Coumarin–malonitrile conjugate as a fluorescence turn-on probe for biothiols and its cellular expression

A nonfluorescent coumarin-malonitrile conjugate (1) was transformed into a strongly fluorescent molecule through the Michael addition of a thiol group to the α,β-unsaturated malonitrile of 1. The molecular probe has exhibited a highly selective fluorescence response toward biothiols (Cys, Hcy, GSH) with micromolar sensitivity both in vitro and in vivo.