Anhydrous Trifluoroacetic Acid Research Articles

Trifluoroacetic Acid Promoted Ring Contraction in 2,3-Di-O-silylated O-Galactopyranosides and Hemiacetals

AbstractA pyranose ring contraction of 2,3-di-O-silylated O-galactopyranosides with retention of aglycone promoted by anhydrous trifluoroacetic acid (TFA) in CH2Cl2 was demonstrated for the first time. In addition, TFA-promoted pyranose ring contraction of 2,3-bis-O-(triisopropylsilyl)-d-galactopyranose with formation of the corresponding anomeric triols in furanose form was successfully performed. A representative series of β-d-galactopyranosides with Me, Bn, allyl, or 3-(trifluoroacetamido)propyl aglycones has been investigated. TBDPS protective groups were found to be more stable than TIPS groups under conditions of TFA-promoted pyranose ring contraction. An easy access to 2,3-di-O-TBDPS-substituted allyl and benzyl galactofuranosides and 2,3-bis-O-(triisopropylsilyl)-β-d-galactofuranose may present an advantage in synthesis of selectively protected monosacharide building blocks, useful for the synthesis of biologically important oligosaccharides.

Structure and gene cluster of the O-antigen of Enterobacter cloacae G3422

The O-polysaccharide (OPS) was isolated by mild acid degradation of the lipopolysaccharide of Enterobacter cloacae G3422 and studied by chemical methods, including sugar analyses, Smith degradation, and solvolysis with anhydrous trifluoroacetic acid, along with 1H and 13C NMR spectroscopy. The following structure of the branched tetrasaccharide repeating unit was established: [Display omitted] The O-antigen gene cluster of Enterobacter cloacae G3422 was sequenced. The gene functions were tentatively assigned by comparison with sequences in the available databases and found to be in a good agreement with the O-antigen structure.

Initial experience in synthesis of (2S,4R)-4-[18 F]fluoroglutamine for clinical application.

We report initial experience in synthesis of (2S,4R)-4-[18 F]fluoroglutamine, [18 F]FGln, which has been used as a tool for monitoring glutamine metabolism in cancer patients. [18 F]FGln was prepared by a fully automated PET-MF-2V-IT-I synthesizer under GMP-compliant conditions for routine clinical studies. The total radiosynthesis time was about 65minutes, the decay-corrected radiochemical yield was 18.0±4.2% (n=59; failure n=15), and the radiochemical purity was greater than 90%. In some situations, the yields were low (less than 5%), and the most likely cause of this problem is the initial fluorination step; the fluoride ion might not have been fully activated. In other occasions, low final radiochemical purity was often associated with the failure of the second step-removal of protection groups by anhydrous trifluoroacetic acid. A trace amount of water led to production of undesired 4-[18 F]fluoroglutamic acid. Knowledge learned from the successes and failures of synthesis may be helpful to identify critical steps and pitfalls for preparation of this clinically useful metabolic probe, [18 F]FGln, for imaging glutamine utilization in tumor of cancer patients.

Structure and gene cluster of the O-antigen of Escherichia coli O54

Mild acid hydrolysis of the lipopolysaccharide of Escherichia coli O54 afforded an O-polysaccharide, which was studied by sugar analysis, solvolysis with anhydrous trifluoroacetic acid, and 1H and 13C NMR spectroscopy. Solvolysis cleaved predominantly the linkage of β-d-Ribf and, to a lesser extent, that of β-d-GlcpNAc, whereas the other linkages, including the linkage of α-l-Rhap, were stable under selected conditions (40 °C, 5 h). The following structure of the O-polysaccharide was established:→4)-α-d-GalpA-(1 → 2)-α-l-Rhap-(1 → 2)-β-d-Ribf-(1 → 4)-β-d-Galp-(1 → 3)-β-d-GlcpNAc-(1→The O-antigen gene cluster of E. coli O54 was analyzed and found to be consistent in general with the O-polysaccharide structure established but there were two exceptions: i) in the cluster, there were genes for phosphoserine phosphatase and serine transferase, which have no apparent role in the O-polysaccharide synthesis, and ii) no ribofuranosyltransferase gene was present in the cluster. Both uncommon features are shared by some other enteric bacteria.

Structure and gene cluster of the O-antigen of Enterobacter cloacae G3421

The O-polysaccharide was isolated by mild acid degradation of the lipopolysaccharide of Enterobacter cloacae G3421 and studied by sugar analysis along with 1D and 2D 1H and 13C NMR spectroscopy. In addition, partial solvolysis with anhydrous trifluoroacetic acid was applied, which cleaved selectively the α-l-rhamnopyranosidic linkages. The following structure of the branched hexasaccharide repeating unit was established. [Display omitted] The O-polysaccharide studied shares the β-l-Rhap-(1→4)-α-l-Rhap-(1→2)-α-l-Rhap trisaccharide fragment with the O-polysaccharide of Shigella boydii type 18. The O-antigen gene cluster of E. cloacae G3421 was sequenced. Functions of genes in the cluster, including those for glycosyltransferases, were tentatively assigned by a comparison with sequences in the available databases and found to be consistent with the O-polysaccharide structure.

Structure and gene cluster of the O-antigen of Escherichia coli O43

The O-polysaccharide (O-antigen) of Escherichia coli O43 was isolated from the lipopolysaccharide and studied by chemical methods, including sugar analyses, Smith degradation, and solvolysis with anhydrous trifluoroacetic acid, along with 1H and 13C NMR spectroscopy. The following structure of the pentasaccharide repeating unit of the O-polysaccharide was established: [Display omitted] Functions of genes in the O-antigen gene cluster of E. coli O43 were assigned by a comparison with sequences in the available databases and found to be in agreement with the O-polysaccharide structure.

Structure and gene cluster of the O-antigen of Escherichia coli O68

The O-polysaccharide (O-antigen) of Escherichia coli O68 was studied by sugar analysis, partial solvolysis with anhydrous trifluoroacetic acid, and 1D and 2D 1H and 13C NMR spectroscopies. The following structure of the branched heptasaccharide repeating unit was established: [Display omitted] The O-antigen gene cluster of E. coli O68 was sequenced. The gene functions were tentatively assigned by comparison with sequences in the available databases and found to be in full agreement with the O-antigen structure.

Structure elucidation and gene cluster annotation of the O-antigen of Escherichia coli O39; application of anhydrous trifluoroacetic acid for selective cleavage of glycosidic linkages

O-Polysaccharide (O-antigen) accompanied by a minor mannan was isolated from the lipopolysaccharide of Escherichia coli O39 and studied by component analyses, methylation, Smith degradation, mass spectrometry, and 1D and 2D NMR spectroscopy. In addition, a new approach, solvolysis with anhydrous trifluoroacetic acid, was applied to cleave selectively the rhamnosidic linkage. The following structure of the O-polysaccharide was established: [Display omitted] where d-Qui4N(R3Hb) indicates 4,6-dideoxy-4-[(R)-3-hydroxybutanoylamino]-d-glucose. The O-antigen gene cluster of E. coli O39 has been sequenced. The gene functions were tentatively assigned by a comparison with sequences in the available databases and found to be in agreement with the O-polysaccharide structure.

Chemical transformations of methane in trifluoroacetic acid

The reaction of methane conversion in anhydrous trifluoroacetic acid (TFA) is shown to take place at room temperature and atmospheric pressure and to result in the formation of a resinous product. Signals of ions with molecular weights of 684 and 700 are observed in MALDI-TOF spectra of the dry residue of methane conversion products.

A push–pull azobenzene is mercurated twice at the ring with less electron density

Treatment of N,N-dialkyl-4-[4-nitrophenyl)diazenyl] anilines with a mercury(II) salt in anhydrous trifluoroacetic acid results in single and double metallation of the ring with less electron density. The seemingly counterintuitive outcome of the reaction was rationalized through experimental and computational investigations of the reaction mechanism.

Conversion of CO2 in a trifluoroacetic acid

It is determined that the conversion of carbon dioxide in anhydrous trifluoroacetic acid (TFA) takes place at room temperature and atmospheric pressure, yielding a resinous product. Activation of CO2 by the oxygen dissolved in a TFA is investigated.

Studies on the Selective Trifluoroacetolytic Scission of Native Peptaibols and Model Peptides Using HPLC and ESI‐CID‐MS

Representative members of a group of linear, N-acylated polypeptide antibiotics (peptaibols) containing alpha-aminoisobutyric acid (Aib) and, in part, isovaline (Iva), as well as proteinogenic amino acids and a C-terminal-bonded 2-amino alcohol, were treated with anhydrous trifluoroacetic acid (TFA) at 37 degrees for 0.5-26 h. The resulting fragments were separated by HPLC and characterized by electrospray ionization collision-induced dissociation mass spectrometry (ESI-CID-MS). The following 16-20-residue peptaibols were investigated: natural, microheterogeneous mixtures of antiamoebins and alamethicin F50, uniform paracelsin A, and synthetic trichotoxin A50/E. In the natural peptides, bonds formed between Aib (Iva) and Pro (Hyp) were rapidly and selectively cleaved within 0.5 h. Furthermore, TFA esters of the C-terminal amino alcohols were formed. Depending on time, release of C-terminal tri- and tetrapeptides as well as amino acids from the major fragments was observed. Synthetic homooligopeptides, namely Z- and Ac-(Aib)(10)-O(t)Bu and Z-(Aib)(7)-O(t)Bu, were analyzed for comparison. On treatment with TFA, a regular series of Z-(Aib)(10-5)-OH from Z-(Aib)(10)-O(t)Bu were detected within 0.5 h, and, after 3 h, release of a regular series of Z-(Aib)(7-3)-OH from Z-(Aib)(7)-O(t)Bu were observed. Moreover, concomitant release of the series of H-(Aib)(10-3)-OH from the decapeptide occurred. From these data, a repetitive cleavage mechanism via intermediate formation of C-terminal oxazolones on trifluoroacetolysis is proposed. Furthermore, their formation and stability in native peptaibols are correlated with subtle structural differences in protein amino acids linked to Aib. From the conspicuous concordance of the formation and abundance of regular series of trifluoroacetolytic fragments and of positive ions of the b-series in CID-MS, the generation of intermediate oxazolonium ions in both gas and liquid phase is concluded.

Anionic Complexes of Cu(I) with the Closo-Decaborate Anion

General procedures for synthesis of anionic Cu(I) complexes with the closo-decaborate anion were worked out; they make it possible to prepare coordination compounds with a wide set of organic cations. The interaction of onium closo-decaborates with [Cu2B10H10] in acetonitrile acidified with anhydrous trifluoroacetic acid was found to be the most effective synthetic method that secures high yield and quality of the obtained products. The structure of (C2H5)3NH[CuB10H10] was determined by X-ray diffraction analysis.

The Chaotrope-soluble Glycoprotein GP2 Is a Precursor of the Insoluble Glycoprotein Framework of the Chlamydomonas Cell Wall

The cell wall of the unicellular green alga Chlamydomonas reinhardtii consists of an insoluble, hydroxyproline-rich glycoprotein framework and several chaotrope-soluble, hydroxyproline-containing glycoproteins. Up to now, there have been no data concerning the amino acid sequences of the hydroxyproline-containing polypeptides of the insoluble wall fraction. Matrix-assisted laser desorption ionization time-of-flight analyses of peptides released from the insoluble cell wall fraction by trypsin treatment revealed the presence of 14 peptide fragments that could be attributed to non-glycosylated domains of the chaotrope-soluble cell wall glycoprotein GP2. However, these peptides cover only 15% of the GP2 polypeptide backbone. Considerably more information concerning the presence of GP2 in the insoluble cell wall fraction was obtained by an immunochemical approach. For this purpose, 407 overlapping pentadecapeptides covering the whole known amino acid sequence of GP2 were chemically synthesized and probed with a polyclonal antibody raised against the deglycosylated, insoluble cell wall fraction. This particular antibody reacted with 297 of the 407 GP2-derived peptides. The peptides that were recognized by this antibody are distributed over the whole known GP2 sequence. The epitopes recognized by polyclonal antibodies raised against the 64- and 45-kDa constituents purified from the deglycosylation products of the insoluble cell wall fraction are also distributed over the whole GP2 backbone, although the corresponding antigens are considerably smaller than GP2. The significance of the latter results for the structure of the insoluble cell wall fraction is discussed.

Thickness control of solution deposited YBCO superconducting films by use of organic polymeric additives

We show that the thickness of yttrium–barium–copper–oxide (YBCO) superconducting films grown from trifluoroacetate precursors can be strongly modified using polymeric additives, while deposition conditions by spin or dip coating remain unchanged. A screening of different families of organic additives has been performed, and the best results have been achieved using polymers having an oxygen functionalized backbone. Two different polymeric additives, polyvinyl pyrrolidone (PVP) and poly(ethylene glycol) (PEG), have been more thoroughly investigated, and thermal analysis suggests that PEG is the most promising alternative because the pyrolysis step of the new complex precursors remains sharp and narrow and hence the final homogeneity of the film is preserved. The combination of anhydrous trifluoroacetic acid (TFA) solutions and poly(ethylene-glycol) (PEG8000) as additive can produce an increase of the YBCO film thickness up to 300%, while keeping a fast pyrolysis process and high critical current densities.

Neuroserpin Binds Aβ and Is a Neuroprotective Component of Amyloid Plaques in Alzheimer Disease

Alzheimer disease is characterized by extracellular plaques composed of Abeta peptides. We show here that these plaques also contain the serine protease inhibitor neuroserpin and that neuroserpin forms a 1:1 binary complex with the N-terminal or middle parts of the Abeta(1-42) peptide. This complex inactivates neuroserpin as an inhibitor of tissue plasminogen activator and blocks the loop-sheet polymerization process that is characteristic of members of the serpin superfamily. In contrast neuroserpin accelerates the aggregation of Abeta(1-42) with the resulting species having an appearance that is distinct from the mature amyloid fibril. Neuroserpin reduces the cytotoxicity of Abeta(1-42) when assessed using standard cell assays, and the interaction has been confirmed in vivo in novel Drosophila models of disease. Taken together, these data show that neuroserpin interacts with Abeta(1-42) to form off-pathway non-toxic oligomers and so protects neurons in Alzheimer disease.

An Osmabenzofuran from Reaction between Os(PhC⋮CPh)(CS)(PPh3)2 and Methyl Propiolate and the C-Protonation of this Compound to Form a Tethered Osmabenzene

Reaction between the diphenylacetylene complex Os(PhC⋮CPh)(CS)(PPh3)2 (1) and two molecules of HC⋮CCO2Me leads to a very stable, blue, osmabicylic complex with osmium at a bridgehead position. One way to consider this complex is as a metalla-aromatic molecule, viz., the osmabenzofuran Os[C7H2O(OMe-7)(CO2Me-4)(Ph-1)(Ph-2)](CS)(PPh3)2 (2). The bicyclic ring system is remarkably robust, and heating this compound in ethanol at reflux with aqueous HCl effects only a transesterification of the ester function in the six-membered ring (at the 4-position), forming Os[C7H2O(OMe-7)(CO2Et-4)(Ph-1)(Ph-2)](CS)(PPh3)2 (3). Reaction of Os[C7H2O(OMe-7)(CO2Me-4)(Ph-1)(Ph-2)](CS)(PPh3)2 (2) with pyridinium tribromide effects bromination in the five-membered ring of the osmabenzofuran at the 6-position to form Os[C7HO(OMe-7)(Br-6)(CO2Me-4)(Ph-1)(Ph-2)](CS)(PPh3)2 (4). Crystal structure determinations of 2, 3, and 4 confirm the osmabicyclic structure of each compound. Treatment of complex 2 with anhydrous trifluoroacetic acid...

The catalytic oxidation of organic compounds in superacids

Transformations of aromatic and aliphatic organic substances in anhydrous trifluoroacetic acid (TFA) at room temperature were studied. TFA was found to be capable of activating molecular oxygen dissolved in it. This activated oxygen endows the acid with strong oxidizer properties. Transformations of organic substances in TFA involved the formation of peroxo compounds, and alkylaromatic molecules were only oxidized at the benzene ring, side chains remaining intact. The transformations of toluene and p-xylene in trifluoroacetic acid were similar in a way to the biochemical oxidation of these substrates by mono-and dioxygenases. Mechanisms were suggested for the oxidation of toluene, p-xylene, and propylene by active oxygen in superacids.

Superacids as catalysts of the oxidation of inorganic substrates

The oxidation of sulfur dioxide, nitrogen dioxide, carbon monoxide, etc., in anhydrous trifluoroacetic acid (TFA) at room temperature was observed. The oxidative ability of anhydrous TFA in reactions with inorganic substances was shown to be related to molecular oxygen dissolved in it. The dissolved molecular oxygen endowed TFA with the properties of a superacid with pK a ≃ −12. Mechanisms of active oxygen reactions with inorganic substrates were suggested.

Synthesis of poly(styrene‐block‐tert‐butyl acrylate) star polymers by atom transfer radical polymerization and micellization of their hydrolyzed polymers

AbstractA series of poly(styrene‐block‐tert‐butyl acrylate) heteroatom star block copolymers having various block lengths were prepared by atom transfer radical polymerization (ATRP), using an “as synthesized” cynurate modified trifunctional initiator. The structure of the star polymers was confirmed by the characterization of the individual arms resulting from hydrolysis. Amphiphilic poly(styrene‐block‐acrylic acid) star copolymers were further synthesized by hydrolyzing PtBA blocks using anhydrous trifluoroacetic acid. The characterization data are reported from analyses using gel permeation chromatography, infrared, 1H and 13C NMR spectroscopies. The stable micelle solution was prepared by dialyzing the solution of these polymers in N,N‐dimethylformamide against deionized water. The temperature‐induced associating behavior of these amphiphilic star polymers were studied using dynamic laser light scattering spectroscopy. The hydrodynamic diameter of both micelles and unassociated chains were obtained in the same solution using light scattering cumulant's calculation method. The homogeneity and the size distribution of the micelle population in the solution were determined using centrifuge/sedimentation particle size distribution analyzer. Field emission scanning electron microscope was used to visualize the size of the micelles formed and the micellar aggregates. The influence of the temperature on the viscosity of the micelle solution was studied using an Ubbelohde viscometer. Thermodynamics of micellization of these block copolymers were also investigated. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6367–6378, 2005