Scope and limitation of the application of the (methoxydimethyl)methyl group in the synthesis of 2'-O-, 6'-O- and 2',6'-di-O-(alpha-L-arabinofuranosyl)-beta-D-galactopyranosyl- (1-->6)-D-galactoses.
For the characterisation of the anticipated epitope of an arabinogalactan, isolated from the extract of Echinacea purpurea, the trisaccharide alpha-L-Araf-(1-->2)-beta-D-Galp- (1-->6)-D-Gal was synthesized. The easily available 3,4-O-isopropylidene-6-O-(methoxydimethyl)methyl-beta-D-galactopyr anosyl- (1-->6)-1,2:3,4-di-O-isopropylidene-alpha-D-galactopyranose having the OH-2' free served as aglycone upon direct arabinosylation at the 2' position under Helferich conditions. The formed HgBr2 cleaved the acid sensitive protecting group at position 6', but under basic conditions the desired, fully protected trisaccharide, or its symmetrical dimerization derivative linked 6'- to 6'-position via an isopropylidene bridge, could be obtained. An alternative route involved arabinosylation of a hepta-O-acetylated digalactose with free OH-2'. Two other oligosaccharides, namely, alpha-L-Araf-(1-->6)-beta-D-Galp-(1-->6)-D-Gal and (alpha-L-Araf)2-(1-->2,6)-beta-D-Galp-(1-->6)-D-Gal were also synthesized and characterised.
Borbás
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Research Group for Carbohydrates, Hungarian Academy of Sciences, Debrecen, Hungary.
Jánossy
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L
Lipták
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D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D007202:Indicators and Reagents; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D009844:Oligosaccharides / Q000138:chemical synthesis* / Q000737:chemistry; D009904:Optical Rotation; D014312:Trisaccharides / Q000138:chemical synthesis* / Q000737:chemistry
D007202:Indicators and Reagents; D009844:Oligosaccharides; D014312:Trisaccharides