Reactivity of 4a,5-epoxy-5-deazaflavins

Reactions of 4a,5-epoxy-5-deazaflavins with aqueous potassium carbonate, Vilsmeier reagent (dimethylformamide-phosphorus oxychloride), acetic anhydride-acetic acid, pyridine and triethanolamine gave the corresponding oxazolonoquinolines, 5-chloro-5-deazaflavins, 4a,5-diacetoxy-5-deazaflavins, 1,5-dihydro-5-deazaflavin-5-ones, and deoxygenated 5-deazaflavins, respectively.     

5-苄氧亚氨基-5-脱氧阿维菌素B1a的合成

以阿维菌素B1a为原料经过选择性氧化合成5-氧代-5-脱氧阿维菌素B1a, 再与O-取代羟胺盐酸盐反应合成了5个5-苄氧亚氨基-5-脱氧阿维菌素B1a (4a～4e), 通过¹H NMR, ¹³C NMR, MS, IR确证了它们的结构. 生测结果表明它们对于棉铃虫和甜菜夜蛾有一定的杀虫活性.     

Synthesis of some 5H-benzo[a]phenoxazin-5-one derivatives

The substituted 6-bromo and 6-chloro-5H-benzo[a]phenoxazin-5-ones, prepared by condensation of substituted 2-aminophenols with 2,3-dibromo or 2,3-dichloro-1,4-naphthoquinone in methanolic potassium hydroxide solution, have been dehalogenated to substituted 5H-benzo[a]phenoxazin-5-ones in the presence of sodium hydrosulfite dissolved in aqueous pyridine under nitrogen atmosphere.     

On a novel coordination mode of phosphinine C5H5P

In an unprecedented coordination mode two phosphinines simultaneously bridge a Mn-Mn bond and the latter with two Mn(CO)3 fragments; the distortion of the resulting central heterobicyclo[1.1.0]butane unit follows from the Mn(18VE) requirement.     

Discrimination between 5-hydroxymethylcytosine and 5-methylcytosine by a chemically designed peptide

An artificial phosphopeptide recognized the difference between methylated and hydroxymethylated cytosines in DNA. The Sp1 zinc finger peptide substituted by phosphotyrosine effectively discriminated between 5-methylcytosine, 5-hydroxymethylcytosine ((hm)C) and unmethylated cytosine. The DNA recognition properties of the peptide differ from those of other chemicals that detect (hm)C.     

Synthesis of some 5H-benzo[a]phenothiazin-5-one derivatives

Several substituted 6-anilino-5H-benzo[a]phenothiazin-5-one derivatives were prepared by condensation of substituted 1,4-naphthoquinones with 2-aminobenzenethiol in pyridine. The reduction and acetylation of the resulting compounds were also investigated.

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Synthese einiger 5H-Benzo[a]phenothiazin-5-on-Derivate

Zusammenfassung Es wurden mittels Kondensation substituierter 1,4-Naphthochinone mit 2-Aminothiophenol in Pyridin einige substituierte 6-Anilino-5H-benzo[a]phenothiazin-5-one dargestellt. Die Reduktion und Acetylierung der resultierenden Verbindungen wurde ebenfalls untersucht.

     

The luminescence of trigonal bipyramidal NbO5−5 and TaO5−5 and a comparison with other niobates and tantalates

The luminescence of La₃NbO₄Cl₆ with trigonal bipyramidal NbO^5?₅ groups is reported. The Nb⁵⁺ coordination does not seem to influence the niobate emission. The luminescence and Raman spectrum of La₃TaO₄Cl₆ are also reported. Finally, differences in luminescence of the M and M′ modifications of YTaO₄ are discussed.     

Simple synthesis of 6-alkyl-5H-benzo[a]phenoxazin-5-ones

6-Alkyl-5H-benzo[a]phenoxazin-5-ones were prepared by the reaction of 5H-benzo[a]phenoxazin-5-one with carboxylic acid in the presence of silver ion and peroxydisulfate.

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Eine einfache Synthese von 6-Alkyl-5H-benzo[a]phenoxazin-5-onen (Kurze Mitteilung)

Zusammenfassung 6-Alkyl-5H-benzo[a]phenoxazin-5-one wurden mittels Reaktion von 5H-Benzo[a]phenoxazin-5-onen mit Carbonsäuren in Gegenwart von Silberionen und Peroxydisulfat dargestellt.

     

Pendular rearrangement of epimeric 3b,4,4a,5-tetramethyl-3b,4,4a,5-tetrahydro-4H-cyclopropa[a]phenalen-5-yl cations

The kinetics of degenerate pendular rearrangement of 3b,exo-4,4a,5-tetramethyl-3b,4,4a,5-tetrahydro-4H-cyclopropa[a]phenalen-5-yl cation and its endo epimer, generated under conditions ensuring their long life, were studied by dynamic NMR spectroscopy. The rearrangement mechanism is discussed with account taken of the results of quantum-chemical calculations and published data for related rearrangements.     

Towards a photophysical model for 5-hydroxyflavone

The photophysics of the 5-hydroxyflavone (5HF) molecule has been revised. Conversely to what has been hitherto reported, the proton-transfer fluorescence of 5HF has been recorded under xenon lamp excitation in cyclohexane, hexane, ethanol, ethyl ether, 2-methyl-2-propanol, and dimethylsulfoxide at room temperature. The 5HF fluorescence spectra only exhibit one emission band centered at ca. 700 nm. A small photoreaction quantum yield of 10(-5)-10(-6) denotes the great photostability exemplified by 5HF in hydrocarbon solvent, ethanol, and dimethylsulfoxide. This great photostability is predominantly explained owing to an internal conversion process from the first excited singlet state 1(pi,pi*)1 (S1), which has a repulsive (proton-transfer) potential energy curve with respect to the stretching of the OH bond and only one energy minimum for the proton-transfer tautomer. The S1'-S0' energy gap proves to be small because of important modifications found in the molecular geometry of 5HF upon photoexcitation. A computational strategy, based upon theoretical calculations at the B3LYP density functional theory (DFT) and time-dependent DFT levels, supports the experimental spectroscopic evidence. Also an abnormal singlet-triplet splitting for a pi,pi* configuration has been found in 5HF.     

Liquid crystals with a 5-phenyltropone core

Liquid crystals with a 5-phenyltropone structure were prepared. 5-(4-Alkanoylaminophenyl)tropone derivatives ( 5 and 6 ) showed smectic A and C phases. From the layer spacing, compound 5q formed an interdigitated bilayer smectic A phase. The variable temperature FTIR spectra of 5q indicated the presence of intermolecular hydrogen bonding between the amide carbonyl group and the NH group on the phenyl ring of neighbouring molecules. The amide groups of the 2-alkanoylamino-5-phenyltropones controlled the occurrence of mesophases through not only inter- and intra-molecular hydrogen bonds, but also dipole-dipole interaction with the tropone carbonyl group of neighbouring molecules.