Naphthyridine-based lanthanide complexes worked as magnetic resonance imaging contrast for guanosine 5'-monophosphate in vivo.

New lanthanide complex Gd-ANAMD containing 2-amino-7-methyl-1,8-naphthyridine was achieved for selective magnetic resonance imaging towards guanosine 5'-monophosphate over other ribonucleotide polyphosphates in aqueous media and in vivo. The formation of strong multi-hydrogen bonds between naphthyridine and guanosine made the phosphate in guanosine 5'-monophosphate positioned on a suitable site to coordinate with the lanthanide ion. The substitution of the coordination naphthyridine by the phosphate oxygen atoms caused obvious relaxivity decrease. The negligible cytotoxicity and appropriate blood circulation time of Gd-ANAMD allow potential application of Magnetic Resonance Imaging in vivo. (1)H NMR confirmed that the selectivity of these lanthanide complexes towards guanosine was attributed to the formation of hydrogen bonds between the guanine moeity and the naphthyridine. The fluorescence detection and lifetime measurement of Tb-ANAMD and Eu-ANAMD suggested that the decrease of the relaxivity is not attributed to the change of the q value, but caused by the prolonging of the residence lifetime of inner-sphere water.