Asymmetric synthesis of optically pure L-p-boronophenylalanine by a hybrid process

Abstract

Optically pure L-p-boronophenylalanine (BPA) was synthesized by a hybrid process involving enantioselective alkylation and subsequent enzymatic hydrolysis. Lithiated (2R)-(–)-2,5-dihydro-2-isopropyl-3,6-dimethoxypyrazine was reacted with 4-bromo-methylbenzeneboronate (2) to yield adduct 4 in a 74% e.e. Stepwise treatment of 4 with hydrochloric acid gave L-BPA methyl ester 6, which was hydrolyzed with chymotrypsin to furnish optically pure L-BPA. © 1996, Taylor & Francis Group, LLC. All rights reserved.