1,721,039 research outputs found
Paraplegia because of hemostatic agents in the costovertebral space : this occurs even in thoracic aorta surgery
No full textSynthesis of PNA in non conventional media
No full textThe growing awareness of the urgent need for greener, more sustainable
technologies has focused the scientific attention on the use of alternative reaction
media that circumvent the problems associated with the traditional volatile organic
solvents (VOCs). The use of non conventional reaction media also provides
opportunities to facilitate the recovery and the recycling of the reaction solvent.
Among the most promising alternatives to classical organic solvents, ionic liquids
(ILs) have been intensely studied in the recent years as potential environmentally
benign reaction media due to their lack of measurable vapour pressure and high
thermal and chemical stability.
Recently, room temperature Ionic liquids (RTILs) have been used as solvents in the
preparation of several classes of biomolecules such as oligosaccharides and
peptides.
In this communication we report a preliminary study on the use of ILs as solvents
in the preparation of peptide nucleic acids (PNAs).
The optimization of the reaction conditions, as well as the recycling of the ILs and
the use of microwave will be discussed
Synthesis of fragments of Salmonella thyphi capsular polysaccharide and their zwitterionic analogues
No full textCapsular polysaccharides (CPS) are T-independent antigens, and therefore they are not able to induce the formation of memory B cells. Their immunogenicity can be enhanced by conjugation with a immunogenic protein, forming a T-dependent glycoconjugate. Recently it has been discovered a new group of CPS that can directly activate T cells through the traditional MHC-II-dependent mechanism. Although these molecules show a wide diversity of chemical structure, they share the common characteristic of presenting a zwitterionic charge motif distributed along the chain, i.e. they contain both positive (e.g. NH3+) and negative (e.g. phosphate or carboxylate) charge centers within a repeating unit structure (zwitterionic polysaccharides, ZPS). This zwitterionic charge motif is believed to be responsible of their peculiar immunological activity, which is unique among bacterial polysaccharides. ZPS might offer previously unrecognized opportunities for the design of new classes of vaccines, based on the artificial introduction of a zwitterionic charge motif by chemical modification of surface glycans of pathogens. The design of new T cell dependent, ZPS-based antigens for vaccine formulation, however, requires a better understanding of how ZPS antigens stimulate the host immune system and a correlation of the ZPS structural and conformational properties with their biological activity.
We report the preparation of fully synthetic oligomers of Salmonella enterica serovar Typhi (often called S. typhi) CPS, and their zwitterionic analogues. S. Typhi is a motile Gram-negative bacterium, whose CPS (often referred to as Vi antigen) is an anionic polymer composed by α-(1-4)-linked N-acetyl galactosaminuronic acid repeating units predominantly O-acetylated at position 3.
The synthesis of Vi oligomers required a strategy based on two versatile intermediates suitably protected for the systematic introduction of charge centres on each repeating unit, and containing non participating protecting groups onto 2-amino functions to allow the formation of 1,2-cis glycosidic linkages. Both are easily attainable from commercially available D-galactosamine hydrochloride.
We employed the non participating azide group, which can be converted into the amino group (ZPS) or into the acetamido function (natural Vi) in the late stages of the synthesis. After extensive exploration, the glycosylation reactions were carried out using N-phenyl-trifluoroacetimidates as glycosyl donors, yielding stereoselectively the desired α product.
The immunological properties of the synthetic oligomers will be investigated in order to correlate the structural features with their biological behaviour
Synthesis of fragments of Salmonella Typhi capsular polysaccharide and their zwitterionic analogues
No full textSalmonella enterica serovar Typhi (often called S. Typhi) is a motile Gram-negative bacterium, whose capsular polysaccharide (often referred to as Vi antigen) is an anionic polymer composed of α-(1-4)-linked N-acetyl-galactosaminuronic acid repeating units predominantly O-acetylated at position 3. The degree of acetylation was found to be crucial for the immunogenicity. We investigated two different synthetic routes for the oligomers assembly: a late stage post-glycosylation oxidation approach and a pre-glycosylation oxidation strategy, the latter employing suitably protected uronates donor and acceptor. Glycosylation reactions were carried out using N-phenyltrifluoroacetimidates as glycosyl donors, and experimental conditions were carefully screened in order to ensure the stereoselective formation of the desired α product. The azido group at C-2 can be converted into either an acetamido function (natural Vi) or a free amino group (zwitterionic derivatives). Finally, a pentenyl linker was installed at C-1 of the reducing end in order to facilitate the subsequent conjugation to protein carrier and/or multivalent scaffolds
Synthesis of fragments of Salmonella Typhi capsular polysaccharide and their zwitterionic analogues
No full textWe will report on the synthesis of oligomers of Salmonella enterica serovar Typhi (often called S. Typhi) CPS, and their zwitterionic analogues. S. Typhi is a motile Gram-negative bacterium, whose CPS (often referred to as Vi antigen) is an anionic polymer composed by α-(1-4)-linked N-acetyl galactosaminuronic acid repeating units predominantly O-acetylated at position 3. We developed a strategy based on versatile intermediates enabling chain elongation either by iterative single monomer attachment or by faster and more flexible approaches using disaccharide donors. All these intermediates were obtained from commercially available D-galactosamine hydrochloride. The non participating azide group was used to mask C-2 amino functionality, which can be converted into the animo group (ZPS) or into the acetamido function (natural Vi) and allows the formation of 1,2-cis glycosidic linkages. Glycosylation reactions were carried out using N-phenyltrifluoroacetimidates as glycosyl donors, yielding
stereoselectively the desired α product. C-6 oxidation was done with TEMPO/NaClO2. By orthogonally protecting
position 3 we were able to obtain both fully 3-O-acetylated and fully 3-O-deactetylated oligomers. Finally, a suitable l
inker was installed at C-1 of the reducing end in order to facilitate a subsequent conjugation to protein carrier and/or
multivalents caffolds. The immunological properties of the synthetic oligomers will be also investigated in order to correlate the structural features (in particular 3-O-acetylation) with their biological behaviour
Synthesis of fragments of salmonella typhi capsular polysaccharide
No full textWe will report on the synthesis of oligomers of Salmonella enterica serovar Typhi (often called S. Typhi) capsular polysaccharide (CPS). S. Typhi is a motile Gram-negative bacterium, whose CPS (often referred to as Vi antigen) is an anionic polymer composed of α-(1-4)-linked N-acetyl galactosaminuronic acid repeating units predominantly O-acetylated at position 3. We developed a strategy based on versatile intermediates enabling chain elongation either by iterative single monomer attachment or by faster and more flexible approach using disaccharide donors. All these intermediates were obtained from commercially available D-galactosamine hydrochloride. Glycosylation reactions were carried out using N-phenyl-trifluoroacetimidates as glycosyl donors, yielding stereoselectively the desired α product. Late stage C-6 oxidation was done by a Dess-Martin/Pinnick oxidation. Finally, a suitable linker was installed at C-1 of the reducing end in order to facilitate the subsequent conjugation to protein carrier and/or multivalent scaffolds
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Synthesis of fragments of Salmonella Typhi capsular polysaccharide and their zwitterionic analogues
No full textCapsular polysaccharides (CPS) are T-independent antigens, and therefore they are not able to induce the formation of memory B cells. Their immunogenicity can be enhanced by conjugation with a immunogenic protein, forming a T-dependent glycoconjugate. Recently it has been discovered a new group of CPS that can directly activate T cells through the traditional MHC-II-dependent mechanism. Although these molecules show a wide diversity of chemical structure, they share the common characteristic of presenting a zwitterionic charge motif distributed along the chain, i.e. they contain both positive (e.g. NH3+) and negative (e.g. phosphate or carboxylate) charge centers within a repeating unit structure (zwitterionic polysaccharides, ZPS). This zwitterionic charge motif is believed to be responsible of their peculiar immunological activity, which is unique among bacterial polysaccharides. ZPS might offer previously unrecognized opportunities for the design of new classes of vaccines, based on the artificial introduction of a zwitterionic charge motif by chemical modification of surface glycans of pathogens. The design of new T cell dependent, ZPS-based antigens for vaccine formulation, however, requires a better understanding of how ZPS antigens stimulate the host immune system and a correlation of the ZPS structural and conformational properties with their biological activity.
We report the preparation of fully synthetic oligomers of Salmonella enterica serovar Typhi (often called S. Typhi) CPS, and their zwitterionic analogues. S. Typhi is a motile Gram-negative bacterium, whose CPS (often referred to as Vi antigen) is an anionic polymer composed by α-(1-4)-linked N-acetyl galactosaminuronic acid repeating units predominantly O-acetylated at position 3.
The synthesis of Vi oligomers required a strategy based on two versatile intermediates suitably protected for the systematic introduction of charge centres on each repeating unit, and containing non participating protecting groups onto 2-amino functions to allow the formation of 1,2-cis glycosidic linkages. Both are easily attainable from commercially available D-galactosamine hydrochloride.
We employed the non participating azide group, which can be converted into the amino group (ZPS) or into the acetamido function (natural Vi) in the late stages of the synthesis. After extensive exploration, the glycosylation reactions were carried out using N-phenyl-trifluoroacetimidates as glycosyl donors, yielding stereoselectively the desired α product.
The immunological properties of the synthetic oligomers will be investigated in order to correlate the structural features with their biological behaviour
Synthesis of fragments of salmonella Typhi capsular polysaccharide and their zwitterionic analogues
No full textCapsular polysaccharides (CPS) are T-independent antigens, and therefore they are not able to induce the formation of memory B cells. Their immunogenicity can be enhanced by conjugation with a immunogenic protein, forming a T-dependent glycoconjugate. Recently it has been discovered a new group of CPS that can directly activate T cells through the traditional MHC-II-dependent mechanism. Although these molecules show a wide diversity of chemical structure, they share the common characteristic of presenting a zwitterionic charge motif distributed along the chain, i.e. they contain both positive (e.g. NH3+) and negative (e.g. phosphate or carboxylate) charge centers within a repeating unit structure (zwitterionic polysaccharides, ZPS). This zwitterionic charge motif is believed to be responsible of their peculiar immunological activity, which is unique among bacterial polysaccharides. ZPS might offer previously unrecognized opportunities for the design of new classes of vaccines, based on the artificial introduction of a zwitterionic charge motif by chemical modification of surface glycans of pathogens. The design of new T cell dependent, ZPS-based antigens for vaccine formulation, however, requires a better understanding of how ZPS antigens stimulate the host immune system and a correlation of the ZPS structural and conformational properties with their biological activity.
We report the preparation of fully synthetic oligomers of Salmonella enterica serovar Typhi (often called S. Typhi) CPS, and their zwitterionic analogues. S. Typhi is a motile Gram-negative bacterium, whose CPS (often referred to as Vi antigen) is an anionic polymer composed by α-(1-4)-linked N-acetyl galactosaminuronic acid repeating units predominantly O-acetylated at position 3.
The synthesis of Vi oligomers required a strategy based on two versatile intermediates suitably protected for the systematic introduction of charge centres on each repeating unit, and containing non participating protecting groups onto 2-amino functions to allow the formation of 1,2-cis glycosidic linkages. Both are easily attainable from commercially available D-galactosamine hydrochloride.
We employed the non participating azide group, which can be converted into the amino group (ZPS) or into the acetamido function (natural Vi) in the late stages of the synthesis. After extensive exploration, the glycosylation reactions were carried out using N-phenyl-trifluoroacetimidates as glycosyl donors, yielding stereoselectively the desired α product.
The immunological properties of the synthetic oligomers will be investigated in order to correlate the structural features with their biological behaviour
- …
