ABSTRACT
In recent decades, cyclomaltoheptaose (β-cyclodextrin or β-CD) has become a popular building block for the design and construction of molecular sensors, switchers, and delivery systems for drugs and genes. 1–6 This naturally occurring cyclooligosaccharide composed of seven α-(1→4)-linked d-glucopyranose units occurs as an inner hydrophobic cavity rimmed by two hydrophilic openings of different diameters. Such feature allows β-CD and its derivatives to form inclusion complexes in aqueous solution with a large variety of hydrophobic organic molecules of suitable size and geometry. 7,8 The chemical modification of β-CD can alter its properties, i.e., to improve its water solubility and its inclusion complexation ability. 9,10 Furthermore, selective chemical modifications allow the attachment of functional groups to provide biological, photochemical, catalytic, or redox properties. When functionalization of the secondary rim is intended, a common strategy is the silylation of the OH-6 groups as tert-butyldimethylsilyl (TBDMS) ether functions. The resulting heptakis(6-O-tert-butyldimethylsilyl)-β-CD (2) has been widely used for the subsequent mono-, hepta-, or tetradeca-functionalization of the secondary face of the macrocycle. 11–39 TBDMS ethers are fully compatible with strong basic conditions, and easily removed in the presence of fluorinated species. As an alternative, the TBDMS ether can be directly converted in high yields into the corresponding 6-bromo derivative by treatment with triphenylphosphine dibromide. 11,15,20,39–41
