Electrochemical N-demethylation of tropane alkaloids,Green Chemistry

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Electrochemical N-demethylation of tropane alkaloids
Green Chemistry ( IF 9.3 ) Pub Date : 2020-09-09 , DOI: 10.1039/d0gc00851f
Ali Alipour Najmi _{1,

2,

3,

4,

5} , Zhangping Xiao _{2,

3,

4,

5,

6} , Rainer Bischoff _{1,

2,

3,

4,

5} , Frank J. Dekker _{2,

3,

4,

5,

6} , Hjalmar P. Permentier _{1,

2,

3,

4,

5}

Affiliation

A practical, efficient, and selective electrochemical N-demethylation method of tropane alkaloids to their nortropane derivatives is described. Nortropanes, such as noratropine and norscopolamine, are important intermediates for the semi-synthesis of the medicines ipratropium or oxitropium bromide, respectively. Synthesis was performed in a simple home-made electrochemical batch cell using a porous glassy carbon electrode. The reaction proceeds at room temperature in one step in a mixture of ethanol or methanol and water. The method avoids hazardous oxidizing agents such as H₂O₂ or m-chloroperbenzoic acid (m-CPBA), toxic solvents such as chloroform, as well as metal-based catalysts. Various key parameters were investigated in electrochemical batch or flow cells, and the optimized conditions were used in batch and flow-cells at gram scale to synthesize noratropine in high yield and purity using a convenient liquid–liquid extraction method without any need for chromatographic purification. Mechanistic studies showed that the electrochemical N-demethylation proceeds by the formation of an iminium intermediate which is converted by water as the nucleophile. The optimized method was further applied to scopolamine, cocaine, benzatropine, homatropine and tropacocaine, showing that this is a generic way of N-demethylating tropane alkaloids to synthesize valuable precursors for pharmaceutical products.

中文翻译：

托烷生物碱的电化学N-去甲基化

描述了一种实用，有效和选择性的将烷烃生物碱转化为正烷烃衍生物的N-脱甲基方法。降冰片烷，例如去甲肾上腺素和降冰片碱是分别半合成异丙托溴铵或溴托昔铵的重要中间体。合成是使用多孔玻璃碳电极在简单的自制电化学批量电池中进行的。反应在室温下在乙醇或甲醇和水的混合物中一步进行。该方法避免了有害的氧化剂如H ₂ ö ₂或米氯过苯甲酸（米-CPBA），有毒溶剂（例如氯仿）以及金属基催化剂。在电化学批量或流通池中研究了各种关键参数，并以克级规模在批量和流通池中使用了最佳条件，以方便的液-液萃取方法无需色谱纯化即可以高收率和高纯度合成去甲托品。机理研究表明，电化学的N-去甲基化通过形成亚胺中间体而进行，该亚胺中间体被水转化为亲核试剂。优化后的方法进一步应用于东pol碱，可卡因，苯扎特罗平，荷马特平和托卡卡因，表明这是一种N的通用方法烷对托烷生物碱进行脱甲基，以合成用于医药产品的有价值的前体。

更新日期：2020-10-05

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