RESUMO
Protein-carbohydrate interactions are implicated in many biochemical/biological processes that are fundamental to life and to human health. Fluorinated carbohydrate analogues play an important role in the study of these interactions and find application as probes in chemical biology and as drugs/diagnostics in medicine. The availability and/or efficient synthesis of a wide variety of fluorinated carbohydrates is thus of great interest. Here, we report a detailed study on the synthesis of monosaccharides in which the hydroxy groups at their 4- and 6-positions are replaced by all possible mono- and difluorinated motifs. Minimization of protecting group use was a key aim. It was found that introducing electronegative substituents, either as protecting groups or as deoxygenation intermediates, was generally beneficial for increasing deoxyfluorination yields. A detailed structural study of this set of analogues demonstrated that dideoxygenation/fluorination at the 4,6-positions caused very little distortion both in the solid state and in aqueous solution. Unexpected trends in α/ß anomeric ratios were identified. Increasing fluorine content always increased the α/ß ratio, with very little difference between regio- or stereoisomers, except when 4,6-difluorinated.
Assuntos
Flúor , Halogenação , Carboidratos , Humanos , EstereoisomerismoRESUMO
We describe the synthesis and characterisation of open fullerene (1) and its reduced form (2) in which CH4 and NH3 are encapsulated, respectively. The 1 Hâ NMR resonance of endohedral NH3 is broadened by scalar coupling to the quadrupolar 14 N nucleus, which relaxes rapidly. This broadening is absent for small satellite peaks, which are attributed to natural abundance 15 N. The influence of the scalar relaxation mechanism on the linewidth of the 1 H ammonia resonance is probed by variable temperature NMR. A rotational correlation time of τc =1.5â ps. is determined for endohedral NH3 , and of τc =57±5â ps. for the open fullerene, indicating free rotation of the encapsulated molecule. IR spectroscopy of NH3 @2 at 5â K identifies three vibrations of NH3 (ν1 , ν3 and ν4 ) redshifted in comparison with free NH3 , and temperature dependence of the IR peak intensity indicates the presence of a large number of excited translational/ rotational states. Variable temperature 1 Hâ NMR spectra indicate that endohedral CH4 is also able to rotate freely at 223â K, on the NMR timescale. Inelastic neutron scattering (INS) spectra of CH4 @1 show both rotational and translational modes of CH4 . Energy of the first excited rotational state (J=1) of CH4 @1 is significantly lower than that of free CH4 .
RESUMO
Organofluorine is a weak hydrogen-bond (HB) acceptor. Bernet et al. have demonstrated its capability to perturb OH···O intramolecular hydrogen bonds (IMHBs), using conformationally rigid carbohydrate scaffolds including levoglucosan derivatives. These investigations are supplemented here by experimental and theoretical studies involving six new levoglucosan derivatives, and complement the findings of Bernet et al. However, it is shown that conformational analysis is instrumental in interpreting the experimental data, due to the occurrence of non-intramolecular hydrogen-bonded populations which, although minor, cannot be neglected and appears surprisingly significant. The DFT conformational analysis, together with the computation of NMR parameters (coupling constants and chemical shifts) and wavefunction analyses (AIM, NBO), provides a full picture. Thus, for all compounds, the most stabilized structures show the OH groups in a conformation allowing IMHB with O5 and O6, when possible. Furthermore, the combined approach points out the occurrence of various IMHBs and the effect of the chemical modulations on their features. Thus, two-center or three-center IMHB interactions are observed in these compounds, depending on the presence or absence of additional HB acceptors, such as methoxy or fluorine.
Assuntos
Glucose/análogos & derivados , Glucose/síntese química , Glucose/química , Ligação de Hidrogênio , Radical Hidroxila/química , Espectroscopia de Ressonância Magnética , Modelos Moleculares , Conformação MolecularRESUMO
A series of neutral ditopic and negatively charged, monotopic host molecules have been evaluated for their ability to bind chloride and dihydrogen phosphate anions, and neutral organophosphorus species dimethyl methylphosphonate (DMMP), pinacolyl methylphosphonate (PMP) and the chemical warfare agent (CWA) pinacolyl methylphosphonofluoridate (GD, soman) in organic solvent via hydrogen bonding. Urea, thiourea and boronic acid groups are shown to bind anions and neutral guests through the formation of hydrogen bonds, with the urea and thiourea groups typically exhibiting higher affinity interactions. The introduction of a negative charge on the host structure is shown to decrease anion affinity, whilst still allowing for high stability host-GD complex formation. Importantly, the affinity of the host for the neutral CWA GD is greater than for anionic guests, thus demonstrating the potential for selectivity reversal based on charge repulsion.
Assuntos
Substâncias para a Guerra Química/química , Ligação de Hidrogênio , Modelos Moleculares , Conformação Molecular , Compostos Organofosforados/química , Solventes/química , Soman/análogos & derivados , Soman/químicaRESUMO
We report a dynamic covalent approach to transmembrane transport of amino acids by the formation of a three-component assembly. A mixture of a squaramide and a lipophilic and electrophilic aldehyde is shown to synergistically transport highly polar glycine (Gly) across vesicle membranes. The transport was investigated by a (13)C NMR assay, an osmotic response assay, a newly developed fluorescence assay suitable for measuring Gly influx, and other fluorescence assays for leakage and pH change. The transport is proposed to occur via a hydrogen-bonded anionic glycine hemiaminal/imine, accompanied by transport of OH(-) in the opposite direction. Several control experiments support the role of hemiaminal/imine in the observed facilitated Gly transport. Proton NMR studies of a biphasic system show the presence of both the hemiaminal and imine formed between Gly and an aldehyde. Interestingly, the synergistic effect has also been observed for sarcosine, which can form hemiaminals but not imines. The results demonstrate the potential of hemiaminal formation for the facilitated transport of substrates containing primary and secondary amino groups.
Assuntos
Glicina/metabolismo , Bicamadas Lipídicas/metabolismo , Aldeídos/química , Aldeídos/metabolismo , Transporte Biológico , Ciclobutanos/química , Ciclobutanos/metabolismo , Cinética , Bicamadas Lipídicas/química , Espectroscopia de Ressonância Magnética , Osmose , Sulfonamidas/química , Sulfonamidas/metabolismoRESUMO
Small molecule synthetic anion transporters may have potential application as therapeutic agents for the treatment of diseases including cystic fibrosis and cancer. Understanding the factors that can dictate the anion transport activity of such transporters is a crucial step towards their application in biological systems. In this study a series of acylthiourea anion transporters were synthesised and their anion binding and transport properties in POPC bilayers have been investigated. The transport activity of these receptors is dominated by their lipophilicity, which is in turn dependent on both substituent effects and the formation and strength of an intramolecular hydrogen bond as inferred from DFT calculations. This is in contrast to simpler thiourea systems, in which the lipophilicity depends predominantly on substituent effects alone.
Assuntos
Cloretos/química , Nitratos/química , Tioureia/química , Ânions/química , Cristalografia por Raios X , Ligação de Hidrogênio , Bicamadas Lipídicas/química , Modelos Moleculares , Estrutura Molecular , Fosfatidilcolinas/química , Teoria Quântica , Tioureia/síntese químicaRESUMO
A Resin-linker-vector (RLV) strategy is described for the radiosynthesis of tracer molecules containing the radionuclide (18)F, which releases the labelled vector into solution upon nucleophilic substitution of a polystyrene-bound arylsulfonate linker with [(18)F]-fluoride ion. Three model linker-vector molecules 7a-c containing different alkyl spacer groups were assembled in solution from (4-chlorosulfonylphenyl)alkanoate esters, exploiting a lipase-catalysed chemoselective carboxylic ester hydrolysis in the presence of the sulfonate ester as a key step. The linker-vector systems were attached to aminomethyl polystyrene resin through amide bond formation to give RLVs 8a-c with acetate, butyrate and hexanoate spacers, which were characterised by using magic-angle spinning (MAS) NMR spectroscopy. On fluoridolysis, the RLVs 8a,b containing the longer spacers were shown to be more effective in the release of the fluorinated model vector (4-fluorobutyl)phenylcarbamic acid tert-butyl ester (9) in NMR kinetic studies and gave superior radiochemical yields (RCY≈60%) of the (18) F-labelled vector. The approach was applied to the synthesis of the radiopharmaceutical O-(2-[(18)F]-fluoroethyl)-L-tyrosine ([(18) F]-FET), delivering protected [(18) F]-FET in >90% RCY. Acid deprotection gave [(18)F]-FET in an overall RCY of 41% from the RLV.
Assuntos
Aminoácidos/química , Radioisótopos de Flúor/química , Compostos Radiofarmacêuticos/síntese química , Tirosina/análogos & derivados , Cromatografia Líquida de Alta Pressão , Cinética , Estrutura Molecular , Tomografia por Emissão de Pósitrons , Radioquímica , Compostos Radiofarmacêuticos/química , Tirosina/síntese química , Tirosina/químicaRESUMO
Tautomeric switching is observed in a series of benzimidazole-based anion receptors upon addition of basic anions. An N-methylbenzimidazole based receptor selectively interacts with dihydrogen phosphate over a variety of other putative anionic guests via a combination of donated and accepted hydrogen bonds.
Assuntos
Benzimidazóis/química , Ligação de Hidrogênio , Isomerismo , Modelos Moleculares , Conformação Molecular , Fosfatos/química , Especificidade por SubstratoRESUMO
The influence of anions on tautomerism in benzimidazole containing anion receptors has been studied via a variety of techniques in both solution and the solid state. The results show that hydrogen bonding interactions between the receptors and guests have a significant effect of the nature of the tautomer present. The compounds show a preference for complexation of lactate over pyruvate.
Assuntos
Benzimidazóis/química , Indóis/síntese química , Ácido Láctico/química , Ácido Pirúvico/química , Ureia/síntese química , Ânions/química , Cristalografia por Raios X , Ligação de Hidrogênio , Indóis/química , Modelos Moleculares , Estrutura Molecular , Ureia/análogos & derivados , Ureia/químicaRESUMO
Fluorination has become an effective tool to optimize physicochemical properties of bioactive compounds. One of the applications of fluorine introduction is to modulate the lipophilicity of the compound. In our group, we are interested in the study of the impact of fluorination on lipophilicity of aliphatic fluorohydrins and fluorinated carbohydrates. These are not UV-active, resulting in a challenging lipophilicity determination. Here, we present a straightforward method for the measurement of lipophilicity of fluorinated compounds by 19F NMR spectroscopy. This method requires no UV-activity. Accurate solute mass, solvent and aliquot volume are also not required to be measured. Using this method, we measured the lipophilicities of a large number of fluorinated alkanols and carbohydrates.
Assuntos
Flúor/química , Lipídeos/química , Espectroscopia de Ressonância Magnética/métodos , Carboidratos/químicaRESUMO
The bacterial stringent response is induced by nutrient deprivation and is mediated by enzymes of the RSH (RelA/SpoT homologue; RelA, (p)ppGpp synthetase I; SpoT, (p)ppGpp synthetase II) superfamily that control concentrations of the 'alarmones' (p)ppGpp (guanosine penta- or tetra-phosphate). This regulatory pathway is present in the vast majority of pathogens and has been proposed as a potential anti-bacterial target. Current understanding of RelA-mediated responses is based on biochemical studies using Escherichia coli as a model. In comparison, the Francisella tularensis RelA sequence contains a truncated regulatory C-terminal region and an unusual synthetase motif (EXSD). Biochemical analysis of F. tularensis RelA showed the similarities and differences of this enzyme compared with the model RelA from Escherichia coli. Purification of the enzyme yielded a stable dimer capable of reaching concentrations of 10 mg/ml. In contrast with other enzymes from the RelA/SpoT homologue superfamily, activity assays with F. tularensis RelA demonstrate a high degree of specificity for GTP as a pyrophosphate acceptor, with no measurable turnover for GDP. Steady state kinetic analysis of F. tularensis RelA gave saturation activity curves that best fitted a sigmoidal function. This kinetic profile can result from allosteric regulation and further measurements with potential allosteric regulators demonstrated activation by ppGpp (5',3'-dibisphosphate guanosine) with an EC50 of 60±1.9 µM. Activation of F. tularensis RelA by stalled ribosomal complexes formed with ribosomes purified from E. coli MRE600 was observed, but interestingly, significantly weaker activation with ribosomes isolated from Francisella philomiragia.
Assuntos
Francisella tularensis/enzimologia , Ligases/metabolismo , Ribossomos/enzimologia , Regulação Alostérica/genética , Escherichia coli/enzimologia , Cinética , Ligases/genéticaRESUMO
A series of supramolecular diamide organogels containing a reactive compound for the remediation of organophosphorus (OP) species, in particular OP chemical warfare agents (CWAs), has been prepared in DMSO. The organogels have been found to absorb, encapsulate and decontaminate various OP CWA simulants in situ. At high simulant concentrations the gels also undergo a gel-sol transition releasing high local concentrations of remediation agent.
RESUMO
The metabolism of polyphosphate is important for the virulence of a wide range of pathogenic bacteria and the enzymes of polyphosphate metabolism have been proposed as an anti-bacterial target. In the intracellular pathogen Francisella tularensis, the product of the gene FTT1564 has been identified as a polyphosphate kinase from the polyphosphate kinase 2 (PPK2) family. The isogenic deletion mutant was defective for intracellular growth in macrophages and was attenuated in mice, indicating an important role for polyphosphate in the virulence of Francisella. Herein, we report the biochemical and structural characterization of F. tularensis polyphosphate kinase (FtPPK2) with a view to characterizing the enzyme as a novel target for inhibitors. Using an HPLC-based activity assay, the substrate specificity of FtPPK2 was found to include purine but not pyrimidine nts. The activity was also measured using (31)P-NMR. FtPPK2 has been crystallized and the structure determined to 2.23 Å (1 Å=0.1 nm) resolution. The structure consists of a six-stranded parallel ß-sheet surrounded by 12 α-helices, with a high degree of similarity to other members of the PPK2 family and the thymidylate kinase superfamily. Residues proposed to be important for substrate binding and catalysis have been identified in the structure, including a lid-loop and the conserved Walker A and B motifs. The ΔFTT1564 strain showed significantly increased sensitivity to a range of antibiotics in a manner independent of the mode of action of the antibiotic. This combination of biochemical, structural and microbiological data provide a sound foundation for future studies targeting the development of PPK2 small molecule inhibitors.
Assuntos
Proteínas de Bactérias/química , Francisella tularensis/enzimologia , Fosfotransferases (Aceptor do Grupo Fosfato)/química , Animais , Proteínas de Bactérias/metabolismo , Cristalografia por Raios X , Francisella tularensis/genética , Camundongos , Fosfotransferases (Aceptor do Grupo Fosfato)/genética , Fosfotransferases (Aceptor do Grupo Fosfato)/metabolismo , Estrutura Secundária de ProteínaRESUMO
Simple, highly fluorinated receptors are shown to function as highly effective transmembrane anion antiporters with the most active transporters rivalling the transport efficacy of natural anion transporter prodigiosin for bicarbonate.
Assuntos
Proteínas de Transporte de Ânions/metabolismo , Fenilenodiaminas/química , Ureia/metabolismo , Proteínas de Transporte de Ânions/química , Bicarbonatos/química , Bicarbonatos/metabolismo , Cristalografia por Raios X , Lipossomos/química , Lipossomos/metabolismo , Conformação Molecular , Prodigiosina/química , Prodigiosina/metabolismo , Tioureia/química , Tioureia/metabolismo , Ureia/químicaRESUMO
A series of low molecular weight tripodal amide/histidine-containing compounds (1-2) have been synthesised and shown to increase the rate of bis-(p-nitrophenyl) phosphate (BNPP) and soman (GD) breakdown in buffered aqueous solution.
Assuntos
Amidas/química , Ésteres/química , Histidina/química , Compostos Organofosforados/química , Hidrólise , Estrutura MolecularRESUMO
Studies of sulfamide, phosphoric triamide and thiophosphoric triamide-based organocatalysts show that the phosphorus containing systems are effective new hydrogen bonding motifs for the recognition and transport of anions.
RESUMO
The formation of tren-based tris-urea supramolecular gels in organic solvents is perturbed by the presence of the nerve agent soman providing a new method of sensing the presence of organophosphorus warfare agents.
RESUMO
The experimental investigation of site-specific intra-ionic hydrogen/deuterium (H/D) exchange in the low-energy collision-induced dissociation (CID) product ion spectra of protonated small molecules generated by electrospray ionisation (ESI) is presented. The observation of intra-ionic H/D exchange in such ions under low-energy CID conditions has hitherto been rarely reported. The data suggest that the intra-ionic H/D exchange takes place in a site-specific manner between the ionising deuteron, localised at either a tertiary amine or a tertiary amine-N-oxide, and a gamma-hydrogen relative to the nitrogen atom. Nuclear magnetic resonance (NMR) spectroscopy measurements showed that no H/D exchange takes place in solution, indicating that the reaction occurs in the gas phase. The compounds analysed in this study suggested that electron-withdrawing groups bonded to the carbon atom bearing the gamma-hydrogen can preclude exchange. The effect of the electron-withdrawing group appears dependent upon its electronegativity, with lower chi value groups still allowing exchange to take place. However, the limited dataset available in this study prevented robust conclusions being drawn regarding the effect of the electron-withdrawing group. The observation of site-specific intra-ionic H/D exchange has application in the area of structural elucidation, where it could be used to introduce an isotopic label into the carbon skeleton of a molecule containing specific structural features. This could increase the throughput, and minimise the cost, of such studies due to the obviation of the need to produce a deuterium-labelled analogue by synthetic means.
Assuntos
Aminas/química , Medição da Troca de Deutério/métodos , Espectrometria de Massas por Ionização por Electrospray/métodos , Modelos Moleculares , Ressonância Magnética Nuclear Biomolecular , Preparações Farmacêuticas/químicaAssuntos
Glutamatos/química , Receptores de Glutamato/química , Calorimetria , Glutamatos/metabolismo , Compostos Heterocíclicos/química , Cinética , Modelos Moleculares , Conformação Molecular , Ressonância Magnética Nuclear Biomolecular , Ligação Proteica , Receptores de Glutamato/metabolismo , Solventes/química , Estereoisomerismo , Tioureia/análogos & derivados , Tioureia/metabolismoRESUMO
Reactions of Fe(C-N-C)(N2)2, 1a, or Fe(C-NMe-C)(N2)2, 1b, C-N-C = 2,6-bis(arylimidazol-2-ylidene)pyridine, C-NMe-C = 2,6-bis(arylimidazol-2-ylidene)-3,5-dimethylpyridine, aryl = 2,6-iPr2C6H3, with silanes are described. Complex 1a with excess SiPhH3 and complex 1b with excess Si(tol)H3, Ph = phenyl, C6H5, tol = 2-methylphenyl, gave the complexes [Fe(C-N-C)(SiH2Ph)2(2-H-SiH2Ph)], 2a, and [Fe(C-NMe-C)(SiH2tol)2(2-H-SiH2tol)], 2b, respectively. Complex 1b with excess SiPhH3 gave [Fe(C-NMe-C)(SiH2Ph)2(H)2], 3, which was formulated as a dihydride based on the relaxation time T1(min) in the 1H-NMR spectra. Reaction of 1a with SiPh2H2 gave complex [Fe(C-N-C)(SiHPh2)2(2-H2)], 4, while reaction with Si(mes)H3 gave complex [Fe(C-N-C)(SiH2mes)2(N2)], 5, mes = mesityl, 2,4,6-trimethylphenyl. The comparison of the reactivity with other pincer complexes of iron and the mechanism leading to 2a-5 are discussed.