Cyclodextrin chemistry. Selective modification of all primary hydroxyl groups of α- and β-cyclodextrins

摘要: Two efficient methods are described for the selective modification of all six primary hydroxyl groups α-cyclodextrin (α-CD, 11). One, using an indirect strategy, involves protection 18 functions as benzoate esters, followed by deprotection alcohol groups. The other, a direct activation via bulky triphenylphosphonium salt, which is then substituted azide anion reaction proceeds. A number modified derivatives have been prepared and fully characterized, among are: useful intermediate α-cyclodextrin-dodeca (2, 3) (3); hexakis (6-amino-6-deoxy)-α-cyclodextrin hexahydrochloride (7); (6-amino-6-deoxy)-dodeca 3)-O-methyl-α-cyclodextrin (9), hexa (6)-O-methyl-α-cyclodextrin (13). substitution shown to be even more β-cyclodextrin (16), giving heptakis (6-azido-6-deoxy)-β-CD-tetradeca 3)acetate (17), while strategy fails. compounds characterized extensive use 13C- 1H-NMR. spectroscopy. steric statistical problems polysubstitution reactions cyclodextrins discussed, possible reasons observed differences in reactivity between α- β-cyclodextrins examined. The dodecabenzoate 3 presents very marked solvent effect on physical properties (IR. NMR. spectra, optical rotation); effects may ascribed unusually strong intramolecular network hydrogen bonds severely distorts ring lowers symmetry from six-fold three-fold.