The synthesis of the per-3,6-anhydro derivatives of α- and β-cyclodextrins (CDs) is described starting from the corresponding per-6-tosylates. These could only be obtained as pure compounds following repeated HPLC under reversed-phase conditions of the crude products isolated after tosylation of α-CD and β-CD in pyridine with p-toluenesulfonyl chloride. Treatment of the per-6-O-tosyl-α- and β-CDs with warm aqueous sodium hydroxide solutions (50-60 °C) afforded the per-3,6-anhydro-α- and β-CDs in good yields. The development of an alternative and successful strategy for the synthesis of per-3,6-anhydro-α-CD from the known per-2,3-di-O-benzoyl-6-O-tosyl-α-CD relies upon the use of triethylamine as base in refluxing aqueous methanol. The per-3,6-anhydro-CDs have been fully characterized by FABMS and NMR spectroscopy. Their specific optical rotations, which are solvent dependent, confirm the chiral nature of these molecules. The anhydrides are soluble in such widely different solvents as dichloromethane and water. There is evidence from FABMS that per-3,6-anhydro-α-CD forms a complex with the triethylammonium cation while per-3,6-anhydro-β-CD solubilizes nitrobenzene in deuterium oxide solutions.
ASJC Scopus subject areas
- Organic Chemistry