Enzymatic synthesis of thioglucosides using almond ß-glucosidase

A selection of different glycosidases was screened for the glycosylation of 1-propanethiol. The g-glucosidases from almond, Aspergillus niger and Caldocellum saccharolyticum were capable of 1-propanethioglucoside (1-PTG) formation. The almond g-glucosidase showed the highest activity in this reversed hydrolysis type of reaction using glucose as glucosyl donor. Besides 1-propanethiol, also thioglucosides of 2-propanethiol and furfuryl mercaptan were formed by the almond g-glucosidase. The substrate specificity of the almond g-glucosidase with respect to thioglucosylation is restricted to primary and secondary aliphatic thiols. Once the thioglucosides are formed, they are not hydrolyzed at a significant rate by almond g-glucosidase. As a consequence the synthesis of 1-PTG could be observed at very low aglycone concentrations (0.5␟/v based on the reaction solution) and high yields (68␋ased on 1-PT and 41␋ased on glucose) were obtained. An excess of aglycone, otherwise frequently applied in reversed hydrolysis glycosylation, is therefore not necessary in the glucosylation of 1-PT.