Hiroyuki Nakamura, Masaru Fujiwara, Yoshinori Yamamoto
Sep 19, 1998
Citations
0
Influential Citations
54
Citations
Journal
The Journal of organic chemistry
Abstract
4-Boronophenylalanine (BPA)1 is a practical boron compound, which is clinically used not only for the treatment of malignant melanoma but also for that of brain tumor, on neutron capture therapy (NCT).1, 2, 3 Since Mishima and co-workers4 revealed that the L-form of BPA is more efficiently incorporated into melanoma cells than racemic one, the enantioselective synthesis of L-BPA has been required. Enriched L-BPA was prepared enzymatically through α-chymotrypsin hydrolysis5 of the ethyl ester of racemic BPA synthesized by the traditional method.1,6 In this case, 50% of another enantiomer (D-BPA) was recovered from the racemic material. Recently, two synthetic routes of L-BPA were reported. Asymmetric hydrogenation route gave L-BPA with enantiomeric excess of up to 88% (96% ee after recrystallization).7 Another route using palladium-catalyzed coupling reaction of iodophenylboronate with the chiral organozinc derived from L-serine needed rather lengthy synthetic steps.8 Herein we report a concise synthesis of enantiomerically pure L-BPA from L-tyrosine using palladium-catalyzed carbon-boron bond formation reaction (eq. 1).