A nicotine agonist, 11C-labeled (S)-nicotine, was synthesized by N-methylation of (S)-nornicotine with [11C]-methyl iodide in dimethylformamide-dimethylsulfoxide in order to study nicotinic receptors in the human brain by positron emission tomography. The radiochemical yield of this N-methylation reaction was more than 90% within 5 min. After purification by high performance liquid chromatography the radiochemical purity of the product was more than 99% and the specific radioactivity was 7.4-11.1 GBq/μmol. The regional distribution of (S)-[11C]nicotine in the mouse brain after intravenous injection was compared with that of (R)-[11C]nicotine. After injection of (S)-[11C]nicotine, the regional uptake of radioactivity was in the following order : cortex > thalamu≈hippocampus>striatum>hypothalamus>cerebellum. Moreover, (S)-[11C]nicotine was displaced from the brain by unlaceled (S)-nicotine, but unlabeled (R)-nicotine caused no change in uptake. In contrast, (R)-[11C]nicotine showed a lower brain uptake and lesser regional differences in radioactivity.
为了通过正电子发射断层扫描(PET)研究人脑中的
烟碱受体,合成了N-甲基化(S)-
假木贼碱与[11C]甲基
碘在二甲基甲酰胺-
二甲基亚砜中的产物,即11C标记的(S)-
尼古丁。该N-甲基化反应的放化产率在5分钟内超过90%。经高效
液相色谱纯化后,产物的放化纯度超过99%,比活度为7.4-11.1 GBq/μmol。比较了静脉注射后(S)-[11C]
尼古丁与(R)-[11C]
尼古丁在小鼠脑中的区域分布。注射(S)-[11C]
尼古丁后,放射性吸收的区域顺序为:皮质>丘脑与海马>纹状体>
下丘脑>小脑。此外,(S)-[11C]
尼古丁可被未标记的(S)-
尼古丁从脑中置换出,但未标记的(R)-
尼古丁不改变吸收量。相比之下,(R)-[11C]
尼古丁显示出较低的脑吸收和较小的区域放射性差异。