Pyrrolidin-2-one linked benzofused heterocycles as novel small molecule monoacylglycerol lipase inhibitors and antinociceptive agents

Eighteen pyrrolidin-2-one linked benzothiazole, and benzimidazole derivatives (10–27) were designed and synthesized. The structure of the compounds was confirmed by elemental and spectral (IR, ¹H-NMR and MS) data analysis. All the compounds were screened by human monoacylglycerol lipase (hMAGL) inhibition assay. Three benzimidazole compounds, 22 (4-Cl phenyl), 23 (3-Cl,4-F phenyl) and 25 (4-methoxy phenyl) were found to be the most potent, having an IC₅₀ value of 8.6, 8.0 and 9.4 nm, respectively. Among them, the halogen-substituted phenyl derivatives, compound 22 (4-Cl phenyl) and compound 23 (3-Cl,4-F phenyl), showed micromolar potency against fatty acid amide hydrolase (FAAH), having an IC₅₀ value of 35 and 24 µm, respectively. Benzimidazole derivative having 4-methoxyphenyl substitution (compound 25) was found to be a selective MAGL inhibitor (IC₅₀ = 9.4 nm), with an IC₅₀ value above 50 µm against FAAH. In the formalin-induced nociception test, compound 25 showed a dose-dependent reduction of pain response in both acute and late phases. At 30 mg/kg dose, it significantly reduced the pain response and showed greater potency than the reference drug gabapentin (GBP).