The synthesis of fluorescent derivatives of adenosine and cytidine, by reaction with chloroacetaldehyde in aqueous solution at mild pH and temperature, yielding 1,N6-ethenoadenosine hydrochloride and 3,N4-ethenocytidine hydrochloride, respectively, is here described. Analogous derivatives of 3′-AMP, 5′-AMP, 3′,5′-cyclic AMP, ADP, ATP, and NAD+ were also synthesized. Observation of the spectroscopic properties of the highly fluorescent adenosine derivatives included the emission maximum for 1,N6-ethenoadenosine at ca. 415 nm (corrected) in buffered aqueous solution at pH 7.0, a quantum yield of 0.56, and a fluorescence lifetime of 20 nsec. Variations in fluorescence with respect to changes in the polarity and viscosity of the solvent and with respect to temperature were also examined, as well as fluorescence excitation and fluorescence polarization spectra. All adenine derivatives had similar fluorescence properties. The 1, N6-etheno-ATP analog showed considerable substrate activity as a replacement of ATP with adenylate kinase, hexokinase, and phosphofructokinase, and exhibited allosteric inhibition of phosphofructokinase. The 1,N6-etheno-ADP analog proved to be an excellent substitute for ADP in the pyruvate kinase system, affording a facile assay for a wide variety of kinases. © 1972, American Chemical Society. All rights reserved.