Stereocontrolled synthesis of sialyl Lewis X ceramide consisting of a pentasaccharide recognized by the selectin family

Convenient enzymatic synthesis of a p-nitrophenyl oligosaccharide series of sialyl N-acetyllactosamine, sialyl Lex and relevant compounds

From the beta-D-Gal-(1-->4)-beta-D-GlcNAc-OC6H4NO2-p (1) prepared by the transglycosylation of beta-galactosidase from Bacillus circulans, alpha-D-Neu5Ac-(2-->3)-beta-D-Gal-(1-->4)-beta-D-GlcNAc-OC6H4NO2-p (9) and alpha-D-Neu5Ac-(2-->6)-beta-D-Gal-(1-->4)-beta-D-GlcNAc-OC6H4NO2-p (10) were effectively synthesized with an equimolar ratio of CMP-Neu5Ac by recombinant rat alpha-(2-->3)-N-sialyltransferase and rat liver alpha-(2-->6)-N-sialyltransferase, respectively. The former enzyme also transferred effectively the Neu5Ac residue from CMP-Neu5Ac to the location of OH-3 in the non-reducing terminal of beta-D-Gal-(1-->4)-beta-D-Gal-OC6H4NO2-p or beta-D-Gal-(1-->4)-beta-D-Gal-(1-->4)-beta-D-GlcNAc-OC6H4NO2-p, while the latter enzyme did not. In the case of equimolar ratio of GDP-Fuc/acceptor, 1 and 9 were further fucosylated quantitatively to form beta-D-Gal-(1-->4)-beta-D-(alpha-l-Fuc-(1-->3)-)-GlcNAc-OC6H4NO2-p (14) and alpha-D-Neu5Ac-(2-->3)-beta-D-Gal-(1-->4)-beta-D-(alpha-l-Fuc-(1-->3)-)-GlcNAc-OC6H4NO2-p (13) by recombinant human alpha-(1-->3)-fucosyltransferase VII, respectively.

Oligosaccharide microarrays for high-throughput detection and specificity assignments of carbohydrate-protein interactions

We describe microarrays of oligosaccharides as neoglycolipids and their robust display on nitrocellulose. The arrays are obtained from glycoproteins, glycolipids, proteoglycans, polysaccharides, whole organs, or from chemically synthesized oligosaccharides. We show that carbohydrate-recognizing proteins single out their ligands not only in arrays of homogeneous oligosaccharides but also in arrays of heterogeneous oligosaccharides. Initial applications have revealed new findings, including: (i) among O-glycans in brain, a relative abundance of the Lewis(x) sequence based on N-acetyllactosamine recognized by anti-L5, and a paucity of the Lewis(x) sequence based on poly-N-acetyllactosamine recognized by anti-SSEA-1; (ii) insights into chondroitin sulfate oligosaccharides recognized by an antiserum and an antibody (CS-56) to chondroitin sulfates; and (iii) binding of the cytokine interferon-gamma (IFN-gamma) and the chemokine RANTES to sulfated sequences such as HNK-1, sulfo-Lewis(x), and sulfo-Lewis(a), in addition to glycosaminoglycans. The approach opens the way for discovering new carbohydrate-recognizing proteins in the proteome and for mapping the repertoire of carbohydrate recognition structures in the glycome.

Synthesis of deoxygalactose-containing sialyl Le(X) ganglioside analogues to elucidate the structure necessary for selectin recognition

Sialyl Lewis X ganglioside analogues containing 4-deoxy-, 6-deoxy-, and 4,6-dideoxy-D-galactopyranose in place of D-galactopyranose have been synthesized. Glycosylations of 2-(trimethylsilyl)ethyl 2,6-di-O-benzyl-beta-D-galactopyranoside and 2-(trimethylsilyl)ethyl beta-D-fucopyranoside with the phenyl 2-thioglycoside derivative of sialic acid, using N-iodosuccinimide (NIS)-trifluoromethanesulfonic acid (TfOH) as the promoter in acetonitrile, gave the desired 2-(trimethylsilyl)ethyl sialyl-alpha-2-->3)-beta-D-galactopyranoside and -beta-D-fucopyranoside, respectively. The sialylgalactose derivative obtained was then modified to 4-deoxy and 4,6-dideoxy derivatives. These were converted, by O-benzoylation, transformation of the 2-(trimethylsilyl)ethyl group to trichloroacetimidates, and introduction of the methylthio group with methylthiomethylsilane, into the corresponding glycosyl donors, which were then coupled with 2-(trimethylsilyl)ethyl O-(2,3,4-tri-O-benzyl-alpha-L-fucopyranosyl)-(1->3)-O-(2-acetamido-6-O- benzyl-2-deoxy-beta-D-glucopyranosyl)-(1->3)-2,4,6-tri-O-benzyl-beta-D- galactopyranoside in the presence of dimethyl(methylthio)sulfonium triflate (DMTST). The resulting pentasaccharides were each converted to the corresponding alpha-trichloroacetimidates, which, on coupling with (2S, 3R, 4E)-2-azido-3-O-benzoyl-4-octadecene-1,3-diol, gave the desired sphingosine derivatives. Selective reduction of the azide group, N-acylation with octadecanoic acid, O-deacylation, and saponification of the methyl ester afforded the target compounds.

Synthesis of sialyl Lewis X ganglioside analogues containing modified L-fucose residues

Sialyl Le(x) ganglioside analogues containing 2-epi-, 2,3-di-epi-, 4-epi-, and 2-O-methyl-L-fucose in place of the L-fucose residue have been synthesized. Glycosylation of 2-(trimethylsilyl)ethyl O-(2-acetamido-4,6-O-benzylidene-2-deoxy-beta-D-glucopyranosyl)-(1-->3)- 2,4,6- tri-O-benzyl-beta-D-galactopyranoside with the methyl 1-thioglycoside derivatives of the respective fucose analogues, using dimethyl(methylthio)sulfonium triflate (DMTST) as a promoter, gave the corresponding protected 2-(trimethylsilyl)ethyl deoxy-alpha-L-hexopyranosyl-(1-->3)-O-(2- acetamido-2-deoxy-beta-D-glucopyranosyl)-(1-->3)-beta-D-galactopyrano sid es. These were transformed by reductive ring-opening of their benzylidene acetal groups into the glycosyl acceptors. Dimethyl (methylthio)sulfonium triflate-promoted glycosylation of these compounds with methyl O-(methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D-glycero-alpha-D-galacto -2- nonulopyranosylonate)-(2-->3)-2,4,6-tri-O-benzoyl-1-thio-beta-D- galactopyranoside afforded the desired pentasaccharides, which were converted via reductive removal of their benzyl groups, O-acetylation, selective removal of the 2-(trimethylsilyl)ethyl group, and reaction with trichloroacetonitrile, into the corresponding alpha-tri-chloroacetimidates. Glycosylation of (2S,3R,4E)-2-azido-3-O-benzoyl-4-octadecene-1,3-diol these in the presence of boron trifluoride etherate afforded the expected beta-glycosides, which were transformed in good yields, via selective reduction of the azido group, coupling with octadecanoic acid, O-deacylation, and deesterification, into the target gangliosides. The 2-(trimethylsilyl)ethyl glycosides of sialyl Le(x) oligosaccharides containing modified fucose were also prepared from the intermediates of the ganglioside synthesis.

Synthesis of the methyl thioglycosides of 2-, 3-, and 4-deoxy-L-fucose

Methyl thioglycoside derivatives of 2-, 3-, and 4-deoxy-L-fucopyranose have been prepared as glycosyl donors for the synthesis of sialyl Le(x) ganglioside analogues containing modified alpha-L-fucopyranose residues. Reductive dethioacylation of 2-(trimethylsilyl)ethyl 3,4-di-O-benzoyl-2-O-(phenoxy)thiocarbonyl-beta-L-fucopyranoside, prepared from L-fucose in eight steps, gave the 2-deoxy compound, which was transformed via selective removal of the 2-(trimethylsilyl)ethyl group, subsequent acetylation, and displacement of the 1-acetoxy group by a methylthio group, into methyl 3,4-di-O-benzoyl-2,6-dideoxy-1-thio- alpha,beta-L-lyxo-hexopyranoside (11). 2-(Trimethylsilyl)ethyl 2,4-di-O-benzoyl-3-O-(phenoxy)thiocarbonyl-beta- L-fucopyranoside, prepared from the unsubstituted glycoside in four steps, and 2-(trimethylsilyl)ethyl 2,3-di-O-benzoyl-4-O-(phenoxy)thiocarbonyl-beta-L-fucopyranoside, similarly prepared in two steps, were transformed via reduction of the (phenoxy)thiocarbonyloxy group, selective removal of the 2-(trimethylsilyl)ethyl group, O-acetylation, displacement of the 1-acetoxy group by a methylthio group as described for 11, and finally replacement of the benzoyl groups by benzyl groups, into the analogous, protected methyl 3- and 4-deoxy-1-thio-beta-L-fucopyranosides.

Synthesis of deoxy-L-fucose-containing sialyl Lewis X ganglioside analogues

Sialyl Lex ganglioside analogs containing 2-, 3-, and 4-deoxyfucose in the place of L-fucose have been synthesized. Glycosylation of 2-(trimethylsilyl)ethyl O-(2-acetamido-4,6-O-benzylidene-2-deoxy-beta-D-glucopyranosyl)-(1-->3)- 2,4,6-triO-benzyl-beta-D-galactopyranoside with the methyl 1-thioglycoside derivatives of the respective deoxyfucoses, using dimethyl(methylthio)sulfonium triflate (DMTST) as a promoter, gave the corresponding three protected 2-(trimethylsilyl)ethyl dideoxy-alpha-L-heoxpyranosyl-(1-->3)- O-2(acetamido-2-deoxy-beta-glucopyranosyl)-(1-->3)-beta-D-galactop yranosides. These were transformed by reductive ring-opening of their benzylidene acetal groups into the glycosyl acceptors 6, 8, and 10. Dimethyl(methylthio)sulfonium triflate promoted glycosylation of 6, 8, and 10 with methyl O-(methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D-glycero-alpha- D-galacto-2-nonulopyranosylonate)-(2-->3)-2,4,6-tri-O-benzoyl-1-th io-beta-D-galactopyranoside afforded the desired pentasaccharides, which were converted via reductive removal of their benzyl groups, O-acetylation, selective removal of the 2-(trimethylsilyl)ethyl group, and reaction with trichloroacetonitrile, into the corresponding alpha-trichloroacetimidates 14, 18, and 22. Glycosylation of (2S,3R,4E)-2-azido-3-O-benzoyl-4-octadecene-1,3-diol with 14, 18, and 22 in the presence of boron trifluoride etherate afforded the expected beta-glycosides, which were transformed in good yields, via selective reduction of the azido group, coupling with octadecanoic acid, O-deacylation, and deesterification, into the target compounds.

Synthesis of the globotetraose tetrasaccharide and terminal tri- and di-saccharide fragments

The 2-(trimethylsilyl)ethyl (TMSEt) beta-glycosides of globotetraose [beta-D-GalNAc-(1-->3)-alpha-D-Gal-(1-->4)-beta-D-Gal-(1-->4)-D-Glc] and the terminal trisaccharide, as well as the methyl alpha-glycoside 1 of the terminal disaccharide, were synthesised by silver trifluoromethanesulfonate-promoted beta-glycosylation of suitably protected galactoside, galabioside, and globotrioside alcohols with 3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-beta-D-galactopyranosyl chloride, followed by removal of protecting groups. Removal of the anomeric TMSEt group of the globotetraoside and of the terminal trisaccharide, using trifluoroacetic acid-dichloromethane, gave the corresponding hemiacetal sugars 8 and 3. The TMSEt glycoside of the terminal trisaccharide was converted, via the 1-acetate, into the corresponding isobutyl (4) and 3-butylsulfonyl-2-[(butylsulfonyl)methyl]propyl (5) glycosides and into the TMSEt thioglycoside 6 via the glycosyl bromide.

Synthesis of chemically modified sialic acid-containing sialyl-LeX ganglioside analogues recognized by the selectin family

Sialyl Lewis X ganglioside analogues containing 5-acetamido-3,5-dideoxy-L-arabino-2-heptulopyranosylonic acid (C7-Neu5Ac), 5-acetamido-3,5-dideoxy-D-galacto-2-octulopyranosylonic acid (C8-Neu5Ac), and 5-acetamido-3,5-dideoxy-L-glycero-D-galacto-1-2-nonulopyranosylonic++ + acid (8-epi-Neu5Ac) in place of N-acetylneuraminic acid (Neu5Ac) have been synthesized. Glycosylation of 2-(trimethylsilyl)ethyl 6-O-benzoyl-beta-D-galactopyranoside with the phenyl or methyl 2-thioglycoside derivatives of the respective sialic acids, using N-iodosuccinimide (NIS)-trifluoromethanesulfonic acid as a promoter in acetonitrile, gave the three required 2-(trimethylsilyl)ethyl (2S)-sialyl-(2-->3)-beta-galactopyranosides. These were converted via O-benzoylation, selective transformation of the 2-(trimethylsilyl)ethyl group to acetyl, and introduction of the methylthio group with methylthiotrimethylsilane into the corresponding glycosyl donors. Glycosylation of 2-(trimethylsilyl)ethyl O-(2,3,4-tri-O-benzyl-alpha-L-fucopyranosyl)-(1-->3)-O-(2-acetamido-6-O- benzyl- 2-deoxy-beta-D-glucopyranosyl)-(1-->3)-2,4,6-tri-O-benzyl-beta-D- galactopyranoside with these donors in the presence of dimethyl(methylthio)sulfonium triflate (DMTST) afforded the expected beta-glycosides, which were converted into the corresponding alpha-trichloroacetimidates, and these, on coupling with (2S, 3R, 4E)-2-azido-3-O-benzoyl-4-octadecene-1,3-diol, gave the required beta-glycosides. Finally, these were transformed via selective reduction of the azide group, condensation with octadecanoic acid, O-deacylation, and de-esterification into the target compounds in good yields.

Novel sulfated ligands for the cell adhesion molecule E-selectin revealed by the neoglycolipid technology among O-linked oligosaccharides on an ovarian cystadenoma glycoprotein

E-selectin is the inducible adhesion protein on the surface of endothelial cells which has a crucial role in the initial stages of recruitment of leucocytes to sites of inflammation. In addition, it is almost certainly involved in tumor cell adhesion and metastasis. This report is concerned with identification of a new class of oligosaccharide ligand--sulfate-containing--for the human E-selectin molecule from among oligosaccharides on an ovarian cystadenoma glycoprotein. This has been achieved by application of the neoglycolipid technology to oligosaccharides released from the glycoprotein by mild alkaline beta-elimination. Oligosaccharides were conjugated to lipid, resolved by thin-layer chromatography, and tested for binding by Chinese hamster ovary cells which had been transfected to express the full-length E-selectin molecule. Several components with strong E-selectin binding activity were revealed among acidic oligosaccharides. The smallest among these was identified by liquid secondary ion mass spectrometric analysis of the neoglycolipid, in conjunction with methylation analysis of the purified oligosaccharide preparation as an equimolar mixture of the Le(a)- and Le(x)/SSEA-1-type fucotetrasaccharides sulfated at position 3 of outer galactose: [formula: see text] To our knowledge this is the first report of a sulfofucooligosaccharide ligand for E-selectin. The binding activity is substantially greater than those of lipid-linked Le(a) and Le(x)/SSEA-1 sequences and is at least equal to that of the 3'-sialyl-Le(x)/SSEA-1 glycolipid analogue.