Synthesis of methyl 3-O-α-d-galactopyranosyl-6-O-α-d-mannopyranosyl-α-d-mannopyranoside, methyl 3-O-α-d-glucopyranosyl-6-O-α-d-mannopyranosyl-α-d-mannopyranoside, methyl 6-O-α-d-galactopyranosyl-3-O-α-d-mannopyranosyl-α-d-mannopyranoside, and methyl 6-O-α-d-glucopyranosyl-3-O-α-d-mannopyranosyl-α-d-mannopyranoside

✍ Scribed by Per J. Garegg; Stefan Oscarson; Anna-Karin Tidén

• Publisher: Elsevier Science
• Year: 1990
• Tongue: English
• Weight: 437 KB
• Volume: 203
• Category: Article
• ISSN: 0008-6215
• DOI: 10.1016/0008-6215(90)80057-a

✦ Synopsis

The title trisaccharide glycosides were needed for studies of the interactions of &tins, receptor sites for bacteriophages with Salmonella lipopolysaccharide corespecificity, and correlation of n.m.r. chemical shifts and structure.

The methods used in the syntheses were conventional. Thus, 2,3,4,6-tetra-Obenzoyl-a-o-mannopyranosyl bromide' was reacted with methyl 2,3,4-tri-O-benzyl-a-D-mannopyranoside* in dichloromethane in the presence of silver triflate3*4 to yield the (l-6)-linked disaccharide derivative, catalytic hydrogenolysis of which gave 89% of 1.

Treatment of 1, first with trimethyl orthoacetate, then with acetic anhydride followed by acidic opening of the cyclic 2,3-orthoester', afforded 94% of methyl 2,4-di-O-acetyl-6-0-(2,3,4,6-tetra-O-benzoyl-a-~-mannopyranosyl)-a-~-mannopyranoside

(2). Glycosylation of the HO-3 of 2 with 2,3,4,6-tetra-O-benzyl-D-galactopyranosyl bro-mide6 under halide-assisted conditions' afforded 83% of the trisaccharide derivative 3, whereas the corresponding reaction of 2 with 2,3,4,6-tetra-O-benzyl-o-glucopyranosyl bromide' afforded 79% of 4. Deprotection of 3 and 4 then gave the first two of the title trisaccharides, 5 and 6.

Similarly, methyl 2-O-benzyl-4,6-O-benzylidene-a-~-mannopyranoside8~9 was glycosylated with tetra-O-benzoyl-a-D-mannopyranosyl bromide' in dichloromethane in the presence of silver triflate to yield 82% of the (143)-linked disaccharide derivative 7. Removal of the 4,6-0-benzylidene group of 7 by acid hydrolysis afforded 92% of 8. Selective glycosylation of HO-6 in 8 with 2,3,4,6-tetra-0-benzyl-D-galactopyranosyl * Owing to a computer error, a number of lines were not taken over from the original text at the bottom of the first page and on page 478 of this article as it was published in Volume 200. This replacement text provides the correct version.