PCS1055 is a potent and selective muscarinic M4 acetylcholine receptor competitive antagonist that exhibits >100-fold selectivity over M1-, M3-, and M5-receptors and 30-fold selectivity at the M2 receptor. PCS1055 was originally described as a potent electric eel AChE inhibitor (IC50 = 22 nM) and less potent at human AChE (IC50 = 120 nM).