Palladium catalyzed synthesis of Ca2+ indicators with aryl bithiophene and terthiophene fluorophores

Five new fluorescent indicators for Ca2+ were synthesized using the Stille reaction. They all consist of the tricarboxylate chelator APTRA (o-aminophenol-N,N,O-triacetic acid) linked to a (substituted) bithiophene or terthiophene fluorophore. The dissociation constants Kd measured via fluorimetric titrations at 21 °C in 100 mM KCl buffered solution, pH 7.05, for the Ca2+ complexes with the new probes are in the range between 10 and 40 μM.