Theoretical Mechanistic Investigation of the Dynamic Kinetic Resolution of N-Protected Amino Acid Esters using Phase-Transfer Catalysts

A detailed theoretical mechanistic investigation on the dynamic kinetic resolution of N-protected amino acid esters using phase-transfer catalysts is described. Semiautomatic exhaustive conformation search of transition state (TS)-like structures were carried out using the ConFinder program and the pseudo-TS conformational search (PTSCS) method. This conformational search method successfully provided reasonable TS structures for determining the stereoselectivity in the asymmetric base hydrolysis of hexafluoroisopropyl (HFIP) esters as well as the racemization mechanism. Furthermore, the independent gradient model (IGM) analysis of the TS structures suggested that the H bonding interactions with the oxyanion hole and p-stacking interactions are the common important features of the proposed TS structures that determine the stereoselectivity.