Synthesis and structure–analgesic activity relationships of a novel series of monospirocyclopiperazinium salts (MSPZ)

A series of monospirocyclopiperazinium salts were designed and synthesized to search for a peripherally-acting analgesic drug with low side effects. Extensive SAR studies revealed that a suitable NR2R3 was critical for the analgesic activity, which might be beneficial to expose the cationic nitrogen to bind to the receptor, and possibly interact with the receptor via π–π interaction. Introduction of substituting group on the N4-phenyl ring could improve the activity, and the best position was the 4-position. Compound 14n showed more potent analgesic activity (63%, 20 μM/kg, sc) and holds promise for development as a mechanically new analgesic drug.

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