The Optical Resolution and Asymmetric Transformation of <scp>Dl</scp>-<i>p</i>-Hydroxyphenylglycine with (+)-1-Phenylethanesulfonic Acid

Abstract

Abstract Optically active 1-phenylethanesulfonic acid was found to be an efficient resolving agent for the optical resolution and asymmetric transformation of Dl-p-hydroxyphenylglycine. When Dl-p-hydroxyphenylglycine was resolved by the fractional crystallization of its diastereomeric salt with (+)-1-phenylethanesulfonic acid, less soluble d-p-hydroxyphenylglycine (+)-1-phenylethanesulfonate [d-HPG·(+)-PES] was obtained in a good yield. Soluble l-HPG·(+)-PES was easily epimerized into Dl-HPG·(+)-PES by heating it at 100 °C in glacial acetic acid in the presence of a small amount of salicylaldehyde. Under such epimerizing conditions, the asymmetric transformation of Dl-HPG·(+)-PES was attempted by simultaneously combining the fractional crystallization of the less soluble d-HPG·(+)-PES and the epimerization of the soluble l-HPG·(+)-PES. This asymmetric transformation was achieved successfully; that is, 80% of the Dl-HPG used as the starting material was converted into d-HPG.