抄録
Oligosaccharides play a lot of important roles in biological processes and in pathology. While the automated synthesis of peptides and oligonucleotides was established decades ago, there have not been a general method for the synthesis of complex oligosaccharides. Recently the development of a broadly applicable synthetic strategy has been desired in this field. Here we wish to report the two efficient and practical strategies based on a one-pot sequential glycosidation and selective deprotection followed by glycosylation toward the automated synthesis of a oligosaccharide library. In the synthesis of heptasaccharide 3 having elicitor activity in soybean, we achieved a onepot 6-step glycosidation using a combination of different leaving groups, i.e., bromide (-Br), ethylthio group (-SEt), phenylthio group (-SPh), and fluoride (-F), with selective activators, AgOTf, MeOTf, DMTST, and HfCp_2(OTf)_2, respectively and differences of the reactivity of hydroxy groups of glycosyl acceptors. This method was applied to synthesize a library of tetra-, penta-, heptasaccharides using a manual synthesizer. For a study of the structure-activity relationship of elicitor active oligosaccharide in rice cell we demonstrated the synthesis of the oligosaccharide library having β(1→6) linkage at the various positions on β(1→3) tetrasaccharide backborn. Selective deprotection of three protecting groups (AOC, Lev, and Fmoc) of tetrasaccharide 4 was sequentially achieved to afford respective three mono-ols, three diols, and one triol, independently. Glycosylation of all glycosyl acceptors provided the corresponding oligosaccharides, respectively. These procedures were achieved on an automated synthesizer and by parallel column chromatography.
