Pavletta S. Denkova

Quantitative analysis of sesquiterpene lactones in extract of Arnica montana L. by 1H NMR spectroscopy

(1)H NMR spectroscopy was used as a method for quantitative analysis of sesquiterpene lactones present in a crude lactone fraction isolated from Arnica montana. Eight main components - tigloyl-, methacryloyl-, isobutyryl- and 2-methylbutyryl-esters of helenalin (H) and 11α,13-dihydrohelenalin (DH) were identified in the studied sample. The method allows the determination of the total amount of sesquiterpene lactones and the quantity of both type helenalin and 11α,13-dihydrohelenalin esters separately. Furthermore, 6-O-tigloylhelenalin (HT, 1), 6-O-methacryloylhelenalin (HM, 2), 6-O-tigloyl-11α,13-dihydrohelenalin (DHT, 5), and 6-O-methacryloyl-11α,13-dihydrohelenalin (DHM, 6) were quantified as individual components.

Theoretical investigation on H1 and C13 NMR chemical shifts of small alkanes and chloroalkanes

Using density functional theory (DFT) with the B3LYP, PBE, and PBE0 exchange-correlation functionals as well as the Moller-Plesset second-order perturbation theory (MP2) combined with a series of rather extended basis sets, 1H and 13C chemical shifts of small alkanes and chloroalkanes (with different numbers of chlorine atoms on specific positions) have been simulated and compared to experimental data. For the 1H chemical shifts, theory tends to reproduce experiment within the limits of the experimental errors. In the case of 13C chemical shift, the differences between theory and experiment increase monotonically with the number of chlorine atoms and exhibit a deviation from additivity. This behavior is related to the saturation of the experimental 13C chemical shifts with the number of chlorine atoms, whereas the evolution is mostly linear at both DFT and MP2 levels of approximation. This difference has been traced back to the relativistic spin-orbit coupling effects, which are exalted as a result of the enhancement of the s character of the C atom when increasing the number of linked Cl atoms. Thus, it was demonstrated that not only electron correlation but also relativistic effects have to be considered for estimating the 13C chemical shifts when several Cl atoms are directly attached to the C atom. Linear (theory/experiment) regressions have then been performed for the different types of C atoms, i.e., bearing one, two, and three Cl atoms, with excellent correlation coefficients. The linear correlation relationships so obtained can then serve to predict and facilitate the interpretation of the nuclear magnetic resonance spectra of more complex compounds. Furthermore, by investigating the basis set effects, the correlation between the chemical shifts calculated using the 6-311 + G(2d,p) basis set and the more extended 6-311 + G(2df,p) and aug-cc-pvtz basis sets is excellent, demonstrating that the choice of the 6-311 + G(2d,p) basis set for calculating the 1H and 13C chemical shifts is relevant.

Combined use of complete lineshape analysis of 1D spectra subjected to reference deconvolution and linear prediction, 2D-EXSY spectra and a double fitting method for the study of chemical exchange. Application to an eight-site exchange system

Obtaining unknown NMR parameters from experimental spectra of exchanging systems is, from a mathematical point of view, associated with the solution of an inverse problem. Inverse problems are usually solved by iterative procedures and calculations may not always converge and the solutions are rarely unique. To attain reliable rate constants we adopted the following experimental–computational scheme: acquirement of perfect NMR lineshapes for complete lineshape analysis (CLSA) by elimination of undesirable effects due to magnetic field inhomogeneity through reference deconvolution and linear prediction; the combined use of 2D exchange spectroscopy (2D‐EXSY) and 1D CLSA for the determination of the rotation rate constants; and application of the double fit method, which is based on the knowledge that the exchange parameters depend on thermally activated processes.

Alkaloids from Mongolian species Hypecoum lactiflorum Kar. et Kir. Pazij.

A new secoberbine alkaloid (–)-N-methylcorydalisol was isolated from the aerial parts of Hypecoum lactiflorum Kar. et Kir. Pazij. (Papaveraceae) of Mongolian origin and was characterised. The known alkaloids of protopine and protoberberine type protopine, allocryptopine, (–)-N-methylcanadine and (–)-N-methylstylopine were also isolated. (–)-N-methylstylopine is a new alkaloid for the genus, while (–)-N-methylcanadine is new for the species. All structures were established by physical and spectral analysis.

Phytochemical Study and Antiinflammatory Properties of Lobelia laxiflora L

Abstract Three new piperidine alkaloids were isolated from stems, leaves and flowers of Lobelia laxiflora L. (Campanulaceae). The structures of racem. cis-8,10-diethyl-3,4-dehydrolobelidiol (1), racem. trans-8-ethyl-10-phenyl-3,4-dehydrolobelidiol (2) and racem. cis-8-ethyl-10-phenyl-3, 4-dehydrolobelidiol (3) were established by spectral analyses. The residues obtained from the ethanol extracts from stems (S), leaves (L), and flowers (F) were applied in carrageenan (Car)-and cobra venom (CV)-induced acute inflammation in mice. A suppression of paw edema formation at a dose of 100 mg kg-1 was established. In this study the antiinflammatory potential of Lobelia I. was regarded in connection with the complement system. The sequential activation and assembly into functional units of complement components can proceed via two different pathways, named classical (CP) and alternative (AP). The ability of the residues, nonalkaloid fractions, alkaloid fractions and the three alkaloids at a concentration from 0.125 to 1.0 mg ml-1 to inhibit complement activation and thus to prevent inflammatory process was estimated in vitro in human serum via both pathways. All of them inhibited complement activity with a predominant action on CP.