Methyl-Beta-Cyclodextrins: The Role of Number and Types of Substituents in Solubilizing Power

Methylated cyclodextrins (CDs) are effective solubilizers of poorly soluble organic compounds. In this work, we compared various methylated β-CDs concerning their structure characterized by nuclear magnetic resonance spectroscopy, composition analyzed by HPLC and solubilizing capability by using model compounds such as cholesterol, fatty acids, furosemide, tamoxifen, and amiodarone. All the commercially available methylated β-CDs are mixtures of various isomers and homologues except trimethyl β-CD. The effects of the degree of methylation, the composition, as well as the influence of further derivatization with ionic groups were studied. The number of methyl groups in a CD ring should be around 14 to get the highest solubility for the included guest molecules. Although the distribution of isomers and related compounds has hardly any effect at constant degree of substitution, the introduction of amino and succinyl moieties on the CD ring adds ionic interactions to the hydrophobic interactions of the inclusion complex formation, which might result in synergic effect in solubilization. © 2014 Wiley Periodicals, Inc. and the American Pharmacists Association.