An efficient synthesis of 3-(E)-hydroxypropenyl cephem derivatives, key intermediates for 3-(E)-ammoniopropenylcephalosporin antibiotics

An efficient synthesis of 3-(E)-hydroxy- and 3-(E)-acetoxypropenylcephem derivatives, key intermediates for the synthesis of 3-(E)-propenylcephalosporins was achievedvia Stille coupling reaction of 3-trifloxycephem with 3-(E)-tributylstannylallylic alcohol.     

Characterization of action potential-triggered [Ca2+]i transients in single smooth muscle cells of guinea-pig ileum

1. To characterize increases in cytosolic free Ca²⁺ concentration ([Ca²⁺]_i) associated with discharge of action potentials, membrane potential and [Ca²⁺]_i were simultaneously recorded from single smooth muscle cells of guinea-pig ileum by use of a combination of nystatin-perforated patch clamp and fura-2 fluorimetry techniques.
2. A single action potential in response to a depolarizing current pulse elicited a transient rise in [Ca²⁺]_i. When the duration of the current pulse was prolonged, action potentials were repeatedly discharged during the early period of the pulse duration with a progressive decrease in overshoot potential, upstroke rate and repolarization rate. However, such action potentials could each trigger [Ca²⁺]_i transients with an almost constant amplitude.
3. Nicardipine (1 μM) and La³⁺ (10 μM), blockers of voltage-dependent Ca²⁺ channels (VDCCs), abolished both the action potential discharge and the [Ca²⁺]_i transient.
4. Charybdotoxin (ChTX, 300 nM) and tetraethylammonium (TEA, 2 mM), blockers of large conductance Ca²⁺-activated K⁺ channels, decreased the rate of repolarization of action potentials but increased the amplitude of [Ca²⁺]_i transients.
5. Thapsigargin (1 μM), an inhibitor of SR Ca²⁺-ATPase, slowed the falling phase and somewhat increased the amplitude, of action potential-triggered [Ca²⁺]_i transients without affecting action potentials. In addition, in voltage-clamped cells, the drug had little effect on the voltage step-evoked Ca²⁺ current but exerted a similar effect on its concomitant rise in [Ca²⁺]_i to that on the action potential-triggered [Ca²⁺]_i transient.
6. Similar action potential-triggered [Ca²⁺]_i transients were induced by brief exposures to high-K⁺ solution. They were not decreased, but rather increased, after depletion of intracellular Ca²⁺ stores by a combination of ryanodine (30 μM) and caffeine (10 mM) through an open-lock of Ca²⁺-induced Ca²⁺ release (CICR)-related channels.
7. The results show that action potentials, discharged repeatedly during the early period of a long membrane depolarization, undergo a progressive change in configuration but can each trigger a constant rise in [Ca²⁺]_i. Intracellular Ca²⁺ stores have a role, especially in accelerating the falling phase of the action potential-triggered [Ca²⁺]_i transients by replenishing cytosolic Ca²⁺. No evidence was provided for the involvement of CICR in the action potential-triggered [Ca²⁺]_i transient.

     

Caffeine inhibits cytoplasmic Ca2+ oscillations induced by carbachol and guanosine 5′-O-(3-thiotriphosphate) in hyperpolarized pancreatic ß-cells

The effects of caffeine on cytoplasmic Ca²⁺ oscillations induced by carbachol and guanosine 5-O-(3-thiotriphosphate) (GTP--S) were studied in individual mouse pancreatic ß-cells clamped at a hyperpolarized potential. Addition of 10 mM caffeine did not affect the cytoplasmic Ca²⁺ concentration ([Ca²⁺]₁) in ß-cells exposed to 20 mM glucose and hyperpolarized with diazoxide. Under similar conditions 100 M carbachol induced a typical response with a marked [Ca²⁺]_i peak followed by a lower sustained elevation. Irrespective of whether 10 mM caffeine was present, there were [Ca²⁺]_i transients with frequencies of 1–5/min superimposed on the sustained phase in 50–60% of the cells. In previously non-exposed cells the introduction of 10 mM caffeine caused temporary lowering of the sustained phase with disappearance of the transients. Subsequent omission of caffeine in the continued presence of carbachol caused a marked [Ca²⁺]_i peak followed by reappearance of the [Ca²⁺]_i, transients. However, in cells oscillating in the presence of caffeine its omission caused disappearance of the transients. In this case reintroduction of caffeine restored the transients.In cells kept at –70 mV by a patch pipette containing 100 M GTP--S and 3 mM Mg-ATP there were [Ca²⁺]_i transients with frequencies of 0.5–2.5/min. These transients were sufficiently pronounced to activate repetitively a K⁺ current. Addition of 10 mM caffeine caused disappearance of the [Ca²⁺]_i transients or reduction of their amplitudes and frequencies.The results indicate that caffeine does not activate Ca²⁺-induced Ca²⁺ release in hyperpolarized ß-cells but inhibits the Ca²⁺-mobilizing effect of inositol 1,4,5-trisphosphate. Correspondence to: E. Gylfe at the above address     

An experimental model of the production of early after depolarizations by injury current from an ischemic region

An ischemic myocardial region contains cells with a depolarized resting membrane potential. This depolarization leads to an intercellular current flow between the ischemic region and the surrounding normal myocardial cells which has been termed an injury current. We have devised an experimental model system in which an isolated guinea pig ventricular cell is electrically coupled to a model depolarized cell in order to evaluate the effects of this injury current on the electrical properties of a normal ventricular cell exposed to drugs which increase calcium current or decrease potassium current. Using low doses of isoproterenol, forskolin, or Bay K 8644 (or 8-bromo-cyclic adenosine monophosphate in the pipette) we found that the action potential duration of the isolated cell was lengthened, but that early after depolarizations (EADs) were not produced unless the cell was also coupled to a depolarized cell model representing an adjacent ischemic region. A similar prolongation of the action potential was produced by low doses of quinidine, but EADs were not produced unless coupling to a depolarized cell model was added. EADs could not be produced in any cells in the absence of the drugs even though the coupling to the depolarized cell model was increased up to the level at which the action potential was indefinitely prolonged. At higher isoproterenol concentrations, EADs or spontaneous activity were produced without coupling to the depolarized cell model. Under these conditions, coupling of the cell to a cell model with normal resting membrane potential stopped the spontaneous activity and prevented the occurrence of EADs even with high levels of resistive coupling. These findings suggest that the electrotonic influences of a localized depolarized region can produce EADs if the calcium current magnitude is increased, which would be the case for sympathetic innervation.     

The Protective effect ofd-sotalol against hypoxia-induced myocardial uncoupling

Summary The effects ofd-sotalol on intercellular electrical coupling and ultrastructure under hypoxic conditions were investigated in myocardial samples from eight young (1–2 months) and four older (10–12 months) guinea pigs. A right ventricular muscle strip was kept simultaneously in two divided chambers and superfused with normoxic and/or hypoxic (97% N₂+ 3% C_O2) Krebs solution. Hypoxia caused shortening of action potential duration (APD) and electrical cellto-cell uncoupling. If the uncoupling appeared after short-term hypoxia (less than 30 min), administration of 3.10^–7M ofd-sotalol to the hypoxic perfusate led to a recovery of electrical coupling. Transmission electron microscopy revealed moderate reversible ultrastructural alterations of the cardiomyocytes. No apparent changes in intercellular junctions were observed. The recoupling effect of sotalol decreased with the time of hypoxia as the ultrastructural damage progressed. After prolonged hypoxia (more than 30min), cardiomyocytes were markedly injured, intercellular junctions were severely affected, and gap junctions occurred less frequently. In these cases, administration ofd-sotalol caused only transient recoupling. After 1h of hypoxia, no recoupling was observed. Pretreatment withd-sotalol prevented hypoxia-induced electrical uncoupling and markedly attenuated ultrastructural damage, although shortening of APD still persisted. Our results indicate that the cardioprotective effect ofd-sotalol on electrical intercellular coupling is closely associated with sotalol-induced prevention of the ultrastructural damage. Considering previous results, we suggest that this protective effect ofd-sotalol may be related to its ability to increase intracellular cyclic adenosine monophosphate and, thereby, to decrease cytosolic free Ca. These effects can explain the antiarrhythmic and defibrillating properties ofd-sotalol.     

Ca2+ dependence of motilide-induced contractions in rabbit duodenal muscle strips in vitro

Summary Recent studies suggested that certain erythromycin A (EM-A) derivatives are motilin receptor agonists. As proposed by Itoh they may be called motilides. We have investigated the Ca²⁺-dependence of contractions induced by two potent motilides, ME-34 [de(N-methyl) 8,9-anhydroeryhtromycin A 6,9-hemiacetal] and EM-523 [de(N-methyl)-N-ethyl-8,9-anhydro-erythromycin A 6,9-hemiacetal], in duodenal tissues and compared the results with those previously obtained with motilin.Isometric and isotonic contractile responses of isolated longitudinal muscle sheets from the rabbit duodenum were tested under normal, Ca²⁺-free and depolarizing conditions. Prior to stimulation with motilides, the maximal response to acetylcholine was recorded and all responses were always expressed as a percentage of this response. Both motilides induced contractions in normally polarized tissue, with an EC₅₀ of 26 ± 5 nM for ME-34 (n = 7), and 27 ± 5 nM for EM-5231 (n = 16) and maximal responses of respectively 88 ± 4% and 80 ± 3%. Like motilin, both compounds induced an extra-contraction in depolarized tissues. The EM-523 response in 140 mM K⁺under isotonic conditions was 84 ± 3% (n = 5) at 10^–5 M, with an EC₅₀ that was shifted to 65 ± 18 nM. Similar figures were obtained for ME-34. When Ca²⁺ was added to Ca²⁺-depleted strips, half-maximal Ca²⁺ values (in mM) were 1.10 ± 0.11 (n = 9) for EM-523 and 1.13 ± 0.12 (n = 3) for ME-34, as compared with 1.12 ± 0.13 (n = 7) for motilin and 2.8 ± 1.1 (n = 9) for K⁺. Both ME-34 and EM-523 also induced a transient contraction in Ca⁺-free solutions under isometric conditions. The response to EM-523 (5 × 10^–6 M) was 49 ± 15% (n = 4) after 3 min. A maximal EM-523 -stimulation reduced a subsequent ACh response by 78 ± 7%, whereas EM-523 and ME-34 could not induce a contraction after ACh.We conclude that motilides depend upon external Ca²⁺ to a similar extent to motilin. Like motilin, they are also able to mobilize intracellular Ca Z + stores. Our results support the hypothesis that motilides act on motilin receptors. Send offprint requests to T. L. Peeters at the above address     

A new approach for 11C–C bond formation: Synthesis of 17α‐(3′‐[11C]prop‐1‐yn‐1‐yl)‐3‐methoxy‐3,17β‐estradiol

A new approach for ¹¹C–C bond formation via a Sonogashira‐like cross‐coupling reaction of terminal alkynes with [¹¹C]methyl iodide was exemplified by the synthesis of 17α‐(3′‐[¹¹C]prop‐1‐yn‐1‐yl)‐3‐methoxy‐3,17β‐estradiol. The LC‐purified title compound was obtained in decay‐corrected radiochemical yields of 27–47% (n=8) based on [¹¹C]methyl iodide within 21–27 min after EOB. In a typical synthesis starting from 9.6 GBq [¹¹C]methyl iodide, 1.87 GBq of 17α‐(3′‐[¹¹C]prop‐1‐yn‐1‐yl)‐3‐methoxy‐3,17β‐estradiol was synthesized in radiochemical purity >99%. The specific radioactivity ranged between 10 and 19 GBq/µmol, and the labeling position was verified by ¹³C‐NMR analysis of the corresponding ¹³C‐labeled compound. Copyright © 2003 John Wiley & Sons, Ltd.     

Fractional Factorial Design Study on the Performance of GAC-Enhanced Electrocoagulation Process Involved in Color Removal from Dye Solutions

The aim of this study was to determine the effects of main factors and interactions on the color removal performance from dye solutions using the electrocoagulation process enhanced by adsorption on Granular Activated Carbon (GAC). In this study, a mathematical approach was conducted using a two-level fractional factorial design (FFD) for a given dye solution. Three textile dyes: Acid Blue 74, Basic Red 1, and Reactive Black 5 were used. Experimental factors used and their respective levels were: current density (2.73 or 27.32 A/m²), initial pH of aqueous dye solution (3 or 9), electrocoagulation time (20 or 180 min), GAC dose (0.1 or 0.5 g/L), support electrolyte (2 or 50 mM), initial dye concentration (0.05 or 0.25 g/L) and current type (Direct Current—DC or Alternative Pulsed Current—APC). GAC-enhanced electrocoagulation performance was analyzed statistically in terms of removal efficiency, electrical energy, and electrode material consumptions, using modeling polynomial equations. The statistical significance of GAC dose level on the performance of GAC enhanced electrocoagulation and the experimental conditions that favor the process operation of electrocoagulation in APC regime were determined. The local optimal experimental conditions were established using a multi-objective desirability function method.     

Functional Films from Silica/Polymer Nanoparticles

High performance functional coatings, based on hybrid organic/inorganic materials, are being developed to combine the polymer flexibility and ease of processing with the mechanical properties and versatility of inorganic materials. By incorporating silica nanoparticles (SiNPs) in the polymeric matrices, it is possible to obtain hybrid polymer films with increased tensile strength and impact resistance, without decreasing the flexural properties of the polymer matrix. The SiNPs can further be used as carriers to impart other functionalities (optical, etc.) to the hybrid films. By using polymer-coated SiNPs, it is possible to reduce particle aggregation in the films and, thus, achieve more homogeneous distributions of the inorganic components and, therefore, better properties. On the other hand, by coating polymer particles with silica, one can create hierarchically structured materials, for example to obtain superhydrophobic coatings. In this review, we will cover the latest developments in films prepared from hybrid polymer/silica functional systems.