Binding of sugars to DNA. An NMR study of D-fructose

The major tautomers of D-fructose in water are the β-pyranose and β-furanose forms, the former predominating. NMR studies have shown that when aqueous DNA is added, there is a shift in the β-pyranose ⇌β-furanose equilibrium, the latter form being favoured. It is suggested that this is caused by weak, preferential binding of the β-furanose form to DNA. This is supported by computer modelling, which shows that for the former, only two hydrogen bonds can be formed between sugar O–H groups and phosphate units, whereas three good bonds can be formed with the latter.Studies of the O–1H resonances of the anomeric groups of the two forms confirm this change in equilibrium. In addition this feature for the β-furanose form shifts to low-field without significant broadening. This indicates that strong hydrogen bonding to DNA occurs, but that the equilibrium is very rapid giving fast averaging of the NMR signals.