An M4 mAChR antagonist (pKi = 7.2 in chicken heart) that produces temporary mydriasis (pupil dilation; EC₅₀ = 6 µg/ml) and cycloplegia (ciliary muscle paralysis; EC₅₀ = 25 µg/ml) when applied as eye drops; used to probe mAChR activity in a mouse model of fragile X syndrome.