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Identification and Development of a New Positron Emission Tomography Ligand 4‑(2-Fluoro-4‑[11C]methoxyphenyl)-5-((1-methyl‑1H‑pyrazol-3-yl)methoxy)picolinamide for Imaging Metabotropic Glutamate Receptor Subtype 2 (mGlu2)

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posted on 22.09.2020, 16:07 by Tomoteru Yamasaki, Xiaofei Zhang, Katsushi Kumata, Yiding Zhang, Xiaoyun Deng, Masayuki Fujinaga, Zhen Chen, Wakana Mori, Kuan Hu, Hidekatsu Wakizaka, Akiko Hatori, Lin Xie, Masanao Ogawa, Nobuki Nengaki, Richard Van, Yihan Shao, Douglas J. Sheffler, Nicholas D. P. Cosford, Steven H. Liang, Ming-Rong Zhang
Metabotropic glutamate receptor 2 (mGlu2) is a known target for treating several central nervous system (CNS) disorders. To develop a viable positron emission tomography (PET) ligand for mGlu2, we identified new candidates 5ai that are potent negative allosteric modulators (NAMs) of mGlu2. Among these candidates, 4-(2-fluoro-4-methoxyphenyl)-5-((1-methyl-1H-pyrazol-3-yl)­methoxy)­picolinamide (5i, also named as [11C]­MG2-1812) exhibited high potency, high subtype selectivity, and favorable lipophilicity. Compound 5i was labeled with positron-emitting carbon-11 (11C) to obtain [11C]5i in high radiochemical yield and high molar activity by O-[11C]­methylation of the phenol precursor 12 with [11C]­CH3I. In vitro autoradiography with [11C]5i showed heterogeneous radioactive accumulation in the brain tissue sections, ranked in the order: cortex > striatum > hippocampus > cerebellum ≫ thalamus > pons. PET study of [11C]5i indicated in vivo specific binding of mGlu2 in the rat brain. Based on the [11C]5i scaffold, further optimization for new candidates is underway to identify a more suitable ligand for imaging mGlu2.