Dynamic kinetic resolution for asymmetric synthesis of α-alkyl amino acids via dual-function catalysis of modified cinchona alkaloids

The electronic property of the N-protecting group of N-carboxyanhydrides (NCA) is found to have a significant influence on the rate of racemization of NCA with modified cinchona alkaloids. Consequently, modified cinchona alkaloids can be applied as dual-function catalysts to catalyze both the racemization and alcoholytic kinetic resolution of alkyl NCA bearing an electron-withdrawing N-protecting group, leading to a dynamic kinetic resolution converting racemic alkyl NCAs to the corresponding amino esters in 59-75% ee and 75-87% yield. Upon recrystallization, the amino ester can be obtained in greater than 99% ee and 53% yield from the racemic NCA.