Synthesis, FT-IR and 1H NMR studies of alkali and alkaline earth metal complexes with guanosine

Abstract

The synthesis of complexes of Li(I), K(I), Mg(II), Ca(II) and Ba(II) with guanosine in basic non aqueous solutions is described. The complexes were of two types: (1) complexes having the general formula, M(Guo) nX m·YH 2O·ZC 2H 5OH, where M = Mg(II), Ca(II), Ba(II) and Li(I), n = 1,2,4, X = Cl −, Br −, NO 3 −, ClO 4 − and OH −, m = 1,2, Y = 0−6 and X = 0−2, and (2) complexes with the general formula, M(GuoH-1)(OH) n −1 ·YH 2O, where M = K(I), Ca(Il) and Ba(II), GuoH-1 =Ionized guanosine at N 1, n = 1,2 and Y = 1−3. The complexes are characterized by their proton nuclear magnetic resonance ( 1H NMR) and Fourier transform infrared (FT-IR) spectra. The FT-IR and 1H NMR data of the non ionized nucleoside complexes suggest that the metal binding is through the N 7-site of guanine and that the anion (X) is hydrogen bonded to N 1H and NH 2 groups. In the N 1-ionized guanosine complexes the metal binding is via the O 6 − of guanine. All the complexes formed exhibited a transition of the sugar conformation from C 2′ -endo/anti in the free nucleoside to C 3′ -endo/anti in the metal complexes.