Tautomerism, Protonation, and Ionization of Formycin in Aqueous Solution by the pH Dependence of13C Chemical Shifts and13C-1H Coupling Constants

Abstract

Abstract Analyses of the pH dependence of 13C chemical shifts and 13C-1H coupling constants of formycin in aqueous soluion revealed two pKa′s, at 4.4 and 9.7, corresponding to a protonation at N4 and an ionization at N1. The N4-protonation results in the transfer of a pyrazolo ring hydrogen from N2 to N2-At physiological pH, formycin was found to exist as a mixture of N1H and N2H tautomers, with the former being predominant (>94%).