Synthesis of fluorescent derivatives of 7-methylguanine through reaction with 2-aryl-substituted malondialdehydes: analysis by HPLC with fluorescence detection.

Fluorescent derivatives of 7-methylguanine were prepared through reaction with 2-aryl-substituted-malondialdehydes and analysed by reversed-phase HPLC with fluorescence detection. Reaction of carbons 1 and 3 of the malondialdehyde molecule at the N1 and N2 positions of 7-methylguanine yielded fluorescent tricyclic structures. Two novel fluorescent derivatives of 7-MeG were obtained, namely, 7-(3,4-dimethoxyphenyl)-10-oxo-1-methyl-9,10-dihydropyrimido[1,2- alpha]purine (yield 15-34%) and 7-(1-naphthyl)-10-oxo-1-methyl-9,10- dihydropyrimido[1,2-alpha]purine (yield 56-70%) after reaction with 3,4-dimethoxyphenylmalondialdehyde and 1-naphthylmalondialdehyde, respectively which were characterized by IR, NMR, MS and UV and fluorescence spectroscopy. The fluorescence intensity of the derivatives was found to be 10-20-fold higher than the intrinsic fluorescence of 7-methylguanine. Concentration versus fluorescence intensity curves exhibit linearity in the picomole to nanomole range. The 2-aryl-substituted malondialdehydes were used to analyse the concentration of 7-methylguanine in neutral hydrolysates obtained from calf thymus DNA samples alkylated with dimethyl sulfate. The results obtained indicate their potential as reagents for the analysis of alkylated guanines in biological samples. Molecular modeling calculations were carried out to generate lowest energy spatial configurations. The results obtained indicated that the aryl-substituents on the malondialdehyde moiety do not lie in the same plane as the tricyclic moiety of the fluorescent derivatives with implications for their fluorescence properties.