Synthesis of p-trifluoroacetamidophenyl 6-deoxy-2-O-3-O- [2-O-methyl-3-O-(2-O-methyl-α-d-rhamnopyranosyl)- α-l-fucopyranosyl]-α-l-rhamnopyranosyl-α-l- talopyranoside: a spacer armed tetrasaccharide glycopeptidolipid antigen of Mycobacterium avium serovar 20

Add time:08/28/2019    Source:sciencedirect.com

The synthesis of the title tetrasaccharide glycoside 38 is reported. p-Nitrophenyl endo-3,4-O-benzylidene-6-deoxy-α-l-talopyranoside (4, 3-O-acetyl-2,4-di-O-benzyl-α-l-rhamnopyranosyl trichloroacetimidate (7), methyl 3-O-acetyl-4-O-benzyl-2-O-methyl-1-thio-β-l-fucopyranoside (15) 3-O-acetyl-4-O-benzyl-2-O-methyl-α-l-fucopyranosyl bromide (16), and ethyl 3-O-acetyl-4-O-benzyl-2-O-methyl-1-thio-α-d-rhamnopyranoside (33) were prepared as intermediates. Compound 4 was glycosylated with imidate 7 as well as with methyl 3-O-acetyl-2,4-di-O-benzyl-1-thio-α-l-rhamnopyranoside (9), affording the same disaccharide derivative 8. Deacetylation of 8 gave crystalline 17. Condensation of 17 with both fucosyl donors 15 and 16 yielded the same trisaccharide derivative 18 stereoselectively. Compound 18 was also prepared by the coupling of 4 with disaccharide glycosyl donor 20. After deacetylation of 18 (→ 34), methyl triflate-promoted glycosylation with compound 33 resulted in tetrasaccharide 35. Conversion of the p-nitrophenyl group of 35 into the p-trifluoroacetamidophenyl group (→ 36) and removal of the protecting groups gave the title tetrasaccharide glycoside 38.

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