Selective acylation of monosaccharides using microbial cells

The microbially catalyzed esterification of different monosaccharides (glucose, alkyl glucosides and fructose) was investigated. Lyophilized cells of Rhizopus delemar and Rhizopus ozyzae gave direct esterification of octanoic acid and glucose in acetonitrile furnishing 6-O-octanoylglucose. R. oryzae showed remarkable selectivity towards beta-glucose which was readily acylated, while little esterification was observed with the alpha-anomer. The effects of substrate concentration, temperature and solvent were studied in the conversion catalyzed by R. oryzae with beta-glucose: 2.5 g l(-1) of monoester were obtained starting from 5 g l(-1) of glucose and 50 g l(-1) of octanoic acid in acetonitrile at 50 degrees C. Interesterification was also studied. Tricaprylin proved to be a good acylating agent allowing 3.5 g l(-1) of 6-O-octanoylglucose to be produced. Esterification of methyl- and octyl glucosides proceeded with interesting selectivity furnishing much higher yields with the beta-alkyl substrates. R. delemar and R, oryzae also catalyzed highly regioselective acylation of fructose with octanoic acid and tricaprylin, giving mono-octanoylfructose with yields ranging from 3.1 to 4.0 g l(-1).