Studies on the coloration mechanism of furostanol derivatives with Ehrlich reagent. I. On the reaction of 3,26-dimethoxy-furost-5,20-diene with Ehrlich reagent.
作者:TENJI KONISHI、SHIU KIYOSAWA、JUNZO SHOJI
DOI:10.1248/cpb.32.2111
日期:——
From the reddish reaction mixture of 3, 26-dimethoxy-furost-5, 20-diene (ψ-diosgenin dimethyl ether, 2) with Ehrlich reagent, a colorless condensation product was isolated and characterized as 3, 26-dimethoxy-23-(p-dimethylaminobenzylidenyl)-furost-5, 20-diene (3). However, a coexisting red product could not be isolated because of its instability. On treatment with dried hydrogen chloride or conc. hydrochloric acid, the colorless chloroform solution of 3 readily changed into a reddish solution, which was reversibly decolorized on addition of 3% ammonia-chloroform solution. Based on ultraviolet and carbon-13 nuclear magnetic resonance spectral analysis, the coloration mechanism of 2 with Ehrlich reagent has been inferred to be as follows. The reaction is initiated by condensation between p-dimethylaminobenzaldehyde and 2 to form 3, followed by protonation to form an iminium cation (3B) under acidic conditions.
从3, 26-二甲氧基-呋喃酯-5, 20-二烯(ψ-地黄苷的二甲基醚,2)与厄尔利希试剂的红色反应混合物中,分离得到了无色的缩合产物,并将其表征为3, 26-二甲氧基-23-(对-二甲氨基苯亚基)-呋喃酯-5, 20-二烯(3)。然而,由于其不稳定性,无法分离出共存的红色产物。在与干燥的氯化氢或浓盐酸处理后,3的无色氯仿溶液迅速变为红色溶液,随后在加入3%的氨-氯仿溶液后可逆性去色。基于紫外光和碳-13核磁共振光谱分析,推测2与厄尔利希试剂的着色机制如下:反应由对-二甲氨基苯甲醛与2的缩合反应开始形成3,随后在酸性条件下发生质子化形成亚胺阳离子(3B)。