Synthesis, spectral properties and evaluation of carboxy-functionalized 3-thiazolylcoumarins as blue-emitting fluorescent labeling reagents

Abstract

A series of UV-light excitable 7-hydroxy-, methoxy- and acetoxy-substituted [3-(thiazol-2-yl)]coumarin derivatives containing a carboxyalkyl functional group on the thiazole fragment were synthesized for the fluorescent labeling of biomolecules. The spectral properties of these compounds in methanol and aqueous buffers (pH 6.3 and 10.5) were studied. The dyes exhibit a bright blue fluorescence with maxima in the range of 438–457 nm and large Stokes shifts of 72–83 nm (in methanol). Emission maxima of the ionized forms of the 7-hydroxyl derivatives in basic medium are located at 482–484 nm. Thiazolylcoumarins are characterized by high fluorescence quantum yields (up to 0.85). Dye conjugates with l-trileucine and (2′-5′)-triadenylate were obtained via the active ester approach.