Asymmetric Transformation of DL-p-Hydroxyphenylglycine by a Combination of Preferential Crystallization and Simultaneous Racemization of the o-Toluenesulfonate

Article abstract of DOI:10.1246/bcsj.58.433

The asymmetric transformation of DL-p-hydroxyphenylglycine was achieved between two enantiomers by a combination of preferential crystallization of desired enantiomer of p-hydroxyphenylglycine o-toluenesulfonate (HPG.o-Ts) and the simultaneous racemization of the antipode.L-HPG.o-TS was easily racemized by heating at 100 deg C in aqueous 95percent (v/v) acetic acid in the presence of small amounts of salicylaldehyde and free DL-HPG.A supersaturated solution of DL-HPG.o-TS placed under such conditions for racemization was seeded with the crystals of D-HPG.o-TS, and added with DL-HPG and o-toluenesulfonic acid in order to provide contonously the supersaturated of DL-HPG.o-TS as a driving force.As a result, 77.2percent of DL-HPG added was transformed to D-isomer.