Synthesis and Characterization of Radioiodinated (S)-5-Iodonicotine: A New Ligand for Potential Imaging of Brain Nicotinic Cholinergic Receptors by Single Photon Emission Computed Tomography.
作者:Hideo SAJI、Akira WATANABE、Yasuhiro MAGATA、Yoshiro OHMOMO、Yasushi KIYONO、Yoshihisa YAMADA、Yasuhiko IIDA、Yoshiharu YONEKURA、Junji KONISHI、Akira YOKOYAMA
DOI:10.1248/cpb.45.284
日期:——
(S)-5-Iodonicotine (4a), an (S)-nicotine analog iodinated at the 5-position of the pyridine ring, was synthesized and evaluated as a potential radiopharmaceutical for investigating brain nicotine receptors by single photon emission computerized tomography (SPECT). [125I]-(S)-5-Iodonicotine ([125I]-4a) was synthesized by the iododestannylation reaction under no-carrier-added conditions and purified by high-performance liquid chromatography (HPLC). The binding affinity of 4a for brain nicotine receptors was measured in terms of displacement of [3H]cytisine from binding sites in rat cortical membranes. The binding data revealed that the affinity of 4a was the same as that of (S)-nicotine and 80-fold higher than that of the (R)-enantiomer (4b). Biodistribution studies in mice disclosed that the brain uptake of [<125;>I]-4a was rapid and profound. Regional cerebral distribution studies in rats by autoradiography disclosed that the accumulation of [125I]-4a was dense in the thalamus, intermediate in the cortex and striatum, and less marked in the cerebellum. Furthermore, the administration of (S)-nicotine reduced the uptake of [125I]-4a in the thalamus and resulted in a nearly identifal level of radioactivity in the cerebellum. [125I]-(R)-5-Iodonicotine ([125I]-4b) showed more rapid washout from the brain and a less extensive regional cerebral distribution than the (S)-enantiomer ([125I]-4a). Thus, 4a bound to brain nicotine receptors in vivo, and therefore iodine-123-labeled 4a may be a potential radioligand for use in in vivo cerebral nicotinic receptor studies by SPECT.
(S)-5-Iodonicotine (4a)是一种(S)-尼古丁类似物,在吡啶环的5-位被碘化,该化合物被合成并评估为一种潜在的放射性药物,可用于通过单光子发射计算机断层扫描(SPECT)研究大脑尼古丁受体。[125I]-(S)-5-碘烟碱([125I]-4a)是在不添加载体的条件下通过碘锡烷化反应合成的,并通过高效液相色谱法(HPLC)纯化。根据[3H]胞嘧啶从大鼠大脑皮层膜结合位点移位的情况,测定了 4a 与大脑尼古丁受体的结合亲和力。结合数据显示,4a 的亲和力与(S)-尼古丁的亲和力相同,比(R)-对映体(4b)的亲和力高 80 倍。对小鼠的生物分布研究表明,[<125;>I]-4a 在大脑中的吸收迅速而深刻。通过自显影法对大鼠进行的区域脑分布研究表明,[125I]-4a 在丘脑中密集聚集,在大脑皮层和纹状体中处于中间位置,而在小脑中则不太明显。此外,施用(S)-尼古丁会减少丘脑对[125I]-4a的吸收,并导致小脑中的放射性水平几乎相同。与(S)-对映体([125I]-4a)相比,[125I]-(R)-5-碘烟碱([125I]-4b)在大脑中的洗脱速度更快,在大脑中的区域分布范围更小。因此,4a与体内脑尼古丁受体结合,碘123标记的4a可能是一种潜在的放射性配体,可用于SPECT体内脑尼古丁受体研究。