A Synthesis of Chiral 1,1,3-Trisubstituted 1,2,3,4-Tetrahydro-β-carbolines by the Pictet–Spengler Reaction of Tryptophan and Ketones: Conversion of (1R,3S)-Diastereomers into Their (1S,3S)-Counterparts by Scission of the C(1)–N(2) Bond
作者:Yoshie Horiguchi、Masayoshi Nakamura、Toshiaki Saitoh、Takehiro Sano
DOI:10.1248/cpb.51.1368
日期:——
The Pictet-Spengler cyclization of the imines (3) prepared by the condensation of L-tryptophan methyl ester (1) and aryl methyl ketones (2), using titanium(IV) isopropoxide as an iminating reagent, quantitatively proceeded, when treated with trifluoroacetic acid (TFA) or formic acid, to provide two diastereomers, that is (1S,3S)-1-aryl-3-isopropoxycarbonyl-1-methyl-1,2,3,4-tetrahydro-beta-carbolines
当用三氟乙酸处理时,使用异丙醇钛(IV)作为酰亚胺化试剂,通过L-色氨酸甲酯(1)和芳基甲基酮(2)的缩合反应制得的亚胺(3)进行Pictet-Spengler环化反应酸(TFA)或甲酸,以提供两种非对映异构体,即(1S,3S)-1-芳基-3-异丙氧基羰基-1-甲基-1,2,3,4-四氢-β-咔啉(4)和它们的(1R,3S)-非对映异构体(5),其中非对映异构体比率根据反应条件从1至5变化。如TFA中的平衡实验所示,(1R,3S)-非对映异构体(5)在热力学上比其(1S,3S)-同源异构体(4)更稳定。应在酸性条件下通过裂解C(1)-N(2)键并在C-3手性中心完全保留构型来实现4至5(也为5至4)的转化。