hydroxyhexanoic acid using branched-chain aminotransferase from Escherichia coli with l-glutamate as an amino donor. Since the branched-chain aminotransferase was severely inhibited by 2-ketoglutarate, the branched-chain aminotransferase reaction was coupled with aspartate aminotransferase and pyruvate decarboxylase. Aspartate aminotransferase converted the inhibitory 2-ketoglutarate back to l-glutamate by using l-aspartate as an amino donor. On the other hand, pyruvate decarboxylase further shifted the reaction equilibrium towards l-6-hydroxynorleucine through decarboxylation of pyruvate to acetaldehyde. The concerted action of the three enzymes significantly enhanced the yield compared to that of branched-chain aminotransferase alone. In the coupled reaction, 90.2 mM l-6-hydroxynorleucine (> 99% ee) was produced from 100 mM 2-keto-6-hydroxyhexanoic acid, whereas in a single branched-chain aminotransferase reaction only 22.5 mM l-6-hydroxynorleucine (> 99% ee) was produced.

Keywords::

• aminotransferase
• branched-chain aminotransferase
• coupling reaction
• l-6-hydroxynorleucine
• unnatural amino acid

Declaration of interest: This research was supported by the Basic Science Research Program (no. 20100028158) through the National Research Foundation of Korea and the 21C Frontier Microbial Genomics & Applications Center Program (no. 1120081800300) funded by the Ministry of Education, Science and Technology. It was also supported by the cooperative R&D Program (no. B551179100300) through the Korea Research Council for Industrial Science and Technology. The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.