Application of Phenyl 1-Selenoglycosides in the Synthesis of a Cell-Wall Tetrameric Fragment of Proteus Vulgaris Strain 5/43

Abstract

DAST-assisted rearrangement of 3-O-allyl-4-O-benzyl-α-l-rhamnopyranosyl azide followed by treatment of the generated fluorides with ethanethiol and BF₃·OEt₂ gave glycosyl donor ethyl 3-O-allyl-2-azido-4-O-benzyl-2,6-dideoxy-1-thio-α/β-l-glucopyranoside. Stereoselective glycosylation of methyl 4,6-O-benzylidene-2-deoxy-2-phthalimido-β-D-glucopyranoside with ethyl 3-O-allyl-2-azido-4-O-benzyl-2,6-dideoxy-1-thio-α/β-l-glucopyranoside, under the agency of NIS/TfOH afforded methyl 3-O-(3-O-allyl-2-azido-4-O-benzyl-2,6-dideoxy-α-l-glucopyranosyl)-4,6-O-benzyli-dene-2-deoxy-2-phthalimido-β-D-glucopyranoside. Removal of the allyl function of the latter dimer, followed by condensation with properly protected 2-azido-2-deoxy-glucosyl donors, in the presence of suitable promoters, yielded selectively methyl 3-O-(3-O-[6-O-acetyl-2-azido-3,4-di-O-benzyl-2-deoxy-α-D-glucopyranosyl]-2-azido-4-O-benzyl-2,6-dideoxy-α-l-glucopyranosyl)-4,6-O-benzylidene-2-deoxy-2-phthalimido-β-D-glucopyranoside. Deacetylation and subsequent glycosylation of the free HO-6 with phenyl 2,3,4,6-tetra-O-benzoyl-1-seleno-β-D-glucopyranoside in the presence of NIS/TfOH furnished a fully protected tetrasaccharide. Deprotection then gave methyl 3-O-(3-O-[6-O-{β-D-glucopyranosyl}-2-acetamido-2-deoxy-β-D-glucopyranosyl)-2-acetamido-2,6-dideoxy-α-L-glucopyranosyl)-2-acetamido-2-deoxy-β-D-glucopyranoside.     

Synthesis of a DI- and A Trisaccharide Related to the Antigen From Klebsiella Type 16

Using methyl triflate as promoter, methyl O-(2,3,4,6-tetra-O-benzyl-α-D-glucopyranosyl)-(1→4)-(methyl 2,3-di-O-benzoyl-β-D-glucopyranosyluronate) and methyl O-(2,3,4,6-tetra-O-benzyl-β-D-galacto-pyranosyl)-(1→-4)-O-(2,3,6-tri-O-benzyl-α-D-glucopyranosyl)-1(1→4)-(methyl 2,3-di-O-benzoyl-β-D-glucopyranosyluronate) have been synthesised. Removal of protecting groups gave the di- and trisaccharide in the form of their methyl ester methyl glycoside related to the antigen of Klebsiella type 16.     

Preparation of trans Diequatorial 2,3-Pyruvate Acetals in a Di- and a Trisaccharide Related to the K-Antigen from E. Coli 0101:K103:H−

Abstract

Using methyl 2,2-bis(ethylthio)propionate as acetalating agent and triflic acid-sulfuryl chloride as catalyst, synthesis of 2,3-trans diequatorial pyruvate ketal was achieved. Starting from D-galactose and L-rhamnose derivatives, methyl 2,3,4,6-tetra-O-benzyl-α-D-galactopyranosyl-(1→4)-6-O-benzyl-2,3-O-(1-methoxycarbonyl)ethylidene- α-D-galactopyranosyl-(1→3)-2,4-di-O-benzyl-α-L-rhamnopyranoside and methyl 4,6-di-O-benzyl-2,3-O-(1-methoxy-carbonyl)ethylidene-α-D-galactopyranosyl-(1→3)-2,4-di-O-benzyl-α-L-rhamnopyranoside were synthesized. Removal of the protecting groups from the former, afforded the trisaccharide repeating unit of the K-antigen from E.coli O101:K103:H^? in the form of its methyl glycoside methyl ester.     

2-Deoxy-2-C-(2,3-dideoxy-α-d-erythro-hexopyranosyl)-β-d-glucopyranoses: Reinvestigation of Synthesis,Use in Glycosylation,and Conformational Analyses by NMR

Abstract

Conformational investigations using 1D TOCSY and ROESY ¹H NMR experiments on 1,3,4,6-tetra-O-acetyl-2-C-(4,6-di-O-acetyl-2,3-dideoxy-α-D-erythro-hexopyranosyl)-2-deoxy-β-D-glucopyranose (8) and related disaccharides showed that for steric reasons the C-linked hexopyranosyl ring occurs in the usually unfavoured ¹C₄ conformation and reconfirmed the structure of 1,3,4,6-tetra-O-acetyl-2-C-(4,6-di-O-acetyl-2,3-dideoxy-α-D-erythro-hex-2-enopyranosyl)-2-deoxy-β-D-glucopyranose (5). Glycosylation of 2,3,6-tri-O-benzyl-α-D-glucopyranosyl 2,3-di-O-benzyl-4,6-(R)-O-benzylidene-α-D-glucopyranoside (13) with acetate 8 using trimethylsilyl triflate as a catalyst afforded the α-D-linked tetrasaccharide 14. A remarkable side product in this reaction was the unsaturated tetrasaccharide 2,3,6-tri-O-benzyl-4-O-[4,6-di-O-acetyl-2,3-dideoxy-2-C-(4,6-di-O-acetyl-2,3-dideoxy-β-D-erythro-hexopyranosyl)-α-D-erythro-hex-2-enopyranosyl]-α-D-glucopyranosyl 2,3-di-O-benzyl-4,6-(R)-O-benzylidene-α-D-glucopyranoside (16) where in the C-linked hexopyranosyl ring an isomerization to the β-anomer had taken place to allow for the favoured ⁴C₁ conformation. The tetrasaccharide 14 was deacetylated and hydrogenolyzed to form the fully deprotected tetrasaccharide 18. The ¹ C ₄ conformation of the C-glycosidic pyranose of this tetrasaccharide was maintained as shown by an in depth NMR analysis of its peracetate 19.     

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-(2-Acetamido-2-Deoxy-β-D-Glucopyranosyl)-(l→2)-O-α-D-Mannopyranosyl-(l→6)-O-β-D-Glucopyranosyl-(1→4)-2-Acetamido-2-Deoxy-D-Glucopyranose. A Potential Acceptor-Substrate for N-Acetylglucosaminyltransferase-V (GnT-V)

Abstract

The reaction of phenyl 3,4,6-tri-O-acetyl-2-deoxy-2-phthaIimido-l-thio-β-D-glucopyranoside with methyl 3,4,6-tri-O-benzyl-α-D-mannopyranoside catalysed by iodonium ion (TfOH-NIS) followed by deacylation-acetylarion afforded disaccharide 11. which was readily converted (in four steps) to bromide 12. A similar glycosylarion with phenyl 2,3,4,6-tetra-O-acetyl-l-thio-D-glucopyranoside of benzyl 2-acetamido-3,6-di-O-benzyl-2-deoxy-α-D-glucopyranoside 16 followed by O-deacetylation of the resulting intermediate gave disaccharide 18. The 4,6-O-benzylidene derivative of 18 was acetylated then deacetaled to give diol 21. This diol acceptor was condensed with bromide 12 (promoted by mercuric cyanide) to give the partially protected tetrasaccharide derivative 22 which was O-deacetylated and then subjected to catalytic hydrogenation to furnish the title tetrasaccharide 6. The structure assigned to 6 was supported by ¹H and ¹³C NMR spectral data and FAB mass spectroscopy.     

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.     

Synthesis Of Ligands Related To The O-Specific Antigen Of Shigella Dysenteriae Type 1.

Abstract

Stereoselective α-D-galactosylation at the position 3 of 4,6-O-substituted derivatives of methyl 2-acetamido-2-deoxy-α-D-glucopyranoside is described. Glycosyl chlorides derived from 3,4,6-tri-O-acetyl-2-O-benzyl- and 2-O-(4-methoxybenzyl)-D-galactopyranose have been used as glycosyl donors. Methyl 2-acetamido-4,6-di-O-acetyl-2-deoxy-3-O-(3,4,6-tri-O-acetyl-α-D-galactopyranosyl)-α-D-glucopyranoside (27) and methyl 2-acetamido-4,6-di-O-benzyl-2-deoxy-3-O-(3,4,6-tri-O-acetyl-α-D-galactopyranosyl)-α-D-glucopyranoside (31) have been prepared.     

Synthesis of the Methyl Glycosides of a Di- and Two Trisaccharide Fragments Specific for the Shigella flexneri Serotype 2a O-Antigen

ABSTRACT

The stereocontrolled synthesis of methyl α-D-glucopyranosyl-(1→4)-α-L-rhamnopyranoside (EC, 1), methyl α-L-rhamnopyranosyl-(1→3)-[α-D-glucopyranosyl-(1→4)]-α-L-rhamnopyranoside (B(E)C, 3) and methyl α-D-glucopyranosyl-(1→4)-α-L-rhamnopyranosyl-(1→3)-2-acetamido-2-deoxy-β-D-glucopyranoside (ECD, 4) is described; these constitute the methyl glycosides of branched and linear fragments of the O-specific polysaccharide of Shigella flexneri serotype 2a. Emphasis was put on the construction of the 1,2-cis EC glycosidic linkage resulting in the selection of 2,3,4,6-tetra-O-benzyl-α-D-glucopyranosyl fluoride (8) as the donor. Condensation of methyl 2,3-O-isopropylidene-4-O-trimethylsilyl-α-L-rhamnopyranoside (11) and 8 afforded the fully protected αE-disaccharide 20, as a common intermediate in the synthesis of 1 and 3, together with the corresponding βE-anomer 21. Deacetalation and regioselective benzoylation of 20, followed by glycosylation with 2,3,4-tri-O-benzoyl-α-L-rhamnopyranosyl trichloroacetimidate (15) afforded the branched trisaccharide 25. Full deprotection of 20 and 25 afforded the targets 1 and 3, respectively. The corresponding βE-disaccharide, namely, methyl β-D-glucopyranosyl-(1→4)-α-L-rhamnopyranoside (βEC, 2) was prepared analogously from 21. Two routes to trisaccharide 4 were considered. Route 1 involved the coupling of a precursor to residue E and a disaccharide CD. Route 2 was based on the condensation of an appropriate EC donor and a precursor to residue D. The former route afforded a 1:2 mixture of the αE and βE condensation products which could not be separated, neither at this stage, nor after deacetalation. In route 2, the required αE-anomer was isolated at the disaccharide stage and transformed into 2,3,4,6-tetra-O-benzyl-α-D-glucopyranosyl-(1→4)-2,3-di-O-benzoyl-α-L-rhamnopyranosyl trichloroacetimidate (48) as the EC donor. Methyl 2-acetamido-2-deoxy-4,6-O-isopropylidene-β-D-glucopyran-oside (19) was preferred to its benzylidene analogue as the precursor to residue D. Condensation of 19 and 48 and stepwise deprotection of the glycosylation product afforded the target 4.     

Synthesis of Tetrasaccharide Repeating Unit of the K-Antigen from Klebsiella Type-16

Abstract

Starting from L-fucose, D-glucose and lactose, methyl O-[2,3-di-O-benzoyl-4, 6-O-(4-methoxybenzylidene)-β-D-glucopyranosyl]-(1→4)-2,3-di-O-benzoyl-α-L-fucopyranoside and methyl O-(2,3,4,6-tetra-O-benzyl-β-D-galactopyranosyl)-(1→4)-O-(2,3,6-tri-O-benzyl-α-D-glucopyranosyl)-(1→4)-O-(methyl 2,3-di-O-benzoyl-β-D-glucopyranosyluronate)-(1→4)-2,3-di-O-benzoyl-α-L-fucopyranoside were synthesized. Removal of protecting groups gave the tetrasaccharide repeating unit of the antigen from Klebsiella type-16 in the form of its methyl ester methyl glycoside.     

Synthetic Studies on Sialoglycoconjugates 54: Synthesis of I-Active Ganglioside Analog

Abstract

A stereocontrolled synthesis of I-active ganglioside analog is described. Glycosylation of 2-(trimethylsilyl)ethyl O-(2-O-benzyl-4,6-O-benzylidene-β-d-galactopyranosyl)-(1 → 4)-2,3,6-tri-O-benzyl-β-d-glucopyranoside (5) with methyl 4-O-acetyl-1,6-di-O-benzyl-2-deoxy-2-phthalimido-1-thio-β-d-glucopyranoside (10) by use of N-iodosuccinimide (NIS)-trifluoromethanesulfonic acid (TfOH) gave the desired trisaccharide 11, which was transformed into trisaccharide acceptor 14 via removal of the phthaloyl group followed by N-acetylation, and debenzylidenation. Glycosylation of 14 with methyl 3-O-benzyl-4,6-O-benzylidene-2-deoxy-2-phthalimido-1-thio-β-d-glucopyranoside (8) gave the biantennary compound 15, which was transformed into the acceptor 16. Dimethyl(methylthio)sulfonium triflate (DMTST)-promoted coupling of 16 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 (17) afforded the desired hexasaccharide 19. Coupling of the hexasaccharide acceptor 20, prepared from 19 by reductive ring-opening of benzylidene acetal, with 17 gave octasaccharide derivative 21. Compound 21 was transformed, via removal of the benzyl group followed by O-acetylation, selective removal of the 2-(trimethylsilyl)ethyl group and subsequent imidate formation, into the final glycosyl donor 24. Condensation of 24 with (2S, 3R, 4E)-2-azido-3-O-benzoyl-4-octadecene-1,3-diol (18) gave the β-glycoside 25, which on channeling through selective reduction of azido group, coupling of the amino group with octadecanoic acid, O-deacylation and saponification of the methyl ester group, gave the title compound 28.     

Chemical-Enzymatic Synthesis of A Branched Hexasaccharide Fragment of Type Ia Group B Streptococcus Capsular Polysaccharide

ABSTRACT

A branched hexasaccharide fragment of type Ia group B streptococcal polysaccharide, α-NeuAc(2→3)-β-D-Gal(1→4)-β-D-GlcNAc(1→3)-[β-D-Glc(1→4)]-β-D-Gal(1→4)-β-D-Glc-OMe (13), has been synthesized by chemical-enzymatic procedures. Chemical synthesis of a pentasaccharide, β-D-Gal(1→4)-β-D-GlcNAc(1→3)-[β-D-Glc(1→4)]-β-D-Gal(1→4)-β-D-Glc-OMe (12), was achieved from glycosyl donor, 4-O-(2,3,4,6-tetra-O-acetyl-β-D-galactopyranosyl)-3,6-di-O-acetyl-2-deoxy-2-phthalimido-β-D-glucopyranosyl trichloroacetimidate (9), and acceptor, methyl O-(2,3,4,6-tetra-O-acetyl-β-D-glucopyranosyl)-(1→4)-O-(2,6-di-O-benzyl-β-D-galactopyranosyl)-(1→4)-2,3,6-tri-O-benzyl-β-D-glucopyranoside (6), by block condensation in 41% yield. Following enzymatic sialylation of 12 at the 3-O-position of its terminal galactopyranosyl residue using recombinant α-(2→3)-sialyltransferase and CMP-NeuAc afforded 13 in 59% yield.     

Synthesis of Terminal Oligosaccharides from Type Specific Lipooligosaccharide of Mycobacterium Tuberculosis

Abstract

The coupling reaction between 1,3-di-O-acetyl-4-O-benzyl-2-O-methyl-α-L-rhamnopyranose (9) and methyl 4-O-benzyl-2-O-methyl-α-L-rhamno-pyranoside (4) was carried out in the presence of boron trifluoride-etherate followed by deacetylation to give the disaccharide (11) containing a free 3′ position. The second glycosylation reaction with 2,3,4,6-tetra-O-acetyl-α-d-glucopyranosyl bromide in the presence of mercuric salts followed by removal of benzyl and acetyl groups provided the trisaccharide 2. The boron trifluoride catalysed condensation of 1,3,4-tri-O-acetyl-2-O-methyl-L-fucopyranose (14) and methyl 2,4,6-tri-O-benzyl-α-d-glucopyranoside (15) gave the disaccharide (16) from which the protecting groups were removed to form the disaccharide (3).     

Selectively Deoxygenated Derivatives of β-Maltosyl-(1→4)-Trehalose as Biological Probes

ABSTRACT

The four derivatives of β-maltosyl-(1→4)-trehalose have been synthesized, which are monodeoxygenated at the site of one of the primary hydroxyl groups. The tetrasaccharides were constructed in [2+2] block syntheses. Thus, 6′″-deoxy-β-maltosyl-(1→4)-trehalose was prepared by selective iodination of allyl 2,3,6,2′,3′-penta-O-acetyl-β-maltoside (3) followed by catalytic hydrogenolysis and coupling with 2,3-di-O-benzyl-4,6-O-benzylidene-α-D-glucopyranosyl 2′,3′,6′-tri-O-benzyl-α-D-glucopyranoside (9), and 6″-deoxy-β-maltosyl-(1→4)-trehalose by selective iodination of allyl 4′,6′-O-isopropylidene-β-maltoside (14), coupling with 9, and one-step hydrogenolysis at the tetrasaccharide level. For the synthesis of 6′-deoxy-β-maltosyl-(1→4)-trehalose, the diol 2,3-di-O-benzyl-4,6-O-benzylidene-α-D-glucopyranosyl 2′,3′-di-O-benzyl-α-D-glucopyranoside (22) was selectively iodinated and glycosylated with acetobromomaltose followed by catalytic hydrogenolysis. The 6-deoxy-β-maltosyl-(1→4)-trehalose was obtained upon selective iodination of a tetrasaccharide diol.     

Synthesis of Rhamnogalacturonan I Fragments

ABSTRACT

The partially deprotected trisaccharide 17 has been synthesized as an analogue of the repeating unit of the backbone of rhamnogalacturonan I. The trisaccharide 17 was obtained after prior selective derivatization of HO-3 and HO-4 of a rhamnopyranose cyanoethylidene glycosyl donor, followed by coupling with a tritylated galactopyranosyluronic acceptor (11), selective removal of the acetyl group at the O-2' position of the formed disaccharide 12, and glycosylation of the HO-2' position with methyl (ethyl 2,3-di-O-benzyl-4-O-p-methoxybenzyl-1-thio-β-D-galactopyranosid)uronate (14) providing methyl (methyl 2,3-di-O-benzyl-4-O-p-methoxybenzyl-α-D-galactopyranosyluronate)-(1→2)-(4-O-benzoyl-3-O-benzyl-α-L-rhamnopyranosyl)-(1→4)-(allyl 2,3-di-O-benzyl-β-D-galactopyranosid)uronate (15). Finally, palladium chloride catalyzed deallylation (16) and hydrogenolysis over Pd-C resulted in methyl (methyl α-D-galactopyranosyluronate)-(1→2)-(4-O-benzoyl-α-L-rhamnopyranosyl)-(1→4)-α/β D-galactopyranuronate (17).     

Synthesis of A Novel Sialyl Lewis X Analogue Containing A Pyrrolidine in Place of N-Acetyl Glucosamine

ABSTRACT

The synthesis of the new sialyl Lewis X analogue, 4-O-(α-L-fucopyranosyl)-3-O-(3-O-sodium sulfonato-β-D-galactopyranosyl)-(2S,3R, 4R)-2-ethyl-3,4-dihydroxypyrrolidine 2 has been achieved. The N-acetyl glucosamine unit of natural Lewis X has been replaced by a rigid 3R/4R-dihydroxylated pyrrolidine 12. This one has been synthezised from the methyl 4-O-benzoyl-2,3-di-O-benzyl-6-deoxy-6-iodo-α-D-altropyranoside sugar precursor 10 using the Ganem/Bernotas one-pot elimination-reductive amination ring contraction reaction. The (2S, 3R, 4R)-1-benzyloxycarbonyl-3,4-dihydroxy-2-ethylpyrrolidine 12 obtained was subsequently regioselectively glycosylated, using 2,3,4-tri-O-benzyl-α-L-fucopyranosyl fluoride and 2,3,4,6-tetra-O-benzoyl-β-D-galactopyranosyl bromide as glycosyl donors. Disaccharide containing pyrrolidine 21 was finally transformed into the target O-sulfated analog 2, after regioselective sulfation and usual deprotection.     

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.     

香菇多糖核心片段六糖的合成研究

以已知的2,3,4,6-四-O-苯甲酰基--D-葡萄吡喃糖-(13)-[2,3,4,6-四-O-苯甲酰基-β-D-葡萄吡喃糖-(16)]-2,4- 二-O-乙酰基-β-D-葡萄吡喃糖-(13)-2,4,6-三-O-乙酰基-α-D-葡萄吡喃糖三氯乙酰亚胺酯(2)为供体, 以2-O-苯甲酰 基-4,6-O-苄叉基-α-D-葡萄吡喃糖烯丙基苷(4)作为受体, 立体专一性地偶联得到β-1,3连接的五糖5. 五糖5酸解脱去4,6-苯亚甲基基后与2,3,4,6-四-O-苯甲酰基-α-D-葡萄吡喃糖三氯乙酰亚胺酯(7)偶联, 区域和立体专一性地得到全保护的β-1,3主链β-1,6支链的六糖8. 六糖8脱保护后得到目标化合物香菇多糖核心片段六糖9. 发展了合成该类化合物的一种新方法.     

Synthetic Mucin Fragments: Methyl-3-O-(2-Acetamido-2-Deoxy-4-O- and 6-O-β-D-Galactopyranosyl-β-D-Glucopyranosyl)-β-D-Galactopyranoside and Methyl 3-O-(2-Acetamido-2-Deoxy-4-O- and 3-O-Methyl-β-D-Glucopyranosyl-3-D-Galactopyranoside

Abstract

Glycosylation of methyl 3-O-(2-acetamido-3, 6-di-O-benzyl-2-deoxy-β-D-glucopyranosyl)-2,4,6-tri-O-benzyl-β-D-galactopyranoside (2) with 2,3,4,6-tetra-O-acetyl-α-D-galactopyranosyl bromide (1), catalyzed by mercuric cyanide, afforded a trisaccharide derivative, which was not separated, but directly O-deacetylated to give methyl 3-O-(2-acetamido-3,6-di-O-benzyl-2-deoxy-4-O-β-D-galactopyranosyl-β-D-giucopyranosyl)-2,4,6-tri-O-benzyl-β-D-galactopyranoside (8). Hydrogenolysls of the benzyl groups of 8 then furnished the title trisaccharide (9). A similar pflyccsylation of methyl 3-O-(2-acetamido-3-O-acetyl-2-deoxy-β-D-glucopyranosyl)-2,4,6-tri-O-benzyl- β-D-galactopyranoside (obtained by acetylation of 4, followed by hydrolysis of the benzylidene acetal group) with bromide 1 gave a tribenzyl trisaccharide, which, on catalytic hydrogenolysls, furnished the isomeric trisaccharide (12). Methylation of 4 and 2 with methyl iodide-silver oxide in 1:1 dichloro-methane-N, N-dimethylformamide gave the 3-O- and 4-O-monomethyl ethers (13) and (15), respectively. Hydrogenolysis of the benzyl groups of 13 and 15 then provided the title monomethylated disaechartdes (15) and (16), respectively. The structures of trisacchacides 9 and 12, and disaccharides 14 and 16 were all established by ¹³C MMR spectroscopy.     

Linear Synthesis of The Methyl Glycosides of Tri-, Tetra-, and Pentasaccharide Fragments of The Shigella Flexneri Serotype 5A O-Antigen

ABSTRACT

The stepwise synthesis of methyl α-D-glucopyranosyl-(1→3)-α-L-rhamnopyranosyl-(1→3)-α-L-rhamnopyranoside (EBC-OMe, 1), methyl α-L-rhamnopyranosyl-(1→2)-[α-D-glucopyranosyl-(1→3)]-α-L-rhamnopyranosyl-(1→3)-α-L-rhamnopyranoside (A(E)BC-OMe, 2), and methyl 2-acetamido-2-deoxy-β-D-glucopyranosyl-(1→2)-α-L-rhamnopyranosyl-(1→2)-[α-D-glucopyranosyl-(1→3)]-α-L-rhamnopyranosyl-(1→3)-α-L-rhamnopyranoside (DA(E)BC-OMe, 3) is described. Compounds 1, 2 and 3 constitute the methyl glycosides of fragments of the O-specific polysaccharide of Shigella flexneri serotype 5a. Methyl 2,4-di-O-benzoyl-α-L-rhamnopyranosyl-(1→3)-2,4-di-O-benzoyl-α-L-rhamnopyranoside was an appropriate BC precursor for the synthesis of 1. For the synthesis of the branched targets 2 and 3, a benzyl group was best suited at position 2 of rhamnose C. Thus, methyl 4-O-benzyl-α-L-rhamnopyranosyl-(1→3)-2,4-di-O-benzyl-α-L-rhamnopyranoside was the key intermediate to the BC portion. In all cases, 2,3,4,6-tetra-O-benzyl-α-D-glucopyranosyl fluoride was a convenient E precursor, when used in combination with titanium tetrafluoride. All along, attention was paid to steric hindrance as a factor of major impact on the condensation steps outcome. Therefore, based on previous experience, 2-O-acetyl-3,4-di-O-allyl-α-L-rhamnopyranosyl trichloroacetimidate and 3,4,6-tri-O-acetyl-2-deoxy-2-trichloroacetamido-α-D-glucopyranosyl trichloroacetimidate were used as donors. Both suited all requirements when used as key precursors for residues A and D in the synthesis of 3, respectively.