Determination of the tautomerism of 5,5-disubstituted analogues of 6-amino-2-thiouracil by 1H and 13C nuclear magnetic resonance spectroscopy

Abstract

5,5-Disubstituted 6-amino-2-thiouracil analogues (1)–(6), prepared by condensation of 2-acylamino-2-cyano aliphatic acids ethyl esters with thiourea, have been studied by ¹H and ¹³C NMR. It has been found that in dimethyl sulphoxide solution the compounds exist as 5-acylamino-5-alkyl-6-imino-2-thioxo-1,2,5,6-tetrahydropyrimidin-4(3H)ones (1B)–(6B). The assignment of this tautomeric form has been based mainly on ¹³C NMR spectra selectively ¹H decoupled with low-power ¹H irradiation.