Isonipecotic acid, also known as piperidine-4-carboxylic acid (P4C), is a conformationally constrained derivative of γ-aminobutyric acid (GABA) and a moderately potent GABAA receptor partial agonist. It consists of a piperidine ring with a carboxylic acid moiety in the iso position. The drug showed moderate-efficacy partial agonism of α1, α2, α3, and α5 subunit-containing GABAA receptors ( = 46–57%), but showed full or near-full agonism of α4 and α6 subunit-containing GABAA receptors ( = 83–104%). Isonipecotic acid is unable to cross the blood–brain barrier. It was first described in the scientific literature by at least 1944 and was identified as a GABAA receptor agonist by 1978.
See also Piperidine-4-sulfonic acid (P4S) Isoguvacine Gaboxadol Muscimol Nipecotic acid
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