Synthesis and properties of a New Familiy of Cyclodextrin Analogues

The chemical synthesis of a series of cyclic oligosaccharides built up from (1-->4)-linked alternating D- and L-pyranosidic units is described for the first time. Key intermediates employed were disaccharides representing minimal repeating units. These disaccharides ('monomers') have been prepared in specifically modified forms so that they bear both 'glycosyl donor' (cyanoethylidene group) and 'glycosyl acceptor' (trityloxy group) functions. Polycondensation-cyclisation of these disaccharide monomers, catalysed by TrClO(4) under normal conditions of dilution, has led to series of homologous cyclic oligosaccharides with an even number of sugar residues (6, 8, 10, 12, etc.) in each case. Cyclic hexa- and octa-saccharides, based on L-rhamnose and D-mannose as the alternating monosaccharides units, have been deprotected to produce analogues of alpha- and gamma-cyclodextrins (CDs) and the X-ray crystal structure of the cyclic octasaccharide has been determined.