GLUCOSE-ISOMERASE (EC-5.3.1.5) AS A REAGENT IN CARBOHYDRATE SYNTHESIS - SUCCESS AND FAILURES WITH THE ISOMERIZATION OF NONNATURAL DERIVATIVES OF D-GLUCOSE INTO THE CORRESPONDING 2-KETOSES

The properties of glucose isomerase (EC 5.3.1.5) and its synthetic applications are briefly reviewed and recent results with non-natural substrates are discussed. Commercially available immobilized glucose isomerase from Streptomyces murinus, previously discovered to accept D-glucose as well as D-fructose derivatives with modifications at C-3, C-5, and C-6, was also found to be an efficient catalyst for the conversion of 5,6-dimodified derivatives of D-glucose as well as 5-modified D-xylofuranose into the corresponding open-chain 2-ketoses. The equilibrium mixture in all but one case investigated favoured the respective ketose in ratios of 3:1 to 4:1. These results are in agreement with molecular modelling experiments suggesting that the free energies of the furanoid aldoses serving as starting materials are generally slightly higher than the values for the corresponding open-chain ketose. Dimerisation of the open-chain sugar derivatives was not observed.