Combined chemoenzymatic synthesis of 20-6-deoxy-α-L-sorbofuranosyl-D-glucose

Abstract

The chemoenzymatic synthesis of 20-6-deoxy-α-L-sorbofuranosyl-D-glucuse has been performed by coupling four enzymatic and one simple chemical step on a preparative scale with 17% overall yield. At first, pyruvic aldehyde dimethyl acetal was reduced stereospecifically to L-lactaldehyde dimethyl acetal by the carbonyl reductase from Candida parapsilosis with approximately 100% ee. Subsequently, the product was converted to L-lactaldehyde by simple treatment with a strong cation exchanger. Secondly, stereoselective condensation between dihydroxyacetone phosphate and L-lactaldehyde was catalyzed by fructose 1,6-bisphosphate aldolase from Staphylococcus carnosus. The resulting sugar phosphate was dephosphorylated by acid phosphatase treatment and further purified by cation exchange chromatography. The structure and stereochemistry of the product, 6-deoxy-L-sorbose, was confirmed by 1H- and 13C-NMR analysis. In the last step sucrose synthase from rice grains was utilized to catalyze the transfer of glucose from UDP-glucose to 6-deoxy-L-sorbose. The structure and stereochemistry of the disaccharide formed, 20-6-deoxy-a-L-sorbofuranosyl-D-glucose, was also confirmed by 1H- and 13C-NMR analysis.