Asymmetric Synthesis of Optically PureL-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.

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