SYNTHESIS OF P-TRIFLUOROACETAMIDOPHENYL 6-DEOXY-2-0-(3-0-[2-0-METHYL-3-0-(2-0-METHYL-ALPHA-D-RHAMNOPYRANOSYL)-ALPHA-L-FUCOPYRANOSYL]-ALPHA-L-RHAMNOPYRANOSYL)-ALPHA-L-TALOPYRANOSIDE - A SPACER ARMED TETRASACCHARIDE GLYCOPEPTIDOLIPID ANTIGEN OF MYCOBACTERIUM-AVIUM SEROVAR 20

The synthesis of the title tetrasaccharide glycoside 38 is reported. p-Nitrophenyl endo-3,4-O-benzylidene-6-deoxy-alpha-L.-talopyranoside (4), 3-O-acetyl-2,4.di-O-benzyl-alpha-L-rhamnopyranosyl trichloroacetimidate (7), methyl 3-O-acetyl-4-O-benzyl-2-O-methyl-1-thio-beta-L-fucopyranoside (15), 3-O-acetyl-4-O-benzyl-2-O-methyl-alpha-L-fucopyranosyl bromide (16), and ethyl 3-O-acetyl-4-O-benzyl-2-O-methyl-1-thio-alpha-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-l-thio-alpha-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.