Studies of the tautomerism of purine and the protonation of purine, and its 7- and 9-methyl derivatives, by nitrogen-15 nuclear magnetic resonance spectroscopy

The nitrogen-15 NMR shifts of purine and its 7- and 9-methyl derivatives were measured at the natural-abundance as a function of pH. The results made it possible for both the sites and magnitudes of protonation of purine and its derivatives to be determined. A semiquantitative determination was made of the position of the N7H-N9H tautomeric equilibria of purine in both water and dimethyl sulfoxide.