The use of tetrabutylammonium fluoride to promote<i>N</i>- and<i>O</i>-<sup>11</sup>C-methylation reactions with iodo[<sup>11</sup>C]methane in dimethyl sulfoxide
作者:Tatsuya Kikuchi、Katsuyuki Minegishi、Hiroki Hashimoto、Ming-Rong Zhang、Koichi Kato
DOI:10.1002/jlcr.3092
日期:2013.11
The N- or O-methylation reactions of compounds bearing amide, aniline, or phenol moieties using iodo[11C]methane (1) with the aid of a base are frequently applied to the preparation of 11C-labeled radiopharmaceuticals. Although sodium hydride and alkaline metal hydroxides are commonly employed as bases in these reactions, their poor solubility properties in organic solvents and hydrolytic activities have sometimes limited their application and made the associated 11C-methylation reactions difficult. In contrast to these bases, tetrabutylammonium fluoride (TBAF) is moderately basic, highly soluble in organic solvents, and weakly nucleophilic. Although it was envisaged that TBAF could be used as the preferred base for 11C-methylation reactions using 1, studies concerning the use of TBAF to promote 11C-methylation reactions are scarce. Herein, we have evaluated the efficiency of the 11C-methylation reactions of 13 model compounds using TBAF and 1. In most cases, the N-11C-methylations were efficiently promoted by TBAF in dimethyl sulfoxide at ambient temperature, whereas the O-11C-methylations required heating in some cases. Comparison studies revealed that the efficiencies of the 11C-methylation reactions with TBAF were comparable or sometimes greater than those conducted with sodium hydride. Based on these results, TBAF should be considered as the preferred base for 11C-methylation reactions using 1.
含有酰胺、苯胺或酚基团的化合物在碘[11C]甲烷(1)作用下,借助碱进行的N-或O-甲基化反应通常用于制备11C标记的放射药物。尽管氢化钠和碱金属氢氧化物在这些反应中常被用作碱,但它们在有机溶剂中的溶解性差以及水解活性,有时限制了其应用,使得相关的11C-甲基化反应变得困难。与这些碱相比,四丁基氟铵(TBAF)具有适中的碱性,高度溶于有机溶剂,并且亲核性较弱。尽管有预想TBAF可以作为11C-甲基化反应的优选碱,但关于TBAF促进11C-甲基化反应的研究却很少。在此,我们评估了使用TBAF和1对13个模型化合物进行11C-甲基化反应的效率。在大多数情况下,TBAF在室温下能有效促进二甲基亚硫酰胺中的N-11C-甲基化,而在某些情况下O-11C-甲基化则需要加热。比较研究表明,使用TBAF进行的11C-甲基化反应的效率可比或有时大于使用氢化钠的反应。基于这些结果,TBAF应被视为使用1进行11C-甲基化反应的优选碱。