Production of uremic toxin methylguanidine from creatinine via creatol on activated carbon

The mixture of creatinine, activated charcoal and water was stirred. As a result the conversion of creatinine into two products was observed. 1H, 13C NMR and HMBC spectra were recorded and the chemical shifts assigned. Two uremic toxins: creatol and N-methylguanidine were identified. To interpret the NMR data obtained, the optimum structure of creatol, which can exist in the forms of seven tautomers, has been calculated using the DFT B3LYP/6-311G(2d,p) method. The influence of the solvent was described by the polarizable continuum model (PCM). The calculated energy of the most energetically stable tautomeric form A is lower by 12.2, 16.9, 33.8, 81.5, 106.3, 130.4 kJ/mol in water than that of the tautomers B-G, respectively, which suggests that the A form of creatol should prevail in solution. In DMSO, the calculated energy of the most energetically stable tautomeric form A is lower than that of both D and B and the remaining tautomeric forms (C, E-G) are less energetically stable. Subsequently, we sought the correlations between the experimental and the calculated chemical shifts of protons and carbons-13 for the forms - A, B (in water) and A, B, D (in DMSO) - of creatol. The population of the A tautomer is predominant in both H2O and DMSO. We have also recorded the spectra of creatol and N-methylguanidine at different pH. Our data are complete enough to be used in the analysis of body fluids.