Synthesis and structure–activity relationships of pyrazolodiazepine derivatives as human P2X7 receptor antagonists

Screening of library compounds has yielded pyrazolodiazepine derivatives with P2X7 receptor antagonist activity. To explore the structure–activity relationships (SAR) of these pyrazolodiazepines as human P2X7 receptor antagonists, derivatives were synthesized by substitutions at positions R2 and R3 of the pyrazolodiazepine skeleton. Using a 2′(3′)-O-(4-benzoylbenzoyl)ATP (BzATP)-induced fluorescent ethidium uptake assay, the activities of these derivatives were tested in HEK-293 cells stably expressing human P2X7 receptors. Moreover, the effect of these derivatives was assessed by measuring their effect on IL-1β release induced by BzATP-induced activation of differentiated THP-1 cells. A 2-phenethyl pyrazolodiazepine derivative with a 1-methyl-1H-3-indolyl group at position R2 had fivefold greater activity than the derivative with a 5-isoquinolinyl at R2. Moreover, a benzyl moiety at R3 had fivefold greater activity than a bicyclic moiety. The stereochemical effect at C-6 showed a preference for the (R)-isomer. Among the series of active derivatives, compound 23b, with a phenethyl group at R1, a 3-methyl indole at R2, and a benzyl at R3, exhibited activity similar to that of the positive control, KN-62, as shown by the inhibitory effects of IL-1β release.

Novel and potent antagonists of P2X7 receptors were developed through optimization of a weak lead compound identified from a potential privileged structure-based library.Figure optionsDownload as PowerPoint slide