Kinetic and NMR spectroscopic study of the chemical stability and reaction pathways of sugar nucleotides.

The alkaline cleavage of two types of sugar nucleotides has been studied by 1H and 31P NMR in order to obtain information on the stability and decomposition pathways in aqueous solutions under alkaline conditions. The reaction of glucose 1-UDP is straightforward, and products are easy to identify. The results obtained with ribose 5-UDP and ribose 5-phosphate reveal, in contrast, a more complex reaction system than expected, and the identification of individual intermediate species was not possible. Even though definite proof for the mechanisms previously proposed could not be obtained, all the spectroscopic evidence is consistent with them. Results also emphasise the significant effect of conditions, pH, ionic strength, and temperature, on the reactivity under chemical conditions.

Metal ion-promoted cleavage of nucleoside diphosphosugars: a model for reactions of phosphodiester bonds in carbohydrates.

Cleavage of five different nucleoside diphosphosugars has been studied in the presence of Cu(2+) and Zn(2+) complexes. The results show that metal ion catalysts promote the cleavage via intramolecular transesterification whenever a neighbouring HO group can adopt a cis-orientation with respect to the phosphate. The HO group attacks the phosphate and two monophosphate products are formed. If such a nucleophile is not available, Cu(2+) complexes are able to promote a nucleophilic attack of an external nucleophile, e.g. a water molecule or metal ion coordinated HO ligand, on phosphate. With the Zn(2+) complex, this was not observed.