The synthesis and structural mapping of unsymmetrical chemically modified α-cyclodextrins by high-field nuclear magnetic resonance spectroscopy

Abstract

Hexakis(2,3-di-O-methyl-6-deoxy-6-iodo)-α-cyclodextrin (I-DMαCD) was prepared from hexakis(2,3-di-O-methyl)-αCD (DMαCD) using iodine and triphenylphosphine. The subsequent attempted substitution of I-DMαCD with the phenoxide anions of either 4-hydroxybenzyl alcohol or 4-benzyloxyphenol produced unexpected products. These products were found to be a result of an elimination reaction involving one of the iodomethyl groups to produce one 6-deoxyhex-5-eno-D-glucopyranoside residue within the DMαCD structure in addition to the substitution of the other five iodomethyl groups either by (4-hydroxymethyl)phenyl or by (4-benzyloxy)phenyl ether functions, respectively. The products have been characterised fully using high resolution positive-ion FABMS and high resolution ¹H and ¹³C NMR spectroscopies.