ACID-CATALYZED HYDROLYSIS OF MALTOSYL-BETA-CYCLODEXTRIN

Maltosyl-beta-cyclodextrin was hydrolyzed via two pathways in acidic solution: (1) ring opening to give noncyclic oligosaccharides and (2) cleavage of maltose in the branched residue to give glucosyl-beta-CyD and glucose. Ring opening was approximately 2-3 times faster than maltose cleavage because of the multiple hydrolysis sites of the beta-cyclodextrin (beta-CyD) ring (seven glycosidic linkages) compared with only one reaction site of the maltose residue in the branch. Values of the enthalpy and entropy of activation of the hydrolyses were positive and in the range reported for maltose, a result indicating that the hydrolyses proceeded according to the A-1 mechanism (i.e., unimolecular decomposition). The alpha-1,6-glycosidic bond of branched beta-CyDs connecting beta-CyD and branched sugar moieties resisted hydrolysis; this property is a potential pharmaceutical advantage because the parent beta-CyD, which has low aqueous solubility, would not precipitate after hydrolysis.