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 app lications are briefly reviewed and recent results with non-natural sub strates are discussed. Commercially available immobilized glucose isom erase from Streptomyces murinus, previously discovered to accept D-glu cose 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 conversio n of 5,6-dimodified derivatives of D-glucose as well as 5-modified D-x ylofuranose into the corresponding open-chain 2-ketoses. The equilibri um mixture in all but one case investigated favoured the respective ke tose in ratios of 3:1 to 4:1. These results are in agreement with mole cular modelling experiments suggesting that the free energies of the f uranoid aldoses serving as starting materials are generally slightly h igher than the values for the corresponding open-chain ketose. Dimeris ation of the open-chain sugar derivatives was not observed.