NMR study of stacking interactions between thymine and 1,3-dimethylxanthine rings

Stacking interactions between thymine and 1,3-dimethylxanthine rings of 7-[omega-(2,4-dioxo-1,2,3,4-tetrahydro-5-methyl-1-pyrimidinyl) alkyl]-1,3-dimethylxanthine were studied by means of H-1 NMR spectroscopy in aqueous solutions and organic solvents. The spectra were compared with those of 1,1'-(alpha,omega-alkanediyl) bis [thymine] and 7,7'-(alpha,omega-alkanediyl) bis [1,3-dimethylxanthine]. On the basis of the chemical shifts of the ring protons and methyl groups of thymine and xanthine rings, a stacked conformation between thymine and 1,3-dimethylxanthine rings in aqueous solutions was estimated.