A new, efficient and highly-regioselective approach to synthesis of 6-O-propionyl-d-glucose by using whole-cell biocatalysts

For the first time, whole microbial-cell biocatalysis method was successfully applied by us to the production of glucose esters by transesterification of glucose with vinyl propionate. Among ten bacterial and fungal strains tested, lyophilized cells of Pseudomonas stutzeri strain GIM 1.273 efficiently catalyzed the reaction with the highest conversion and initial rate. C NMR analysis showed that the reaction catalyzed by P. stutzeri yielded 6-O regiomer predominantly (>99%), clearly indicating high regioselectivity of the biocatalyst toward the 6-O-hydroxy group of glucose. Efficiency of the reaction catalyzed by lyophilized cells was evidently solvent-dependent. With the exception of acetonitrile-pyridine and tetrahydrofuran-pyridine systems, the substrate conversion rate clearly increased with increasing hydrophobicity of the organic solvent media used. The best results were obtained in isooctane-pyridine (3:7 v/v) system. Other optimal conditions were: water content 2% (v/v), molar ratio of the acyl donor to glucose 10:1, biocatalyst dosage 80mg/mL and reaction temperature 35°C, under which glucose conversion and reaction rate were 97.2% and 29.7mmol/Lh over the duration of 24h. A tenfold scale-up production of the 6-O-glucose ester further demonstrated that whole-cell P. stutzeri was an efficient and highly-regioselective alternative to purified enzymes for synthesis of glucose esters