Syntheses of anomerically phosphodiester-linked oligomers of the repeating units of the Haemophilus influenzae types c and f capsular polysaccharides.

Spacer-equipped dimers and trimers of the repeating units of the capsular polysaccharide of Haemophilus influenzae type c, -4)-3-O-Ac-beta-D-GlcpNAc-(1-->3)-alpha-D-Galp-(1-OPO(3-)-, and type f, -3)-beta-D-GalpNAc-(1-->4)-3-O-Ac-alpha-D-GalpNAc-(1-OPO(3-)-, have been synthesized for use in immunological studies. H-Phosphonate chemistry was used for the formation of the interglycosidic phosphate diester linkages. Two types of building blocks, a spacer glycoside disaccharide starting monomer (15 and 22) and an anomeric monoester alpha-H-phosphonate disaccharide elongating monomer (12 and 27), were built up for each serotype structure from properly protected monosaccharide precursors using mainly thioglycosides as glycosyl donors. Stereospecificity in the formation of the alpha-linked monoester H-phosphonate was possible in type c through crystallization of the pure alpha-anomer of the precursor hemiacetal from an alpha/beta-mixture, whereas in type f, the hemiacetal was isolated directly as exclusively the alpha-anomer. Subsequent phosphonylation using triimidazolylphosphine was performed without anomerization. Formation of the anomeric phosphate diester linkages was performed using pivaloyl chloride as coupling reagent followed by I(2)/H(2)O oxidation of the formed diester H-phosphonates. Original experiments afforded no diester product at all, but optimization of the oxidation conditions (lowering the temperature and dilution with pyridine prior to I(2) addition) gave the dimers in good yields (71% and 81%) and, subsequently, after removal of a temporary silyl protecting group in the dimers, the trimers in fair yields (36% and 37%), accompanied by hydrolysis of the dimer phosphate linkage. One-step deprotection through catalytic hydrogenolysis efficiently afforded the target dimer (30 and 36) and trimer structures (32 and 39). The synthetic scheme allows for further elongation to give higher oligomers.

Synthesis of oligosaccharides corresponding to structures found in capsular polysaccharides of Cryptococcus neoformans--II.

Formula 1 depicts a generalized structure of the capsular polysaccharides of four serotypes of the opportunistic microorganism Cryptococcus neoformans, which appears as one of the major infections in the late stages of development of AIDS. Syntheses are now described of two tetrasaccharides with corresponding structures. These are methyl O-alpha-D-mannopyranosyl-(1-->3)-[O-beta-D-xylopyranosyl-(1-->2)] -O-alpha-D-mannopyranosyl-(1-->3)-alpha-D-mannopyranoside and methyl O-alpha-D-mannopyranosyl-(1-->3)-[O-beta-D-glucopyranosyluronic acid-(1-->2)]-O-alpha-D-mannopyranosyl-(1-->3)-alpha-D-mannopyranoside.

Synthesis of 2-(4-trifluoroacetamidophenyl)ethyl O-(L-glycero-alpha-D-manno-heptopyranosyl)-(1----7)-O-(L-glycero-alpha- D-manno- heptopyranosyl)-(1----3)-L-glycero-alpha-D-manno-heptopyranoside, corresponding to the heptose region of the Salmonella Ra core structure.

The title trisaccharide was synthesized from methyl 2,3,4-tri-O-benzyl-L-glycero-alpha-D-manno-heptopyranoside by acetolysis, followed by conversion into ethyl thioglycosides and also glycosyl bromides, which were both used in glycosylation reactions. In glycosylations using thioglycosides as glycosyl donors, N-iodosuccinimide-silver triflate and dimethyl(methylthio)sulfonium triflate were used as promoters, and in glycosylations with glycosyl bromides silver triflate was used. The protecting groups introduced into intermediates during the synthesis of the title trisaccharide were designed to allow later glycosylation at O-3' to give larger oligosaccharide fragments of the Salmonella LPS core region, and also to allow the introduction of phosphate groups at O-4 and O-4', a structural element that is suggested to be present in the Ra core.

Synthesis of an artificial antigen that corresponds to a disaccharide repeating unit of the capsular polysaccharide of Haemophilus influenzae type d. A facile synthesis of methyl 2-acetamido-2-deoxy-beta-D-mannopyranoside.

The synthesis is described of p-nitrophenyl 2-acetamido-3-O-(2-acetamido-2-deoxy-beta-D-glucopyranosyl)-2-deoxy-beta -D- mannopyranosiduronic acid, corresponding to the disaccharide repeating unit of the capsular polysaccharide of Haemophilus influenzae type d, which, after conversion of the p-nitro- into a p-amino-phenyl residue, may be attached to a protein to make an artificial antigen for immunological studies. The synthesis incorporates a facile route to the 2-acetamido-2-deoxy-beta-D-mannopyranosyl unit.

Structure-activity relationships of oligo-beta-glucoside elicitors of phytoalexin accumulation in soybean.

The abilities of a family of chemically synthesized oligo-beta-glucosides, ranging in size from hexamer to decamer, to induce phytoalexin accumulation in soybean cotyledons were investigated to determine which structural elements of the oligoglucosides are important for their biological activity. The results of the biological assays established that the following structural motif is necessary for the oligo-beta-glucosides to have high elicitor activity: [formula; see text] The branched trisaccharide at the nonreducing end of the oligoglucosides was found to be essential for maximum elicitor activity. Substitution of either the nonreducing terminal backbone glucosyl residue or the side-chain glucosyl residue closest to the nonreducing end with glucosaminyl or N-acetylglucosaminyl residues reduced the elicitor activity of the oligoglucosides between 10-fold and 10,000-fold. Elicitor activity was also reduced 1000-fold if the two side-chain glucosyl residues were attached to adjacent backbone glucosyl residues rather than to glucosyl residues separated by an unbranched residue. In contrast, modifications of the reducing terminal glucosyl residue of an elicitor-active hepta-beta-glucoside by conjugation with tyramine and subsequent iodination had no significant effect on the elicitor activity of the hepta-beta-glucoside. These results demonstrate that oligo-beta-glucosides must have a specific structure to trigger the signal transduction pathway, which ultimately leads to the de novo synthesis of phytoalexins in soybean.

Synthesis of methyl 3-O-(alpha-D-glucopyranosyl)-7-O-(L-glycero-alpha-D- manno-heptopyranosyl)-L-glycero-alpha-D-manno-heptopyranoside.

The title trisaccharide glycoside, which is related to part of the core region of the lipopolysaccharide from Salmonella, and the disaccharide glycosides methyl 3-O-alpha-D-glucopyranosyl-L-glycero-alpha-D-manno-heptopyranoside and methyl 7-O-L-glycero-alpha-D-manno-heptopyranosyl-L-glycero-alpha-D-manno- heptopyranoside have been synthesised. Methyl 2,3,4-tri-O-benzyl-L-glycero-alpha-D-manno- heptopyranoside, obtained via a one-carbon elongation at C-6 of methyl 2,3,4-tri-O-benzyl-alpha-D-manno- hexodialdo-1,5-pyranoside, was used as precursor both for the heptosyl donor and acceptor.

Use of the methylsulfenyl cation as an activator for glycosylation reactions with alkyl (aryl) 1-thioglycopyranosides: synthesis of methyl O-(2-acetamido-2- deoxy-beta-D-glucopyranosyl)-(1----6)-O-alpha-D-glucopyranosyl-(1----2) -alpha-D -glucopyranoside, a derivative of the core trisaccharide of E. coli K12.

Methylsulfenyl bromide (MSB) and methylsulfenyl trifluoromethanesulfonate (MST) have been used to prepare 1,2-cis-linked disaccharides. Ethyl (phenyl) 1-thio-beta-D-gluco- and galacto-pyranosides having non-participating (benzyloxy) protecting groups were used as the donors. The alpha beta-ratio of the products depended on the promoter and conditions of reaction. Intimate ion-pairs, formed initially, may be responsible for the steric outcome of the glycosylations. Thus, with ethyl 2,3,4,6-tetra-O-benzyl-alpha-D-mannopyranoside as a donor, moderate quantities of the beta-linked disaccharide could be produced using MSB as the activator. The synthesis of the title trisaccharide glycoside that contains 1,2-cis and 1,2-trans-linkages is described.

Synthesis of p-trifluoroacetamidophenyl beta-D-glucopyranoside 4-(D-ribit-5-yl phosphate) corresponding to the Haemophilus influenzae type A capsular antigen.

The synthesis is described of the title glycoside which corresponds to the Haemophilus influenzae type a capsular antigen. The hydrogenphosphonate method was used with 3,3'-(chlorophosphonylidene)bis(2-oxo-1,3-oxazolidene) as the condensing agent.

Synthesis of three 3-C-hydroxymethylpentoses with the D-ribo-, D-xylo- and L-lyxo-configurations. Identification of the latter with a monosaccharide isolated from phase I Coxiella burnetii lipopolysaccharide.

Three 3-C-hydroxymethylpentoses with the D-ribo-, D-xylo and L-lyxo-configurations, were synthesised via nitromethane addition for the first two and 1,3-dithiane addition for the last one, to appropriate 3-ulose derivatives. 3-C-Hydroxy-methyl-L-lyxose is identical with a monosaccharide component previously isolated from hydrolysates of the phase I Coxiella burnetii lipopolysaccharide.

Synthesis of a glucoheptaose and a glucooctaose that elicit phytoalexin accumulation in soybean.

The glucoheptaose 1 and the glucooctaose 2 have been synthesized using unambiguous methods. The former is identical with an elicitor-active heptasaccharide obtained from partially hydrolyzed mycelium of Phytophthora megasperma f. sp. glycinea. The octasaccharide is also elicitor active, although to a lesser extent than the heptasaccharide. 1:R = H; 2:R = beta-D-Glcp. (Formula: see text)

Comparison of the structures and elicitor activities of a synthetic and a mycelial-wall-derived hexa(beta-D-glucopyranosyl)-D-glucitol.

The elicitor activity and structural characteristics of chemically synthesized hepta- and octa-beta-D-glucopyranosides were compared with the same properties of an elicitor-active mycelial-wall-derived hexa(beta-D-glucopyranosyl)-D-glucitol. The specific elicitor activities, retention times on reversed-phase liquid chromatography columns, glycosyl-linkage compositions, 1H NMR analyses, and glycosyl-sequence analyses of the synthetic and mycelial-wall-derived hexa(beta-D-glucopyranosyl)-D-glucitols were indistinguishable. This work provided conclusive proof that elicitor activity was associated with the structure proposed (Sharp, J. K., McNeil, M., and Albersheim, P. (1984) J. Biol. Chem. 259, 11321-11336) for the elicitor-active mycelial-wall-derived hexa(beta-D-glucopyranosyl)-D-glucitol.

The conformation of Salmonella O-antigenic polysaccharide chains of serogroups A, B, and D1 predicted by semi-empirical, Hard-Sphere (HSEA) calculations.

The preferred conformation of the tetrasaccharide repeating units of Salmonella Serogroups A, B, and D1 have been calculated. The semiempirical calculations used the Hard-Sphere, Exo-Anomeric (HSEA) approach to derive a conformational model, which could be used to assist the interpretation of conformations significantly populated in aqueous solution. The calculated model was extended to include a pentasaccharide repeating unit bearing an alpha-D-glucopyranose-branch point. The 3,6-dideoxyhexose to D-mannose linkage was shown to possess a steep energy surface with a minimum, which results in good exposure of the dideoxyhexose O-2 and O-4 atoms. Stereochemical changes involving the equatorial or axial disposition of these atoms are the distinguishing structural features of the A, B, and D1 serogroups. A lipophilic surface involving the 6-deoxy groups of the dideoxy-D-hexose and L-rhamnose residues was identified, and the possible implications of these features in antigenic determinants is discussed. The preferred conformation predicted by the HSEA method correlates with the known antigenic specificities of polysaccharides belonging to these Salmonella serogroups.

The conformation of Salmonella O-antigenic oligosaccharides of serogroups A, B, and D1 inferred from 1H- and 13C-nuclear magnetic resonance spectroscopy.

The conformational model derived by the HSEA calculation method was used to interpret the n.m.r. data for solutions of oligosaccharides corresponding to the Salmonella serogroups A, B, and D1 antigenic determinants. The favored conformer, derived by calculation, accounted for the observed, chemical-shift changes and accurately predicted the existence and magnitude of inter-ring proton n.O.e.'s. Extensive proton-density and compression of proton, Van der Waals radii were correlated with deshielding of specific proton-resonances. The model of lipopolysaccharide conformation accounts for the known antigenic properties of Salmonella O-antigens.

Synthesis of di- and tri-saccharides corresponding to receptor structures recognised by pyelonephritogenic E. coli fimbriae (pili).

Syntheses are described of di- and tri-saccharides required for studies of the inhibition of adhesion by means of fimbriae of pyelonephritogenic E. coli bacteria to epithelium cells in the urinary tract containing suitable receptor sites. The disaccharides are the rho-nitrophenyl and methyl glycosides of 4-omicron-alpha-D-galactopyranosyl-beta-D-galactopyranose, and the trisaccharides are the rho-nitrophenyl and methyl glycosides of 4-omicron-(4-omicron-alpha-D-galactopyranosyl-beta-D-galactopyranosyl)-beta- D-glucopyranose. The key aglycons were the 1,2,3,6-tetrabenzoate of alpha-D-galactose and the 1,2,3,6,-2',3',6'-heptabenzoate of alpha-lactose. Glycosidations were performed with 2,3,4,6-tetra-omicron-benzyl-alpha-D-galactopyranosyl chloride as glycosylating agent and silver triflate as promoter.

A 500-MHz proton-magnetic-resonance study of several fragments of the carbohydrate-protein linkage region commonly occurring in proteoglycans.

The proton-magnetic-resonance spectra of three partial structures of the carbohydrate-protein linkage region that frequently occurs in proteoglycans, namely, beta-D-Galp-(1 leads to 3)-beta-D-Galp-(1 leads to 4)-beta-D-Xylp-(1 leads to O)-L-Ser, were recorded in 2H2O at 500 MHz; they could be completely interpreted, both for the glyco-serines and for the corresponding glyco-xylitols. The chemical shifts and the coupling constants were refined by computer simulation of the spectra. The change in the chemical shift of H-4 of a D-galactopyranosyl residue upon substitution at C-3 by a beta-D-galactopyranosyl group is proposed to be characteristic for this particular attachment, making H-4 of galactose a structural-reporter group. The three constituting monosaccharides adopt the 4C1 (D) ring conformation. The terminal galactopyranosyl group and the internal galactopyranosyl residue differ as to the population of rotamers around the C-5/C-6 axis. Concomitantly, the flexibility of their glycosidic linkages is distinct.