4,6-Thioanhydro-hexopyranosides,synthesis and chemical behaviour of methyl 2-0-p-toluenesulfonyl-4,6-thioanhydro-α-d-gulopyranoside

Methyl 4-0-benzoyl-6-bromo-6-deoxy-α-D-glucopyranoside ($\text{1}$, Figure 1) was converted, via the corresponding ditosylate $\text{2}$, into methyl 2,3-di-0-p-toluenesulfonyl-4-0-benzoyl-6-S-acetyl-6-thio-α-D-glucopyranoside ($\text{3}$) by a selective nucleophilic displacement of 6-bromo-group with thioacetate. Unexpectedly, on treating the compound $\text{3}$ with an excess of sodium methoxide in benzene-methanol (1:1) at room temperature, methyl 2-0-p-toluenesulfonyl-4,6-thioanhydro-α-D-gulopyranoside ($\text{4}$) was obtained in a yield of 84%. In order to determine the structure of the relatively unstable oily product $\text{4}$, some stable crystalline derivatives ($\text{5}$, $\text{6}$ and $\text{7}$) were prepared. Detailed analysis of the ¹H-NMR-spectra (200 MHz) of $\text{6}$ and $\text{7}$ gave the conclusive evidence for the structure of $\text{4}$ A self-imposing mechanism of the clean and smooth transformation of $\text{3}$ to $\text{4}$ is proposed, involving: a) formation of $\text{9}$ (Figure 2) as a crucial intermediate and b) a highly regioselective epoxide opening in $\text{9}$ (at C-4) by an intramolecular nucleophilic attack of the mercaptide anion from C-6.     

Measurement of the essential oil in inclusion complexes with cyclodextrin by means of capillary gas chromatography

The oil content in inclusion complexes of cyclodextrin and essential oils can be determined efficiently by extraction at high temperature followed by capillary gas chromatography of the extracted oil. The total amount of complexed oil is calculated by comparison of the total peak area of the examined material with that of the relevant authentic sample. A computer program is outlined for the calculations.     

Characterization of Porous Graphitic Carbon LC Phase with some Carbohydrate Derivatives

Stereoselective CE method for investigations of pharmacokinetics of ketoprofen enantiomers (KTP) in patients taking also other drugs is proposed, to establish relation between levels of KTP enantiomers in blood and synovial fluid of patients with rheumatoid arthritis. Resolution of the analytes was obtained in silica capillary filled with chiral selector-heptakis 2,3,6-tri-O-methyl–β-cyclodextrin in triethanolamine-phosphate buffer. Calibration curves for enantiomers in plasma and synovial fluid were linear in the range of 0.25–50.0 mg L⁻¹, but 1.0–250.0 mg L⁻¹ in urine. Concentrations of KTP enantiomers in synovial fluid measured at 4 h after the administration of a tablet with racemic KTP were insignificantly greater [(−)-R = 1.07 ± 0.66; (+)-S-KTP = 1.13 ± 0.65 mg L⁻¹] than in plasma [(−)-R = 0.86 ± 0.37; (+)-S-KTP = 0.96 ± 0.42 mg L⁻¹]. The validated method has been successfully applied for the determination of KTP enantiomers in biological fluids of patients with rheumatoid arthritis.

     

Chromatographic Index–Intensity Fingerprint: Identification of Multicomponent Samples

Identification of multicomponent samples is one of the most common tasks of chromatographers, and one of the most difficult. This task can be computerized and one possible computer-assisted solution is discussed in this paper. Identification is based on comparison of retention index and peak intensity for all the peaks. Three different match factors are defined for better evaluation of the comparison, to reveal samples having the same components in different ratios or samples containing impurities. The basics of the calculations and some applications are discussed. Application of this method of chromatogram identification is tested by identification of several pine species by recognition of their needle oils and by identification of wine samples from their aroma composition. Tests were also performed in an inter-laboratory environment.     

Retention index calculation without n-alkanes--the virtual carbon number

For the fast gas chromatographic identification of separated components the retention index is still one of the most often used tools, although mass spectrometry is available in almost all analytical laboratories. For the calculation of the retention indices it is not necessary to use n-alkanes or any other homologous series. If the analyte contains some compounds, not necessarily belonging to a homologous series, with well-known retention indices those compounds can be used as index references and the index of the other compounds can be calculated as is done using n-alkanes. The only difference is that instead of the carbon number of the n-alkanes, virtual carbon numbers of the reference compounds should be used. The method of calculation, and the effect of this method of calculation on the reproducibility are discussed in this paper, and analyses of some halogenated compounds and marjoram oil are used as experimental examples.     

Chemo-, stereo- and regioselective hydrogenolysis of carbohydrate benzylidene acetals. Synthesis of benzyl ethers of benzyl α- -, methyl β-D-mannopyranosides and benzyl α-D-rhamnopyranoside by ring cleavage of benzylidene derivatives with the LiAlH4-AlCl3 reagent

Treatment of benzyl α-(1) and methyl β- -mannopyranoside (2) with α,α-dimethoxytoluene gave the exo and endo isomers (3,5 and 4,6) of the dibenzylidene derivatives of 1 and 2. Hydrogenolysis of the exo isomers (3 and 5) with a molar equivalent of AlH₂Cl gave the 3-0-benzyl-4,6-0-benzylidene derivatives (7 and 21), whereas the endo isomers (4 and 6) gave the 2-0-benzyl-4,6-0-benzylidene compounds (8 and 22). The 2-0-allyl ether 9 of 7, the 3-0-allyl derivative (10) of 8 and compounds 21 and 22 were treated with an additional molar equivalent of AlH₂Cl at reflux and the products were the 4-0-benzyl-6-hydroxyl derivatives (11, 12, 23 and 24), whereas in the case of 22 the 6-0-benzyl-4-hydroxyl isomer (25) was also isolated. By deallylation of 11 and 12, 3,4-(13) and 2,4-di-0-benzyl (14) ethers of 1 were prepared. Tosylation of 11 and 12, and subsequent reduction of the products (15 and 16) made possible the preparation of the partially protected benzyl α- -rhamnopyranoside derivatives (17–20). The structures of the compounds synthesized were characterized by ¹H and ¹³C NMR spectroscopic investigation and by chemical methods.     

Mosaic increments for predicting the gas chromatographic retention data of the chlorobenzenes

The chlorinated organic compounds are very important from the point of view of the chemical industry and environmental protection, and therefore the gas chromatographic analysis of these compounds is very interesting for analytical chemists. In this paper we studied the relationship between the molecular structure and gas chromatographic retention on several stationary phases having different polarity and at several temperatures of benzene and 12 chlorobenzene compounds as model compounds. A coding system involving primary (mosaic increments) and secondary (bond increments)calculation methods was developed. The retention indices of benzene and the chlorobenzenes calculated on HP-5 at 120 degrees C shows a better performance of the mosaic increments (average absolute deviation delta of 1.7 retention index units) compared with the bond increments (delta = 11.7 retention index units). Retention factors, k, calculated with mosaic increments for chlorobenzenes on SPB-1 and WAX-10, at 140 degrees C, yield average relative errors of epsilon = 0.9 and 3.5%, respectively. Therefore, the presented paper provides a new possibility for precalculation of the retention data.     

Large dimensional sets not containing a given angle

We say that a set in a Euclidean space does not contain an angle α if the angle determined by any three points of the set is not equal to α. The goal of this paper is to construct compact sets of large Hausdorff dimension that do not contain a given angle α ∈ (0,π). We will construct such sets in ℝ ⁿ of Hausdorff dimension c(α)n with a positive c(α) depending only on α provided that α is different from π/3, π/2 and 2π/3. This improves on an earlier construction (due to several authors) that has dimension c(α) log n.