Racemization of the unwanted isomer (R-1) of (S)-(-)-5, 7-dihydroxy-1-(3, 4, 5-trimethoxybenzyl)-1, 2, 3, 4-tetrahydroisoquinoline (TA-073) via the imine 6 was examined. Reduction of 6 with NaBH4 followed by hydrogenolysis over 10% Pd-C gave (±)-TA-073 in a good yield. Asymmetric reduction of 6 to S-4, the precursor of TA-073, by the use of the chiral reducing agent (I), prepared from NaBH4 (1 eq) and (S)-N-benzyloxycarbonylproline (3 eq), was also investigated. Treatment of 6 with I in a halogenated alkane such as CHCl2CH3 or CHCl2CHCl2 at -30°C afforded S-4 in an excellent optical yield (87% e.e.).
研究了(S)-(-)-5, 7-二羟基-1-(3, 4, 5-
三甲氧基苄基)-1, 2, 3, 4-
四氢异喹啉(TA-073)的无用异构体(R-1)通过
亚胺 6 的消旋化。用 NaBH4 还原 6,然后在 10% Pd-C 上进行氢解,得到了 (±)-TA-073,收率很高。此外,还研究了使用由 NaBH4(1 eq)和 (S)-
N-苄氧羰基脯
氨酸(3 eq)制备的手性还原剂 (I) 将 6 不对称还原为 S-4(TA-073 的前体)的过程。在 -30°C 下,在卤代
烷烃(如 CHCl2CH3 或 CHCl2CHCl2)中用 I 处理 6,可以得到 S-4,光学产率极高(87%e.e.)。