AN NMR AND VIBRATIONAL STUDY OF 5-BROMOURIDINE AND ITS BASE-PAIRING WITH GUANOSINE AND ADENOSINE

A multinuclear magnetic resonance and vibrational study on 5-bromourid ine and its base pairing with guanosine and adenosine in deuterated di methyl sulfoxide at different concentrations is reported. A dicarbonyl ic non-self-associated form is suggested for 5-bromouridine on the bas is of the H-1-, N-15-NMR, and Raman data. When guanosine is added in e quimolar amounts, a downfield shift of the (N-3)H proton of 5-bromouri dine and of the (N-1)H and NH2 protons of guanosine is observed; these results can be interpreted, according to the Raman ones, considering that only a fraction of guanosine is ''wobble base paired'' with 5-bro mouridine, whereas the remaining part is self-associated. When 5-bromo uridine is mixed with adenosine, the proton chemical shift of the amin ic NH2 of adenosine increases and the (N-3)H iminic of 5-bromouridine moves downfield at a value higher than that observed for the 5-bromour idine-guanosine mixture. This behavior supports the hypothesis that 5- bromouridine interacts more with adenosine than with guanosine, but th e results obtained are not able to establish which type of pairing (Wa tson-Crick or Hoogsteen) is present. Finally, the infrared spectrum of the solid 5-bromouridine : adenosine adduct, for which X-ray measurem ents of other authors suggested a Hoogsteen pairing, is reported and t he observed bands are discussed. (C) 1997 John Wiley & Sons, Inc.