D-Pyroglutamic Acid Production from L-Glutamic Acid by Successive Racemization, Resolution and Dehydration

A synthesis process has been developed to produce D-pyroglutamic acid (D-PGA) from L-glutamic acid (L-GA) by employing successive racemization of L-GA, resolution of D,L-glutamic acid (D,L-GA) and dehydration of D-glutamic acid (D-GA). Aqueous NaOH solution of pH＞13 at 160'C has been selected as the best racemization medium. The system of 140% supersaturation that contains 1 g of seeds at sot was further screened as the best condition by use of preferential crystallization. An irreversible first-order kinetics has been employed to simulate the dehydration of D-GA, in which the activation energy of 40.0 kJ/mol was determined. Increasing the temperature results in high dehydration rate with low stereopurity for the desired D-PGA, in which 130°C was selected as the best dehydration tempearture.