N‑Adamantyl-1-alkyl-4-oxo-1,4-dihydroquinoline-3-carboxamide Derivatives as Fluorescent Probes to Detect Microglia Activation through the Imaging of Cannabinoid Receptor Subtype 2 (CB2R)

Cannabinoid receptor subtype 2 (CB2R) is emerging as a pivotal biomarker to identify the first steps of 10 inflammation-based diseases such as cancer and neurodegenerative infection. There is an urgent need to find specific probes that 11 may result in green and safe alternatives to the commonly used radiative technologies, to deepen the knowledge of the CB2R 12 pathways impacting the onset of the above-mentioned pathologies. Therefore, based on one of the CB2R pharmacophores, we 13 developed a class of fluorescent N-adamantyl-1-alkyl-4-oxo-1,4-dihydroquinoline-3-carboxamide derivatives spanning from the green 14 to the near-infrared (NIR) regions of the light spectrum. Among the synthesized fluorescent ligands, the green-emitting compound 15 55 exhibited a favorable binding profile (strong CB2R affinity and high selectivity). Notably, this ligand demonstrated versatility as 16 its use was validated in different experimental settings such as flow cytometry saturation, competitive fluorescence assays, and in vitro 17 microglia cells mimicking inflammation states where CB2R are overexpressed.