Synthesis and characterization of <sup>11</sup>
C-labeled benzyl amidine derivatives as PET radioligands for GluN2B subunit of the NMDA receptors
作者:Takeshi Fuchigami、Noriko Fujimoto、Terushi Haradahira、Yumiko Nojiri、Takashi Okauchi、Jun Maeda、Tetsuya Suhara、Fumihiko Yamamoto、Morio Nakayama、Minoru Maeda、Takahiro Mukai
DOI:10.1002/jlcr.3691
日期:2018.12
GluN2B-containing NMDA receptors (NMDARs) play fundamental roles in learning and memory, although they are also associated with various brain disorders. In this study, we synthesized and evaluated three 11C-labeled N-benzyl amidine derivatives 2-[11C]methoxybenzyl) cinnamamidine ([11C]CBA), N-(2-[11C]methoxybenzyl)-2-naphthamidine ([11C]NBA), and N-(2-[11C]methoxybenzyl)quinoline-3-carboxamidine ([11C]QBA) as PET radioligands for these receptors. The 11C-benzyl amidines were synthesized via conventional methylation of corresponding des-methyl precursors with [11C]CH3I. In vitro binding characteristics were examined in brain sagittal sections using various GluN2B modulators and off-target ligands. Further, in vivo brain distribution studies were performed in normal mice. The 11C-labeled benzyl amidines showed high-specific binding to the GluN2B subunit at in vitro. In particular, the quinoline derivative [11C]QBA had the best binding properties in terms of high-brain localization to GluN2B-rich regions and specificity to the GluN2B subunit. Conversely, these 11C-radioligands showed the brain distributions were inconsistent with GluN2B expression in biodistribution experiments. The majority of the radiolabeled compounds were identified as metabolized forms of which amido derivatives seemed to be the major species. Although these 11C-ligands had high-specific binding to the GluN2B subunit, significant improvement in metabolic stability is necessary for successful positron emission tomography (PET) imaging of the GluN2B subunit of NMDARs.
含 GluN2B 的 NMDA 受体(NMDARs)在学习和记忆中发挥着重要作用,但它们也与各种脑部疾病有关。在这项研究中,我们合成并评估了三种 11C 标记的 N-苄基脒衍生物 2-[11C]甲氧基苄基)肉桂脒([11C]CBA)、N-(2-[11C]甲氧基苄基)-2-萘脒 ([11C]NBA)和 N-(2-[11C]甲氧基苄基)喹啉-3-甲脒 ([11C]QBA),作为这些受体的 PET 放射配体。11C 苄基脒是通过[11C]CH3I 对相应的去甲基前体进行常规甲基化合成的。使用各种 GluN2B 调节剂和非目标配体在脑矢状切片中检测了体外结合特性。此外,还在正常小鼠体内进行了脑分布研究。11C 标记的苄基脒在体外显示出与 GluN2B 亚基的高特异性结合。尤其是喹啉衍生物[11C]QBA,其结合特性最好,能高度定位在富含 GluN2B 的脑区,并对 GluN2B 亚基具有特异性。相反,在生物分布实验中,这些 11C 放射性配体的脑部分布与 GluN2B 的表达不一致。大多数放射性标记化合物被鉴定为代谢形式,其中氨基衍生物似乎是主要种类。虽然这些 11C 配体与 GluN2B 亚基的结合特异性很高,但要成功地对 NMDARs 的 GluN2B 亚基进行正电子发射断层扫描(PET)成像,必须显著提高代谢稳定性。