Characterization and TLC-Bioautographic Detection of Essential Oils from Some Thymus Taxa. Determination of the Activity of the Oils and their Components Against Plant Pathogenic Bacteria

JPC – Journal of Planar Chromatography – Modern TLC - The chemical composition of the oils of four thyme (Lamiaceae) chemotypes (Thymus vulgaris L., Thymus serpyllum L., Thymus x...     

Cinchona based squaramide catalysed enantioselective Michael addition of α-nitrophosphonates to aryl acrylates: enantioselective synthesis of quaternary α-aminophosphonates

Several cinchona based squaramide catalysts were applied to the asymmetric Michael addition of α-nitroethylphosphonates to acrylic acid aryl esters, resulting in high yields and enantioselectivities. The absolute configuration of one of the quaternary α-nitrophosphonate adducts was deduced from its experimental and calculated CD spectra. The adducts were reduced to their cyclic aminophosphonates by catalytic hydrogenation.     

Lipophilicity determination of some new crown ethers by reversed-phase thin-layer chromatography

Summary The lipophilicity of 28 modified crown ether derivatives was determined by reversed-phase thin-layer chromatography (RPTLC) using various organic phases and supports. The lipophilicity values determined in different RPTLC systems showed good correlations, however the quality of the organic phase (methanol, acetone, acetonitrile) and the support characteristics influenced to a small extent the determination.     

Effect of the type of ion-pairing reagent in reversed-phase ion-pair chromatography

Summary The retention of positively and negatively charged and neutral solutes was studied in an aqueous phosphate buffer eluent, with constant inorganic-counterion concentration, on ODS-Hypersil stationary phase in the presence of various sulfonic acid ion-pairing reagents. The adsorption isotherms of the ion-pairing reagents d-camphor-10-sulfonic acid, sodium cyclohexylsulfamic acid and sodium alkylsulfonates (butyl-, hexyl- and octyl-) were determined by the breakthrough method.Dedicated to Professor J. F. K. Huber on the occasion of his 60th birthday.     

Synthesis of PAF,an Antifungal Protein from P. chrysogenum,by Native Chemical Ligation: Native Disulfide Pattern and Fold Obtained upon Oxidative Refolding

The folding of disulfide proteins is of considerable interest because knowledge of this may influence our present understanding of protein folding. However, sometimes even the disulfide pattern cannot be unequivocally determined by the available experimental techniques. For example, the structures of a few small antifungal proteins (PAF, AFP) have been disclosed recently using NMR spectroscopy but with some ambiguity in the actual disulfide pattern. For this reason, we carried out the chemical synthesis of PAF. Probing different approaches, the oxidative folding of the synthetic linear PAF yielded a folded protein that has identical structure and antifungal activity as the native PAF. In contrast, unfolded linear PAF was inactive, a result that may have implications concerning its redox state in the mode of action.     

The Effect of Silver Perchlorate of the Reaction of Trialkyl Phosphite with α-Halogenoketones

Abstract

Trialkyl phosphites are known to react with α-halogenoketones to yield β-ketophosphonates (Arbuzov product) or vinyl phosphates (Perkow product) according to coniiitions.¹ α-Hydroxyphosphonate may be formed in addition, in prcltic media.² We have now shown that none of these products is formed in the presence of silver perchlorate (in benzene sclutim); nor could we detect the ketophosphonium perchlorate reported previously. Phosphorus-31 nmr showed the formation of trimethyl phosphate and tetramethyl pyrophosphate as the exclusive phosphorus-containing products. The sequence of possible reaction is complex and the overall stoichiometry may vary somewhat according to the rate and order of rixing. Trialkyl phosphate could be formed by elimination of alkyne from vinyloxyphosphonium intermediate produced together with silver iodine in first stage of the interaction. Pyrophosphate formation would then result from nucleophilic attack of trimethyl phosphate on the trimethoxy(1-nethylvinyloxy)phosphoniun ion, which may be formed as a reactive intermediate. Evidence for formation of methyl perchlorate in the final dealkylation of the quasiphosphonium intermediate is provided by proton nmr spectroscopy and by the formation of the N-methylquino-linium salt on addition of quinoline. No change in the ³¹P nmr spectrum occurs at this stage. Other by-products of the main reactions include the dehalogenated ketone (acetone from iodoacetone or acetnphenone from α-iodoacetophenone).     

Synthesis of Ristriose

ABSTRACT

A new reducing trisaccharide 0-α-D-arabinofuranosyl-(1→ 2)-0-α-D-mannopyranosyl-(1→2)-0-D-glucopyranose (11), named ristriose, has been synthesized in twenty one steps, starting from D-glucose, D-mannose and D-arabinose, with an overall yield of 3.5 %.     

Ready-made matrix-assisted laser desorption/ionization target plates coated with thin matrix layer for automated sample deposition in high-density array format.

The methodology for ready-made matrix-assisted laser desorption/ionization (MALDI) target plates covered with an optimized thin layer consisting of matrix and nitrocellulose has been developed. Piezoelectric microdispensing enabled sample depositions in a high-density array format of 2000 sample depositions on a conventionally sized target plate (45 x 47 mm). The sample depositions were made reproducibly in a fully automated mode by using an in-house developed computer-controlled piezoelectric flow-through microdispenser. Additionally, the piezoelectric technique facilitated significant analyte enrichment that increased the detection sensitivity. The MS signal was obtained rapidly, generally within ten laser pulses. An airbrush device was used to generate a fine spray of matrix and nitrocellulose dissolved in acetone. The acetone evaporated instantly when reaching the target plate leaving the entire surface with a thin and uniform matrix/nitrocellulose coating consisting of very small crystals of matrix embedded in the nitrocellulose. These crystals acted as a seed-layer on subsequent analyte depositions, rendering homogeneous sample spots when using alpha-cyano-4-hydroxycinnamic acid (CHCA) as matrix. The relative standard deviation of the signal intensity between spots was (20-30)% (n = 30). The detection sensitivity was improved by restricting the sample spot diameter to 300 microm. The spot size was affected by the deposition rate and the evaporation rate of the dispensed sample volume. Mass spectra of a 25-amol peptide mixture deposition were successfully recorded.     

Comparative bioanalytical study of3H-deramciclane in dog plasma, using a gas chromatography-nitrogen-selective detection (GC-NPD), a new GC-radiochemical detection (GC-RD) and a liquid scintillation method

Summary A new, highly sensitive and selective gas chromatography method, using radiochemical detection (GC-DR) was developed for the selective determination of³H-labelled deramciclane and its N-desmethyl metabolite in dog plasma. Inter-day accuracy and precision, as well as system suitability of the GC-RD method was investigated during the method validation. The calibration curve was proved to be linear (r=0.9986) in a wide concentration range (13–1000 ngeqv mL⁻¹) The lower limit of quantitation (LLOQ) was 13.7 ngeqv mL⁻¹, and the limit of the detection (LOD) was 1 ngeqv mL⁻¹. Using this new GC-RD method, plasma levels of³H-labelled deramciclane and its metabolite were determined in dogs, after the administration of a single 10 mg kg⁻¹ oral dose. Pharmacokinetic curves and the calculated pharmacokinetic parameters were compared to those obtained using a previously elaborated gas chromatography-nitrogen selective detection method (GC-NPD) and to those obtained by measuring the plasma level of total radioactivity (liquid scintillation counting, LSC). Pharmacokinetic curves and the calculated pharmacokinetic parameters obtained with the two different gas chromatography detection methods (NPD and RD) showed good correlation. Comparison of these results to those acquired by total radioactivity measurement demonstrated that deramciclane was intensively metabolised. Moreover, the biological half-life (t ₁ ^2/β ) of the unknown metabolites proved to be more than a magnitude longer than the half-life of the parent compound or that of N-desmethyl metabolite. Presented at: Balaton Symposium on High-Performance Separation Methods, Siófok, Hungary, September 3–5, 1997.     

Quasiliving Carbocationic Polymerization. XV. Forced Ideal Copolymerization of Isobutylene-lsoprene

Forced ideal carbocationic copolymerization of isobutylene and isoprene has been achieved by continuous addition of monomer mixtures of different compositions to cumyl chloride/TiCl₄ charges at -50°C. The overall rate of copolymerization could be kept equal to that of addition rate with up to 10 mol% isoprene in the mixed monomer feed. In this monomer concentration range the composition of the copolymer was identical to that of the feeds. At higher diene concentrations in the feed, chain transfer to monomer and other side reactions (intramolecular cyclization, gel formation) could not be completely avoided. The number-average molecular weight of the copolymers increased almost linearly with the amount of consumed monomers at 10 mol% isoprene concentrations in the feed (i.e., in the quasiliving range). According to ¹H-NMR and ¹³C-NMR spectroscopy, the products are random copolymers.