Development of new methods for the synthesis of oligosaccharide and conformational analysis of oligosaccharide in aqueous solution

Elicitor-active hexa-beta-D-glucopyranosyl-D-glucitol (1) (oligosaccharin), isolated from mycelial wall of Phytophthora megasperma f. sp. glycinea, induces antibiotic phytoalexin accumulation in soybeans. Our interests associated with the elicitor-active oligosaccharide are to develop a new synthetic method for the oligosaccharin and to elucidate three dimensional structure of the oligosaccharin in water. Synthesis of the oligosaccharides has made considerable progress as a result of the development of new glycosyl donors and glycosylation reagents. However, only a few methodologies directed to the synthesis of oligosaccharides has been developed. In the first part of this report we describe a development of a new one-pot glycosylation methodology that allows us to construct two glycosidic linkages sequentially in one-pot operations, and its application to the synthesis of an elicitor-active hexaglucoside 2. In the second part, we describe the development of a protocol for revealing the stable conformation of oligosaccharide in aqueous solution based on AMBER(united atom), GB/SA solvation model and NMR experiments. Its application to the conformational analyses of trisaccharide 41 and hexaglucoside 2 in water is also presented. In the last part we focused our attention on a remote glycosylation that allows us to form a branched trisaccharide in intramolecular fashion. The molecular design of the spacer molecule for the remote glycosylation was examined based on molecular mechanics calculations.