Biomedical subjects

Kurt Hostettmann

Publications and source records attributed to Kurt Hostettmann.

At least 19 recordsLinked to original sources

PubMed2007

Identification of natural products using HPLC-SPE combined with CapNMR.

Two major development areas in HPLC-NMR hyphenation are postcolumn solid-phase extraction (HPLC-SPE-NMR) and capillary separations with NMR detection by means of solenoidal microcoils (CapNMR). These two techniques were combined off-line into HPLC-SPE-CapNMR, which combines the advantage of high loadability of normal-bore HPLC columns with high mass sensitivity of capillary NMR probes with an active volume of 1.5 microL. The technique was used for rapid identification of complex sesquiterpene lactones and esterified phenylpropanoids present in an essentially crude plant extract (toluene fraction of an ethanolic extract of Thapsia garganica fruits). Elution profiles of 10 x 1 mm i.d. SPE cartridges filled with poly(divinylbenzene) resin were found to be only marginally broader than those observed upon direct injection of 6-microL samples into the probe. Thus, the technique focuses analytes emerging in the HPLC elution bands of 0.5-1 mL into volumes of approximately 10 microL, compatible with the CapNMR probe. Using this technique, nine natural products (1-9) present in the plant extract in amounts varying from 0.1 to 20% were identified by means of 1D and 2D NMR spectra, supported by parallel HPLC-ESIMS measurements. Therefore, HPLC-SPE-CapNMR should be regarded as an attractive alternative to other applications of CapNMR for mixture analysis.

Biological Products↗

PubMed2007

Cardiovascular effects of an n-butanol extract from fresh fruits of Randia siamensis.

Randia siamensis is used in Thai folklore medicine for inducing abortion and controlling blood pressure. The present study investigated the cardiovascular effects of an R. siamensis fruit extract, and mechanisms involved in anesthetized normal and reserpinized rats. R. siamensis (0.4-12 mg/kg) i.v. increased the mean arterial pressure (MAP) and heart rate. Both effects were significantly inhibited by phentolamine (2 mg/kg, i.v.) or propranolol (0.6 mg/kg, i.v.). The combination of phentolamine and propranolol, or reserpine pretreatment, inhibited the positive chronotropic effect with a slight decrease in the MAP. In vitro, R. siamensis (0.001-0.3 mg/ml) increased the rate of beating of the right atrium and the strength of the electrical field-stimulated contraction of the left atrium, both effects were inhibited by propranolol, or with reserpine pretreated rats. R. siamensis (0.01-3 mg/ml) produced a contraction of isolated thoracic aorta, which was potentiated by N(G)-nitro-L-arginine (LNA), or by removal of the vascular endothelium, but inhibited by phentolamine, or reserpine. R. siamensis (0.3-3 mg/ml) caused a relaxation of phenylephrine-preconstricted aortic rings, which was potentiated with reserpine pretreatment, and abolished after removal of the vascular endothelium, or in the presence of LNA. These results suggest that R. siamensis extract exerts both hypertensive and positive chronotropic effects via the alpha- and beta-adrenergic receptors of blood vessels and the heart, due to release of endogenous catecholamines, likely from nerve ending and adrenal medulla. The hypotensive activity results from the release of nitric oxide causing dilatation of the blood vessels. The present data support the folklore therapeutic uses of this plant.

1-Butanol↗

PubMed2006

Antileishmanial activities associated with plants used in the Malian traditional medicine.

Sixty-four extracts issued from twenty-one plants used in the Malian traditional medicine--several of them as antiparasitic drugs--were assayed for their antileishmanial effects against both extracellular and intracellular forms of Leishmania major. Seven extracts from six different plants--Sarcocephalus latifolius, Zanthoxylum zanthoxyloides, Entada africana, Bobgunnia madagascarensis, Pseudocedrela kotschyi and Psorospermum guineense--were found to be significantly active against the intracellular form of the parasite.

Anti-Infective Agents↗

PubMed2006

Identification of flavonols in leaves of Maytenus ilicifolia and M. aquifolium (Celastraceae) by LC/UV/MS analysis.

A comparative analysis of the flavonoid components of the leaves of two medicinal plants known in Brazil as "espinheira santa", namely, Maytenus ilicifolia Mart. ex Reiss. and M. aquifolium Mart. (Celastraceae), and a hybrid plant, M. aquifoliumxM. ilicifolia, has been carried out using high-performance liquid chromatography coupled with photodiode array UV detection and mass spectrometry. One methoxyflavonoid glycoside and 18 flavonol-3-O-glycosides were identified in the extracts on the basis of their on-line UV spectra (measured in the absence and presence of shift reagents) and multiple stage mass spectral data. Fingerprint analysis of the flavonoid extracts revealed significant differences in the profiles of the two Maytenus species, while the hybrid plant contained flavonoids found in both parent species.

Chromatography, High Pressure Liquid↗

PubMed2006

New and bioactive aromatic compounds from Zanthoxylum zanthoxyloides.

In the course of a study of medicinal plants from Mali, the root bark of Zanthoxylum zanthoxyloides Lam. (Rutaceae) was investigated. The root bark of this plant is used as a toothbrush by West African people. Phytochemical investigation of the MeOH extract of Zanthoxylum zanthoxyloides Lam. (Rutaceae) led to the isolation of different biologically active compounds. The separation of acetylcholinesterase inhibitors was performed by centrifugal partition chromatography (CPC). The fractions were monitored by direct TLC bioautographic assays. The bio-guided isolation led to the isolation of a new peroxide derivative. In addition, LC/UV/MS analysis performed on the crude MeOH extract allowed on-line identification of some known compounds. The structures of the isolated compounds were elucidated by classical spectroscopic methods including UV, NMR, MS and HR-MS.

Antifungal Agents↗

PubMed2006

Bioactive diterpenes from the fruits of Detarium microcarpum.

A fruit pulp extract of Detarium microcarpum showed inhibition of the growth of the plant pathogenic fungus Cladosporium cucumerinum and of the enzyme acetylcholinesterase, implicated in Alzheimer's disease. Fractionation of this extract led to the isolation of four new clerodane diterpenes, 3,4-epoxyclerodan-13E-en-15-oic acid (1), 5alpha,8alpha(2-oxokolavenic acid) (2), 3,4-dihydroxyclerodan-13E-en-15-oic acid (4), and 3,4-dihydroxyclerodan-13Z-en-15-oic acid (5). Also isolated were 2-oxokolavenic acid (3) and copalic acid (6). Structure elucidation of the compounds was carried out by spectroscopic data interpretation and by the X-ray crystallography of 2 and 4. Three of the new clerodane diterpenes (1, 2, and 5) showed both antifungal activity and inhibition of acetylcholinesterase, and 3 showed a slight inhibition of this enzyme.

Antifungal Agents↗

PubMed2005

On-line identification of sugarcane (Saccharum officinarum L.) methoxyflavones by liquid chromatography-UV detection using post-column derivatization and liquid chromatography-mass spectrometry.

Sugarcane (Saccharum officinarum L., Gramineae) bagasse and leaves were investigated for their flavonoid content and transgenic sugarcane ("Bowman-Birk" and "Kunitz") was compared with non-modified ("control") plants. Analyses were carried out by high-performance liquid chromatography coupled to diode array UV detection (LC/UV), also using post-column addition of shift reagents, and tandem MS (atmospheric pressure chemical ionization-MS/MS and collision-induced dissociation-MS). On-line UV and MS data demonstrated the presence of methoxyflavone glycosides and aglycones in a total of seven compounds. Three naturally occurring flavones glycosides and two unusual erythro- and threo-diastereoisomeric flavolignan 7-O-glucosides were identified together with their aglycones.

Chromatography, High Pressure Liquid↗

PubMed2005

Effects of flavonoids on cell proliferation and caspase activation in a human colonic cell line HT29: an SAR study.

A library of 42 natural and synthetic flavonoids has been screened for their effect on cell proliferation and apoptosis in a human colonic cell line (HT-29). Examples of different classes of flavonoids have been screened, and the effects of hydroxylation, methoxylation and/or C-alkylation at various positions in the A- and B-rings have been assessed. Flavones and flavonols possess greater antiproliferative activity than chalcones and flavanones. With respect to structural modification of flavonoids, C-isoprenylation was by far the most effective, with substitution at the 8-position and longer chains, such as geranyl giving the best results. Finally, most compounds that significantly reduced cell survival also increased caspase activity, suggesting that at least part of their antiproliferative activity might be attributable to an apoptotic response.

Alkylation↗

PubMed2005

Phytochemistry in the microgram domain - a LC-NMR perspective.

Plants represent an extraordinary reservoir of novel molecules and there is currently a resurgence of interest in the vegetable kingdom as a possible source of new lead compounds for introduction into therapeutical screening programs. In order to discover potential new bioactive natural products, the dereplication of crude plant extracts performed prior to isolation work is of crucial importance for avoiding the isolation of a known constituent. In this respect, chemical screening strategies have been developed using hyphenated techniques (LC/UV-DAD, LC-MS and LC-NMR). In our laboratory, these techniques have been fully integrated into the isolation process and are used for the chemical screening of crude plant extracts in complement with on-line or at-line bioassays. LC-UV-MS is used as a first dereplication step in combination with UV and MS databases, while LC-NMR is performed in a second step for de novo on-line structure determination. This approach enables the partial or the complete on-line identification of natural products in complex matrices such as crude plant extracts. These methods also give a unique possibility to study unstable compounds, which rapidly degrade or which are not separable at a preparative level. In the multi-hyphenated approach used (hypernation), LC-NMR plays a key role since it provides the most detailed structural information. The relatively low sensitivity of this technique, however, requires that strategies for high loading of plant extracts are developed and compromises for solvent selection have to be made. For more demanding experiments, at-line strategies based on the microfractionation of the LC-peak of interest and recording of spectra in fully deuterated solvents in microflow probes represent a promising alternative.

Alkaloids↗

PubMed2005

Bio-guided isolation of cholinesterase inhibitors from the bulbs of Crinum x powellii.

In a search for potential acetylcholinesterase (AChE) inhibitors, the ethanol extract of the bulbs of Crinum x powellii (Amaryllidaceae) was found to demonstrate a marked inhibition of this enzyme. Using a bio-guided isolation strategy, linoleic acid ethyl ester has been identified as the compound responsible for this inhibition. Three other molecules - the alkaloid hippadine, the glycosylated benzyl alcohol derivative calleryanin and 4'-hydroxy-7-methoxyflavan - were also isolated and characterized for the first time from Crinum x powellii. The structures of these compounds were elucidated by spectrometric methods including EI, D/CI mass spectrometry, (1)H, (13)C and 2D NMR experiments. Linoleic acid was also found to inhibit AChE.

Amaryllidaceae Alkaloids↗

PubMed2005

Methylpyrrole tropane alkaloids from the bark of Erythroxylum vacciniifolium.

Nine new tropane alkaloids substituted by a methylpyrrole moiety were isolated from the bark of Erythroxylum vacciniifolium, a Brazilian endemic plant used in traditional medicine and locally known as catuaba. All compounds were elucidated as tropanediol or -triol alkaloids esterified by at least one 1-methyl-1H-pyrrole-2-carboxylic acid. One of the isolated compounds was identified as a tropane alkaloid N-oxide. Their structures were determined by high-resolution mass spectrometry and multidimensional NMR spectroscopy.

Alkaloids↗

PubMed2005

Flavonoids from the stem of Eriophorum scheuchzeri.

Activity-guided isolation of antifungal, antibacterial, and antioxidant compounds from the dichloromethane extract of the aerial parts of Eriophorum scheuchzeri led to the isolation of eight flavonoids. Three isoflavones and one flavanone are new natural compounds. The isolation of the bioactive compounds was performed by centrifugal partition chromatography. Fractions and pure compounds were monitored by a direct TLC bioautographic assay. Their structures were elucidated by spectroscopic and chemical methods.

Anti-Bacterial Agents↗

PubMed2004

On-line structure characterization of pyrrolizidine alkaloids in Onosma stellulatum and Emilia coccinea by liquid chromatography-ion-trap mass spectrometry.

On-line structure characterization of pyrrolizidine alkaloids in two various plant species (Onosma stellulatum W.K., family Boraginaceae and Emilia coccinea Sims., family Compositae) was performed by a newly elaborated RP-HPLC ion trap MS method with atmospheric pressure chemical ionization (APCI) interface. Different PAs (N-oxides, free bases, otonecine alkaloids) isolated were separated on Waters XTerra C18 column using a gradient elution. The combination of a CE-SPE with multiple isolation and fragmentation steps for specific masses in ion trap MS detector enabled fast and sensitive analysis of various types of PAs (N-oxides and free bases). In O. stellulatum, spectra 12 various types of structures (13 different alkaloids) have been determined for the first time: leptanthine-N-oxide, lycopsamine-N-oxide, heliospathuline, lycopsamine, trachelanthamine-N-oxide, dihydroechinatine, leptanthine, heliospathuline-N-oxide, 7-acetylintermedine, uplandicine, echimidine and echimidine-N-oxide. In E. coccinea, the following types of PAs were found: platyphylline-N-oxide, platyphylline (three stereoisomers with the same MS(n) spectrum), ligularidine, neoligularidine, neosenkirkine and also previously reported senkirkine. The method elaborated can be applied in the structural analysis of PAs in newly examined plant materials or food products but further analysis is needed to determine the stereochemistry in details.

Asteraceae↗

PubMed2004

On-line characterisation of apple polyphenols by liquid chromatography coupled with mass spectrometry and ultraviolet absorbance detection.

Apple polyphenols were characterised by means of hyphenated techniques such as HPLC coupled to UV photodiode array detection (LC-DAD) and to mass spectrometry (LC-MS). LC-MS using atmospheric pressure ionisation (APCI) in the positive ion mode provided the molecular weight, the number of hydroxyl groups, the number of sugars and an idea about the substitution pattern of the polyphenols. LC-DAD with postcolumn addition of UV shift reagents afforded precise structural information about the position of the free hydroxyl groups in the polyphenolic nucleus. Five isorhamnetin glycosides, two hydroxyphloretin glycosides and quercetin were reported in apple peel for the first time. Postcolumn addition of UV shift reagents in LC-DAD analysis confirmed the presence of isorhamnetin glycosides and not the isomeric glycosides of rhamnetin. Moreover, isorhamnetin-3-O-rhamnoglucoside was identified unambiguously by comparison with a standard. These results are relevant not only from a chemotaxonomic point of view, but also in the control of authenticity of fruit derived products in order to detect fraudulent admixtures.

Chromatography, High Pressure Liquid↗

PubMed2004

Rapid analysis of nucleotide-activated sugars by high-performance liquid chromatography coupled with diode-array detection, electrospray ionization mass spectrometry and nuclear magnetic resonance.

A generally applicable method for HPLC analysis of sugar nucleotides was established. Separation was achieved using ion-pair chromatography on a reversed-phase column. Ion-pair reagents were selected and various parameters optimized with respect to separation of 11 of the most important sugar nucleotides and compatibility with on-line detection by electrospray ionization MS and NMR. The method was applied to the on-line analysis of the GDP-D-mannose-4,6-dehydratase (Gmd) and GDP-4-keto-6-deoxy-D-mannose reductase (Rmd) catalyzed conversion of GDP-D-mannose to GDP-D-rhamnose. By LC-NMR, the intermediate product of the reaction was shown to be a mixture of GDP-4-keto-6-deoxy-D-mannose and GDP-3-keto-6-deoxy-D-mannose. Nucleotide co-factors of enzymatic reactions such as ATP and NADH did not interfere with the analysis of nucleotide-activated sugars.

Carbohydrates↗

PubMed2004

Screening of non-alkaloidal natural compounds as acetylcholinesterase inhibitors.

Acetylcholinesterase (AChE) inhibitors are currently the only approved therapy for the treatment of Alzheimer's disease, only a limited number of drugs are commercially available. A library of non-alkaloidal natural compounds was investigated. To this end, a convenient microtitre plate method for assaying AChE inhibition, which allows a complete kinetic analysis of AChE inhibitors, was developed. Seven active compounds with Ki values in the micromolar range were identified, six of which were xanthones. This is the first report that a promising potential for AChE inhibition exists in such non-nitrogenous natural compounds. Furthermore, four xanthones among these xanthones had already been described as monoamine oxidase (MAO) inhibitors, making then dual AChE/MAO inhibitors of great interest.

Acetylcholinesterase↗

PubMed2004

Antileishmanial and antifungal acridone derivatives from the roots of Thamnosma rhodesica.

Eight furanocoumarins, one coumarin and four acridone derivatives have been identified in the roots of Thamnosma rhodesica (Rutaceae). Rhodesiacridone, one of these acridone derivatives, is reported here for the first time. Its structure was elucidated by spectrometric methods including ESI-HR, EI, DCI mass spectrometry, 1H, 13C and 2D NMR experiments. This novel compound showed activities against the intracellular form of a human pathogen, the protozoan parasite Leishmania major. Two known acridone related compounds, gravacridonediol and 1-hydroxy-10-methylacridone, exhibited activities against the intracellular form of the same parasite and the fungus Cladosporium cucumerinum, respectively.

Acridines↗

PubMed2004

ent-Labdane glycosides from the aquatic plant Potamogeton lucens and analytical evaluation of the lipophilic extract constituents of various Potamogeton species.

Two new ent-labdane glycosides, one known furano-ent-labdane and a new hydroxylated fatty acid were isolated from the dichloromethane extract of the freshwater aquatic plant Potamogeton lucens. The new compounds were assigned the structures of beta-d-glucopyranosyl-8(17),13-ent-labdadien-16,15-olid-18-oate, 18-beta-d-glucopyranosyloxy-8(17),13-ent-labdadien-16,15-olide and 13(R)-hydroxy-octadeca-(9Z,11E,15Z)-trien-oic acid by spectroscopic means. The algicidal activity of these compounds was tested against Raphidocelis subcapitata. Based on our previous study of Potamogeton pectinatus, other constituents were identified in P. lucens by LC-UV-MS, LC-NMR and GC-MS. The lipophilic extract profiles of both species are presented. Two other species, Potamogeton perfoliatus and P. crispus, were also investigated by analytical comparison of their non-polar extracts. The distribution of ent-labdanes characterized in Potamogeton is summarized.

Chlorophyta↗