Dimethyl(methylthio)sulfonium Triflate Research Articles

ChemInform Abstract: A Facile Synthesis of 2-Deoxy-2,3-didehydroneuraminic Acid Derivatives.

The 2-thio- or 2-selenoglycosides of N-acetylneuraminic acid methyl ester were transformed by successive treatment with dimethyl(methylthio)sulfonium triflate (DMTST) and 1,8-diazabicyclo[5.4.0]-7-undecene (DBU) to give the corresponding methyl 2-deoxy-2,3-didehydroneuraminates in excellent yields. Their acids and their analogues are sialidase inhibitors of pharmaceutical interest.

Efficient Synthesis of Three Types of Sialyl 6-O-Sulfo Lewis X: Probes for the Comprehensive Search for the Interaction between Carbohydrates and Other Biomoleclues

Synthesis of three kinds of 6-O-sulfated sLe x glyco probes with their relevance to ligand processing pathway of L-selectin has been described. The glycosylation of the suitably protected hexasaccharide acceptor 6 with the sialyl-a-(2→3)-D-galactopyranosyl SMe donors (3 and 4) using dimethyl(methylthio)sulfonium triflate (DMTST), afforded the protected tetrasaccharides 7 and 8, respectively. Removal of all the benzyl protecting groups and the subsequent acetylation afforded the sLe x derivatives (9 and 10), which were converted to the target compounds (15 and 16) by the selective removal of 4-methoxyphenyl group, followed by 6-O-sulfation of the GlcNAc residue, and removal of all the protective groups under basic conditions. Finally 16 was lactamized with HBTU and HOBT, to give the desired target compound 17.

A Convenient Method for Regeneration of Free Thiol from a tert-Butyl Thioether

When dimethylmethylthiosulfonium triflate (DMTST) is added to a tert-butyl-protected thiol (RSt-Bu), the unsymmetrical disulfide RSSMe is formed. At this point the free thiol (RSH) can be obtained by the addition of trimethylphosphine and water. Most byproducts are small organic molecules that are easily removed.

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.

A facile synthesis of 2-deoxy-2,3-didehydroneuraminic acid derivatives.

The 2-thio- or 2-selenoglycosides of N-acetylneuraminic acid methyl ester were transformed by successive treatment with dimethyl(methylthio)sulfonium triflate (DMTST) and 1,8-diazabicyclo[5.4.0]-7-undecene (DBU) to give the corresponding methyl 2-deoxy-2,3-didehydroneuraminates in excellent yields. Their acids and their analogues are sialidase inhibitors of pharmaceutical interest.

Synthetic studies on glycosphingolipids from the parasite Echinococcus multilocularis

Novel neutral glycosphingolipids isolated from the metacestodes of Echinococcus multilocularis by Persat, may be expected to be involved in host–parasite interactions. We have synthesized these glycosphingolipid analogues containing 2-branched fatty alkyl residues in place of ceramide. The glycosylation of galactosyl donors 4 and 5 with each of the acceptors 2 and 11 in the presence of N-iodosuccinimide (NIS)/TfOH, and the glycosylation of fucosyl donor 13 with acceptors 12 and 20 in the presence of dimethyl(methylthio)sulfonium triflate (DMTST) gave the desired oligosaccharide derivatives at good yield. The fully per- O-acylated 2-(trimethylsilyl)ethyl glycosides 6, 15, 21, and 26 were converted to glycosylimidates 7, 16, 22, and 27, which were condensed with 2-(tetradecyl)hexadecanol and subsequently deacylated give four target glycosphingolipid analogues.

Total synthesis of a cholinergic neuron-specific ganglioside GT1a alpha: a high affinity ligand for myelin-associated glycoprotein (MAG).

An efficient total synthesis of a cholinergic neuron-specific ganglioside GT1a alpha (IV3NeuAcIII6NeuAcII3NeuAc-GgOse4Cer) is described. The suitably protected sialyl-alpha(2-->6)-gangliotriose (III6NeuAc-GgOse3) derivative was glycosylated with the phenyl 2-thioglycoside of sialic acid in the presence of N-iodosuccinimide (NIS) and trimethylsilyl trifluoromethane-sulfonate (TMSOTf) in acetonitrile medium, giving the disialogangliotriose (III6NeuAcII3NeuAc-GgOse3) derivative which contains both sialyl-alpha(2-->6)-GalNAc and sialyl-alpha(2-->3)-Gal structures (Route I). This pentasaccharide was efficiently synthesized also by the coupling of (methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D-glycero-alpha-D-galacto -2-nonulopyranosylonate)-(2-->6)-2-deoxy-3,4-O-isopropylidene-2-ph thalimido-D-galactopyranosyl trichloroacetimidate with 2-(trimethylsilyl)ethyl (methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D-glycero-alpha-D-galacto -2-nonulopyranosylonate)-(2-->3)-(2,6-di-O-benzyl-beta-D-galactopy ranosyl)-(1-->4)-2,3,6-tri-O-benzyl-beta-D-glucopyranoside, followed by conversion of the phthalimido group to the acetamido group (Route II). O-Deisopropylidenation and further glycosylation with methyl (methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D-glycero-alpha-D-gala ct-2-nonulopyranosylonate)-(2-->3)-2,4,6-tri-O-benzoyl-1-thio-b eta-D-galactopyranoside, promoted by dimethyl(methylthio)sulfonium triflate (DMTST), gave the desired trisialogangliotetraose (IV3NeuAcIII6NeuAcII3NeuAc-GgOse4) derivative, which was converted stepwise into the title ganglioside GT1a alpha by the introduction of the ceramide part and then complete deprotection. The ganglioside obtained was shown to be identical with the native GT1a alpha on TLC-immunostaining.

Synthetic Studies on Sialoglycoconjugates 104: Synthesis of Kdn-Lewis X Ganglioside Analogs Containing Modified Reducing Terminal and L-Rhamnose in Place of L-Fucose1 2

KDN-Lex ganglioside analogs (10, 13, 16 and 19) containing the modified reducing terminal and L-rhamnose in place of L-fucose have been synthesized. Glycosidation of methyl 2,3,4-tri-O-benzyl-1-thio-α-L-rhamnopyranoside (1) with 2-(trimethylsilyl)ethyl O-(2-acetamido-4,6-O-benzylidene-2-deoxy-β-D-glucopyranosyl)-(1→3)-O-(2,4,6-tri-O-benzyl-α-D-galacopyranoside (2), followed by reductive ring opening of the benzylidene acetal, gave 2-(trimethylsilyl)ethyl O-(2,3,4-tri-O-benzyl-α-L-rhamnopyranosyl)-(1→3)-O-(2-acet-amido-6-O-benzyl-2-deoxy-β-D-glucopyranosyl)-(1→3)-O-(2,4,6-tri-O-benzyl-β-D-galactopyranosyl)-(1→4)-2,3,6-tri-O-benzyl-β-D-glucopyranoside (4). The tetrasaccharide 4 was coupled with methyl O-(methyl 4,5,7,8,9-penta-O-acetyl-3-deoxy-D-glycero-α-D-galacto-2-nonulopyranosylonate)-(2→3)-2,4,6-tri-O-benzoyl-1-thio-β-D-galactopyranoside(5), using dimethyl(methylthio)sulfonium triflate (DMTST), to give the hexasaccharide 6, which was converted into compound 11 in the usual manner. Compounds 8 and 11 were transformed, via bromination of the reducing terminal, radical reduction, O-deacylation and saponification of the methyl ester, into the desired KDN-Lex hexasaccharides (10, 13). On the other hand, glycosylation of 2-(tetradecyl)hexadecanol with α-trichloroacetimidates 14 and 17, afforded the target ganglioside analogs 16 and 19. 1. Dedicated to the memory of Professor Akira Hasegawa. 2. For Part 103, see T. Ikami, T. Kakigami, K. Baba, H. Hamajima, T. Jomori, T. Usui, Y. Suzuki, H. Tanaka, H. Ishida, A. Hasegawa and M. Kiso, J. Carbohydr. Chem., in press.

Synthesis of sialyl Le x ganglioside analogues modified at C-6 of the galactose residue to elucidate the mechanism of selection recognition

Sialyl Lewis X ganglioside analogues modified at C-6 of the galactose residue, having 6- O-methoxy, 6-acetamido and 6-amino functional groups, have been synthesized. Treatment of 2-(trimethylsilyl)ethyl (methyl 5-acetamido-4,7,8,9-tetra- O-acetyl-3,5-dideoxy- D-glycero- α- D-galacto-2-nonulopyranosylonate)-(2→3)-2- O-benzoyl- β- D-galactopyranoside with trimethyloxonium tetrafluoroborate or Tf 2O, followed by NaN 3, gave the 6- O-methyl and 6-azido derivatives, respectively, which were converted into their respective methyl 1-thioglycoside derivatives. The glycosyl donors obtained were coupled with 2-(trimethylsilyl)ethyl 2-acetamido-6- O-benzyl-2-deoxy-3- O-(4-methoxybenzyl)- β- D-glucopyranosyl-(1→3)-2,4,6-tri- O-benzyl- β- D-galactopyranosyl-(1→4)-2,3,6-tri-O-benzyl- β- D-galactopyranoside in the presence of dimethyl(methylthio)sulfonium triflate (DMTST) to give their respective pentasaccharides. The glycosylation of the pentasaccharide acceptors derived from their precursors by removal of the 4-methoxybenzyl group, with phenyl 1-thioglycoside derivative of L-fucose using N-iodosuccinimide–TfOH afforded the corresponding hexasaccharides, which were transformed in good yield, via reductive removal of the benzyl group, the simultaneous transformation of azide to amine and acetamide, O-deacylation and saponification of the methyl ester into the target compounds without the ceramide groups. On the other hand, the proper manipulation of the protecting group of the hexasaccharides, including a transformation of azide into acetamide and trifluoroacetamide, gave the hexasaccharide imidates, which were coupled with (2 S,3 R,4 E)-2-azido-3- O- tert-butyldiphenylsilyl-4-octadecene-1,3-diol. Selective reduction of the azido group, N-acylation with octadecanoic acid, and the complete removal of the protecting groups gave the desired sialyl Le X ganglioside analogues.

A convenient and efficient synthesis of sialyl Lewis X.

A convenient synthesis of the sialyl Lewis X (sLe(x)) tetrasaccharide, NeuAc alpha 2-3Gal beta 1-4(Fuc alpha 1-3)GlcNAc (8), as a carbohydrate ligand for selectins is described. The key step is the reaction between NeuAc alpha 2-3GalSMe (5) as a glycosyl donor and the suitably protected Fuc alpha 1-3GlcNAc derivative (4) as the glycosyl acceptor by using dimethyl(methylthio)sulfonium triflate (DMTST) as the promoter.

First total synthesis of ganglioside GT1aα

A first total synthesis of ganglioside GT1aα (IV 3III 6II 3Neu5AcGg4Cer) is described. The suitably protected sialyl α-(2 → 6) ganglioside was glycosylated with the phenylthioglycoside of sialic acid in the presence of N-iodosuccinimide (NIS)-trimethylsilyl trifluoromethanesulfonate (TMSOTf), followed by further glycosylation with the methyl thioglycoside promoted by dimethyl(methylthio)sulfonium triflate (DMTST), to give the heptasaccharide. The oligosaccharide obtained was converted into the title ganglioside by the introduction of ceramide and then complete deprotection.

Synthetic Studies on Sialoglycoconjugates 91: Total Synthesis of Gangliosides GD1C and GT1A

A first total synthesis of gangliosides GD1c and GT1a containing Neu5Acα(2→8) Neu5Acα(2→3)Gal residue in their non-reducing terminal is described. Condensation of methyl O-[methyl 5-acetamido-8-O-(5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D-glycero-α-D-galacto-2-nonulopyranosylono-11,9-lactone) -4,7- di-O-acetyl-3,5-dideoxy-D-glycero-α-D-galcto-2-nonulopyranosyranosylanate]-(2→3)-2,4,6-tri-O-benzoyl-1-thio-β-D-gala-ctopyranoside (1) with 2-(trimethylsilyl)ethyl O-(2-acetamido-4,6-O-benzylidene-2-deoxy-β-D-galactopyranosyl)- (1→4) -O -(2,3,6-tri-O-benzyl-β-D-galactopyranosyl)-(1→4)-2,3,6-tri-O-benzyl-β-D-glucopyranoside (2) or 2-(trimethylsilyl)ethyl O-(2-acetamido-6-O-benzyl-2-deoxy-β-D-galactopyranosyl)-(1→4)-(9-[methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D-glycero-α-D-galacto-2-nonulopyranosylonate)-(2→3)]-O-(2,6-di-O-benzyl-β-D-galactopyranosyl) - (1→4) - 2,3,6-tri-O-benzyl-β-D-glucopyranoside (3) in the presence of dimethyl(methylthio)sulfonium triflate (DMTST) gave the corresponding hexa-and heptasaccharide derivatives 4 and 5, respectively. These oligosaccharides were converted into the α-trichloroacetimidates 10 and 11 via reductive removal of the benzyl groups and/or benzylidene group, O-acetylation, selective removal of the 2-(trimethylsilyl)ethyl group and treatment with trichloroacetonitrile, which, on coupling with 2-azidosphingosine derivatives 12 or 13, gave the β-glycosides 14 and 15, respectively. Finally, 14 and 15 were transformed, via selective reduction of the azido group, coupling with octadecanoic acid and removal of all protecting groups, into the title gangliosides GD1c 18 and GT1a 19.

Synthesis and biological activities of three sulfated sialyl Le x ganglioside analogues for clarifying the real carbohydrate ligand structure of L-selectin

Sulfated sialyl Le x ganglioside analogues at C-6 of d-galactose, N- acetyl- d- glucosamine , and of both d-galactose and N- acetyl- d- glucosamine residues have been synthesized, in order to clarify the structure of the real carbohydrate ligand of L-selectin. Coupling of the suitably protected N- acetyl- d- glucosaminyl-β(1 → 3)- lactose derivatives 13 and 16 with the sialyl α(2 → 3)- d- galactopyranosyl trichloroacetimidates 10 and 12 (glycosyl donors), via glycosylation of 2-(trimethylsilyl)ethyl 4,6-O- benzylidene-β- d- galactopyranoside (1) with the phenyl 2-thioglycoside derivative (2) of N-acetylneuraminic acid (Neu5Ac) using N-iodosuccinimide/TfOH, O-benzoylation, removal of the benzylidene group affording 5, selective 6- O-levulinoylation, O-benzoylation, removal of the 2-(trimethylsilyl)ethyl group, and imidate formation, or via O-acetylation of 5, removal of the 2-(trimethylsilyl)ethyl group, then imidate formation, gave the pentasaccharides 18–20. The glycosylation of the pentasaccharide acceptors (21–23) derived from 18–20 by removal of the 4-methoxybenzyl group, with phenyl 1-thioglycoside derivative 27 of l-fucose using dimethyl(methylthio)sulfonium triflate (DMTST) afforded the corresponding hexasaccharides 28–30, which were transformed in good yields, via reductive removal of their benzyl groups, O-acetylation, selective removal of the 2-(trimethylsilyl)ethyl group, imidate formation, coupling with (2 S,3 R,4 E)-2-azido- O-benzoyl-4-octadecene-1,3-diol (35) in the presence of boron trifluoride etherate, selective reduction of the azido group, coupling with octadecanoic acid, selective removal of the levulinoyl groups, treatment with sulfur trioxide-pyridine complex, then removal of the protecting groups, into the desired sulfated sialyl Le x ganglioside analogues 50–52.

Synthetic Studies on Sialoglycoconjugates 85: Synthesis of Sialyl Lewis X Ganglioside Analogs Containing a Variety of Anionic Substituents in Place of Sialic Acid

Abstract Three sialyl-Lex ganglioside analogs containing carboxymethyl, sulfate, and phosphate groups in place of the sialic acid moiety, have been synthesized. Glycosylation of 2-(trimethylsilyl)ethyl O-(2,3,4-tri-O-benzyl-α-L-fucopyranosyl)-(1→3)-O-(2-acetamido-6-O-benzyl-2-deoxy-β-d-glucopyranosyl) - (1→3) - 2, 4, 6-tri-O-benzyl-β-d-galactopyranoside (10) with methyl 2,4,6-tri-O-benzoyl-3-O-(methoxycarbonyl)methyl-1-thio-β-d-galactopyranoside (6) or methyl 2-O-benzoyl-4,6-O-benzylidene-3-O-levulinoyl-1-thio-β-d-galactopyranoside (9) using dimethyl-(methylthio)sulfonium triflate (DMTST) as a promoter, afforded the corresponding tetrasaccharide derivatives 11 and 19. Compounds 11 and 19 were converted into the α-trichloroacetimidates 14 and 23, via reductive removal of the benzyl and benzylidene groups, O-acetylation, removal of the 2-(trimethylsilyl)ethyl group, and treatment with trichloroacetonitrile, which, on coupling with (2S, 3R, 4E)-2-azido-3-O-benzoyl-4-octadecene-1,3-diol (15) or 2-(tetradecyl)hexadecan-1-ol (24), gave the lipophilic derivatives 16 and 25. Compound 16 was transformed, via selective reduction of the azido group, condensation with octadecanoic acid, O-deacylation, and hydrolysis of the methyl ester group, into the title compound 18 in good yield. Compound 25 was treated with hydrazine acetate to give compound 26, which in turn was transformed, via sulfation or phosphorylation, and O-deacylation, into the target compounds 28 and 31.

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.

Synthetic Studies on Sialoglycoconjugates 81: Synthesis of Positional Isomers of Sialyl Lewis X Epitope Containing 1-Deoxy-dGlucose in Place ofN-Acetylglucosamine, and Their Inhibitory Activity to Selectin-Mediated Adhesion

Abstract Three sialyl-Lex epitope analogs, which carry fucose and α-sialyl-(2→3)-galactose residues at O-2 and O-3, O-3 and O-2, and O-4 and O-6 positions of 1-deoxy-D-glucose backbone, respectively, have been synthesized. Glycosylation of 1,5-anhydro-4,6-O-benzylidene-D-glucitol (1) or 1,5-anhydro-6-O-benzoyl-2,3-di-O-benzyl-d-glucitol (4) prepared from 1,5-anhydro-d-glucitol, with methyl 2,3,4-tri-O-benzyl-1-thio-β-L-fucopyranoside (5) using dimethyl(methylthio)sulfonium triflate (DMTST) as a promoter, afforded the corresponding fucosyl 1,5-anhydro-d-glucitol derivatives 7, 8 and 9. Glycosylation of 7, 8 or 10 derived from 9, with methyl O-(methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-d-glyceroα-d-galacto-2-nonulopyranosylonate)-(2→3)-2,4,6-tri-O-benzoyl-1-thio-β-d-galactopyranoside (11) in the presence of DMTST gave the expected tetrasaccharide derivatives 12, 16 and 20. Hydrolysis of the benzylidene group in 12 and 16 gave compounds 13 and 17. Finally 13, 17 and 20 were transformed, by reduct...

Synthesis of Oligosaccharide Structures from the Lipopolysaccharide of Moraxella catarrhalis.

The synthesis of the octasaccharide [p-(trifluoroacetamido)phenyl]ethyl 4-O-[2-O-(2-acetamido-2-deoxy-alpha-D-glucopyranosyl)-beta-D-glucopyranosyl]-6-O-[2-O-[4-O-(4-O-alpha-D-galactopyranosyl-beta-D-galactopyranosyl)-alpha-D-glucopyranosyl]-beta-D-glucopyranosyl]-3-O-beta-D-glucopyranosyl-alpha-D-glucopyranoside, representing the outer part of the lipooligosaccharide from Moraxella catarrhalis serotype A, is described, together with a hepta-, a hexa-, and a pentasaccaride, composing parts thereof with shorter oligosaccharide chains substituted in the 6-position of the central 3,4,6-branched glucose moiety. The versatility of the use of thioglycosides in oligosaccharide synthesis is shown, since throughout the synthesis thioglycosides are used as glycosyl donor precursors, either directly in dimethyl(methylthio)sulfonium triflate (DMTST)-promoted coupling reactions or after conversion to the corresponding glycosyl bromide in silver triflate-promoted couplings. The effects of different protecting groups, anomeric leaving groups, and solvents used in the various coupling reactions are often substantial, which necessitates the use of easily convertible intermediates.

Synthesis of d-Fructofuranosides Using Thioglycosides as Glycosyl Donors

Benzylated and benzoylated ethyl thioglycosides of d-fructofuranose have been synthesized and tested as glycosyl donors in couplings to various primary and secondary carbohydrate acceptors. Treatment of 2-O-acetyl-1,3,4,6-tetra-O-benzoyl-d-fructofuranose with ethyl mercaptan in a BF3·etherate-promoted reaction gave the benzoylated ethyl 2-thio-α,β-d-fructofuranosides, which after deacylation and benzylation afforded the benzylated derivatives. These thiofructofuranosides, using dimethyl(methylthio)sulfonium triflate (DMTST) or N-iodosuccinimide as promoter, were found to be excellent donors, which gave disaccharide coupling products in quantitative or almost quantitative yields with all tested acceptors, yields rarely found in oligosaccharide synthesis. The benzoylated donors gave only α-linked fructofuranosides, due to participation of the 3-O-benzoyl group, whereas the benzylated donors gave α/β-mixtures.

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-β- d-glucopyranosyl)-(1 → 3)-2,4,6-tri- O-benzyl-β- 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-α- l-hexopyranosyl-(1 → 3)- O-(2-acetamido-2-deoxy-β- d-glucopyranosyl)-(1 → 3)-β- d-galactopyranosides. 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-α- d-galacto-2-nonulopyranosylonate)-(2 → 3)-2,4,6-tri- O-benzoyl-1-thio-β- 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 α-trichloroacetimidates. Glycosylation of (2 S,3 R,4 E)-2-azido-3- O-benzoyl-4-octadecene-1,3-diol these in the presence of boron trifluoride etherate afforded the expected β-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.

Synthetic Studies on Sialoglycoconjugates 74: Synthesis of KDN-gangliosides GM1, GM2, and GD1a

Abstract KDN-containing gangliosides GM1, GM2, and GD1a have been synthesized. Glycosylation of 2-(trimethylsilyl)ethyl O-(methyl 4,5,7,8,9-penta-O-acetyl-3-deoxy-d-glycero-α-d-galacto-2-nonulopyranosylonate)-(2→3)-O-(2,6-di-O-benzyl-β-d-galactopyranosyl)-(1→4)-2,3,6-tri-O-benzyl-β-d-glucopyranoside (3) with methyl 6-O-benzyl-2-deoxy-3,4-O-isopropylidene-2-phthalimido-1-thio-β-d-galactopyranoside (5) gave the tetrasaccharide (6), which was converted, via de-esterification, removal of the phthaloyl group, N-acetylation, and O-deisopropylidenation, into the tetrasaccharide acceptor (9). Reductive removal of the benzyl groups in 9, O-acetylation and subsequent removal of the 2-(trimethylsilyl)ethyl group followed by imidate formation, gave the KDN-GM2 oligosaccharide glycosyl donor 12. Glycosylation of 9 with methyl 2,4,6-tri-O-benzoyl-3-O-benzyl-1-thio-β-d-galactopyranoside (13) and methyl (methyl 4,5,7,8,9-penta-O-acetyl-3-deoxy-d-glcero-α-d-galacto-2-nonulopyranosylonate)-(2→3)-2,4,6-tri-O-benzoyl-1-thio-β-d-galactopyranoside (18), using dimethyl(methyl-thio)sulfonium triflate (DMTST), gave the penta- and hexasaccharides 14 and 19, 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 α-trichloroacetimidates 17 and 22. Glycosylation of (2S,3R,4E)-2-azido-3-O-benzoyl-4-octadecene-1,3-diol with 12, 17, and 22 in the presence of boron trifluoride etherate afforded the expected β-glycosides, which were transformed in good yields, via selective reduction of the azido group, coupling with octadecanoic acid, O-deacylation, and de-esterification, into the target gangliosides 26 29, and 32.