Bifunctional diaminoterephthalate scaffolds as fluorescence turn-on probes for thiols

The fluorescent diaminoterephthalate scaffold was equipped by amidation with three types of reactive functions: thiols for metal-surface binding, alkynes for click reactions, and maleimides for ligation with proteins. Starting from a succinyl succinate derivative with two orthogonally cleavable ester functions, three monoamides (38-57% yield over three steps) and two bisamides (19 and 25% yield over five steps) were prepared. Although alkyne and thiol derivatized compounds showed reasonable luminescence behavior (Φ≈1-4%), the fluorescence was quenched by the maleimide moiety. It was turned on (10- to 20-fold increase of fluorescence quantum yield) by conjugate addition of thiols.