Investigation of the circular dichroism spectra of bromine-substituted nucleic acid fragments I. Circular dichroism spectra of 8-bromine-substituted purine nucleotides

The CD spectra of 8-bromo-AMP, 8-bromo-dAMP, 8-bromo-GMP, and 8-bromo-dGMP in acid, neutral, and alkaline media and, in some cases, in methanol have been obtained. In the 200–300 nm region three Cotton effects have been recorded which correspond to π-π* in the B2u, B1u, and E1ua bands (280–265, 240–250, and 200–220 nm, respectively). The CD spectra obtained differ from the spectra known in the literature for unbrominated compounds of this class. It has been shown that in ribonucleotides the syn conformation is stabilized by the formation of an intramolecular hydrogen bond with the participation of the ribose 2′-hydroxyl and the N3 atom of the purine base. The 5′-phosphate group in the molecule of a purine nucloside of the syn type changes the CD profile, particularly in the short-wave region of the spectrum, as compared with the CD spectra of the unbrominated analogs given in the literature.