SYNTHESIS OF SOME MONODEOOXYFLUORINATED METHYL AND 4-NITROPHENYL α-D-MANNOBIOSIDES AND A RELATED 4-NITROPHENYL α-D-MANNOTRIOSIDE

Article abstract of DOI:10.1016/0008-6215(90)84297-8

Treatment of methyl 3,4,6-tri-O-benzyl-2-O-(2,3,4-tri-O-acetyl-α-D-mannopyranosyl)-α-D-mannopyranoside with N,N-diethylaminosulfur trifluoride (Et2NSF3), followed by O-deacetylation and catalytic hydrogenolysis, afforded methyl 2-O-(6-deoxy-6-fluoro-α-D-mannopyranosyl)-α-D-mannopyranoside (8).Methyl 6-deoxy-6-fluoro-2-O-α-D-mannopyranosyl-α-D-mannopyranoside (11) was similarly obtained from methyl 3-O-benzyl-2-O-(2,3,4,6-tetra-O-acetyl-α-D-mannopyranosyl-α-D-mannopyranoside. 1,2,3,4-Tetra-O-acetyl-6-deoxy-6-fluoro-β-D- mannopyranose (13), used for the sythesis of the 4-nitrophenyl analogs of 8 and 11, as well as their 3-O-linked isomers, was obtained by treatment of 1,2,3,4-tetra-O-acetyl-β-D-mannopyranose with Et2NSF3.Treatment of 13 with 4-nitrophenol in the presence of tin(IV) chloride, followed by sequential O-deacetylation, isopropylidenation, acetylation, and cleavage of the acetal group, afforded 4-nitrophenyl 4-O-acetyl-6-deoxy-6-fluoro-α-D-mannopyranoside (18).Treatment of 13 with HBr in glacial acetic acid furnished the 6-deoxy-6-fluoro bromide 19.Glycosylation of diol 18 with 20 gave 4-nitrophenyl 4-O-acetyl-6-deoxy-6-fluoro-3-O-(21) and -2-O-(2,3,4,6-tetra-O-acetyl-α-D-mannopyranosyl)-α-D-mannopyranoside (23) in the ratio of ca. 2:1, together with a small proportion of a branched trisaccharide. 4-Nitrophenyl 4,6-di-O-acetyl-α-D-mannopyranoside was similarly glycosylated with bromide 19 to give 4-nitrophenyl 4,6-di-O-acetyl-3-O- and -2-O-(2,3,4-tri-O-acetyl-6-deoxy-6-fluoro-α-D-mannopyranosyl)-α-D-mannopyranoside.The various di- and tri-saccharides were O-deacetylated by Zemplen transesterification.