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PubMed2005

Synthesis of phosphorofluoridates and phosphorofluoridothioates via the phosphoramidite approach.

We present a very efficient synthetic procedure leading to the phosphorofluoridates RO-P(O)(OH)F 1 or phosphorofluoridothioates RO-P(S)(OH)F 2, which is based on the intermediary of fluorophosphoramidites (RO)P(F)N(i)Pr2 5 [R = 9-(hydroxyethyloxymethyl)guaninyl), 3'azido-3'deoxythymidinyl, thymidinyl, anhydrothymidinyl, cholesteryl, N6-benzoyl-5'-O-(4,4'-dimethoxytrityl)-2'-deoxyadenosinyl]. The activation of the amino group was performed with trimethylchlorosilane (TMCS).

Fluorides↗
PubMed2005

Elemental fluorine. Part 18. Selective direct fluorination of 1,3-ketoesters and 1,3-diketones using gas/liquid microreactor technology.

1,3-Ketoesters and 1,3-diketones react with fluorine gas, using Durham multichannel modular microreactor technology, on a preparatively useful scale. High conversions and yields of monofluorinated products were obtained. A consideration of the mechanism of fluorination of dicarbonyl systems provides a rationale of the scope and limitations of the use of microreactor technology for such direct fluorination processes. We conclude that it is especially appropriate for the fluorination of diketones and ketoesters that exist mainly in the enol form at equilibrium and/or undergo rapid keto-enol interconversion. A one-stage route to fluoroketones from ketoesters was achieved by allowing the crude product mixture obtained from the fluorination of the ketoesters to stand for a period of time before reaction work-up.

Biotechnology↗
PubMed2005

Excited state hydrogen transfer in fluorophenol.ammonia clusters studied by two-color REMPI spectroscopy.

Two-color (1 + 1') REMPI mass spectra of o-, m- and p-fluorophenol.ammonia (1 ration) clusters were measured with a long delay time between excitation and ionization lasers. The appearance of NH(4)(NH(3))(n-1)(+) with 100 ns delay after exciting the S(1) state is a strong indication of generation of long-lived species via S(1). In analogy with the phenol.ammonia clusters, we conclude that an excited state hydrogen transfer reaction occurs in o-, m- and p-fluorophenol.ammonia clusters. The S(1)-S(0) transition of o-, m- and p-fluorophenol.ammonia (1 : 1) clusters were measured by the (1 + 1') REMPI spectra, while larger (1 ration) cluster (n = 2-4) were observed by monitoring the long-lived NH(4)(NH(3))(n-1) clusters action spectra. The vibronic structures of m- and p-fluorophenol.ammonia clusters are assigned based on vibrational calculations in S(0). The o-fluorophenol.ammonia (1 : 1) cluster shows an anharmonic progression that is analyzed by a one-dimensional internal rotational motion of the ammonia molecule. The interaction between the ammonia molecule and the fluorine atom, and its change upon electronic excitation are suggested. The broad action spectra observed for the o-fluorophenol.ammonia (1 : n) cluster (n>== 2) suggest the excited state hydrogen transfer is faster than in m- and p-fluorophenol.ammonia clusters. The different reaction rates between o-, m- and p-fluorophenol.ammonia clusters are found from comparison between the REMPI and action spectra.

Ammonia↗
PubMed1995

Probing the ionization state of substrate alpha-D-glucopyranosyl phosphate bound to glycogen phosphorylase b.

The ionization state of the substrate alpha-D-glucopyranosyl phosphate bound at the active site of glycogen phosphorylase has been probed by a number of techniques. Values of Ki determined for a series of substrate analogue inhibitors in which the phosphate moiety bears differing charges suggest that the enzyme will bind both the monoanionic and dianionic substrates with approximately equal affinity. These results are strongly supported by 31P- and 19F-NMR studies of the bound substrate analogues alpha-D-glucopyranosyl 1-methylenephosphonate and 2-deoxy-2-fluoro-alpha-D-glucopyranosyl phosphate, which also suggest that the substrate can be bound in either ionization state. The pH-dependences of the inhibition constants K1 for these two analogues, which have substantially different phosphate pK2 values (7.3 and 5.9 respectively), are found to be essentially identical with the pH-dependence of K(m) values for the substrate, inhibition decreasing according to an apparent pKa value of 7.2. This again indicates that there is no specificity for monoanion or dianion binding and also reveals that binding is associated with the uptake of a proton. As the bound substrate is not protonated, this proton must be taken up by the proton.

Animals↗
PubMed1998

2'-Fluoropyrimidine RNA-based aptamers to the 165-amino acid form of vascular endothelial growth factor (VEGF165). Inhibition of receptor binding and VEGF-induced vascular permeability through interactions requiring the exon 7-encoded domain.

Vascular endothelial growth factor (VEGF) has been implicated in the pathological induction of new blood vessel growth in a variety of proliferative disorders. Using the SELEX process (systematic evolution of ligands by exponential enrichment), we have isolated 2'-F-pyrimidine RNA oligonucleotide ligands (aptamers) to human VEGF165. Representative aptamers from three distinct sequence families were truncated to the minimal sequence capable of high affinity binding to VEGF (23-29 nucleotides) and were further modified by replacement of 2'-O-methyl for 2'-OH at all ribopurine positions where the substitution was tolerated. Equilibrium dissociation constants for the interaction of VEGF with the truncated, 2'-O-methyl-modified aptamers range between 49 and 130 pM. These aptamers bind equally well to murine VEGF164, do not bind to VEGF121 or the smaller isoform of placenta growth factor (PlGF129), and show reduced, but significant affinity for the VEGF165/PlGF129 heterodimer. Cysteine 137 in the exon 7-encoded domain of VEGF165 forms a photo-inducible cross-link to a single uridine residue in each of the three aptamers. The aptamers potently inhibit the binding of VEGF to the human VEGF receptors, KDR and Flt-1, expressed by transfected porcine aortic endothelial cells. Furthermore, one of the aptamers is able to significantly reduce intradermal VEGF-induced vascular permeability in vivo.

Amino Acid Sequence↗
PubMed2002

Tyrosinase-catalyzed oxidation of fluorophenols.

The activity of the type 3 copper enzyme tyrosinase toward 2-, 3-, and 4-fluorophenol was studied by kinetic methods and (1)H and (19)F NMR spectroscopy. Whereas 3- and 4-fluorophenol react with tyrosinase to give products that undergo a rapid polymerization process, 2-fluorophenol is not reactive and actually acts as a competitive inhibitor in the enzymatic oxidation of 3,4-dihydroxyphenylalanine (L-dopa). The tyrosinase-mediated polymerization of 3- and 4-fluorophenols has been studied in detail. It proceeds through a phenolic coupling pathway in which the common reactive fluoroquinone, produced stereospecifically by tyrosinase, eliminates an inorganic fluorine ion. The enzymatic reaction studied as a function of substrate concentration shows a prominent lag that is completely depleted in the presence of L-dopa. The kinetic parameters of the reactions can be correlated to the electronic and steric effects of the fluorine substituent position. Whereas the fluorine electron withdrawing effect appears to control the binding of the substrates (K(m) for 3- and 4-fluorophenols and K(I) for 2-fluorophenol), the k(cat) parameters do not follow the expected trend, indicating that in the transition state some additional steric effect rules the reactivity.

Antioxidants↗
PubMed2004

Hexafluorine vs. standard decontamination to reduce systemic toxicity after dermal exposure to hydrofluoric acid.

INTRODUCTION: Dermal exposure to hydrofluoric acid (HF) may cause severe burns and systemic toxicity. Hexafluorine (Prevor, France) is a product marketed as an emergency decontamination fluid for HF skin and eye exposures. Documentation concerning Hexafluorine is scanty, and a recent study indicates that its ability to reduce HF burns is at most equal to that of water. OBJECTIVE: The present study was conducted to evaluate Hexafluorine's capacity to reduce HF-induced systemic toxicity. METHODS: Sprague Dawley rats were anesthetized, catheterized in the left femoral artery, and shaved on their back. A filter paper (3.5 x 6 cm) was soaked in 50% HF and applied on the back of each rat for 3 min. Thirty seconds after removal of the paper, a 3-min rinsing with either 500 mL Hexafluorine (group H), 500 mL water (group W), or 500 mL water followed by a single application of 2.5% calcium gluconate gel (group Ca) was carried out. Blood samples were analyzed for ionized calcium and potassium (before injury and 1, 2, 3, and 4 h after) and also for ionized fluoride (1, 2, and 4 h after injury). RESULTS: The animals developed hypocalcemia, hyperkalemia, and hyperfluoridemia after the HF exposure. The only significant difference observed among the groups was in serum potassium at 1 h between group Ca and group W. However, there was a constant trend toward milder hypocalcemia and less pronounced hyperkalemia in group Ca compared to the other groups. There were no differences in the electrolyte disturbances between the Hexafluorine-treated animals and those treated with water only. Five of 39 animals died before completion of the experiment as a result of the HF exposure, one from group Ca and two from each of the other two groups. CONCLUSION: In this experimental study, decontamination with Hexafluorine was not more effective than water rinsing in reducing electrolyte disturbances caused by dermal exposure to hydrofluoric acid.

Animals↗
PubMed1999

Pheromone-triggered orientation flight of male moths can be disrupted by trifluoromethyl ketones.

In a wind tunnel trifluoromethyl ketones (TFMKs) have been found to disrupt the orientation flight of male moths to pheromone sources (virgin females or synthetic pheromone). This is demonstrated by comparison of the flight parameters of the Egyptian armyworm Spodoptera littoralis and the Mediterranean corn borer Sesamia nonagrioides, which had been topically treated with TFMKs, with those calculated for untreated insects. Inhibition occurred in all types of behavior and that of the source contact has been quantified and found to be dose-dependent. The same effect has also been noticed in Mediterranean corn borer males flying to an attraction source consisting of mixtures of (Z)-11-hexadecenyl trifluoromethyl ketone (8), a closely related analogue of the major component of the pheromone, and the natural pheromone blend. The most active TFMKs are those closest in structure to the natural pheromone, along with those chemicals which easily hydrate in solution, such as the beta-thiosubstituted derivatives. Along with the previously reported reduction of catches in the field, our results suggest the possible application of these chemicals in future new pest control strategies.

Animals↗
PubMed1996

Secondary structure of the r(CUUCGG) tetraloop.

The oligonucleotide r(GGACUUCGGUCC) has been observed to adopt a hairpin conformation by solution NMR and a double helical conformation by X-ray diffraction. In order to understand this apparent conflict, we used time-resolved fluorescence depolarization and 19fluorine NMR to follow the secondary structure of this dodecamer as the solution composition was changed stepwise from the NMR experimental conditions to those used for crystallization. Calculation of the dodecamer concentration in the crystal (180 mM strands) and the cation concentration needed for neutrality (>2 M) prompted investigation of a tethered species, in which two dodecamers are connected by a string of 4 nt, geometrically equivalent to approximately 100 mM strands, in 2.5 M NaCl. The RNA tetraloop and its DNA analog maintain a single-strand hairpin conformation in solution, even under the conditions used to grow the crystal. Under high salt conditions, the tethered RNA and DNA analogs of this sequence yield secondary components which could be the double helical conformation. Crystal contacts in addition to solvent changes and high RNA concentrations are needed to obtain the double helix as the predominant species.

Chemical Phenomena↗
PubMed1997

2'-Fluoro modified nucleic acids: polymerase-directed synthesis, properties and stability to analysis by matrix-assisted laser desorption/ionization mass spectrometry.

Fragmentation is a major factor limiting mass range and resolution in the analysis of DNA by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). Protonation of the nucleobase leads to base loss and backbone cleavage by a mechanism similar to the depurination reactions employed in the chemical degradation method of DNA sequencing. In a previous study [Tang,W., Zhu,L. and Smith,L.M. (1997) Anal. Chem ., 69, 302-312], the stabilizing effect of substituting the 24 hydrogen with an electronegative group such as hydroxyl or fluorine was investigated. These 24 substitutions stabilized the N-glycosidic linkage, blocking base loss and subsequent backbone cleavage. For such chemical modifications to be of practical significance, it would be useful to be able to employ the corresponding 24-modified nucleoside triphosphates in the polymerase-directed synthesis of DNA. This would provide an avenue to the preparation of 24-modified PCR fragments and dideoxy sequencing ladders stabilized for MALDI analysis. In this paper methods are described for the polymerase-directed synthesis of 24-fluoro modified DNA, using commercially available 24-fluoronucleoside triphosphates. The ability of a number of DNA and RNA polymerases to incorporate the 24-fluoro analogs was tested. Four thermostable DNA polymerases [Pfu (exo-), Vent (exo-), Deep Vent (exo-) and UlTma] were found that were able to incorporate 24-fluoronucleotides with reasonable efficiency. In order to perform Sanger sequencing reactions, the enzymes' ability to incorporate dideoxy terminators in conjunction with the 24-fluoronucleotides was evaluated. UlTma DNA polymerase was found to be the best of the enzymes tested for this purpose. MALDI analysis of enzymatically produced 24-fluoro modified DNA using the matrix 2,5-dihydroxy benzoic acid showed no base loss or backbone fragmentation, in contrast to the extensive fragmentation evident with unmodified DNA of the same sequence.

DNA↗
PubMed1998

EIR1, a root-specific protein involved in auxin transport, is required for gravitropism in Arabidopsis thaliana.

The EIR1 gene of Arabidopsis is a member of a family of plant genes with similarities to bacterial membrane transporters. This gene is expressed only in the root, which is consistent with the phenotypes of the eir1 mutants-the roots are agravitropic and have a reduced sensitivity to ethylene. The roots of eir1 mutants are also insensitive to the excess auxin produced by alf1-1 and fail to induce an auxin-inducible gene in the expansion zone. Although they fail to respond to internally generated auxin, they respond normally to externally applied auxin. Expression of the EIR1 gene in Saccharomyces cerevisiae confers resistance to fluorinated indolic compounds. Taken together, these data suggest that the EIR1 protein has a root-specific role in the transport of auxin.

Amino Acid Sequence↗