Formation of a Rare Tautomeric Form of 5-Hydroxy-6-Methyluracil in Complexation with Copper(II) and Manganese(II) Chlorides in Alkaline Media

Abstract

Reactions of uracils with metals have been reviewed in [1, 2]. Although uracil and its 5and 6-substituted derivatives can theoretically exist as six tautomers [3, 4], X-ray diffraction analysis revealed that complexation involves their dilactam form only [1, 2]. The exceptions are complexes with the lactim form of 1-methyluracil, 1-methylthymine, and unsubstituted uracil [5–7]. In this study, based on the IR spectra of copper(II) and manganese(II) complexes with 5-hydroxy-6-methyluracil, we assumed for the first time stabilization of the lactim tautomer by the metal ion. Synthesis of a(e 5 c 5 N 2 e 3 ) 2 · 2c 2 e (a = Cu , Mn ) . A weighed sample of 5-hydroxy-6-methyluracil (HL) was dissolved in an equimolar aqueous solution of NaOH to complete homogenization. Then, a corresponding metal chloride was added (HL : MCl 2 = 2 : 1). The resulting solution was stirred at room temperature for 20 min. The complexes were obtained as powdered yellow-green (M = Cu) or yellow (M = Mn) precipitates in 51 and 82% yields, respectively. The compositions of the complexes ML 2 · 2 H 2 O were determined by elemental analysis.