Aldehyde-based racemization in the dynamic kinetic resolution of N-heterocyclic α-amino esters using Candida antarctica lipase A

The present research introduces approaches for the dynamic kinetic resolution of the methyl esters of proline and pipecolic acid. As the result, a method was developed which is based on the acylation of the secondary amino group of the amino esters with vinyl butanoate by Candida antarctica lipase A. In the optimized method, acetaldehyde as a racemizing agent is released in situ from vinyl butanoate in the presence of triethylamine, allowing ca. 90% of the racemic proline and 70% of the pipecolic acid methyl esters to be acylated in the forms of highly enantiopure (ee=97%) butanamides with the S-absolute configurations.