Highly Reactive Hydrocarbon Soluble Alkylsodium Reagents for Benzylic Aroylation of Toluenes using Weinreb Amides

Deaggregating the alkyl sodium NaCH₂SiMe₃ with polydentate nitrogen ligands enables the preparation and characterisation of new, hydrocarbon soluble chelated alkylsodium reagents. Equipped with significantly enhanced metalating power over their organolithium counterparts, these systems can promote controlled sodiation of weakly acidic benzylic C−H bonds from a series of toluene derivatives under mild stoichiometric conditions. This has been demonstrated through the benzylic aroylation of toluenes with Weinreb amides, that delivers a wide range of 2-arylacetophenones in good to excellent yields. Success in isolating and determining the structures of key organometallic intermediates has provided useful mechanistic insight into these new sodium-mediated transformations.     

Characterization of the glycosidic linkage of underivatized disaccharides by interaction with Pb(2+) ions

Electrospray ionization in combination with tandem mass spectrometry and lead cationization is used to characterize the linkage position of underivatized disaccharides. Lead(II) ions react mainly with disaccharides by proton abstraction to generate [Pb(disaccharide)(m)-H](+) ions (m = 1-2). At low cone voltages, an intense series of doubly charged ions of general formula [Pb(disaccharide)(n)](2+) are also observed. Our study shows that MS/MS experiments have to be performed to differentiate Pb(2+)-coordinated disaccharides. Upon collision, [Pb(disaccharide)-H](+) species mainly dissociate according to glycosidic bond cleavage and cross-ring cleavages, leading to the elimination of C(n)H(2n)O(n) neutrals (n = 2-4). The various fragmentation processes allow the position of the glycosidic bond to be unambiguously located. Distinction between glc-glc and glc-fru disaccharides also appears straightforward. Furthermore, for homodimers of D-glucose our data demonstrate that the anomericity of the glycosidic bond can be characterized for the 1 --> n linkages (n = 2, 4, 6). Consequently, Pb(2+) cationization combined with tandem mass spectrometry appears particularly useful to identify underivatized disaccharides.     

Intracellular Delivery of Peptidyl Ligands by Reversible Cyclization: Discovery of a PDZ Domain Inhibitor that Rescues CFTR Activity

A general strategy was developed for the intracellular delivery of linear peptidyl ligands through fusion to a cell‐penetrating peptide and cyclization of the fusion peptides via a disulfide bond. The resulting cyclic peptides are cell permeable and have improved proteolytic stability. Once inside the cell, the disulfide bond is reduced to produce linear biologically active peptides. This strategy was applied to generate a cell‐permeable peptide substrate for real‐time detection of intracellular caspase activities during apoptosis and an inhibitor for the CFTR‐associated ligand (CAL) PDZ domain as a potential treatment for cystic fibrosis.     

Desorption electrospray ionization - orbitrap mass spectrometry of synthetic polymers and copolymers

Desorption ElectroSpray Ionization (DESI) - Orbitrap Mass Spectrometry (MS) was evaluated as a new tool for the characterization of various industrial synthetic polymers (poly(ethylene glycol), poly(propylene glycol), poly(methylmethacrylate), poly(dimethylsiloxane)) and copolymers, with masses ranging from 500 g.mol(-1) up to more than 20?000 g.mol(-1) . Satisfying results in terms of signal stability and sensitivity were obtained from hydrophobic surfaces (HTC Prosolia) with a mixture water/methanol (10/90) as spray solvent in the presence of sodium salt. Taking into account the formation of multiplied charged species by DESI-MS, a strategy based on the use of a deconvolution software followed by the automatic assignment of the ions was described allowing the rapid determination of M(n) , M(w) and PDI values. DESI-Orbitrap MS results were compared to those obtained from matrix-assisted laser desorption/ionization- time-of-flight MS and gel permeation chromatography. An application of DESI-Orbitrap MS for the detection and identification of polymers directly from cosmetics was described. Copyright ? 2012 John Wiley & Sons, Ltd.     

Liquid Chromatography-Mass Spectrometry Hyphenation for Exhaustive and Unambiguous Characterization of Polyoxyethylene Surfactants

A rapid, specific and reliable high performance liquid chromatographic (HPLC) assay of sildenafil in pharmaceutical dosage forms has been developed and evaluated. Reversed phase chromatography was conducted using a mobile phase of methanol: water: acetonitrile (60:20:20) v/v/v, pH 6.1, 0.1% glacial acetic acid, and detection at λ 290 nm. The recovery and coefficient of variation from six tablets containing 50 mg of sildenafil were 100.90% and 0.45% respectively. Replicate regression analysis of three standard plots in the concentration range (0.01–0.2) μg mL^?1 obtained on three different days gave a correlation coefficient >0.999 and the coefficient of variation of the slopes <1.5%. The assay was precise within day and between days as indicated by ANOVA test. It is suggested that the proposed HPLC method should be used for routine quality control and dosage form assay of sildenafil citrate. The proposed method was also used to study the stability of sildenafil citrate in different dosage forms of the drug.     

Spectres de Masse de la Methyl-2 Thiazolidinethione-2 et de la Dimethyl-2,4 Δ2-Thiazoline

The mass spectra of the title compounds point to rupture of S? C-2 and N? C-4 bonds as being the dominant reaction under electron impact. 13C labelling of a selected position of the ring allows some fragmentation pathways to be confirmed.     

Structural characterization of hexoses and pentoses using lead cationization. An electrospray ionization and tandem mass spectrometric study

The analytical potential of the complexation of isomeric underivatized hexoses (D-glucose, D-galactose, D-mannose, D-talose, D-fructose), methylglycosides (1-O-methyl-alpha-D-glucose and 1-O-methyl-beta-D-glucose) and pentoses (D-ribose, D-xylose, D-arabinose and D-lyxose) by Pb(2+) ions, was investigated by electrospray ionization and tandem mass spectrometry (MS/MS). Pb(2+) ions react mainly with monosaccharides by proton abstraction to generate [Pb(monosaccharide)(m) - H](+) ions (m = 1-3). At low cone voltage, a less abundant series of doubly charged ions of general formula [Pb(monosaccharide)(n)](2+) is also observed. The maximum number n of monosaccharides surrounding a single Pb(2+) ion depends on the metal : monosaccharide ratio. Our study shows that MS/MS experiments have to be performed to differentiate Pb(2+)-coordinated monosaccharides. Upon collision, [Pb(monosaccharide) - H](+) species mainly dissociate according to cross-ring cleavages, leading to the elimination of C(n)H(2n)O(n) neutrals. The various fragmentation processes observed allow the C(1), C(2) and C(4) stereocenters of aldohexoses to be characterized, and also a clear distinction aldoses and fructose. Furthermore, careful analysis of tandem mass spectra also leads to successful aldopentose distinction. Lead cationization combined with MS/MS therefore appears particularly useful to identify underivatized monosaccharides.     

Creatinine determination in urine samples by batchwise kinetic procedure and flow injection analysis using the Jaffé reaction: chemometric study

The classical Jaffé reaction for the determination of creatinine in urine samples is tested. A comparative study of the main analytical characteristics focussed to minimize the bias error and improve the precision, for the batchwise and flow injection (FI) methods is realized. Also, the effect of the albumin concentration in the determination of creatinine has been studied. Different analytical signals were studied. Absorbance increments at different times permit to estimate the creatinine concentration free from bias error in urine by the batchwise method using the calibration graph obtained with creatinine standards and no measurement of the blank solution is needed. The lineal interval was 0.92-50 mg l(-1) and seven samples can be processed per hour by an operator. No previous treatment of the urine sample is necessary. The FI method provides also good results. The lineal interval was 30-100 mg l(-1) and the sample rate was around 20 samples per hour. If increased albumin levels are detected in the urine, standard addition method or the calibration graphs with standards in presence of albumin are needed in order to obtain accurate results when FI method is employed. The obtained accuracy of the both methods allows its application as diagnostic tool to establish the urinary creatinine levels.     

Association of Cu2+ with uracil and its thio derivatives: a theoretical study.

The structures and relative stabilities of the complexes between Cu2+ and uracil, 2-thiouracil, 4-thiouracil, and 2,4-dithiouracil were investigated by B3LYP/6-311+G(2df,2p)//B3LYP/6-31G* DFT calculations. In those systems in which both types of basic centers, that is, a carbonyl and a thiocarbonyl group, are present, association of Cu2+ with the oxygen atom is systematically favored, in contrast to what was found for the corresponding Cu+ complexes. This can be understood by considering that association of Cu2+ is immediately followed by oxidation of the base, which accumulates the negative charge at the oxygen atoms. Similarly, for 2,4-dithiouracil the most basic site for Cu+ attachment is the sulfur atom at the 4-position, while for association of Cu2+ it is sulfur at the 2-position. In contrast, differences between uracil-Cu+ and uracil-Cu2+ complexes are very small, and in both cases the oxygen atom at the 4-position is the most basic. Cu2+ binding energies are about 4 and 1.2 times larger than Cu+ binding energies and proton affinities, respectively. Uracil- and thiouracil-Cu2+ complexes are thermodynamically unstable but kinetically stable with respect to their dissociation into uracil*+ + Cu+ or thiouracil*+ + Cu+. The Cu2+ binding energies vary with the difference between the second ionization potential of the metal and the first ionization potential of the base. regardless of the reference acid (H+, Cu+, Cu2+) the basicity trend is 2,4-dithiouracil > 4-thiouracil > 2-thiouracil > uracil.