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The repeating units 2-O-beta-D-glucopyranosyl-L-ribitol 4'- and 1-phosphate of Haemophilus influenzae type a capsular antigen have been synthesised by condensation of an alpha-D-glucopyranosyl bromide derivative with 5-O-allyl-1,2,3-tri-O-benzyl-D-ribitol followed by selective deprotection of HO-4' or HO-1, phosphorylation, and removal of the blocking groups.
The oligosaccharide core region, beta-D-Glcp-(1----3)-beta-D-Glcp-(1----4)-alpha-D-Glcp- 1----1)-alpha-D-Glcp (1), of the lipo-oligosaccharide-type antigens isolated from M. kansasii has been synthesised from 2,3,2',3',4',6'-hexa-O-benzyl-6-O-(1-phenylethyl)-alpha, alpha-trehalose (4). Compound 4 was obtained by LiAlH4-AlCl3-type hydrogenolysis of 2,3,2',3',4',6'-hexa-O-benzyl-4,6-O-(S)-(1-phenylethylidene)-alpha , alpha-trehalose. The beta-laminaribiosyl part of the molecule was built-up by sequential glycosylation steps using 2,4,6-tri-O-acetyl-3-O-allyl-alpha-D-glucopyranosyl bromide in the presence of HgBr2 and methyl 2,3,4,6-tetra-O-acetyl-1-thio-beta-D-glucopyranoside promoted by methyl triflate. The complete a priori 13C-n.m.r. spectrum assignment of 1 was achieved by applying 2D methods.
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Selective ring-opening polymerization and copolymerization of 1,5-anhydro-D-xylofuranose derivatives were studied. Stereoregular (1----5)-alpha-D-xylofuranan was synthesized from a new monomer, 1,5-anhydro-2,3-di-O-(tert-butyldimethylsilyl)-beta-D-xylofuranose , with phosphorus pentafluoride and antimony pentachloride as catalysts in dichloromethane. Copolymerization of 3 with 1,5-anhydro-2,3-di-O-benzyl-beta-D-xylofuranose, and desilylation of the copolymer with tetrabutylammonium fluoride gave a partially benzylated stereoregular (1----5)-alpha-D-xylofuranan which was glycosylated with 3,4,6-tri-O-acetyl-beta-D-mannose 1,2-(methyl orthoacetate) to give a branched polymer. Deprotection of the benzylated polymer having D-mannosyl branches with sodium in liquid NH3 gave (1----5)-alpha-D-xylofuranans having 2- or 3-O-alpha-D-mannopyranosyl branches. Sulfation of the free D-xylofuranans was achieved with piperidine sulfate. The sulfated D-xylofuranan having branches showed high blood-anticoagulant activity.
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Methyl (5-acetoxyacetamido-4,7,8,9-tetra-O-acetyl-3,5- dideoxy-D-glycero-beta-D-galacto-2-nonulopyranosyl chloride)onate, prepared from N-glycolyl-neuraminic acid, was used for the glycosylation of benzyl O-(2,6-di-O-benzyl-beta-D- galactopyranosyl)-(1----4)-2,3,6-tri-O-benzyl-beta-D-glucopyranoside to give benzyl O-[methyl (5-acetoxyacetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D-glycero- alpha- and beta-D-galacto-2-nonulopyranosyl)onate]-(2----3)-O-(2,6-di-O -benzyl-beta- D-galacto-pyranosyl)-(1----4)-2,3,6-tri-O-benzyl-beta-D-glucopyranoside, and a regioisomer. Compounds 9 and 13 were converted into the corresponding glycotriaosyl glycosyl donors which, upon coupling with (2S,3R,4E)-3-O-tert-butyldiphenylsilyl-2-N- tetracosanoylsphingenine, afforded completely protected hematoside and a stereoisomer 26, respectively. Deprotection of 22 and 26 completed the first total synthesis of both hematoside and a stereoisomer, beta-NeuGc-(2----3)-beta-Gal-(1----4)-beta-Glc-(1----1)-Cer.
3-Azi-1-methoxybutyl beta-D-galactopyranoside, prepared from 2,3,4,6-tetra-O-acetyl-alpha-D-galactopyranosyl bromide in four steps, had an affinity constant for antigalactans IgA (Fab') J539 and X24 of 1550 and 1730 M-1, respectively. 3-Azi-1-methoxybutyl beta-D-(4-3H)galactopyranoside, when photolysed in the presence of IgA X24, specifically labelled the galactan-binding area of the immunoglobulin.
A strategy for the synthesis of Brucella O-antigenic determinants containing 2-linked 4,6-dideoxy-4-formamido-alpha-D-mannopyranosyl residues is described. The approach adopted also permits the N-acyl moiety to be varied. A high-yield synthesis of methyl 4-azido-4,6-dideoxy-alpha-D-mannopyranoside from D-mannose on the 10-20-g scale provided the key intermediate. Regioselective acetylation of 7 gave the 2-acetate 8, which, on treatment with benzyl trichloroacetimidate, provided methyl 2-O-acetyl-4-azido-3-O-benzyl-4,6-dideoxy-alpha-D-mannopyranoside. This compound served as a common precursor to the glycosyl donor 12 and acceptor 10 molecules. Silver trifluoromethanesulphonate-promoted glycosylation of 10 by 12 gave a disaccharide derivative, hydrogenolysis of which gave methyl 4-amino-2-O-(4-amino-4,6-dideoxy-alpha-D-mannopyranosyl)-4,6-dideoxy- alpha-D-mannopyranoside from which the N-formyl and N-acetyl derivatives were obtained. Deacetylation of 13 followed by glycosylation with 12 gave a trisaccharide derivative. The N-formylated disaccharide 17 inhibited the binding of Brucella O-polysaccharide to Brucella-specific monoclonal antibodies.
The protected glycopeptide N-(benzyloxycarbonyl)-L-alanyl-[O-(2,3,4,6-tetra-O-benzoyl-beta-D- galactopyranosyl)-(1----3)-O-(2,4,6-tri-O-benzyl-alpha-D-galactopyranosy l)- (1----3)]-L-threonyl-L-alanine 2,2,2-trichloroethyl ester was made by coupling the respective disaccharide and tripeptide blocks. The disaccharide block was generated by coupling tetra-O-benzoyl-alpha-D-galactopyranosyl bromide to allyl 2,4,6-tri-O-benzyl-alpha-D-galactopyranoside and converting the product into O-(2,3,4,6-tetra-O-benzoyl-beta-D-galactopyranosyl)-(1----3)-2,4,6-tri-O -benzyl - alpha-D-galactopyranosyl chloride via the 1-propenyl glycoside and the free (1-OH) sugar. Alternatively, the 1-propenyl intermediate was obtained directly by using 1-propenyl 2,4,6-tri-O-benzyl-alpha-D-galactopyranoside as the acceptor in the initial coupling reaction. An efficient 3-step synthesis of 10 was accomplished by the dibutyltin oxide-assisted, selective crotylation of allyl alpha-D-galactopyranoside at O-3, followed by benzylation and treatment of the product with potassium tert-butoxide. The N-benzyloxycarbonyl (Z) and N-tert-butoxycarbonyl (Boc) 2,2,2-trichloroethyl esters of Thr-Ala and Ala-Thr-Ala were formed by sequential coupling. The silver triflate-promoted glycosylation of the Z-protected dipeptide and tripeptide by 2,3,4,6-tetra-O-benzyl-alpha-D-galactopyranosyl chloride, and of the tripeptide by 6, proceeded with excellent alpha-stereoselectivity. From the disaccharide tripeptide 21, the carboxyl-deprotected and fully deprotected derivatives were prepared.
The heptasaccharide O-alpha-D-mannopyranosyl-(1----6)-O-[alpha-D-mannopyranosyl-(1----3)]-O- alpha-D-mannopyranosyl-(1----6)-O-[alpha-D-mannopyranosyl-(1----3)]-O-be ta- D-mannopyranosyl-(1----4)-O-(2-acetamido-2-deoxy-beta-D-glucopyranosyl)- (1----4)-2-acetamido-2-deoxy-D-glucopyranose, isolated from the urine of swainsonine-intoxicated sheep, was peracetylated and was converted into the glycosyl azide by three alternative procedures, the most successful of which was formation of peracetyl oxazoline by treatment with trimethylsilyl trifluoromethanesulfonate, followed by treatment with trimethylsilyl azide. Reduction of the glycosyl azide in the presence of Lindlar catalyst gave the glycosylamine derivative, which was coupled with 1-benzyl N-fluoren-9-ylmethoxycarbonyl-L-aspartate to yield a protected glycosylasparagine. The benzyl ester group was easily removed by hydrogenolysis to form an intermediate suitable for glycopeptide synthesis.
Total synthesis of O-beta-D-galactopyranosyl-(1----3)-O-[(5-acetamido-3,5-dideoxy- D-glycero-alpha-D-galacto-2-nonulopyranosylonic acid)-(2----6)]-O-(2-acetamido-2-deoxy-alpha-D-galactopyranosyl)-(1----3 )-L- serine was achieved by use of the key glycosyl donor O-(2,3,4,6-tetra-O-acetyl-beta-D-galactopyranosyl)-(1----3)-O- [methyl (5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D-glycero-alpha-D-galact o-2- nonulopyranosyl)onate-(2----6)]-4-O-acetyl-2-azido-2-deoxy-a lpha-D- galactopyranosyl trichloroacetimidate and the key glycosyl acceptor N-(benzyloxycarbonyl)-L- serine benzyl ester in a regiocontrolled way.
N-(Benzyloxycarbonyl)-O-[methyl (5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D-glycero-alpha-D-galact o-2- nonulopyranosyl)onate]-(2----3)-O-(2,4,6-tri-O-acetyl-beta-D - galactopyranosyl)-(1----3)-O-[methyl (5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D-glycero-alpha-D-galact o-2- nonulopyranosyl)onate-(2----6)]-O-(2-acetamido-4-O-acetyl-2- deoxy-alpha-D- galactopyranosyl)-(1----3)-L-serine benzyl ester was synthesized by using O-[methyl (5-acetamido-4,7,8,9-tetra-O-acetyl-3,5- di-deoxy-D-glycero-alpha-D-galacto-2-nonulopyranosyl)onate]- (2----3)-O-(2,4,6- tri-O-acetyl-beta-D-galactopyranosyl)-(1----3)-O-[methyl (5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D-glycero-alpha-D-galact o-2- nonulopyranosyl)onate-(2----6)]-4-O-acetyl-2-azido-2-deoxy-a lpha- and -beta-D-galactopyranosyl trichloroacetimidate as a key glycotetraosyl donor which, upon reaction with N-(benzyloxycarbonyl)-L-serine benzyl ester, afforded a 44% yield of a mixture of the alpha- and beta-glycosides in the ratio of 2:5.
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The following disaccharide glycosides were obtained in yields of 10-35% from the appropriate donor and acceptor glycosides by employing glycosidases as catalysts: alpha-D-Galp-(1----3)-alpha-D-GalpNAc-OEt (alpha-D-galactosidase), beta-D-Galp-(1----3)-alpha-D-GalpNAc-OEt and beta-D-Galp-(1----3)-beta-D-GalpNAc-OEtBr (beta-D-galactosidase), beta-D-GlcpNAc-(1----6)-beta-D-Galp-OMe and beta-D-GlcpNAc-(1----6)-alpha-D-Manp-OMe (beta-N-acetylglucosaminidase). With beta-D-GlcpNAc-OEtSiMe3 as the acceptor, beta-D-galactosidase gave beta-D-Galp-(1----3)-beta-D-GlcpNAc-OEtSiMe3 almost exclusively, whereas, with beta-D-GlcpNAc-OMe as the acceptor, beta-D-Galp-(1----3)-beta-D-GlcpNAc-OMe was formed in only slightly excess over teh analogous beta-(1----4)-linked glycoside. The use of beta-D-galactosidase and beta-D-galactoside 3-alpha-sialyltransferase in sequence provided a convenient route to the trisaccharide glycosides alpha-D-Neup5Ac-(2----3)-beta-D-Galp-(1----3)-alpha-D-GalpNAc-OEt, alpha-D-Neup5Ac-(2----3)-beta-D-Galp-(1----3)-beta-D-GalpNAc-OE tBr, and alpha-D-Neup5Ac-(2----3)-beta-D-Galp-(1----3)-beta-D-GlcpNAc-OMe.
Gangliosides GM3, containing three different fatty acyl groups at the ceramide moiety, have been synthesized. Coupling of 2-(trimethylsilyl)ethyl O-(6-O-benzoyl-beta-D-galactopyranosyl)-(1----4)- 2,6-di-O-benzoyl-beta-D-glucopyranoside (4), prepared from 2-(trimethylsilyl)ethyl beta-lactoside (1) by selective 3'-O-benzylation, O-benzoylation, and subsequent removal of the benzyl group, with methyl (methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-2-thio-D-glycero-alpha-D- galacto - 2-nonulopyranosid)onate (5) using dimethyl(methylthio)sulfonium triflate as a glycosyl promoter, gave 2-(trimethylsilyl)ethyl O-(methyl 5-acetamido-4,7,8,9-tetra-O- acetyl-3,5-dideoxy-D-glycero-alpha-D-galacto-2-nonulopyranosylonate++ +)-(2----3)- O-(6-O- benzoyl-beta-D-galactopyranosyl)-(1----4)-2,6-di-O-benzoyl-beta-D- glucopyranoside (6), which was converted, via O-acetylation, selective removal of the 2-(trimethylsilyl)-ethyl group, and subsequent imidate formation, into the alpha-N-acetylneuraminyl-(2----3')-lactose trichloroacetimidate 9. Glycosylation of (2S,3R,4E)-2-azido-3-O-benzoyl-4-octadecene-1,3-diol (10) with 9 afforded the beta-glycoside 11, which was converted, via selective reduction of the azide group, coupling with fatty acids, O-deacetylation, and de-esterification, into the title compounds.
The acidic capsular polysaccharide from the museum strain 2211 of Klebsiella ozaenae serotype K4 is built up of pentasaccharide repeating-units that contain residues of D-glucose, D-mannose, D-glucuronic acid, and 3-deoxy-D-glycero-D-galacto-nonulosonic acid (Kdn) in the ratios 2:1:1:1, as well as an O-acetyl group. The last-named sugar, which is reported in bacterial polysaccharides for the first time, was identified as the methyl (methyl 3-deoxynonulopyranosid)onate obtained by methanolysis of the polysaccharide. On the basis of the results of partial acid hydrolysis, Smith degradation, and computer-assisted 13C-n.m.r. analysis, it was concluded that the capsular polysaccharide has the following structure: (formula see text)
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