First stereoselective synthesis and assignment of the absolute configuration of the nebracetam eutomer and derivatives
作者:Evanoel C. Lima、Jorge L.O. Domingos、Ayres G. Dias、Paulo R.R. Costa
DOI:10.1016/j.tetasy.2008.04.012
日期:2008.5
(-)-Nebracetam 1 was stereoselectively prepared for the first time, allowing the determination of its absolute configuration as (R). The pivotal intermediate in the synthesis, 1-benzyl-4-[(S)-2,2-dimethyl-1,3-dioxolan-4-yl]-pyrrolidin-2-one 6, was previously obtained in 60% yield and 90% ee from an enoate derived from D-mannitol. Two approaches were investigated to synthesize (R)-(-)nebracetam 1 and analogues 4 and 5 from 6. Compound 6 was transformed into WEB-1868 2. Mesylation of the hydroxyl group in 2, followed by nucleophilic substitution with azide and reduction led to target 1. Compounds 4 and 5 were synthesized by using morpholine and N-methyl piperazine as nucleophiles. Compounds 4 and 5 were also prepared, in higher yields and similar ee, through the reductive amination of aldehyde 10, obtained in two steps from 6. (C) 2008 Elsevier Ltd. All rights reserved.
(-)-Nebracetam 1 首次通过立体选择性方法制备,从而确定了其绝对构型为 (R)。合成中的关键中间体 1-benzyl-4-[(S)-2,2-dimethyl-1,3-dioxolan-4-yl]-pyrrolidin-2-one 6,从前体 D-甘露醇衍生而来的烯酸酯获得,产率为 60%,对映体过量 (ee) 为 90%。研究了两种方法,从 6 合成 (R)-(-)nebracetam 1 以及类似物 4 和 5。化合物 6 转化为 WEB-1868 2。将 2 中的羟基甲磺化后,通过与叠氮化物的亲核取代反应,随后还原,得到目标化合物 1。化合物 4 和 5 则使用吗啉和 N-甲基哌嗪作为亲核试剂进行合成。此外,通过从 6 经过两步制得的醛 10 进行还原胺化,可以更高产率和类似对映体过量地制备化合物 4 和 5。(C) 2008 Elsevier Ltd. 一切权利保留。