Synthetic antigenic determinants of the Brucella A polysaccharide: A disaccharide thioglycoside for block synthesis of pentasaccharide and lower homologues of α1,2-linked 4,6-dideoxy-4-formamido-α-D-mannose

Abstract

. Can. J. Chem. 67, 491 (1989). Methyl glycosides 13, 18, and 22, which represent potential antigenic determinants of the Brucella A polysaccharide, are the first synthetic analogues of this antigen. Their synthesis was necessitated by crystallographic studies of a Fab combining site obtained from a monoclonal antibody that binds the Brucella A antigen and synthetic pentasaccharide. Monosaccharide synthon 3 and disaccharide 7, S-ethyl glycoside derivatives of 4-azido-4,6-dideoxy-D-mannose, have been used successfully as key intermediates in a convergent strategy to synthesize a1,2-linked homo-oligosaccharides of 4,6-dideoxy-4-formamido-D-mannose. The disaccharide thioglycoside 7 was activated by methyl triflate in the presence of selectively protected mono-or trisaccharide alcohols 1, 6, or 10 to give al,2-linked tri-and pentasaccharides 8, 9, and 19. Despite the non-participating glycosyl substituent at position two of the thioglycoside, 1,2-trans glycosidic products appeared to be formed exclusively. Conversion of 3 to the glycosyl bromide 5 by bromine under mild conditions provided routes to both the disaccharide building block 7 and a tetrasaccharide 15 using conventional silver triflate promoted glycosylation reactions. Deprotection was accomplished by transesterification, hydrogen sulphide reduction of azido groups, followed by N-formylation and finally hydrogenolysis of benzyl ethers.Key words: Brucella A antigen, pentasaccharide synthesis, thioglycosides, oligosaccharide building units, 4,6-dideoxy-4-formamido-D-mannose, antibody combining sites.THOMAS PETERS et DAVID R. BUNDLE. Can. J. Chem. 67,491 (1989). Les glycosides de mCthyle 13, 18 et 22 qui reprtsentent des dkterminants antigtniques potentiels du polysaccharide de la Brucella A sont les premiers analogues de synthbse de cet antigkne. On a d13 rkaliser leur synthbse pour effectuer des analyses de structure par diffraction des rayons-X sur un Fab cristallin combinant le site de liaison de l'antigbne Brucella A et le pentasaccharide de synthbse. Le monosaccharide de synthbse 3 ainsi que le disaccharide 7, des dCrivts glycoside de S-Cthyle de l'azido-4 didksoxy-4,6 D-mannose, ont Ctt utilisCs avec succbs comme intermtdiaires clCs dans une strattgie convergente conduisant ?i la synthbse d'homo-oligosaccharides liCs en a1,2 du didCsoxy-4,6 formamido-4 D-mannose. On a activt le thioglycoside du disaccharide 7 par le triflate de mCthyle en prksence des mono-ou tri-saccharides alcools 1 , 6 ou 10, protCgCs d'une fagon stlective, et on a obtenu les tri-et penta-saccharides 8, 9 ou 19 lies par les positions a1,2. MalgrC la prCsence d'un substituant glycosyle non-participant en position deux du thioglycoside, il semble que les produits glycosidiques 1,2-trans se foment d'une fagon exclusive. La transformation du compost 3 en bromure de glycosyle, par l'action du brome dans des conditions douces, fournit des voies pouvant conduire, par des rCactions de glycosylation conventionnelles activtes par le triflate d'argent, soit au disaccharide 7 ou au tttrasacchar...

Glycosylation under Thermodynamic Control: Synthesis of the Di‐ and the Hexasaccharide Fragments of the O‐SP of Vibrio Cholerae O:1 Serotype Ogawa from Fully Functionalized Building Blocks

“…The poor stereoselectivity of glycosylations, compared with similar reactions involving 4-azido intermediates which lack the acylamido group at the same position, [18,22,24,33] could not be improved by the solvent effect or by changing nature of the glycosyl donor. However, glycosylations with the same reactants could be made more α-selective when they were conducted under thermodynamic control, showing that with the complex synthons involved, temperature is the key parameter to control the formation of the thermodynamically more stable α-product.…”

“…Very similar, closely related 4-azido-oligosaccharides made by blockwise assembly from intermediates lacking the acylamido group, were obtained with much better α stereoselectivity. [22,24,33] Attempts to improve the yield of 25 by changing the glycosyl donor and promoter were unsuccessful (Table 1, Entry 9). The latter two obser- [c] The reaction was performed in a well-ventilated hood.…”

“…Assignment of 13 C NMR spectra of some higher oligosaccharides was aided by comparison with spectra of related substances reported previously from this laboratory or elsewhere. [33] When the latter approach was used, to aid in the 13 C NMR signal-nuclei assignments, advantage was taken of variations of line intensity expected for oligosaccharides belonging to the same homologous series. [34,35] Thus, spectra showed close similarity of chemical shifts of equivalent carbon atoms of the internal residues, and an increase in the relative intensity of these signals with the increasing number of -perosamine residues in the molecule.…”

Conformational analysis of key disaccharide components of Brucella A and M antigens

“…The model compounds 1-8 were of synthetic origin (7)(8)(9). Samples were dissolved in 0.5 mL D20 (99.996 at.% D, Aldrich) after repeated lyophilization from D20 (99.96 at.% D, Aldrich).…”

“…were synthesized in addition to tri-, tetra-, and pentasaccharides (7)(8)(9). The structural variation at the 4-amino group was considered to be a necessity in the conformational analysis of antigen fragments because 4,6-dideoxy-4-formamido-D-mannose exists in solution as both E and Z isomers (2, 10, 1 I), a complication that prevents a practical analysis of conformation at the level of trisaccharide or higher homologues.…”