A facile synthesis of [3,6-di-O-acetyl-4-O-(chloroacetyl)-1,2-dideoxy-α-D-glucopyrano]-[2,1-d]-2-methyl-2-oxazoline for use in oligosaccharide synthesis

Chemical characterization and immunomodulatory properties of polysaccharides isolated from probiotic Lactobacillus casei LOCK 0919

The Lactobacillus casei strain, LOCK 0919, is intended for the dietary management of food allergies and atopic dermatitis (LATOPIC® BIOMED). The use of a probiotic to modulate immune responses is an interesting strategy for solving imbalance problems of gut microflora that may lead to various disorders. However, the exact bacterial signaling mechanisms underlying such modulations are still far from being understood. Here, we investigated variations in the chemical compositions and immunomodulatory properties of the polysaccharides (PS), L919/A and L919/B, which are produced by L. casei LOCK 0919. By virtue of their chemical features, such PS can modulate the immune responses to third-party antigens. Our results revealed that L919/A and L919/B could both modulate the immune response to Lactobacillus planatarum WCFS1, but only L919/B could alter the response of THP-1 cells (in terms of tumor necrosis factor alpha production) to L. planatarum WCFS1 and Escherichia coli Nissle 1917. The comprehensive immunochemical characterization is crucial for the understanding of the biological function as well as of the bacteria-host and bacteria-bacteria cross-talk.

Structural differences between the alkali-extracted water-soluble cell wall polysaccharides from mycelial and yeast phases of the pathogenic dimorphic fungus Paracoccidioides brasiliensis

Paracoccidioides brasiliensis is a pathogenic dimorphic fungus causing paracoccidioidomycosis, the most widespread systemic mycosis in Latin America. We have studied the structure of the alkali-extracted water-soluble cell wall polysaccharides (F1SS) from both mycelial and yeast phases of this fungus by using chemical analysis and NMR spectroscopic techniques. The F1SS polysaccharide from the mycelial phase consists of a trisaccharidic repeating unit of -->6)-[alpha-Galf -(1-->6)-alpha-Manp-(1-->2)]-alpha-Manp-(1-->. The F1SS polysaccharide of the yeast phase maintains 10% of the structure of the mycelium phase, but the main structure contain a disaccharide repeating unit of -->6)-[-alpha-Manp-(1-->2)]-alpha-Manp-(1-->, alternating with a trisaccharide repeating block of -->6)-[beta-Galf -(1-->6)-alpha-Manp-(1-->2)]-alpha-Manp-(1-->.

1,3,4,6-Tetra-O-acetyl-2-chloroacetamido-2-deoxy-beta-D-glucopyranose as a glycosyl donor in syntheses of oligosaccharides

1,3,4,6-Tetra-O-acetyl-2-chloroacetamido-2-deoxy-beta-D-glucopyran ose was tested as a glycosyl donor for oligosaccharide synthesis via a ferric chloride-catalyzed coupling reaction. Glycosyl acceptors tried (6 in all) were O-benzyl-protected D-galactosides having free OH groups at positions 3 and 4, respectively, and similarly protected glycosides of D-glucose and 2-acetamido-2-deoxy-D-glucose unsubstituted on O-4. Existing syntheses of all the acceptors were improved, in four instances by exploitation of Garegg and Hultberg's cyanoborohydride procedure for the conversion 4,6-O-benzylidene----6- O-benzyl [Carbohydr. Res., 93 (1981) c10-c11; 108 (1982) 97-101]. Good to excellent yields of beta-linked disaccharides were obtained from the galactoside and glucoside acceptors, but with allyl 2-acetamido-3,6-di-O-benzyl-2-deoxy-alpha-D-glucopyranoside, stereoselectivity was lost (alpha:beta-ratio 1:2). Allyl and benzyl 2-acetamido-3,6-di-O-benzyl-2-deoxy-beta-D-glucopyranosides gave, respectively, the allyl and benzyl beta-glycosides of the donor as major products. A mechanism is proposed for this transglycosidation reaction. The N-chloroacetyl groups in the disaccharide products were readily converted into N-acetyl by reduction with zinc-acetic acid.

Synthesis of 2-methyl-[2-acetamido-4-O-acetyl-6-O-benzyl-3-O-(2-butenyl)-1,2-dideoxy-alpha-D -glucopyrano]-[2,1-d]-2-oxazoline, a versatile intermediate for the synthesis of complex oligosaccharides of bacterial cell-wall, human milk, and blood-group substances

2-Methyl-[2-acetamido-4-O-acetyl-6-O-benzyl-3-O-(2-butenyl)-1,2-dideoxy-alpha-D-glucopyrano]-[2,1-d]-2-oxazoline (2), a glycosylating agent in which the three hydroxyl groups are blocked with protecting groups of differing "persistence", is of utility in the synthesis of oligosaccharides containing highly branched 2-acetamido-2-deoxy-D-glucosyl residues, and it was synthesized in a ten-step sequence from 2-acetamido-2-deoxy-D-glucose via allyl 2-acetamido-4,6-O-benzylidene-2-deoxy-beta-D-glucopyranoside (3). Alkylation of 3 with 2-butenyl (crotyl) bromide, hydrolysis of the benzylidene acetal group, benzylation of the 6-hydroxyl group, and acetylation of the 4-hydroxyl group afforded allyl 2-acetamido-4-O-acetyl-6-O-benzyl-3-O-(2-butenyl)-2-deoxy-beta-D-glucopyranoside(10). Treatment of 10 with chlorotris(tri-phenylphosphine)rhodium(I) gave mainly the corresponding 1-propenyl beta-glycoside, which was converted into oxazoline 2 by the action of mercuric chloride-mercuric oxide in acetonitrile. Glycosylation of benzyl 2-acetamido-3,6-di-O-benzyl-2-deoxy-alpha-D-glucopyranoside with 2, and subsequent O-deacetylation at O-4' gave a glycosyl acceptor, benzyl 2-acetamido-4-O-[2-acetamido-6-O-benzyl-3-O-(2-butenyl) -2-deoxy-beta-D-glucopyranosyl]-3,6-di-O-benzyl-2-deoxy-alpha-D-glucopyranoside .