The solubility of 1 and 2 was tested in 50 mM MOPS/NaOH buffer pH 7 and 50 mM glycine/NaOH buffer pH 9 at RT. In a total volume of 0.3 to 10 mL, the nucleobases were dissolved to concentrations of 1 mM, 5 mM, 10 mM and 20 mM. The solutions were observed for the occurrence of precipitate.