Nucleophilic reactivity of biothiols toward coumarin-based derivatives containing a chalcone moiety

TheMichael addition reactions of the biothiols cysteine (Cys), glutathione (GSH), homocysteine (Hcy) and cysteinylglycine (Cys-Gly) with (E)-3-(3-(2-methoxyphenyl)acryloyl)-7-methoxy-2H-chromen-2-one and (E)-3-(3-(3-methoxyphenyl) acryloyl)-7-methoxy-2H-chromen-2-one (ChC2 and ChC3, respectively) in aqueous solution (25 °C, ionic strength 0.2M KCl) were followed fluorimetrically and evaluated kinetically. With a large excess of biothiol, pseudo-first-order rate coefficients (k_obsd) were found. Plots of k_obsd versus [biothiolate] are linear, with a pH-independent slope (k_N). With the kinetic results obtained, the following conclusions can be drawn: (i) the reactivity increases in the sequence Cys-Gly<Hcy GSH<Cys; (ii) similar reactivity toward biothiols was found for ChC2 and ChC3, and both probes are more reactive than (E)-3-cinnamoyl-7- methoxy-2H-chromen-2-one (ChC1); (iii) ChC2 and ChC3 display a highly selective fluorescence enhancement with biothiols, allowing these probes to be used for fluorimetric biothiol determination in SH-SY5Y cells.