Stereoselective synthesis of cytoxazone and its analogues

A variety of synthetic routes to (−)-cytoxazone 1, a cytokine modulator isolated from Streptomyces cultures, and its stereomers 2 and regioisomers 3 have been reviewed.     

Asymmetric catalysis in fragrance chemistry: a new synthetic approach to enantiopure Phenoxanol®, Citralis® and Citralis Nitrile®

A new approach to the synthesis of the single stereomers of the fragrances Phenoxanol^®, Citralis^® and Citralis Nitrile^® is reported. The key step of the synthesis is the asymmetric hydrogenation of (Z)- or (E)-3-methyl-5-phenyl-pent-2-en-1-ol, which leads to the single enantiomers of Phenoxanol^® from which both enantiomers of Citralis^® are obtained by oxidation. Treatment of these compounds with hydroxylamine finally led to Citralis Nitrile^® without any loss of enantiopurity. The odour profiles of the single enantiomers of these fragrances are reported as well.     

Asymmetric Synthesis of All Possible Stereomers of 4‐Aminoglutamic Acid via Michael Condensation of Chiral Ni(II) Complexes of Glycine and Dehydroalanine

A new method for asymmetric synthesis of all possible stereomers of 4‐aminoglutamic acid has been developed. The method is based on asymmetric Michael condensation of the nucleophilic moiety of glycine and electrophilic moiety of dehydroalanine in their chiral Ni(II) complexes of the Schiff's bases with (S)‐ and (R)‐2‐N‐(N′‐benzylprolyl)aminobenzophenones, resulting in the formation of dimeric complexes of 4‐aminoglutamic acid. Stereoselectivity of the asymmetric condensation of the complexes exceeded 94%. The condensation of nucleophilic and electrophilic complexes in four possible combinations has resulted in the formation of dimeric complexes of all the stereomers of 4‐aminoglutamic acid: (2S,4S), (2S,4R)‐meso and (2R,4R). Optically active stereomers of 4‐aminoglutamic acid with high optical purity were isolated after decomposition of the dimeric complexes.     

Uncatalyzed solventless Diels-Alder reaction of 2-amino-3-nitroacrylate: synthesis of new epimeric 2-amino-3-nitro-norbornene- and norbornane-2-carboxylic acids

A highly diastereoselective Diels-Alder reaction between cyclopentadiene and ethyl (Z)-2-N-Boc-amino-3-nitroacrylate in neat conditions affords the ethyl 2-t-butoxycarbonylamino-3-endo-nitro-bicyclo[2.2.1]hept-5-ene-2-exo-carboxylate: a new constrained carbocyclic amino acid. Catalytic hydrogenation of this cycloadduct gave the corresponding reduced norbornane derivative. A preliminary investigation into the chemistry of these two amino acids was performed. In particular, the epimerization to their corresponding 3-exo-nitro compounds by treatment both with acid and base was studied. From this study, valuable information on the endo/exo process at the C-3 carbon atom, as well as on the stability of the different stereomers, was obtained. The stability is closely related to the presence or the absence of the double bond in the ring and to the substitution pattern. Finally, deprotection of the amino acid function has been performed.     

Electrocapillary studies of fluoride solutions on mercury using polyethylene capillary

The electrocapillary curves in concentration range 0.001 M to 1 M in sodium and potassium fluoride solutions and in 12.25 M potassium fluoride were measured using a glass capillary with a polyethylene tip. In very dilute solutions the lowering of the interfacial tension at potentials more positive than p.z.c. described several times in experiments with glass capillary electrometer was not observed, and the electrocapillary curves coincided very well with those obtained from double integration of capacitance data. At large concentration of fluoride an increase of maximum interfacial tension was noticed. The fabrication of polyethylene capillary electrode is described and its advantages discussed.     

Design,synthesis and computational evaluation of a novel intermediate salt of N-cyclohexyl-N-(cyclohexylcarbamoyl)-4-(trifluoromethyl) benzamide as potential potassium channel blocker in epileptic paroxysmal seizures

The narrow therapeutic range and limited pharmacokinetics of available Antiepileptic drugs (AEDs) have raised serious concerns in the proper management of epilepsy. To overcome this, the present study attempts to identify a candidate molecule targeting voltage gated potassium channels anticipated to have superior pharmacological than existing potassium channel blockers. The compound was synthesized by reacting (S)-(+)-2,3-dihydro-1H-pyrrolo[2,1-c][1,4] benzodiazepine5,11(10H,11aH)-dione with 4-(Trifluoromethyl) benzoic acid (C₈H₅F₃O₂) in DMF and N,N′-dicyclohexylcarbodiimide (DCC) which lead to the formation of an intermediate salt of N-cyclohexyl-N-(cyclohexylcarbamoyl)-4-(trifluoromethyl)benzamide with a perfect crystalline structure. The structure of the compound was characterized by FTIR, ¹H NMR and ¹³C NMR analysis. The crystal structure is confirmed by single crystal X-ray diffraction analysis. The Structure-Activity Relationship (SAR) studies revealed that substituent of fluoro or trifluoromethyl moiety into the compound had a great effect on the biological activity in comparison to clinically used drugs. Employing computational approaches the compound was further tested for its affinity against potassium protein structure by molecular docking in addition, bioactivity and ADMET properties were predicted through computer aided programs.     

Transformed steroids—part 95 : High pressure induced 1,3-dipolar cycloaddition of nitronic esters to 16-dehydro-20-oxo steroids

High pressure induced cycloaddition of Z and E nitronic esters (2) to 16-dehydro-20-oxo steroids (1) leads to regiospecific formation of steroido [16α,17α-d] tetrahydro-l',2'-oxazoles (3 and 4). It is shown that both modes (“exo-endo”) of dipolarophile approach to the dipole are realized for most steroids examined. All four possible isomers are isolated and their preferred conformations are established. It is shown that conversion of unstable stereomers to stable ones (3'→ 4; 4'→ 3) proceeds as a simultaneous nitrogen inversion and isoxazolidine cycle conformational change (_NE→E^N).     

Integral heat of dissolution of potassium chlorate in water at 298.15 K

The heat of dissolution of potassium chlorate in water at 298.15 K has been measured on an LKB 8700-1 calorimeter in the concentration range 0.063–0.659 m. The concentration dependence of the measured data was fitted by an empirical equation ΔH_m (kJ mole^?1) = 41.353₈ + 1.862₆m^{$\text{1}\text{2}$} ? 6.430₀m which was derived from our and Andauer—Lange data. The heat of crystallization calculated from this dependence was ΔH_cryst. = 34.7 ± 0.5 kJ mole^?1, which agrees with data calculated for potassium chlorate from solubility and activity data.     

Reaction of 1-substituted 3-aminoquinolinediones with isocyanic and isothiocyanic acid

1-Substituted-3-aminoquinoline-2,4(1H,3H)-diones react with potassium cyanate or potassium thiocyanate in boiling acetic acid to give ureido- or thioureidooxindoles, spiro-oxindoles and dihydroimidazoquinolones. However, if the starting compounds are substituted with a benzyl group at position 3, a C-debenzylation proceeds to give imidazoquinolones. According to a proposed reaction mechanism, a molecular rearrangement of the primarily formed mono-substituted urea or thiourea takes place. All compounds were characterized by ¹H, ¹³C and IR spectroscopy and MS data.     

Identification of aminophospholipid stereomers by positive-ion fast atom bombardment combined with collisional activation mass-analysed ion kinetic energy analysis and high-performance liquid chromatography

Two methods for the identification of aminophospholipid stereomers are described. After a chemical derivatization, 9-fluorenylmethoxycarbonyl derivatives of diacyl-sn-2- and diacyl-sn-3-phosphoserine and diacyl-sn-2- and diacyl-sn-3-phosphoethanolamine can be characterized by positive-ion fast atom bombardment combined with collisional activation mass-analysed ion kinetic energy analysis based on the differentiation of relative abundances [M + H + diethanolamine ? 89]⁺ and [M + H]⁺ fragments derived from [M + H + diethanolamine]⁺ ions, the protonated solvated molecules, and normal phase high-performance liquid chromatography on the basis of different elution times of the derivatives of the aminophospholipid stereomers on an aminopropyl-bonded column.     

Oxidation of organic substances with compounds of trivalent manganese: XXIII. Preparation,stability, and determination of the titer of standard solutions of the fluoride complex of trivalent manganese

A method of preparation of 10^?2 ?10^?3M standard solutions of the fluoride complex of manganese(III) by the reaction of manganese(II) with permanganate in a medium of potassium fluoride acidified with sulfuric acid has been developed. It has been found that in a medium of 1 M sulfuric acid, 0.5 M manganese(II) sulfate, and 0.1 M potassium fluoride these solutions are sufficiently stable for both direct and indirect titrimetric determinations. The titer was determined using potassium iodide as a primary standard and potentiometric, bipotentiometric, or biamperometric titration.     

Analytical control of the preparation of single crystal materials by inductively coupled plasma atomic emission spectrometry

The present paper shows that inductively coupled plasma atomic emission spectrometry (ICP-AES) and the Q concept, in accordance with Boumans and Vrakking [Spectrochim. Acta Part B 43 (1988) 69] can be used in the determination of a large number of dopants with different characteristics (charge and ionic radius) in the single crystals of potassium titanylphosphate [KTiOPO₄], some of its structural analogues and potassium gadolinium tungstate [KGd (WO₄)₂]. The basic conclusion from the analytical data obtained in this work is that the incorporation of Me⁺, Me²⁺, Me³⁺, Me⁴⁺ and Me⁵⁺ ions in the crystal lattice depend on its ionic radii. The effect of the ionic charge of the dopant ions is negligible. The light on the regularities of dopant incorporation in the crystal lattice was thrown and hence on the possibilities of modifying the properties of the single crystal materials.     

Evolution structurale sous haute pression des phases K2MO3 (M = Zr,Hf, Sn,Pb)

The study of the high-pressure modifications of the oxides K₂MO₃ (M = Zr, Hf, Sn, Pb) confirms the tendency of potassium to adopt the trigonal prismatic coordination in layer oxides: The β form is characterized by layers of (K, M)O₆ octahedra with common edges, between which other potassium atoms are inserted with prismatic coordination. For M = Zr and Hf, an increase of pressure or temperature transforms β to the γ or δ variety, both derived from the NaCl structure. The influence of the electronegativity of M on the potassium coordination in layer structures is discussed.     

XPS study of potassium-promoted molybdenum carbides for mixed alcohols synthesis via CO hydrogenation

The X-ray photoelectron spectroscopy (XPS) was used to investigate the surface characteristic of potassium-promoted or un-promoted both β-Mo_2C and α-MoC_(1-x) pretreated by syngas at different temperatures, and the promotional effect of potassium on the catalytic performance was also studied. XPS results revealed that the content of surface Mo and its valence distribution between β-Mo_2C and α-MoC_(1-x) were quite different. Promoted by potassium, the remarkable changes were observed for surface composition and valence of Mo distribution over β-Mo_2C. Potassium had strong electronic effect on β-Mo_2C, which led to a higher Mo~(4+) content. On the contrary, potassium had little electronic effect on α-MoC_(1-x), and K-Mo interaction was weak. Therefore, Mo~0 and Mo~(2+) became the dominant species on the catalyst surface, and the Mo~(4+) content showed almost no increase as the pretreatment temperature enhanced. In terms of catalytic performance of molybdenum carbides, the increase in Mo~0 most likely explained the increase in hydrocarbon selectivity, yet Mo~(4+) might be responsible for the alcohols synthesis.     

Spectral interference in the determination of Ho,Tm and Ga as dopants in single crystals of potassium titanylphosphate by inductively coupled plasma atomic emission spectrometry

The present article discusses the spectral interferences affecting the determination of Ga, Ho and Tm as dopants in single crystals of potassium titanylphosphate (KTiOPO₄) by inductively coupled plasma atomic emission spectrometry (ICP-AES). The Q concept, as proposed by Boumans and Vrakking [Spectrochim. Acta Part B 43 (1988) 69] was used for this study, which covers: (a) spectral data for potassium, titanium and phosphorous as interferents (at a concentration of 4 mg/ml) in 400 pm wide spectral windows around the prominent lines of the analytes; (b) a database of Q values for line interferences (Q_I) and for wing interferences (Q_W); and (c) the interelement interferences in doubly doped crystals of KTP.     

Sine-wave polarographic determination of small amounts of indium in the presence of large amounts of cadmium,lead or tin

The sine-wave polarographic determination of small amounts of indium in the presence of large amounts of cadmium, lead or tin was investigated. The determination of indium in cadmium was possible down to 0.01 % in 1 M potassium iodide at pH 2, the determination of indium in lead was possible down to 0.02 % in 1 M potassium chloride at pH 2, and the determination of indium in tin was possible down to 0.3 % in 1 M hydrochloric acid and down to 0.2 % in 2 M perchloric acid with 0.5 M sodium chloride.     

muelectrode studies in cultured epithelial cells

The present analysis was done to elucidate the electrical properties of an established mammalian epithelial cell line, i.e. the Madin Darby canine kidney (MDCK) cell. Rapid changes of the extracellular fluid were made to identify conductive pathways across the cell membrane. During control conditions mimicking in vivo extracellular fluid, the potential difference across the cell membrane (U_m) approached −51.0±0.5 mV (n = 122). With potassium-sensitive muelectrodes, a potential difference of +14,4 ± 1.4 mV (n = 5) was determined. Rapid increase of the extracellular potassium concentration from 5.4 to 20 mmol/dm³ depolarized U_m (dU_mK) by +17.0 ± 0.4 mV (n = 85). Accordingly, some 50% of the cell membrane conductance is due to potassium conductive pathways, i.e. the transference number for potassium (t_K) approaches 0.5. When 10 μmol/dm³ valinomycin was added to the extracellular fluid, U_m increased gradually to −74.7 ± 0.8 mV and t_K increased to 0.86. Barium at a concentration of 1 mmol/dm³ in the extracellular fluid depolarized U_m by +20.2 ± 0.4 mV and virtually abolished t_K. However, when extracellular potassium was increased from 5.4 to 35 mmol/dm³, further depolarization was observed, indicating that barium can be displaced by high potassium concentrations. Rapid reduction of the extracellular sodium concentration from 133 to 19 mmol/dm³ led to a significant sustained hyperpolarization (dU_mNa) of −13.5±0.6 mV (n =15). Additional experiments indicated that the hyperpolarization was at least partly due to opening of potassium conductive pathways.In conclusion, the cell membrane conductance of MDCK cells is partially due to a potassium conductance which can be blocked by barium and stimulated by the reduction of extracellular sodium. Intracellular potassium is higher than that for electrochemical equilibrium across the cell membrane, and thus potassium diffusion is directed from the cell to the extracellular fluid.     

Flow-injection chemiluminescence determinations for human blood lead using controlled reagent release technology

A flow-through CL method for the determination of lead combined with controlled-reagent-release technology has been developed. Chemiluminescence (CL) reagents luminol and potassium permanganate were immobilized on anion exchange resin by electrostatic interaction. Lead ion was determined by its enhancing effect on the CL reaction between luminol and potassium permanganate. Both luminol and potassium permanganate were eluted from the anion exchange resin column by sodium phosphate solution. The linear range of the system was 10 μg mL^?1, and the detection limit was 5?×?10^–9 g mL^?1 lead (3σ). A complete analysis could be performed in 1 min with a relative SD 3.2% (1.0?×?10^–7 g mL^?1, n?=?9). The column shows remarkable stability and can be reused over 350 times and 21 days. The method has been applied to determine lead in human blood samples.     

A new bismuth potassium nitrate oxide, Bi1.7K0.9O2(NO3)2: Synthesis, structure, thermal behavior, and photocatalytic properties

We report here the first observation of a bismuth potassium nitrate Bi_1.7K_0.9O₂(NO₃)₂, obtained via thermal decomposition of bismuth and potassium nitrate mixtures. The new compound is orthorhombic, space group Immm (71), Z = 2, with a = 3.8698(7) Å, b = 3.8703(7) Å, and c = 24.1271(4) Å. Its crystal structure was refined from powder X-ray diffraction data by analogy with the mineral beyerite, Bi₂O₂Ca(CO₃)₂. The morphology and elemental composition of Bi_1.7K_0.9O₂(NO₃)₂ were characterized using scanning electron microscopy (SEM) with energy dispersive X-Ray spectroscopy (EDS). Its phase transformations upon heating and products of its thermal decomposition were studied using XRD, TGA and FTIR. At 440 °C, Bi_1.7K_0.9O₂(NO₃)₂ transforms to another basic bismuth potassium nitrate with demonstrates a very similar XRD pattern but slightly larger cell parameters. At 520 °C, the intermediate oxide nitrate decomposes into a mixture of crystalline α-Bi₂O₃ and KNO₃. The as prepared Bi_1.7K_0.9O₂(NO₃)₂ showed lower than TiO₂ (Degussa P25) photocatalytic activity upon decomposition of a widely used model pollutant, Rhodamine B (RhB) and photooxidation of potassium iodide under UV-vis light irradiation. Interaction with potassium iodide in alkaline media resulted in formation of Bi₅O₇I.     

Synthesis and CO2 capture evaluation of Li2−xKxZrO3 solid solutions and crystal structure of a new lithium-potassium zirconate phase

Solid solutions of lithium and potassium metazirconates Li_2−xK_xZrO₃ (where, 0?x?2) were prepared by coprecipitation. Samples were characterized by powder X-ray diffraction, scanning electron microscopy, and thermogravimetric analyses. Results showed that the solubility limits of potassium into Li₂ZrO₃ is x=0.2. Furthermore, at higher potassium concentrations, a new phase was synthesized, Li_2.27K_1.19Zr_2.16O_6.05. For structural studies of this new phase, XRD data were analyzed by Rietveld refinements. Additionally, at high potassium concentrations different phases of ZrO₂ were found, as potassium tends to sublimate. On the other hand, lithium-potassium metazirconate solid solutions, Li_2−xK_xZrO₃, were tested as CO₂ captors. Thermal analyses into a CO₂ flux showed that Li_2−xK_xZr₂O₃ solid solutions present a better CO₂ absorption than Li₂ZrO₃ pure. The differences observed in the CO₂ sorption processes were explained with thermodynamic data.