NMR study of 5-substituted pyrazolo[3,4-c]pyridine derivatives
Substituted pyrazolopyridines are potent inhibitors of phosphodiesterases and cyclin-dependent kinases. In this study, NMR was used to investigate the potential NI-H and N2-H tautomerism of 5-substituted pyrazolo[3,4-c]pyridine derivatives. Six compounds were fully characterized by using 1H, 13C, and 15N chemical shifts and indirect 1H-13C and 1H-15N coupling constants. The 1H NMR spectra were measured over a broad range of temperatures. All of the compounds were shown to exist predominantly in the NI-H tautomeric form. Complementary quantum-chemical calculations of the chemical shieldings and indirect spin-spin couplings support the structural conclusions drawn. Copyright