The 18O Isotope Shift in 13C Nuclear Magnetic Resonance Spectroscopy. 14. Kinetics of Oxygen Exchange at the Anomeric Carbon of D-Ribose and D-2-Deoxyribose

Article abstract of DOI:10.1021/jo00003a009

The kinetics of the oxygen-exchange reaction at the anomeric carbon atoms of D-ribose and D-2-deoxyribose (2-deoxy-D-erythro-pentose) were compared using the 18O isotope induced shift in 13C NMR spectroscopy.Measurements were made at a number of temperature and pH values.The oxygen-exchange reaction for these sugars is strongly pH-dependent, displaying regions of acid, water, and base catalysis.At 25 deg C the oxygen-exchange rate of D-ribose was found to be approximately 20-fold greater than the rate for D-glucose between pH 2 and 9.In turn, the oxygen-exchange rate for D-2-deoxyribose was greater than the rate for D-ribose by approximately 5-fold above pH 4 and by greater than 10-fold below pH 4.The results are analyzed in terms of steric and inductive effects on the hydration kinetics of the open-chain forms and by comparison with the hydration reaction of simple aldehydes.The study also includes quantitative data, based upon 13C NMR line intensities, for the various anomeric forms that exist in solutions of these sugars at the different temperature and pH values used in the kinetic measurements reported here.In each case, the oxygen-exchange reactions of the anomers are slow relative to the rate of anomerization, so that the anomers appear to exchange oxygen at the same rate.