NUCLEOPHILIC CATALYSIS OF GLYCOSIDE HYDROLYSIS - THE HYDROLYSIS OF 4-NITROPHENYL ALPHA-D-GLUCOPYRANOSIDE AND BETA-D-GLUCOPYRANOSIDE TETRAPHOSPHATES

The octaanion of the tetraphosphate of 4-nitrophenyl beta-D-glucopyran oside is hydrolysed up to 100 times faster than model compounds, in a reaction which is pH-independent above pH 9. The mechanism involves in tramolecular nucleophilic catalysis by the phosphate group in the 2-po sition: the intermediate five-membered 1,2-cyclic phosphate can be obs erved directly by P-31 NMR spectroscopy under suitable conditions. In base this gives alpha-D-glucopyranose 1,3,4,6-tetraphosphate and inorg anic phosphate: it appears that glucose 2,3,4,6-tetraphosphate is not stable under;basic conditions, but is converted into the triphosphate of a saccharinic acid. The tetraphosphate of 4-nitrophenyl alpha-D-glu copyranoside shows no significant acceleration.