Synthesis of a common trisaccharide fragment of glycoforms of the outer core region of the Pseudomonas aeruginosa lipopolysaccharide

The first synthesis of the common trisaccharide of glycoforms of the outer core region of the Pseudomonas aeruginosa lipopolysaccharide is reported. A fully protected trisaccharide precursor was prepared via a highly efficient α-(1→4)-glucosylation of a β-(1→3)-linked 6-O-benzyl-2-azido-2-deoxy-3-O-(2,3,4,6-tetra-O-acetyl-β-d-glucopyranosyl)-α-d-galactopyranoside. In contrast, an alternative sequence of glycosylations, which involves β-glucosylation of an α-(1→4)-linked Glc-GalN₃ unit, did not lead to the target trisaccharide backbone. Further O-deacetylation, azido group reduction and debenzylation of the protected trisaccharide precursor gave the corresponding trisaccharide amine. The latter structure was used in the synthesis of a series of trisaccharides bearing an acetyl group, an l-alanine or an N-acetylated l-alanine residue on its amino group at C-2 of GalN.     

Synthesis of undecaprenyl pyrophosphate-linked glycans as donor substrates for bacterial protein N-glycosylation

Synthesis of undecaprenyl pyrophosphate (Und-PP)-linked glycans is described. Bacterial ([E]₃,[Z]₇)-undecaprenol was synthesized from trans-geranylgeranyl sulfone and isoprenoid building blocks, which was converted to undecaprenyl phosphate (Und-P). It was coupled with glycosyl phosphates to afford Und-PP-linked glycans, including core trisaccharide of Campylobacter jejuni N-glycan. Our synthetic method for Und-PP-linked glycan would provide various substrates as a useful tool for systematic analysis of bacterial protein N-glycosylation.     

A new one-pot synthesis of Gb3 and isoGb3 trisaccharide analogues

Gb₃ and isoGb₃ are both biologically important oligosaccharides. A new efficient synthesis of Gb₃ and isoGb₃ trisaccharide analogues has been achieved by one-pot sequential glycosylation strategy starting from simple monosaccharide building blocks promoted by N-(phenylthio)-?-caprolactam at room temperature.     

Selective sialylation of 2,3-di-O-(β-d-galactopyranosyl)-d-galactose catalyzed by Trypanosoma cruzi trans-sialidase

Trypanosoma cruzi, the agent of Chagas’ disease, expresses on its surface a trans-sialidase (TcTS) that transfers sialic acid from host glycoconjugates to terminal β-galactopyranosyl units of parasite mucins. This process is involved in infection and pathogenesis. The trisaccharide 2,3-di-O-(β-d-galactopyranosyl)-d-galactose 1 is an external unit in the larger oligosaccharides of the mucins and a site for sialylation. The trisaccharide was previously synthesized in our laboratory. The last step of the synthesis was the hydrogenolysis of the crystalline benzyl trisaccharide. Herein we prove that the trisaccharide 1, its alditol 3 and the benzyl glycoside 2 are good acceptors of sialic acid and effective inhibitors of the sialylation of N-acetyllactosamine catalyzed by TcTS. Furthermore, selective sialylation of the 1→3 linked galactopyranose in glycoside 2 was determined by one and two-dimensional NMR analysis. In contrast, the flexible 2,3-di-O-(β-d-galactopyranosyl)-d-galactitol 3 is sialylated in either one of the two possible sites.     

Synthesis of trisaccharide-coated magnetic nanoparticles for antibody removal

An efficient strategy for the synthesis of blood group A trisaccharide antigen has been developed. Magnetic nanoparticles having Fe₃O₄-Silica core-shell structure were prepared and functionalized with the prepared blood group A trisaccharide antigen derivative, and its excellent removal ability toward anti-A antibody was explored.     

First synthesis of 3′-deoxy Lewisx pentasaccharide

The total synthesis of 3′-deoxy Lewis^x pentasaccharide is reported. 4-O-Acetyl-2,6-di-O-benzoyl-3-deoxy-β-d-xylo-hexopyranosyl trichloroacetimidate was condensed with a diol of glucosamine to give a disaccharide, which was further fucosylated to a Lewis^x trisaccharide analogue. Glycosylation of a lactoside diol with this trisaccharide provided a pentasaccharide, which after deprotection, afforded the target pentasaccharide.     

Synthesis of Chitin Oligosaccharides Using Dried <Emphasis Type="Italic">Stenotrophomonas maltophilia</Emphasis> Cells Containing a Transglycosylation Reaction-Catalyzing β<Emphasis Type="Italic">-N-</Emphasis>Acetylhexosaminidase as a Whole-Cell Catalyst

Bacterial strain NYT501, which we previously isolated from soil, was identified as Stenotrophomonas maltophilia, and it was confirmed that this strain produces an intracellular β-N-acetylhexosaminidase exhibiting transglycosylation activity. Several properties of this enzyme were characterized using a partially purified enzyme preparation. Using N,N′-diacetylchitobiose (GlcNAc)₂ and N,N′,N″-triacetylchitotriose (GlcNAc)₃ as substrates and dried cells of this bacterium as a whole-cell catalyst, chitin oligosaccharides of higher degrees of polymerization were synthesized. (GlcNAc)₃ was generated from (GlcNAc)₂ as the major transglycosylation product, and a certain amount of purified sample of the trisaccharide was obtained. By contrast, in the case of the reaction using (GlcNAc)₃ as a substrate, the yield of higher-degree polymerization oligosaccharides was comparatively low.     

First synthesis of 5,6-branched galacto-hexasaccharide,the dimer of the trisaccharide repeating unit of the cell-wall galactans of Bifidobacterium catenulatum YIT 4016

α-d-Galactopyranosyl-(1→6)-[β-d-galactofuranosyl-(1→5)]-β-d-galactofuranosyl-(1→6)-β-d-galactofuranosyl-(1→5)-[α-d-galactopyranosyl-(1→6)]-β-d-galactofuranose, the dimer of the trisaccharide repeating unit of the cell-wall galactans of Bifidobacterium catenulatum YIT 4016, has been synthesized as its dodecyl glycoside 2 by coupling of 2,3,4,6-tetra-O-benzyl-α-d-galactopyranosyl-(1→6)-[6-O-acetyl-2,3,5-tri-O-benzoyl-β-d-galactofuranosyl-(1→5)]-2-O-acetyl-3-O-benzyl-β-d-galactofuranosyl trichloroacetimidate 14 with dodecyl 2,3,4,6-tetra-O-benzyl-α-d-galactopyranosyl-(1→6)-[2,3,5-tri-O-benzoyl-β-d-galactofuranosyl-(1→5)]-2-O-acetyl-3-O-benzyl-β-d-galactofuranoside 16. The trisaccharide trichloroacetimidate donor 14 and trisaccharide acceptor 16 were regiospecifically prepared by employing 3-O-benzyl-1,2-O-isopropylidene-α-d-galactofuranose 4 as the glycosyl acceptor, and isopropyl 2,3,4,6-tetra-O-benzyl-1-thio-β-d-galactopyranoside 5 and 6-O-acetyl-2,3,5-tri-O-benzoyl-β-d-galactofuranosyl trichloroacetimidate 9 as glycosyl donors.     

Efficient synthesis of pyruvate ketals of carbohydrates

An efficient method for the preparation of pyruvate ketals of carbohydrates has been developed using N-iodosuccinimide or 1,3-dibromo-5,5-dimethylhydantoin as activator and methyl 2,2-di(ethylthio)propionate. The method has been applied for the preparation of a pyruvate ketal-containing trisaccharide present in the bacterial cell-wall of Mycobacterium smegmatis.     

Synthesis of the repeating trisaccharide unit of the cell wall lipopolysaccharide of Escherichia coli type 8

NIS/TfOH mediated glycosidation of methyl 3,4,6-tri-O-benzyl-α-d-mannopyranoside with phenyl 2-O-acetyl-3,4,6-tri-O-benzyl-1-thio-α-d-mannopyranoside furnished the corresponding disaccharide derivative in excellent yield and α-selectivity. Zémplen deacetylation of the same followed by reaction with BSP/Tf₂O-preactivated phenyl 4,6-O-benzylidene-2,3-di-O-benzyl-1-thio-α-d-mannopyranoside generated methyl 4,6-O-benzylidene-2,3-di-O-benzyl-β-d-mannopyranosyl-(1→2)-3,4,6-tri-O-benzyl-α-d-mannopyranosyl-(1→2)-3,4,6-tri-O-benzyl-α-d-mannopyranoside in very good yield and excellent β-selectivity. Pd/C catalyzed hydrogenation of the latter finally afforded the repeating trisaccharide of Escherichia coli 8 O-antigen as its methyl glycoside.     

Synthesis of a Trisaccharide Related to the Cytotoxic Triterpenoid Saponins Isolated from the Bark of Albizia procera

Chemical synthesis of a trisaccharide related to the cytotoxic triterpenoid saponins isolated from the bark of Albizia procera has been accomplished through a concise stepwise glycosylation strategy starting from commercially available D ‐xylose, 2‐acetamido‐2‐deoxy‐D ‐glucose and L ‐arabinose. The target trisaccharide was designed with a 4‐methoxyphenyl (MP) aglycone to extend the scope of conversion to suitable glycoconjugates via selective removal of 4‐methoxyphenyl (MP) group. An unexpected phenomenon, i.e., the arabinosyl residue assumed the ¹C₄ conformation instead of the typical ⁴C₁ form, was observed. Deprotection could restore the normal conformation.     

Synthesis of a new glycosphingolipid from the marine ascidian Microcosmus sulcatus using a one-pot glycosylation strategy

A novel neutral glycosphingolipid found in Microcosmus sulcatus containing a β-d-Galp(1→4)[α-d-Fucp-(1→3)]β-d-Glcp-(1→)Cer motif was synthesized. Trisaccharide derivatives were synthesized using trimethylsilyltrifluoromethanesulfanate (TMSOTf) and N-iodosuccimide (NIS)/trifluoromethane sulfonic acid (TfOH) as the promoters. Synthesis was achieved with an efficient one-pot glycosylation strategy. This is the first report of a one-pot glycosylation strategy using the procedure of Boons et al. for the synthesis of a natural product. Coupling of trisaccharide derivative 19 and ceramide derivative 20 by TMSOTf afforded the glycosphingolipid derivative 21. The fully protected glycoside was deprotected to give the target glycosphingolipid 2.     

Structural Elucidation of the Component Trisaccharide Obtained from the Acrosome Reaction-Inducing Substance of the Starfish Asterias Amurensis by Chemical Synthesis

Abstract

Okinaga et al.¹ have recently reported a novel trisaccharide obtained from the acrosome reaction-inducing substance (ARIS) of the starfish Asterias amurensis. The ARIS is essential for triggering the acrosome reaction in homologous spermatozoa, and the biological activity is due to the sugar moiety. The trisaccharide, composed of xylose (Xyl), galactose (Gal), and fucose (Fuc), and proposed to have a sequence of Xyll→3Gall→3 or 4[4 or 3-(So₃ ^?)]Fuc, was deduced to be one of the major structural units constructing the side chain of the high molecular carbohydrate portion of the ARIS. The sequence differs from similar oligosaccharides, found in hemicellulose² and composed of d-xylose, d-galactose, and l-fucose. The ARIS contains a unique saccharide chain having sulfated l-fucose as an internal residue. This unique structure prompted us to synthesize the trisaccharide as well as to reveal the anomeric configuration of Xyl and Gal moieties and the sulfated position of Fuc residue.     

Concise synthesis of two pentasaccharides corresponding to the α-chain oligosaccharides of Neisseria gonorrhoeae and Neisseria meningitidis

Two pentasaccharides containing a common tetrasaccharide (lacto-N-neotetraose) core, and d-galactosamine and N-acetyl neuraminic acid in the non-reducing ends, respectively, corresponding to the lipooligosaccharides of Neisseria gonorrhoeae and Neisseria meningitidis were synthesized in a very concise manner from a common trisaccharide derivative using minimum number of steps. Thioglycosides and glycosyl trichloroacetimidate have been used as glycosyl donors for glycosylations and yields were excellent in every step.     

Synthesis of H (type 4) trisaccharide,key structural fragment of globo-H and fucosyl-GM1 cancer-associated antigens

A convenient synthesis of Fucα1-2Galβ1-3GalNAcβ-OCH₂CH₂CH₂NH₂ (trisaccharide H type 4) is described. This glycan is the terminal part of glycosphingolipids globo-H and fucosyl-GM1 known as cancer-associated carbohydrate antigens.     

Convergent synthesis of a common pentasaccharide-repeating unit corresponding to the O-specific polysaccharide of Escherichia coli O4:K3, O4:K6, and O4:K12

A convergent chemical synthesis of a pentasaccharide found in the O-specific polysaccharide of Escherichia coli O4:K3, O4:K6, and O4:K12 has been achieved in excellent yield. A [3+2] block synthetic strategy has been adopted to couple a disaccharide donor 11 with a trisaccharide acceptor 10 for the construction of the pentasaccharide derivative 12 which on deprotection furnished target pentasaccharide 1 as its 4-methoxyphenyl glycoside. Disaccharide thioglycoside donor 11 and trisaccharide acceptor 10 were prepared from suitably protected monosaccharide intermediates. Yields were excellent in all steps.     

Total synthesis of the aminopropyl functionalized ganglioside GM1

GM1 is a common ganglioside pentasaccharide present on mammalian cell surface.It has been shown to play important roles in cellular communications and initiation of β-amyloid aggregation.In order to synthesize GM1,an efficient synthetic route was developed via a [3+2] strategy.The GM3 trisaccharide acceptor bearing an azido propyl group at the reducing end was prepared using the traditional acetamide protected sialyl thioglycosyl donor,which gave better stereoselectivity than sialyl donors protected with trichloroacetamide or oxazolidinone.The glycosylation of the axial 4-hydroxyl group of GM3 by the disaccharide donor was found to be highly dependent on donor protective groups.Donor bearing the more rigid benzylidene group gave low glycosylation yield.Replacing the benzylidene with acetates led to productive coupling and formation of the fully protected GM1 pentasaccharide.Deprotection of the pentasaccharide produced GM1 functionalized with the aminopropyl side chain,which will be a valuable probe for biological studies.     

Highly stereoselective synthesis of imino-C-di- and trisaccharides as hydrolytically stable glycomimetics

A new straightforward route to glycomimetics containing a piperidine unit is reported. The key step of the methodology is the intramolecular 1,3-dipolar cycloaddition of easily accessible glycosyl alkenyl nitrones. The reaction takes place in most cases with a complete selectivity in favor of the exo–exo adduct, which facilitates the synthesis of all-cis piperidines bearing the glycosyl units. The direct transformation of adducts into the final imino-C-di and trisaccharide analogues is achieved in one step using simple reagents. Inhibition properties against two glycosidases have been tested but no positive results have been found.     

Synthesis of modular building blocks using glycosyl phosphate donors for the construction of asymmetric N-glycans

Glycosyl phosphates are known as versatile donors for the synthesis of complex oligosaccharides both chemically and enzymatically. Herein, we report the stereoselective construction of modular building blocks for the synthesis of N-glycan using glycosyl phosphates as donors. We have synthesized four trisaccharide building blocks with orthogonal protecting groups, namely, Manβ2GlcNAc(OAc)₃β6GlcNAc (9), Manβ2GlcNAc-β6GlcNAc(OAc)₃ (15), Manβ2GlcNAc(OAc)₃β4GlcNAc (18) and Manβ2GlcNAcβ4GlcNAc(OAc) (22) for further selective elongation using glycosyltransferases. The glycosylation reaction using glycosyl phosphate was found to be high yielding with shorter reaction time. Initially, The phthalimide protected glucosamine donor was exploited to ensure the formation of β-glycosidic linkage and later converted to the N-acetyl group before the enzymatic synthesis. The selective deprotection of O-benzyl group was performed prior to enzymatic synthesis to avoid its negative interference.     

Stereoselective Synthesis of the Hexasaccharide Repeating Unit of the Cell Wall Polysaccharide from Kineosporia aurantiaca VKM Ac-720T Employing the Direct Glycosylation with Anomeric Hydroxy Sugars Involving Glycosyl Phthalate Intermediates

Synthesis of a suitably protected form of the hexasaccharide repeating unit of the cell wall polymer from Kineosporia aurantiaca VKM Ac-720 ^T has been achieved by the stereoselective direct glycosylation of a trisaccharide acceptor with a trisaccharide donor having an anomeric hydroxy group involving a glycosyl phthalate intermediate. Both the trisaccharide acceptor and the trisaccharide donor were obtained from a common trisaccharide, of which two β-mannopyranosyl linkages were constructed stereoselectively by employing the direct glycosylation method with the anomeric hydroxy sugar involving a glycosyl phthalate intermediate and the 2′-carboxybenzyl glycoside method, respectively.