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101.
Dedicated to Professor Gerhard Kempter on the occasion of his 70th birthday Quinoxaline‐2‐aldoximes and ‐ketoximes ( 6 ) react with hydrazine, alkylhydrazines or arylhydrazines under acidic conditions to afford lH‐pyrazolo[3,4‐b]quinoxalines (flavazoles) ( 1 ). Since the oximes ( 6 ) are easily available from phenylenediamine, the herein described methodology provides a convenient two step entry to various functionalized flavazoles. Furthermore, acylation and alkylation of the 1‐unsubstituted lH‐pyrazolo[3,4‐b]quinoxalines 7 proceeds smoothly and in good yield to afford 31 different flavazoles 11 and 12. 相似文献
102.
Wahl F Weiler A Landenberger P Sackers E Voss T Haas A Lieb M Hunkler D Wörth J Knothe L Prinzbach H 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(24):6255-6267
“One‐pot” substitution of the twenty hydrogen atoms in pentagonal dodecahedrane (C20H20) by OH, F, Cl, and Br atoms is explored. Electrophilic insertion of oxygen atoms with DMDO and TFMDO as oxidizing reagents ended, far off the desired C20(OH)20, in complex polyol mixtures (up to C20H10(OH)10 decols, a trace of C20H(OH)19?). Perfluorination was successful in a NaF matrix but (nearly pure) C20F20 could be secured only in very low yield. “Brute‐force” photochlorination (heat, light, pressure, time) provided a mixture of hydrogen‐free, barely soluble C20Cl16 dienes in high yield and C20Cl20 as a trace component. Upon electron‐impact ionization of the C20Cl16 material sequential loss of the chlorine atoms was the major fragmentation pathway furnishing, however, only minor amounts of chlorine‐free C20+ ions. “Brute‐force” photobrominations delivered an extremely complex mixture of polybromides with C20HBr13 trienes as the highest masses. The MS spectra exhibited exclusive loss of the Br substituents ending in rather intense singly, doubly, and triply charged C20H4–0+(2+)(3+) ions. The insoluble ~C20HBr13 fraction (C20Br14 trienes as highest masses) obtained along a modified bromination protocol, ultimately allowed the neat mass selection of C20? ions. The C20Cl16 dienes and C20H0–3Br14–12 tri‐/tetraenes, in spite of their very high olefinic pyramidalization, proved resistant to oxygen and dimerization (polymerization) but added CH2N2 smoothly. Dehalogenation of the respective cycloaddition products through electron‐impact ionization resulted in C22–24H4–8+(2+) ions possibly constituting bis‐/tris‐/tetrakis‐methano‐C20 fullerenes or partly hydrogenated C22, C23, and C24 cages. 相似文献
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104.
Laura Machin Martin Piontek Sara Todhe Katrin Staniek Lianet Monzote Werner Fudickar Torsten Linker Lars Gille 《Molecules (Basel, Switzerland)》2022,27(20)
Leishmaniasis is a vector-borne disease caused by protozoal Leishmania parasites. Previous studies have shown that endoperoxides (EP) can selectively kill Leishmania in host cells. Therefore, we studied in this work a set of new anthracene-derived EP (AcEP) together with their non-endoperoxidic analogs in model systems of Leishmania tarentolae promastigotes (LtP) and J774 macrophages for their antileishmanial activity and selectivity. The mechanism of effective compounds was explored by studying their reaction with iron (II) in chemical systems and in Leishmania. The correlation of structural parameters with activity demonstrated that in this compound set, active compounds had a LogPOW larger than 3.5 and a polar surface area smaller than 100 Å2. The most effective compounds (IC50 in LtP < 2 µM) with the highest selectivity (SI > 30) were pyridyl-/tert-butyl-substituted AcEP. Interestingly, also their analogs demonstrated activity and selectivity. In mechanistic studies, it was shown that EP were activated by iron in chemical systems and in LtP due to their EP group. However, the molecular structure beyond the EP group significantly contributed to their differential mitochondrial inhibition in Leishmania. The identified compound pairs are a good starting point for subsequent experiments in pathogenic Leishmania in vitro and in animal models. 相似文献
105.
A series of tetracyanoborate salts M[B(CN)4] with the singly charged cations of Li+, Na+, Rb+, Cs+, [NH4]+, Tl+, and Cu+ as well as the THF solvate tetracyanoborates Na[B(CN)4] x THF and [NH4][B(CN)4] x THF were synthesized and their X-ray structures, vibrational spectra, solubilities in water, and thermal stabilities determined and compared with already known M[B(CN)4] salts. Crystallographic data for these compounds are as follows: Na[B(CN)4], cubic, Fd3m, a = 11.680(1) A, Z= 8; Li[B(CN)4], cubic, P43m, a = 5.4815(1) A, Z= 1; Cu[B(CN)4], cubic, P43m, a = 5.4314(7) A, Z= 1; Rb[B(CN)4], tetragonal, /4(1)/a, a = 7.1354(2) A, c= 14.8197(6) A, Z= 4; Cs[B(CN)4], tetragonal, /4(1)/a, a = 7.300(2) A, c = 15.340(5) A, Z= 4; [NH4][B(CN)4], tetragonal, /4(1)/a, a = 7.132(1) A, c = 14.745(4) A, Z= 4; Tl[B(CN)4], tetragonal, /4(1)/a, a = 7.0655(2) A, c = 14.6791(4) A, Z= 4; Na[B(CN)4] x THF, orthorhombic, Pnma, a = 13.908(3) A, b = 9.288(1) A, c = 8.738(1) A, Z= 4; [NH4][B(CN)4] x THF, orthorhombic, Pnma, a = 8.831(1) A, b = 9.366(2) A, c = 15.061(3) A, Z= 4. The cubic Li+, Na+, and Cu+ salts crystallize in a structure consisting of two interpenetrating independent tetrahedral networks of M cations and [B(CN)4]- ions. The compounds with the larger countercations (Rb+, Cs+, Tl+, and [NH4]+) crystallize as tetragonal, also with a network arrangement. The sodium and ammonium salts with the cocrystallized THF molecules are both orthorhombic but are not isostructural. In the vibrational spectra the two CN stretching modes A1 and T2 coincide in general and the band positions are a measure for the strength of the interionic interaction. An interesting feature in the Raman spectrum of the copper salt is the first appearance of two CN stretching modes. 相似文献
106.
Ahmed AY Oekermann T Lindner P Bahnemann D 《Physical chemistry chemical physics : PCCP》2012,14(8):2774-2783
The photooxidation of methanol as a model substance for pollutants on rutile TiO(2) (001) and (100) surfaces was investigated using intensity modulated photocurrent spectroscopy (IMPS). The results are analyzed in view of the influence of the surface structure, the methanol concentration and the electrode potential on the rate constants of charge transfer and recombination. The obtained results have been explained with a model combining the theory of IMPS for a bulk semiconductor surface and the nature of the surface-bound intermediates (alternatively mobile or immobile OH˙ radicals). The results indicate that water photooxidation proceeds via mobile OH˙ radicals on both surfaces, while methanol addition gives rise to the involvement of immobile OH˙ radicals on the (100) surface. Detailed analysis in view of the surface structures suggests that the latter observation is due to efficient electron transfer from bridging OH˙ radicals on the (100) surface to methanol, while coupling of two of these radicals occurs in the absence of methanol, making them appear as mobile OH˙ radicals. In the case of the (001) surface, the coupling reaction dominates even in the presence of methanol due to the smaller distance between the bridging OH˙ radicals, leading to more efficient water oxidation, but less efficient methanol photooxidation on this surface. 相似文献
107.
C,C‐ and N,C‐Coupled Dimers of 2‐Aminotetraphenylporphyrins: Regiocontrolled Synthesis,Spectroscopic Properties,and Quantum‐Chemical Calculations 下载免费PDF全文
Dr. Torsten Bruhn Dipl.‐Chem. Franziska Witterauf Dr. Daniel C. G. Götz Carina T. Grimmer Dipl.‐Chem. Max Würtemberger Prof. Dr. Udo Radius Prof. Dr. Gerhard Bringmann 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(14):3998-4006
β,β′‐Bisporphyrins are intrinsically chiral porphyrin dimers with fascinating properties. The configurational stability at their axes can be directed by variation of the central metal atoms. Herein, we present a regioselective functionalization of the monomeric 2‐amino‐tetraphenyl‐porphyrin as a versatile substrate for dimerization by oxidative coupling. By simple variation of the reaction conditions (solvent and oxidant), the oxidation selectively gave either the axially chiral C,C‐coupled diaminobisporphyrin in high yields or, under Ullmann conditions, the twofold N,C‐linked achiral dimer, also in good yields. A generalized mechanism for the coupling reaction is proposed based on DFT calculations. The axially chiral β,β′‐coupled porphyrin dimers were isolated as racemic mixtures, but can be resolved by HPLC on a chiral phase. TDDFT and coupled‐cluster calculations were used to explain the spectroscopic properties of the aminoporphyrins and their dimers and to elucidate the absolute configurations of the C,C‐coupled bisporphyrins. 相似文献
108.
Rzepecki P Hochdörffer K Schaller T Zienau J Harms K Ochsenfeld C Xie X Schrader T 《Journal of the American Chemical Society》2008,130(2):586-591
Self-association of aminopyrazole peptide hybrid 1 leads to stacked nanorosettes. This remarkable, well-ordered structure obeys the laws of nucleic acid self-assembly. In a strictly hierarchical process, formation of aminopyrazole "base" triplets via a hydrogen bond network is accompanied by pi-stacking with a second rosette and final dimerization of two double rosettes to a four-layer superstructure, stabilized by a six-fold half-crown alkylammonium lock. The final complex is soluble in organic as well as in aqueous solution. It was characterized in the solid state by X-ray crystallography, in water by NMR spectroscopy, and in silico by quantum chemical shift calculation. All these methods provide strong evidence for the same hexameric complex geometry. Its structural features bear striking similarity to nucleic acid architectures and their peptidic counterparts, especially alanyl-PNA. The whole self-assembly process is highly solvent- and temperature-dependent and occurs with a high degree of cooperativity--no intermediates are observed. Formation and dissociation of the nanorosette, however, are kinetically slow. The limitation to a hexameric aggregate can be explained by six sterically demanding valine residues, whose replacement by alanines may result in formation of infinite fibers. 相似文献
109.
110.