Synthesis, characterization and potential application of monoacyl-cyclodextrins

Although the preparation of cyclodextrin (CD) monoesters with a variety of carboxylic acids has been already described in the literature, the direct regioselective CD acylation has proved to be critical, often requiring to be replaced with a more elaborate synthetic process. In this paper we describe the one-step preparation of several monoacylated CDs from acyclic or aromatic carboxylic acid derivatives. The ability of β-CD to enclose cupric ions in a sandwich-type manner was exploited to lead to high regioselectivity in the acylation of β-CD with benzoyl chloride, cinnamoyl chloride and phenyl acetyl chloride in water. Long chain aliphatic monoesters of α-, β- and γ-CD were best prepared in DMF. The results of our study showed that solvent and general conditions determined an overwhelming regioselectivity of acylation. 1H, 13C and 2D NMR experiments could easily discriminate the position of the ester. Monoacylated CDs were evaluated as a carrier of silibinin, the inclusion complexes were prepared and characterized by thermal analysis.