Quinolizidines. VII. Structure of O-methylpsychotrine: The endocyclic versus the exocyclic double bond structure in the dihydroisoquinoline moiety.
作者:TOZO FUJII、MASASHI OHBA、OSAMU YONEMITSU、YOSHIO BAN
DOI:10.1248/cpb.30.598
日期:——
By comparison of its ultraviolet spectra in H2O at various pH's with those of model compounds, 11, 14, 16, 17, and 18, the Ipecac alkaloid O-methylpsychotrine has been shown to have the genuine 3, 4-dihydroisoquinoline structure (1), not the exocyclic double bond structure (4), in the free base form as well as in the protonated form. The 1H nuclear magnetic resonance (NMR) and 13C NMR spectra of the alkaloid have also confirmed this endocyclic double bond structure in the dihydroisoquinoline moiety. These results indicate that the position of the double bond for simple 1-alkyl-3, 4-dihydroisoquinolines is endocyclic, and factors that stabilize the exocyclic double bond structure are discussed. 1-tert-Butyl-3, 4-dihydro-6, 7-dimethoxy-2-methylisoquinolinium iodide (30) has been found to be unstable in H2O. On heating in H2O at 90°C for 10 min, it underwent ring opening to give 27 in good yield. The acid dissociation constants for 1-methyl-(16) and 1-tert-butyl-3, 4-dihydro-6, 7-dimethoxyisoquinoline (18) in H2O at 20°C were spectrometrically determined to be 9.16±0.02 and 8.80±0.02, respectively.
通过将不同 pH 值下的水中紫外光谱与模型化合物 11、14、16、17 和 18 进行比较,吐根生物碱 O-甲基精神烟碱已被证明具有真正的 3, 4-二氢异喹啉结构 (1) ,不是环外双键结构 (4),无论是游离碱形式还是质子化形式。该生物碱的1H核磁共振(NMR)和13C NMR谱也证实了二氢异喹啉部分的这种环内双键结构。这些结果表明简单的1-烷基-3,4-二氢异喹啉的双键位置是环内的,并且讨论了稳定环外双键结构的因素。 1-叔丁基-3, 4-二氢-6, 7-二甲氧基-2-甲基异喹啉碘化物 (30) 被发现在水中不稳定。在 H2O 中于 90°C 加热 10 分钟后,它发生开环,以良好的收率得到 27。 1-甲基-(16) 和 1-叔丁基-3, 4-二氢-6, 7-二甲氧基异喹啉 (18) 在 20°C 水中的酸解离常数经光谱测定分别为 9.16±0.02 和 8.80±分别为 0.02。