Synthesis and Structure of 4-O,6-O-Glycosylidene Glycosides
摘要:
Interglycosidic spiro ortho esters (9-20) were efficiently prepared from methyl 2,6-di-O-benzylgluco-or galactopyranoside and various sugar lactones in the presence of methoxytrimethylsilane and a catalytic amount of trimethylsilyl triflate; All of the prepared sugar ortho esters possess perhydrospiro[2H-pyran-2,2'-pyrano[3,2-d] [1,3]dioxin] ring systems commonly in their molecules and, remarkably, were afforded as single isomers. The configurations of the spiro centers in their molecules were determined or estimated by X-ray single crystallographic analysis and molecular modeling studies. By comparing the conformations of prepared ortho esters, we revealed that the difference in the stability between two possible isomers was principally caused from that between the spiro ring systems in their molecules in each case.
Interglycosidic spiro ortho esters (9-20) were efficiently prepared from methyl 2,6-di-O-benzylgluco-or galactopyranoside and various sugar lactones in the presence of methoxytrimethylsilane and a catalytic amount of trimethylsilyl triflate; All of the prepared sugar ortho esters possess perhydrospiro[2H-pyran-2,2'-pyrano[3,2-d] [1,3]dioxin] ring systems commonly in their molecules and, remarkably, were afforded as single isomers. The configurations of the spiro centers in their molecules were determined or estimated by X-ray single crystallographic analysis and molecular modeling studies. By comparing the conformations of prepared ortho esters, we revealed that the difference in the stability between two possible isomers was principally caused from that between the spiro ring systems in their molecules in each case.
A Highly Stereoselective Construction of β-Glycosyl Linkages by Reductive Cleavage of Cyclic Sugar Ortho Esters
作者:Hiro Ohtake、Naoto Ichiba、Shiro Ikegami
DOI:10.1021/jo0005870
日期:2000.12.1
The preparation of beta-glycosides by the reductivecleavage of spiro sugar ortho esters is described in this report. This procedure is based on a concept completely different from those of other methods for glycosylation. Twelve sugar ortho esters that commonly possess perhydrospiro[2H-pyran-2,2'-pyrano[3,2-d][1,3]dioxin] ring systems in their molecules were reduced by LiAlH(4)/AlCl(3) or NaCNBH(3)/AlCl(3)