A new method for the construction of the β-D-ManNAcp-(1→4)-D-Glc framework from lactose avoiding the β-mannosaminylation step was developed starting from 4-O-(2-acetamido-2-deoxy-3,4-O-isopropylidene-6-O-trityl-β-D-talopyranosyl)-2,3:5,6-di-O-isopropylidene-aldehydo-D-glucose di-Me acetal, obtained from 6'-O-triyl-triacetonelactose di-Me acetal. After preliminary modification of the protecting groups on the β-D-talosamine unit into the 3',6'-di-O-benzyl deriv., a new stereoselective protocol of C-4' epimerization was applied using: a regioselective dehydration providing the 4'-deoxyhex-3'-eno deriv. through a simultaneous activation-elimination reaction with NaH-sulfuryldiimidazole system; followed by its regio- and stereoselective hydroboration-oxidn to give the protected β-D-mannosamine disaccharide, with an overall 64% yield. The completely deprotected β-D-ManNAcp-(1→4)-D-Glc disaccharide was, finally, obtained with high yield, as an about 45:55 mixt. of α- and β-pyranose forms, through catalytic debenzylation followed by acid hydrolysis of the protected β-D-mannosamine disaccharide.
A new preparation of the disaccharide beta-D-ManNAcp-(1-->4)-D-Glc from lactose through a highly stereoselective beta-D-Galp to beta-D-ManNAcp transformation
CATELANI, GIORGIO;D'ANDREA, FELICIA;
2004-01-01
Abstract
A new method for the construction of the β-D-ManNAcp-(1→4)-D-Glc framework from lactose avoiding the β-mannosaminylation step was developed starting from 4-O-(2-acetamido-2-deoxy-3,4-O-isopropylidene-6-O-trityl-β-D-talopyranosyl)-2,3:5,6-di-O-isopropylidene-aldehydo-D-glucose di-Me acetal, obtained from 6'-O-triyl-triacetonelactose di-Me acetal. After preliminary modification of the protecting groups on the β-D-talosamine unit into the 3',6'-di-O-benzyl deriv., a new stereoselective protocol of C-4' epimerization was applied using: a regioselective dehydration providing the 4'-deoxyhex-3'-eno deriv. through a simultaneous activation-elimination reaction with NaH-sulfuryldiimidazole system; followed by its regio- and stereoselective hydroboration-oxidn to give the protected β-D-mannosamine disaccharide, with an overall 64% yield. The completely deprotected β-D-ManNAcp-(1→4)-D-Glc disaccharide was, finally, obtained with high yield, as an about 45:55 mixt. of α- and β-pyranose forms, through catalytic debenzylation followed by acid hydrolysis of the protected β-D-mannosamine disaccharide.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
