Synthesis of galactofuranose disaccharides of biological significance.
Methyl beta-D-galactofuranoside was readily obtained by tin(IV) chloride-catalyzed glycosylation of penta-O-benzoyl-alpha,beta-D-galactofuranose, followed by debenzoylation with sodium methoxide. Glycosylation of 1 with 2,3,5-tri-O-benzoyl-D-galactono-1,4-lactone or with the 6-O-trityl-lactone derivative 5 gave the benzoylated beta-D-galactofuranosyl-(1----6)-D-galactono-1,4-lactone 6 in excellent yield. The structure of disaccharide 6 was confirmed by borohydride reduction to the glycosyl-alditol 7. A byproduct of the condensation reaction of 1 with 4 or 5 was identified as the benzoylated (1----1)-beta,beta'-D-galactofuranosyl disaccharide 8. Compound 8 was readily prepared (88% yield) by controlled addition of water to 1, in the presence of stannic chloride. O-Debenzoylation of 8 afforded crystalline beta'-D-galactofuranosyl-(1----1)-beta-D-galactofuranoside. The glycosyl-lactone 6 constitutes a key intermediate for the synthesis of a disaccharide derivative having both units in the furanoid form. Thus, diisoamylborane reduction of the lactone function of 6 led to the disaccharide derivative 10, from which the methyl glycoside 12 was prepared. O-Debenzoylation of 12 gave the corresponding methyl beta-D-galactofuranosyl-(1----6)-beta-D-galactofuranoside. The free disaccharide beta-D-Galf-(1----6)-D-Galp and its acetylated derivative were also synthesized from 10.
Marino
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Departamento de Química Orgánica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Argentina.
Varela
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de Lederkremer
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RM
D002236:Carbohydrate Conformation; D055598:Chemical Phenomena; D002621:Chemistry; D004187:Disaccharides / Q000138:chemical synthesis*; D005690:Galactose; D005697:Galactosides; D006027:Glycosides; D006031:Glycosylation; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D009166:Mycobacterium leprae / Q000032:analysis; D009169:Mycobacterium tuberculosis / Q000032:analysis; D009176:Mycoplasma mycoides / Q000032:analysis; D010084:Oxidation-Reduction
D004187:Disaccharides; D005697:Galactosides; D006027:Glycosides; D005690:Galactose