Search PubMed⌕ Search

Biomedical subjects

K Hostettmann

Publications and source records attributed to K Hostettmann.

At least 109 records · Page 6Linked to original sources
PubMed1984

On the use of plants and plant-derived compounds for the control of schistosomiasis.

The rising costs of chemotherapy and synthetic molluscides have led to an increasing interest in plants which are lethal to the intermediate host of schistosomiasis (bilharzia). Over one thousand species have been tested but only a few have been phytochemically examined. Approximately fifty molluscicidal compounds have so far been isolated from plants, including saponins, terpenoids, flavonoids, naphthoquinones and tannins. The saponins from Phytolacca dodecandra are the most active and have been successfully employed in field tests. The latest results in this area and the problems involved in the use of plants and natural products for the control of schistosomiasis are discussed here.

Animals↗
PubMed1983

[New chromatography. Technics for the isolation and separation of natural products].

Besides high-performance liquid chromatography (HPLC) which is now a well-established and currently used technique, several emerging methods for the isolation and separation of natural products are receiving considerable attention. Centrifugal thin-layer chromatography is a very rapid technique, but limited in resolution. Of special interest are the recently developed support-free liquid-liquid chromatography methods such as droplet counter-current chromatography (DCCC) and rotation locular counter-current chromatography (RLCC). This latter method was applied to the separation of the enantiomers of (+/-)-norephedrine.

Chromatography↗
PubMedDate not supplied

The potential of LC-NMR in phytochemical analysis.

The coupling of high performance liquid chromatography with nuclear magnetic resonance spectroscopy (LC-NMR) is one of the most powerful methods for the separation and structural elucidation of unknown compounds in mixtures. The recent progress in pulse field gradients and solvent suppression, the improvement in probe technology, and the construction of high field magnets have given a new stimulus to this technique, which has emerged since the mid 1990s as a very efficient method for the on-line identification of organic molecules. LC-NMR thus represents a potentially interesting complementary technique to LC-UV-MS in phytochemical analysis for the detailed on-line structural analysis of natural products. Recent applications have fully demonstrated the usefulness of this technique. A brief review of the applications of LC-NMR in natural product chemistry is presented in this paper, and a summary of the basic principles and modes of operation of LC-NMR is provided. Selected examples of LC-NMR analyses of plant metabolites in crude extracts or in enriched fractions are outlined and used to illustrate the different strategies for employing the technique. The practical possibilities and limitations of LC-NMR in its application to the analysis of crude plant extracts are discussed by means of several examples. Analytical strategies involving LC multi-coupled (hyphenated) techniques for the chemical screening and dereplication of crude plant extracts are presented. An analysis of the future development of the technique with respect to its application in phytochemical analysis is also given.

Biochemistry↗
PubMedDate not supplied

NMR and LC-MSn characterisation of two minor saponins from Ilex paraguariensis.

Two minor saponins obtained from the methanolic extract of the leaves of Ilex paraguariensis have been characterised by 13C-NMR, 1H-NMR, API-MS and chemical hydrolysis as oleanolic acid-3-O-(beta-D-glucopyranosyl-(1-->3)-alpha-L-arabinopyranosyl)-(28-->1)- beta-D-glucopyranosyl ester (guaiacin B) and oleanolic acid-3-O-(beta-D-glucopyranosyl-(1-->3)-(alpha-L-rhamnopyranosyl- (1-->2))-alpha-L-arabinopyranosyl)-(28-->1)-beta-D-glucopyranosyl ester (nudicaucin C). Both are isomeric forms of the known matesaponins 1 (MSP 1) and 2 (MSP 2) and differ only by the nature of the aglycone: they have oleanolic acid instead of ursolic acid, as found in the matesaponins. These minor saponins have not been fully separated from their major isomers MSP 1 and 2 and were characterised by in-mixture NMR analysis, LC-MS and LC-MSn experiments.

Base Sequence↗
PubMedDate not supplied

A rapid TLC bioautographic method for the detection of acetylcholinesterase and butyrylcholinesterase inhibitors in plants.

A simple and rapid bioautographic enzyme assay on TLC plates has been developed for the screening of acetylcholinesterase and butyrylcholinesterase inhibition by plant extracts. Enzyme activity was detected by the conversion of naphthyl acetate into naphthol and the formation of the corresponding purple-coloured diazonium dye with Fast Blue B salt. Inhibitors of cholinesterases produced white spots on the dye-coloured background of the TLC plates. The alkaloids galanthamine and physostigmine, which are known inhibitors of acetylcholinesterase, were used to determine the sensitivity of the assay. Various plant extracts were tested using the bioassay.

Acetylcholinesterase↗
PubMedDate not supplied

Determination of the absolute configuration of 6-alkylated alpha-pyrones from Ravensara crassifolia by LC-NMR.

The absolute configuration of asymmetric centres of two alpha-pyrones isolated from Ravensara crassifolia was determined using the Mosher method. The conventional analysis of the purified ester derivatives by 1H-NMR was replaced by a rapid and sensitive method in which the alpha-pyrones were analysed under isocratic reversed-phase LC-NMR conditions prior to and after derivatisation reactions. Comparison of the LC-1H-NMR spectra of the actual alpha-pyrones with those of the corresponding Mosher's esters recorded in the acetonitrile:deuterated water solvent system exhibited shifts comparable with those obtained using conventional deuterated solvents. Based on the shifts recorded, determination of the absolute configuration was possible by application of Mosher rules. The use of LC-NMR has permitted a direct analysis of crude reaction mixtures containing less than 50 microg of the starting material. Completion of the reaction was checked by LC-MS and the crude reaction mixture was analysed by stop-flow LC-NMR. This methodology seems very promising for the determination at the micro-scale level of the absolute configuration of natural products which are available only in very small amounts.

Alkylation↗
PubMedDate not supplied

On-line identification of unstable catalpol derivatives from Jamesbrittenia fodina by LC-mS and LC-NMR.

LC-UV-MS analysis of the methanol extract of Jamesbrittenia fodina O. M. Hilliard (Scrophulariaceae) revealed the presence of cinnamic ester derivatives. Two isomeric pairs of these constituents were detected, but could not be isolated. In order to identify these unstable compounds, LC-1H-NMR spectra were obtained for each individual isomer and standard NMR measurements were performed in-mixture. The spectra clearly demonstrated that the fractions consisted of mixtures of cis and trans cinnamoyl catalpol glycoside esters.

Chromatography, Liquid↗
PubMedDate not supplied

Structural investigations of isomeric oxidised forms of hyperforin by HPLC-NMR and HPLC-MSn.

The prenylated phloroglucinol hyperforin, thought to be an essential component for the anti-depressant activity of St. John's Wort (Hypericum perforatum), is unstable. The facile oxidative degradation of hyperforin poses serious problems for standardisation, and may also dramatically affect the pharmacological activity of the extracts. Hyperforin was dissolved in hexane and stored at room temperature for 3 days and yielded various closely related degradation products which, although difficult to isolate on the preparative scale, have been analysed by on-flow and stop-flow HPLC-NMR and HPLC-MS/MS. From on-line spectroscopic data, and with the aid of complementary in-mixture standard NMR two-dimensional correlation experiments, the different oxidised forms of hyperforin were found to be phloroglucinol derivatives in which a hydroxy-dihydrofuran ring is formed involving the enol OH at C-7 or C-9 (tautomeric form) and the prenyl chain at C-8 of the core nucleus of hyperforin. The strategy followed for the on-line identification of these constituents is discussed.

Bridged Bicyclo Compounds↗
PubMedDate not supplied

HPLC-UV/PAD and HPLC-MS(n) analyses of leaf and root extracts of Vismia guineensis and isolation and identification of two new bianthrones.

In order to evaluate the possible use of the leaves instead of the roots of Vismia guineensis as a new source for the traditional use of this drug, the chemical composition of both organs were compared by HPLC-UV/PAD and HPLC-MS analyses. The leaves are analysed here for the first time. The results show the presence of five major classes of secondary metabolites having specific chromophores: anthraquinones, vismiones, flavonoids, xanthones and benzophenones. The molecular weights and characteristic fragments, compared with previous EI or HPLC-MS literature data, allowed the partial identification of the major peaks in the chromatograms. Six additional isomeric bianthrones and one anthraquinone were detected in the dichloromethane extract of the roots after long storage in solution; the targeted isolation of the bianthrones was performed and enabled the identification of two original C-geranyl derivatives. The chemical compositions of the extracts demonstrated that only a minority of the constituents is shared by both organs. Thus, in order to establish a definitive phytoequivalence, additional pharmacological investigations are required.

Anthracenes↗