The glycosyl-aldonolactone approach for the synthesis of beta-D-Galf-(1-->3)-D-Manp and 3-deoxy-beta-D-xylo-hexofuranosyl-(1-->3)-D-Manp.
A convenient synthesis of free beta-D-Galf-(1-->3)-D-Manp (8a) is reported. The disaccharide is present as external unit in the lipopeptidophosphoglycan (LPPG) of Trypanosoma cruzi and internally in the lipophosphoglycan (LPG) of Leishmania. Condensation of 2,5,6-tri-O-benzoyl-D-mannono-1,4-lactone (1) with 1,2,3,5,6-penta-O-benzoyl-D-galactofuranose, promoted by SnCl4, led to the beta-glycosyl-lactone, a key intermediate for disaccharide 8a, readily obtained by successive reduction of the lactone with diisoamylborane and debenzoylation. As in the LPG of Leishmania the HO-3 group of the galactofuranose is glycosylated by alpha-D-Galp, we also synthesized 3-deoxy-beta-D-xylo-hexofuranosyl-(1-->3)-D-Manp (8b) and p-nitrophenyl 3-deoxy-beta-D-xylo-hexofuranoside for studying the influence of HO-3 in the interaction with specific glycosidases. The disaccharide 8a, and its corresponding alditol, were good substrates for the beta-D-galactofuranosidase from Penicillium fellutanum, whereas the 3-deoxyglycosides were not hydrolyzed by the enzyme.
Marino
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CIHIDECAR, Departamento de Química Orgánica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Argentina.
Chiocconi
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A
Varela
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de Lederkremer
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RM
D002240:Carbohydrate Sequence; D004187:Disaccharides / Q000138:chemical synthesis*; D006026:Glycoside Hydrolases; D006028:Glycosphingolipids / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D008956:Models, Chemical; D008969:Molecular Sequence Data; D010407:Penicillium / Q000201:enzymology; D013379:Substrate Specificity; D001616:beta-Galactosidase / Q000378:metabolism*
C116178:3-deoxy-xylo-hexofuranosyl-(1-3)-Manp; D004187:Disaccharides; D006028:Glycosphingolipids; C008290:lipophosphonoglycan; D006026:Glycoside Hydrolases; C023112:exo-beta-D-galactofuranosidase; D001616:beta-Galactosidase