Stereoselective entry into the d-GalNAc series starting from the d-Gal one: a new access to N-acetyl-d-galactosamine and derivatives thereof |
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Authors: | Lorenzo Guazzelli,Felicia D&rsquo Andrea,Alessia Giannarelli |
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Affiliation: | Dipartimento di Chimica Bioorganica e Biofarmacia, Università di Pisa, Via Bonanno, 33-I-56126 Pisa, Italy |
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Abstract: | A new stereoselective preparation of N-aceyl-d-galactosamine (1b) starting from the known p-methoxyphenyl 3,4-O-isopropylidene-6-O-(1-methoxy-1-methylethyl)-β-d-galactopyranoside (10) is described using a simple strategy based on (a) epimerization at C-2 of 10 via oxidation-reduction to give the talo derivative 11, (b) amination with configurational inversion at C-2 of 11 via a SN2-type reaction on its 2-imidazylate, (c) anomeric deprotection of the p-methoxyphenyl β-d-galactosamine glycoside 14, (d) complete deprotection. Applying the same protocol to 2,3:5,6:3′,4′-tri-O-isopropylidene-6′-O-(1-methoxy-1-methylethyl)-lactose dimethyl acetal (4), directly obtained through acetonation of lactose, the disaccharide β-d-GalNAcp-(1→4)-d-Glcp (1a) was obtained with complete stereoselectivity in good (40%) overall yield from lactose. |
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Keywords: | N-Acetyl- smallcaps" >d-galactosamine Amination with inversion Epimerization Lactose β- smallcaps" >d-Galactopyranosides |
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