Thin-Layer Chromatographic Quantifcation of trans-Resveratrol in Cosmetic Raw Materials of Botanic Origin

JPC – Journal of Planar Chromatography – Modern TLC - Recently, a growing interest has been observed in preventive and “anti-ageing” medicine, accompanied by a dynamic...     

Spontaneous and diastereoselective aldol reactions of cyclic β-amino ketones in the presence of water

Direct aldol reactions of 4-methyl-1-piperidone, tropinone and granatanone (pseudopelletierine) take place spontaneously in the presence of water without any catalyst or additional reagents. The anti/syn-diastereoselectivity of the aqueous aldol reaction depends on the amount of water used. The syn-selectivity of the reaction is probably due to the thermodynamic control. Excellent atom economy and low E factors together with anti-selectivity as high as 98:2 for the tropinone aldol were obtained.     

Synthesis of unsymmetrical alkyl acetals via addition of primary alcohols to allyl ethers mediated by ruthenium complexes

Abstract  

Ru-catalyzed synthesis of mixed alkyl–alkyl acetals via addition of primary alcohols to allyl ethers has been extended to include long-chain and/or functionalized substrates. The catalytic systems for these reactions were generated from RuCl₂(PPh₃)₃ and [RuCl₂(1,5-COD)]_x and phosphines [PPh₃ or P(p-chlorophenyl)₃] or SbPh₃. Of particular importance is the almost quantitative elimination of transacetalization. The addition proceeds through allyl complexes, not via isomerization of allyl ethers––subsequent addition of ROH to vinyl ethers.     

Ring-expanded bicyclic β-lactams: a structure-chiroptical properties relationship investigation by experiment and calculations

In the present work, the validity of the helicity rule relating the absolute configuration of the bridgehead carbon atom in bicyclic β-lactams to the sign of the 220 nm band observed in their electronic circular dichroism (ECD) spectra is examined for ring-expanded cephalosporin analogues. To this end, a series of model compounds with a seven-membered ring condensed with the β-lactam unit was synthesized. A key step of their synthesis was either the ring-closing metathesis (RCM) or the free radical cyclization leading to the seven-membered ring with an S, O, or C atom at the 6 position in the bicyclic skeleton. To investigate the scope and limitations of the simple, empirically established helicity rule, a combination of ECD spectroscopy, variable-temperature ECD measurements, X-ray analysis, and time-dependent density functional theory (TD-DFT) calculations was used. A comparison of the experimental ECD spectra with the spectra simulated by TD-DFT calculations gives a reasonable interpretation of the Cotton effects observed in the 240-215 nm spectral range. The results suggest that the helicity rule does not apply to the investigated compounds because of the planarity of their amide chromophore. Thus, these compounds do not constitute an exception to the rule that was established for bi- and polycyclic β-lactams with the nonplanar amide chromophore only.     

Thermodynamic characteristics of the activity of selected chromatographic sorbents

Summary The possibility of comparing various chromatographic sorbents in respect of their activity is discussed utilizing a simple thermodynamic approach presented earlier.     

Investigation of the self association of higher fatty alcohols and acids on chromatographic sorbents

Summary Three different sorbents, one with high activity (silica gel), the second with medium activity (cellulose powder) and the third having low activity (chromatographic paper) were compared in respect of their usefulness for the evaluation of the self association of selected higher fatty alcohols and acids. The obtained results are correlated with IR spectroscopic data and theoretical considerations.     

The influence of hydrogen-bond association on the destruction of hydroperoxides in the autoxidation process of oleyl alcohol, oleic acid, and methyl oleate

The autoxidation process of oleyl alcohol, oleic acid, and methyl oleate at 40, 50, and 60 °C was considered with the special stress laid upon the mechanism of cumulating and destruction of peroxidic products. Interpretation of the observed differences was based on the hydrogen-bond association patterns.     

Characteristics of the oxidation process in the methyl oleate-propionic acid system by means of dielectric constant measurements

In our paper the influence of association in the methyl oleate-propionic acid system on the course of autoxidation of this system was discussed. The course of autoxidation of the a/m system was characterized with the help of peroxide number and dielectric constant measurements.