1H and 13C NMR spectra and solution structures of novel derivatives of 5-substituted creatinines.

Five creatinine derivatives were prepared by the treatment of creatinine with activated carbon and appropriate alcohol (1-4), or ammonia solution (5). Product structures were determined by 1H and 13C NMR spectroscopy in solution, including 2D HSQC and HMBC experiments. Then, the proton and carbon chemical shifts for these compounds were calculated using GIAO-DFT [B3LYP/6-311G(2d,p)] method and the Gaussian 03W program and furthermore for 1 and 5 using polarizable continuum model (PCM). The conclusions coming from the comparison of the experimental and theoretical spectra supported the adopted signal assignments and solved the structural problems due to the potential annular tautomerism of the investigated compounds. One can predict that 5-substituted creatinines, just like creatinine, appear in solution in the form of 2-amino-1,5-dihydro-1-methyl-4-imidazolone. Correlations between experimental and calculated substituent-induced chemical shifts for two tautomeric forms of 5-substituted creatinines indicate that the mechanism of the substituent influence in both tautomers for the investigated compounds appears to be analogous. We can predict that in solution this accepting inductive effect of substituent groups does not significantly influence the structure of creatinine molecule in solution. The analysis of coupling constants for 5-substituted creatinines gives information about conformation of the investigated molecules in solution.