Syntheses and bioactivities of tricyclic pyrones

In search of compounds that ameliorate the toxicity of amyloid-β (Aβ) peptides, new derivatives of tricyclic pyrones (1-7) were synthesized and their biological activities evaluated. The carboxylic ester and amide derivatives 1-4 were synthesized from a selective carboxylation of C3 methyl of (5aS,7S)-{7-Isopropenyl-3-methyl-1H,7H-5a,6,8,9-tetrahydro-1-oxopyrano[4,3-b][1]benzopyran (8) with LDA followed by benzyl chloroformate or carbon dioxide to provide ester 1 and carboxylic acid 9, respectively. Three isomeric tricyclic pyrone, 5-7, containing adenine moiety at C7 side chain were synthesized from the alkylation of mesylate 13 with adenine, and displacement of chloropurine 15 with amine 14. Although C3-benzyloxycarbonylmethyl analogs 1-3 have marginal ACAT and CETP activities, their modified aspartate analog 4 and C3-methyl-C7-(N3-adeninyl)-2-propyl analog 6 show a significant effect in protecting against neuron-cell death from the toxicity of intracellular accumulation of Aβ or Aβ-containing C-terminal fragments (CTF) of amyloid β precursor protein (APP). N9-Adenine analog 5 is 20-fold less effective than N3-adenine derivative 6 in the protection of neuron-cell death induced by Aβ, while N10-adenine analog 7 was inactive. As a result of this study, compounds 4 and 6 will well serve as lead compounds for further studies of the mechanism of action of Aβ-and CTF-induced neuron-cell death, studies which should enhance the future development of new drugs for the prevention and treatment of AD.     

Studies on pyrrolidinones. Synthesis of 1-[(N-acetylarylamino)methyl]pyroglutamic acid derivatives

Pyroglutamic acid was transformed into 1-[(N-Acetylarylamino)methyl]pyroglutamic acid derivatives by using trimethylsilyl variations of the Mannich reaction.     

Identifizierung organischer Säuren durch thermische Analyse und Bestimmung des Säuregehaltes in Anhydriden

Zusammenfassung Ein thermisches Analysenverfahren wurde ausgearbeitet, das die Identifizierung einiger organischer Säuren nebeneinander und zugleich deren sehr empfindliche Bestimmung in kleinen Einwaagen ermöglicht. Die dazu entwickelte Anlage verwendet einen Gaschromatographendetektor.

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Identification of organic acids through thermoanalysis and determination of the acid content of anhydrides

Summary A thermoanalytic procedure has been developed which permits to identify several organic acids in the presence of one another, and at the same time to determine them in very small samples. The apparatus employs a gaschromatograph-detector.

     

Pharmacokinetics of Tetra (m-hydroxyphenyl)chlorin in Human Plasma and Individualized Light Dosimetry in Photodynamic Therapy

The pharmacokinetics of the photosensitizer 5,10,15,20-tetra( m -hydroxyphenyl) chlorin(mTHPC) was investigated in the plasma of 20 patients by absorption and fluorescence spectroscopy. The temporal behavior was characterized by a rapid decrease in concentration during the first minutes after intravenous injection of 0.15 mg/kg mTHPC. A minimum concentration in the plasma was reached after about 45 min. The drug concentration then increased again, attaining a maximum after about 10 h, after which it decreased again with a halflife of about 30 h. Irradiation tests in the oral cavity at different time intervals after the injection revealed that the tissue re-action was only partially correlated with the mTHPC plasma level. The tissue response was stronger at later drug-light intervals (1–4 days) than during the first hours after injection even though the mTHPC plasma concentration was higher at the shorter times. Relative mTHPC concentrations were also measured in the mucosae of the oral cavity, the esophagus and the bronchi of 27 patients by light-induced fluorescence spectroscopy using an optical fiber-based spectrometer. These measurements were performed prior to photodynamic therapy (PDT), 4 days after injection of the photosensitizer. Highly significant linear correlations were found between the relative mTHPC concentrations in the mucosae of these three organs. Likewise, the plasma levels of mTHPC measured just before PDT were significantly correlated with the mTHPC concentrations in the three types of mucosae mentioned above. These results indicate that mTHPC plasma levels measured just before PDT can be used for PDT light dosimetry.     

Heteronuclear selective refocusing 2D NMR experiments for the spectral analysis of enantiomers in chiral oriented solvents

We report the use of carbon-proton heteronuclear selective refocusing 2D NMR experiments dedicated to the spectral analysis of enantiomers dissolved in weakly ordering chiral liquid crystalline solvents. The method permits the extraction of carbon-proton residual dipolar couplings for each enantiomer from a complex or unresolved proton-coupled 13C spectral patterns. Illustrative examples are analysed and discussed. It is shown that an accurate determination of enantiomeric excess is possible.     

Molecular dynamics at the root of expansion of function in the M69L inhibitor-resistant TEM beta-lactamase from Escherichia coli

Clavulanate, an inhibitor for beta-lactamases, was the very first inhibitor for an antibiotic resistance enzyme that found clinical utility in 1985. The clinical use of clavulanate and that of sulbactam and tazobactam, which were introduced to the clinic subsequently, has facilitated evolution of a set of beta-lactamases that not only retain their original function as resistance enzymes but also are refractory to inhibition by the inhibitors. This article characterizes the properties of the clinically identified M69L mutant variant of the TEM-1 beta-lactamase from Escherichia coli, an inhibitor-resistant beta-lactamase, and compares it to the wild-type enzyme. The enzyme is as active as the wild-type in turnover of typical beta-lactam antibiotics. Furthermore, many of the parameters for interactions of the inhibitors with the mutant enzyme are largely unaffected. The significant effect of the inhibitor-resistant trait was a relatively modest elevation of the dissociation constant for the formation of the pre-acylation complex. The high-resolution X-ray crystal structure for the M69L mutant variant revealed essentially no alteration of the three-dimensional structure, both for the protein backbone and for the positions of the side chains of the amino acids. It was surmised that the difference in the two enzymes must reside with the dynamic motions of the two proteins. Molecular dynamics simulations of the mutant and wild-type proteins were carried out for 2 ns each. Dynamic cross-correlated maps revealed the collective motions of the two proteins to be very similar, yet the two proteins did not behave identically. Differences in behavior of the two proteins existed in the regions between residues 145-179 and 155-162. Additional calculations revealed that kinetic effects measured experimentally for the dissociation constant for the pre-acylation complex could be mostly attributed to the electrostatic and van der Waals components of the binding free energy. The effects of the mutation on the behavior of the beta-lactamase were subtle, including the differences in the measured dissociation constants that account for the inhibitor-resistant trait. It would appear that nature has selected for incorporation of the most benign alteration in the structure of the wild-type TEM-1 beta-lactamase that is sufficient to give the inhibitor-resistant trait.     

Toward new camptothecins. Part 4: On the reactivity of nitro and amino precursors of aza analogs of 5-methoxycarbonyl camptothecin

In the context of formation of new aza analogs of camptothecin, nitration then reduction of condensed pyridones was realized, leading to new derivatives of pyrrolo-aza-indoles. Treatment of these compounds with hydrobromic acid led to new structure rearrangements while oxidation of the α-position was unsuccessful. Mechanisms of formation of the new products are discussed.     

Amino acid-type edited NMR experiments for methyl-methyl distance measurement in 13C-labeled proteins

New NMR experiments are presented for the measurement of methyl-methyl distances in (13)C-labeled proteins from a series of amino acid-type separated 2D or 3D NOESY spectra. Hadamard amino acid-type encoding of the proximal methyl groups provides the high spectral resolution required for unambiguous methyl-methyl NOE assignment, which is particularly important for fast global fold determination of proteins. The experiments can be applied to a wide range of protein systems, as exemplified for two small proteins, ubiquitin and MerAa, and the 30 kDa BRP-Blm complex.     

The use of advanced calorimetric techniques in polymer synthesis and characterization

Progress in the understanding of polymer synthesis, including the crucial step of initiation and undesired side reactions, and in characterization of polymers, especially their thermal behaviour, are directly related to advances in calorimetric technologies.

In polymer synthesis, since polymerization reactions are highly exothermic, reaction calorimetry (RC) is an appropriate technique for on-line process monitoring. Measurements are non-invasive, rapid, and straightforward. Viscosity increase and fouling at the reactor wall are typical features of many polymerizations. The global heat transfer coefficient, UA, also changes drastically when viscosity increases and affects the accuracy of calorimetric measurements. Our approach was focused on oscillating temperature calorimetry (TOC). Reactions were performed with two different reaction calorimeters, i.e. an isoperibolic calorimeter and a Calvet-type high sensitivity differential calorimeter, respectively. Special attention was paid to the interpretation of the measured signals to obtain reliable calorimetric data. The evolution of heat transfer coefficient was followed by performing two Joule effect calibration experiments, before and after the reaction, and the two values interpolated to obtain the desired profile of UA. A differentiation method based on the convolution of the measured heat flow by the generated one was used for determining the time constants and deconvoluting the measured heat flow.

With respect to polymer characterization, pressure-controlled scanning calorimetry, also called scanning transitiometry, is now a well established technique. The transitiometer was coupled to an ultracryostat to work at low temperature. The assembly was used to follow the pressure effect on phase change phenomena such as fusion/crystallization and glass transition temperature T_g of low molecular weight substances or high molecular weight polymers.