Bioactive Phenylenediamine Derivatives of Dehydroacetic Acid: Synthesis, Structural Characterization and Deuterium Isotope Effects

Several phenylenediamine derivatives of dehydroacetic acid, 3-acetyl-4-hydroxy-6-methyl-2H-pyran-2-one have been synthesized and their structure elucidated by using NMR and IR spectroscopies and mass spectrometry. Spectral analyses have pointed toward the localized keto-amine form as the predominant tautomeric form in solution and solid-state which was in agreement with X-ray data. The relatively broad N-H stretching bands observed in IR spectra and significant N-H proton down-field and keto C=O up-field shifts in NMR spectra indicated the presence of intra-molecular hydrogen bonds in all studied compounds. In order to gain further insights into nature of these interactions in solution deuterated isotopomers have been prepared and deuterium isotope effects in C-13 NMR spectra have been determined and analyzed. The magnitude and sign of isotope effects have confirmed the existence of intra-molecular hydrogen bonds. Observed differences in isotope effects reflected different hydrogen bond structure and dynamics in studied compounds. The results presented in this paper might help in better understanding of biological properties of the related compounds.(doi: 10.5562/cca1825)