A Practical Method for the Synthesis of Enantiomerically Pure 4-Borono-<b>L</b>-phenylalanine
作者:Hiroyuki Nakamura、Masaru Fujiwara、Yoshinori Yamamoto
DOI:10.1246/bcsj.73.231
日期:2000.1
Enantiomerically pure L-BPA (4-borono-L-phenylalanine) was synthesized from L-tyrosine or 4-iodo-L-phenylalanine derivatives using the palladium-catalyzed cross-coupling reaction of pinacolborane (2,3-dimethyl-2,3-butanediolatoboron). Cbz-Tyr(Nf)-OBzl (2b) underwent the cross-coupling reaction with pinacolborane (1) in the presence of [PdCl2(PPh3)2] catalyst to give N-benzyloxycarbonyl-4-(2,3-dimethyl-2,3-butanediolatoboryl)-L-phenylalanine benzyl ester (3a) in 58% yield. The reaction of the 4-iodo-L-phenylalanine derivatives, such as N-benzyloxycarbonyl-4-iodo-L-phenylalanine benzyl ester (2c), N,N-dibenzyl-4-iodo-L-phenylalanine benzyl ester (2d), (4S)-3-benzyloxycarbonyl-4-(4-iodobenzyl)-5-oxazolidinone (2e), and (4S)-3-t-butyloxycarbonyl-4-(4-iodobenzyl)-5-oxazolidinone (2f), with 1 proceeded very smoothly in the presence of [PdCl2(dppf)] catalyst, giving N-benzyloxycarbonyl-4-(2,3-dimethyl-2,3-butanediolatoboryl)-L-phenylalanine benzyl ester (3a), N,N-dibenzyl-4-(2,3-dimethyl-2,3-butanediolatoboryl)-L-phenylalanine benzyl ester (3b), (4S)-3-benzyloxycarbonyl-4-[4-(2,3-dimethyl-2,3-butanediolatoboryl)benzyl]-5-oxazolidinone (3c), and (4S)-3-butyloxycarbonyl-4-[4-(2,3-dimethyl-2,3-butanediolatoboryl)benzyl]-5-oxazolidinone (3d), respectively, in high yields. Deprotection of 3a—d gave enantiomerically pure L-BPA in high total yields.
利用钯催化的频哪醇硼烷(2,3-二甲基-2,3-丁二醇硼)交叉偶联反应,从 L-酪氨酸或 4-碘-L-苯丙氨酸衍生物合成了对映体纯度极高的 L-BPA(4-硼-L-苯丙氨酸)。在[PdCl2(PPh3)2]催化剂存在下,Cbz-Tyr(Nf)-OBzl (2b) 与频哪醇硼烷 (1) 发生交叉偶联反应,得到 N-苄氧羰基-4-(2,3-二甲基-2,3-丁二醇基)-L-苯丙氨酸苄酯 (3a),收率为 58%。4-碘-L-苯丙氨酸衍生物的反应,如 N-苄氧羰基-4-碘-L-苯丙氨酸苄酯 (2c)、N,N-二苄基-4-碘-L-苯丙氨酸苄酯 (2d)、(4S)-3-苄氧羰基-4-(4-碘苄基)-5-恶唑烷酮(2e)和(4S)-3-叔丁氧羰基-4-(4-碘苄基)-5-恶唑烷酮(2f),其中 1 在[PdCl2(dppf)]催化剂存在下进行得非常顺利、得到 N-苄氧羰基-4-(2,3-二甲基-2,3-丁二醇二硼酸基)-L-苯丙氨酸苄酯 (3a)、N,N-二苄基-4-(2,3-二甲基-2,3-丁二醇二硼酸基)-L-苯丙氨酸苄酯 (3b)、(4S)-3-苄氧羰基-4-[4-(2、3-(2,3-二甲基-2,3-丁二醇基)苄基]-5-恶唑烷酮 (3c) 和 (4S)-3-丁酰氧羰基-4-[4-(2,3-二甲基-2,3-丁二醇基)苄基]-5-恶唑烷酮 (3d)。对 3a-d 进行脱保护处理后,可得到对映体纯度很高的 L-BPA,总产率也很高。