Isomerism and fluxional behaviour in η2 -vinyl complexes resulting in inversion of configuration at an asymmetric carbon atom. The crystal and molecular structures of two isomeric forms of [MoCl{η2 -C(CF3)C(CF3)(PEt3)} (CF3CCCF3)(η5 -C5H5)]

η² -Vinyl complexes [MCl{η² -C(CF₃)C(CF₃)L} (CF₃CCCF₃)(η⁵ -C₅H₅)] (M = Mo, W: L = tertiary phosphine or phosphite or pyridine) have been shown by NMR and X-ray diffraction studies to exist in two distinct isomeric forms which exhibit (a) different orientations of the η² -vinyl ligand (b) different configurations at the asymmetric carbon atom of the η² -vinyl ligand: variable temperature NMR studies reveal fluxional behaviour thought to involve reversible inversion of configuration at this carbon atom.     

Diastereoselective addition of enantiopure lithium tert-butylsulfinylferrocene to imines

(S)-tert-Butylsulfinylferrocene was submitted to ortho-metalation, and the corresponding lithium derivative was trapped by alkyl or aryl imines bearing various electron-withdrawing groups on the nitrogen atom (Ts, Dpp, Boc). New aminosulfoxides were obtained with complete diastereocontrol when Dpp or Boc groups were used. The absolute configuration (SS,SFc,S) has been determined by single-crystal X-ray analysis and chemical correlation. An unusual pseudocyclic boatlike transition state has been proposed to explain the stereochemical course of this reaction.     

Local round robin test for determination of aromatics in diesel fuels by HPLC

Determination of aromatics in diesel fuels by HPLC is covered by European Standard EN 12916 (April 2000). The Standard is based on former standards IP 391/90 and IP 391/95. The method used for measurements is NP HPLC and separation is performed on silica or modified silica columns with RI detection. The precision of the method was checked by determining the repeatability and reproducibility. The content of aromatics was measured in a number of commercial samples. The measurements have been performed in three different laboratories and under different working and instrumental conditions. Satisfactory agreement was established for repeatability and was slightly poorer for reproducibility. The content of polyaromatics is within the tolerance range (IP 590/99) and the content of tricyclic and higher aromatics (tri+) is close to the limit of quantitition in some samples. Clear differences in the content of polycyclic aromatics in domestic diesel and eurodiesel fuels were observed. The results have confirmed the ruggedness and robustness of the measuring method.     

On the metalation of 4-substituted pyridazines

A series of new pyridazines bearing ortho-directing groups at C-4 (protected/activated amino or carboxylic acid functionalities) was prepared and their metalation with lithium 2,2,6,6-tetramethylpiperidide was studied. Reactions of the ortho-lithiated species thus obtained with aldehydes as electrophiles opens an access to 4,5-disubstituted pyridazines 3, 4, 14 , and 15 .     

Calixarenes: Structure of an acetonitrile inclusion complex and some transition metal rimmed derivatives

The hostt-butylcalix[4]arene,1a, forms a 11 inclusion compound with acetonitrile as guest. The inclusion compound has been isolated and characterised by X-ray analysis of a twinned crystal at 123 K. The acetonitrile guest lies on a crystallographic four-fold symmetry axis passing through the centre of the bowl of1a which adopts a regular cone conformation. A known tetradentate and a new tridentate phosphinitocalix[4]arene derivative,2a and2c respectively, have been synthesized from1a and Ph₂Cl. Both2a and2c show a strong ability to coordinate with late transition metals and new complexes of gold(I), palladium(II) and platinum(II) are reported. Supplementary Data relating to this paper have been deposited with the British Library as Supplementary Publication No. SUP 92171 (5 pp.)This paper is dedicated to the commemorative issue on the 50th anniversary of calixarenes.     

Buffer gas effect on laser photoacoustic spectra of methyl chloride

Spectra of coincidence of CH₃C1 IR absorption with CO₂-laser emission were recorded by a photoacoustic detection method in the whole range of CO₂-laser emission. The samples were neat gas and mixtures with argon, at several pressures (10 to 600Torr) so that pressure effects could be observed. The results show that argon affects absorption of CO₂-laser emission quite differently from neat chloromethane, both regarding the most prominent coincidences and background absorption.     

Green chemistry approach to the synthesis of 3-substituted-quinazolin-4(3H)-ones and 2-methyl-3-substituted-quinazolin-4(3H)-ones and biological evaluation

ABSTRACT

A synthesis of two series of 3-substituted quinazolinones was performed utilizing a green chemistry approach, deep eutectic solvents and microwaves, namely. 2-Methyl-3-substituted-quinazolin-4(3H)-one derivatives were synthesized in a two-step reaction, using choline chloride:urea deep eutectic solvent (DES). 3-Substituted-quinazolin-4(3H)-ones were synthesized in one-pot one-step reaction of anthranilic acid, amines and orthoester in a microwave reactor. For the synthesis of 2-methyl-3-substituted-quinazolin-4(3H)-ones, first conventional synthesis of benzoxazinone, as an intermediate, was performed. Further, benzoxazinone in reaction with corresponding amines, in choline choline:urea deep eutectic solvent, furnished desired compounds. These procedures are based on green principles with the aim of developing synthetic routes for the potential antitumor agents. All compounds were characterized by LC/MS, ¹H NMR and ¹³C NMR spectral techniques. Compound 1 bearing trifluoromethoxyphenyl group showed promising activity against HuT-78 cell line with IC₅₀ of 51.4?±?5.1?µM.     

A novel bifunctional N-acetylglutamate synthase-kinase from <Emphasis Type="Italic">Xanthomonas campestris</Emphasis> that is closely related to mammalian N-acetylglutamate synthase

Background  

In microorganisms and plants, the first two reactions of arginine biosynthesis are catalyzed by N-acetylglutamate synthase (NAGS) and N-acetylglutamate kinase (NAGK). In mammals, NAGS produces an essential activator of carbamylphosphate synthetase I, the first enzyme of the urea cycle, and no functional NAGK homolog has been found. Unlike the other urea cycle enzymes, whose bacterial counterparts could be readily identified by their sequence conservation with arginine biosynthetic enzymes, mammalian NAGS gene was very divergent, making it the last urea cycle gene to be discovered. Limited sequence similarity between E. coli NAGS and fungal NAGK suggests that bacterial and eukaryotic NAGS, and fungal NAGK arose from the fusion of genes encoding an ancestral NAGK (argB) and an acetyltransferase. However, mammalian NAGS no longer retains any NAGK catalytic activity.