ISSN:
0749-1581
Keywords:
Protonation
;
Tautomerism
;
NMR
;
Imidazo[1,2-a]imidazole
;
Chemistry
;
Analytical Chemistry and Spectroscopy
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The tautomerism and protonation of the putative inotropic 2-(2′,4′-dimethoxy)phenyl-1H-imidazo[1,2-a]imidazole (2) has been studied in several solvents by comparing its 1H and 13C chemical shifts with those of its 1- and 7-methyl derivatives 3 and 4, respectively, and acid salts. Tautomer and rotamer populations were also estimated from measurements of proton relaxation rates and NOE effects. Heterocycle 2 exists predominantly as the 1H-tautomer in CDCl3, but as the 7H-tautomer in DMSO-d6 and methanol-d4-D2O solutions. In CDCl3 solution, 2 appears to exist with the N-1-H and 2′-OMe groups adjacent, but in DMSO-d6 the conformation is the rotated form with N-7-H and H-6′ adjacent; 3 exists as a mixture of rotamers in CDCl3 and in DMSO-d6 whereas 4 is in the form with the N-7-Me and H-6′ adjacent in both solvents. The observed conformational preferences have been compared with the results of semi-empirical molecular orbital calculations and found to be in broad agreement. Protonation of 2 occurs mainly at N-1 in DMSO-d6 and at N-7 in CDCl3, as expected from observed tautomeric ratios in the free base.
Additional Material:
5 Tab.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/mrc.1260291112
