Synthetic Antigens: Synthesis of 4-Aminophenyl O-α-D-Mannopyranosyl-(1→2)-O-α-D-mannopyranosyl-(1→6)-O-α-D-Mannopyranoside and A Related Di- and A Trisaccharide

Abstract

4-Nitrophenyl 2,3-O-isopropylidine-α-D-mannopyranoside 2 was condensed with O-(2,3,4,6-tetra-O-acetyl-α-D-mannopyranosyl)-(1→2)-3,4,6-tri-O-acetyl-α-D-mannopyranosyl bromide 1 and 2,3,4,6-tetra-O-acetyl-α-D-mannopyranosyl bromide 11 in the presence of mercuric cyanide. Products were deprotected to yield, respectively, 4-nitrophenyl O-α-D-mannopyranosyl-(1→2)-O-α-D-mannopyranosyl-(1→6)-α-D-mannopyranoside 6 and 4-nitrophenyl O-α-D-mannopyranosyl-(1→6)-α-D-mannopyranoside 14. The 4-nitrophenyl group of 6 was reduced to give title trisaccharide. Bromide 1 was also condensed with methyl 2,3,4-tri-O-benzyl-α-D-manopyranoside 3 in the presence of silver trifluoromethanesulfonate and tetramethylurea to give protected trisaccharide derivative which was deprotected to furnish, methyl O-α-D-mannopyranosyl-(1→2)-O-α-D-mannopyranosyl-(1→6)-α-D-mannopyranoside 10. The identities of all protected and deprotected compounds were supported by ¹H and ¹³C NMR spectral data.     

SYNTHESIS OF O-METHYLATED DISACCHARIDES RELATED TO EXCRETORY/ SECRETORY ANTIGENS OF TOXOCARA LARVAE[1]

The disaccharides 2-O-Me-α-L-Fucp-(1→2)-β-D-Galp-(1→OAllyl) 12, α-L-Fucp-(1→2)-4-O-Me-β-D-Galp-(1→OAllyl) 15, and 2-O-Me-α-L-Fucp-(1→2)-4-O-Me-β-D-Galp-(1→OAllyl) 18 have been synthesized. Glycosylation reactions were performed using ethyl 1-thiofucopyranosides as glycosyl donors and N-iodosuccinimide-triflic acid as the activating agent. The O-methylated disaccharides correspond to highly immunogenic O-glycan antigens occurring at the surface of Toxocara canis and Toxocara cati larvae.     

SYNTHESIS OF SIALYL-α-(2→3)-NEOLACTOTETRAOSE DERIVATIVES MODIFIED AT C-2 OF THE N-ACETYLGLUCOSAMINE RESIDUE: PROBES FOR INVESTIGATION OF ACCEPTOR SPECIFICITY OF HUMAN α-1,3-FUCOSYLTRANSFERASES,FUC-TVII,AND FUC-TVI *

A variety of sialyl-α-(2→3)-neolactotetraose (IV³NeuAcnLcOse₄ or IV³NeuGcnLcOse₄) derivatives (23, 31–37, 58–60) modified at C-2 of the GlcNAc residue have been synthesized. The phthalimido group at C-2 of GlcNAc in 2-(trimethylsilyl)ethyl (3,6-di-O-benzyl-2-deoxy-2-phthalimido-β-d-glucopyranosyl)-(1→3)-(2,4,6-tri-O-benzyl-β-d-galactopyranosyl)-(1→4)-2,3,6-tri-O-benzyl-β-d-glucopyranoside (5) was systematically converted to a series of acylamino groups, to give the per-O-benzylated trisaccharide acceptors (6–11). On the other hand, modification of the hydroxyl group at C-2 of the terminal Glc residue in 2-(trimethylsilyl)ethyl (4,6-O-benzylidene-β-d-glucopyranosyl)-(1→3)-(2,4,6-tri-O-benzyl-β-d-galactopyranosyl)-(1→4)-2,3,6-tri-O-benzyl-β-d-glucopyranoside (42) gave three different kinds of trisaccharide acceptors containing D-glucose (49), N-acetyl-d-mannosamine (50), and D-mannose (51) instead of the GlcNAc residue. Totally ten trisaccharide acceptors (5–11 and 49–51) were each coupled with sialyl-α-(2→3)-galactose donor 12 to afford the corresponding pentasaccharides (14–21 and 52–54) in good yields, respectively, which were then transformed into the target compounds. Acceptor specificity of the synthetic sialyl-α-(2→3)-neolactotetraose probes for the human α-(1→3)-fucosyltransferases, Fuc-TVII and Fuc-TVI, was examined.     

Mimics of the Structural Elements of Type III Group B Streptococcus Capsular Polysaccharide. Part I: Synthesis of a Carboxylate-Containing Pentasaccharide

Abstract

A carboxylate-containing pentasaccharide, methyl O-(β-d-galactopyranosyl)-(1→4)-O-(β-d-glucopyranosyl)-(1→6)-O-{3-O-[(S)-1-carboxyethyl]-β-d-galactopyranosyl-(1→4)-O}-(2-acetamido-2-deoxy-β-d-glucopyranosyl)-(1→3)-β-d-galactopyranoside (27) was synthesized by block condensation of suitably protected donors and acceptors. Phenyl 3-O-benzyl-4,6-di-O-chloroacetyl-2-deoxy-2-phthalimido-1-thio-β-d-glucopyranoside (17) was condensed with methyl 2,4,6-tri-O-benzyl-β-d-galactopyranoside (4) to afford a disaccharide, methyl O-(3-O-benzyl-4,6-di-O-chloroacetyl-2-deoxy-2-phthalimido-β-d-glucopyranosyl)-(1→3)-2,4,6-tri-O-benzyl-β-d-galactopyranoside (18). Removal of chloroacetyl groups gave 4,6-diol, methyl 0-(3-O-benzyl-2-deoxy-2-phthalimido-β-d-glucopyranosyl)-(1→3)-2,4,6-tri-O-benzyl-β-d-galactopyranoside (19), in which the primary hydroxy group (6-OH) was then selectively chloroacetylated to give methyl O-(3-O-benzyl-6-O-chloroacetyl-2-deoxy-2-phthalimido-β-d-glucopyranosyl)-(1→3)-2,4,6-tri-O-benzyl-β-d-galactopyranoside (20). This acceptor was then coupled with 2,4,6-tri-O-acetyl-3-O-[(S)-1-(methoxycarbonyl)ethyl]-α-d-galactopyranosyl trichloroacetimidate (14) to afford a trisaccharide, methyl O-{2,4,6-tri-O-acetyl-3-O-[(S)-l-(methoxycarbonyl)ethyl]-β-d-galactopyranosyl}-(1→4)-O-(3-O-benzyl-6-O-chloroacetyl-2-deoxy-2-phthalimido-β-d-glucopyranosyl)-(1→3)-2,4,6-tri-O-benzyl-β-d-galactopyranoside (21). Removal of the 6-O-chloroacetyl group in 21 gave 22, which was coupled with 4-O-(2,3,4,6-tetra-O-acetyl-β-d-galactopyranosyl)-2,3,6-tri-O-acetyl-α-d-glucopyranosyl trichloroacetimidate (23) to yield protected pentasaccharide 24. Standard procedures were used to remove acetyl groups and the phthalimido group, followed by N-acetylation, and debenzylation to yield pentasaccharide 27 and a hydrazide by-product (28) in a 5:1 ratio, respectively. Compound 27 contains a complete repeating unit of the capsular polysaccharide of type III group B Streptococcus in which terminal sialic acid is replaced by an (S)-1-carboxyethyl group.     

Syntheses of P-Nitrophenyl 6-O-α- and 6-O-β-D-Xylopyranosyl-β-D-glucopyranoside

Condensation of p-nitrophenyl 2,3,4-tri-O-benzoyl-β-D-glucopyranoside 3 with 2,3,4-tri-O-(chlorosulfonyl)-β-D-xylopyranosyl chloride by the Koenigs-Knorr method afforded the α-linked product in a high yield. Dechlorosulfation with sodium iodide and debenzoylation by the Zemplen method gave crystalline p-nitrophenyl 6-O-(α-D-xylopyranosyl)-β-D-glucopyranoside 7.

Compound 3 was condensed with 2,3,4-tri-O-benzoyl-α-D-xylopyranosyl bromide in the presence of mercury (II) cyanide in acetonitrile, and after debenzoylation, crystalline p-nitrophenyl 6-O-(β-D-xylopyranosyl)-β-D-glucopyranoside 10 was obtained.     

Syntheses of β-Mannopyranosedes by Enzymatic Approaches

Abstract

The transmannosylation activity of β-mannosidase from snail and β-galactosidase from Aspergillus oryzae was used for the synthesis of methyl, ethyl, 1-propyl, 2-propyl, 1-butyl, 2-butyl, 1-hexyl, cyclohexyl, and 1-octyl β-D-mannopyranosides (3a-i), respectively. The regioisomeric specificities and wide substrate acceptance of this galactosidase are demonstrated. Thus, 4-nitrophenyl 4-O-(α-D-glucopyranosyl)-β-D-glucopyranoside (6), 4-nitrophenyl 2-O-(β-D-glucopyranosyl)-β-D-glucopyranoside (7), 4-nitrophenyl 2-deoxy-2N-acetyl-6-O-(2-deoxy-2-N-acetyl-β-D-glucopyranosyl)-β-D-glucopyranoside(8),4-nitropheny 13-O-(β-D-mannopyranosyl)-α-D-mannopyranoside (9), and 4-nitrophenyl 4-O-(β-D-mannopyranosyl)-β-D-mannopyranoside (10) were prepared by chemoenzymatic self-transfer reaction.     

Solid‐Phase Synthesis of Sialyl Tn Antigen

Solid‐phase synthesis of sialyl Tn [α‐Neu5Ac‐(2→6)‐α‐GalNAc‐(1→O)‐Ser] antigen with Kenner's acylsulfonamide linker is described. The acylsulfonamide bond was found to be stable under glycosylation reactions using dimethyl(methylthio)sulfonium triflate (DMTST) as a promoter and basic conditions used for the removal of protecting groups. The solid‐phase reaction was monitored by the inverse gated decoupling ¹³C NMR technique, which enabled quantitative analysis of the reaction progress. At the end of the synthesis, the sulfamyl group of the linker was activated by treatment with (trimethylsilyl)diazomethane to provide a N‐methyl‐N‐acylsulfonamide. The acyl group was displaced with hydroxide to give the corresponding precursors of sialyl Tn antigen and its anomeric isomers, which were deprotected to afford the target molecules.