ABSTRACT
Early reports mainly used nucleobase-modied analogs where the purine ring system was part of the uorophore, such as 1, N6-etheno-cAMP [2], 2-aza-1, N6-etheno-cAMP [3] or the cyclic phosphate of 2-aminopurine riboside [4]. However, these compounds are far from being optimal with regard to membrane permeability, cAMP-dependent protein kinase (PKA) binding anity and stability towards phosphodiesterases (PDEs). Further more, the uorophores lack brilliance and possess unfavorable spectral properties, e.g., excitation is to be performed in the UV range, which can be harmful to intact cells and monitoring of the relatively short emission wavelengths is often disturbed by intrinsic uorescent components of the cell.
