Selective acylation of monosaccharides using microbial cells

The microbially catalyzed esterification of different monosaccharides (gluc ose, 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 acyla ted, while little esterification was observed with the alpha-anomer. The ef fects of substrate concentration, temperature and solvent were studied in t he conversion catalyzed by R. oryzae with beta-glucose: 2.5 g l(-1) of mono ester were obtained starting from 5 g l(-1) of glucose and 50 g l(-1) of oc tanoic acid in acetonitrile at 50 degrees C. Interesterification was also s tudied. 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 octy l glucosides proceeded with interesting selectivity furnishing much higher yields with the beta-alkyl substrates. R. delemar and R, oryzae also cataly zed highly regioselective acylation of fructose with octanoic acid and tric aprylin, giving mono-octanoylfructose with yields ranging from 3.1 to 4.0 g l(-1).