Christian Terreaux

Modern screening techniques for plant extracts.

In order to discover new bioactive compounds from plant sources which could become new leads or new drugs, extracts should be simultaneously evaluated by chemical screening and by various biological or pharmacological targets. Chemical screening using hyphenated techniques such as LC/UV and LC/MS, and more recently LC/NMR, quickly provides ample structural information, leading in many cases to the identification of compounds. This allows researchers to distinguish between known compounds (dereplication) and new molecules directly from crude plant extracts. Thus, the tedious isolation of known compounds can be avoided, and a targeted isolation of constituents presenting novel or unusual spectroscopic features can be undertaken. In parallel, extracts are also subjected to various bioassays that should be simple, reproducible, and rapid. This approach will be illustrated by the search for new molluscicidal, antioxidant, and antifungal compounds from tropical plants.

Absolute Configuration of Two New 6-Alkylatedα-Pyrones (=2H-Pyran-2-ones) fromRavensara crassifolia

The stem bark CH2Cl2 extract of Ravensara crassifolia showed antifungal activity against the phytopathogenic fungus Cladosporium cucumerinum in a bioautographic TLC assay. Activity-guided fractionation afforded two new alpha -pyrones : (6S)-5,6-dihydro-6-[(2R)-2-hydroxy-6-phenylhexyl]-2H-pyran-2-one (1) and (6R)-6-[(4R,6R)-4,6-dihydroxy-10-phenyldec-1-enyl]-5,6-dihydro-2H-pyran-2-one (2). Their structures and absolute configurations were established by NMR spectroscopy, chemical methods, and CD spectroscopy. The antifungal activity against C. cucumerinum was determined for both compounds.

A phenolic glycoside and N-(p-coumaroyl)-tryptamine from Ravensara anisata

Abstract A new phenolic glycoside, 1-(α- l -rhamnosyl(1-6)-β- d -glucopyranosyloxy)-3,4,5-trimethoxybenzene, together with the alkaloid N -( p -coumaroyl)-tryptamine and four known flavonoids were isolated from the methanolic bark extract of Ravensara anisata Danguy (Lauraceae). Their structures have been established by NMR spectroscopy, and chemical methods.

Xanthones from Schultesia lisianthoides

Abstract Nine xanthone aglycones and one xanthone glycoside have been identified in Schultesia lisianthoides . Seven of the aglycones have been isolated and their structures elucidated by UV, mass and NMR spectroscopy; three xanthones were identified on-line by HPLC-UV and HPLC-mass spectrometry. 5-Hydroxy-1,2,3-trimethoxyxanthone is a new natural product. The other constituents have already been encountered in different Gentianaceae species.

Triterpenes and triterpene glycosides from Paradrymonia macrophylla

Abstract Seven pentacyclic triterpenes and triterpene glycosides have been isolated from the stems and roots of Paradrymonia macrophylla and their structures elucidated by means of 1H and 13C NMR spectroscopy. Three of them are described for the first time as natural products, namely: 2α,3β,19α-trihydroxy-24-oxo-urs-12-en-28-oic acid (24-epi-pinfaensic acid), 2α,3β,19α-trihydroxy-24-oxo-urs-12-en-28-oic acid ester glucoside (24-epi-pinfaensin) and 2α,3β,19α-trihydroxy-24-oxo-olean-12-en-28-oic acid ester glucoside (paradrymonoside).

The Importance Of LC-MS And LC-NMR In The Discovery Of New Lead Compounds From Plants

Rapid detection of biologically active natural products plays a key role in the phytochemical investigation of crude plant extracts. In order to perform an efficient screening of the extracts, both biological assays and HPLC analysis with various detection methods are used. Techniques such as HPLC coupled to UV photodiode array detection (LC/DAD-UV) and to mass spectrometry (LC/MS or LC/MS/MS) provide numerous on-line structural data on the metabolites prior to isolation. The recent introduction of HPLC coupled to nuclear magnetic resonance (LC/NMR) represents a powerful complement to LC/UV/MS screening. Various plant species belonging to the Gentianaceae and Leguminosae have been analysed by LC/UV, LC/MS, LC/MS/MS and LC/NMR. These hyphenated techniques allow a rapid structural determination of known plant constituents with only a minute amount of plant material. Simple bioautographic assays such as those used for screening antifungal constituents can also be performed on-line directly by collecting HPLC peaks and measuring the activity against the fungi of interest. These bioassays permit a rapid localisation of the bioactive natural products. With such a combined approach, the time consuming isolation of common natural products is avoided and an efficient targeted isolation of compounds presenting interesting spectroscopical or biological features is performed. Several representative applications of the use of LC/MS and LC/NMR for the dereplication and identification of antifungal constituents are presented in the present paper.

Antifungal benzoic acid derivatives from Piper Dilatatum in honour of Professor G. H. Neil Towers 75th birthday

Abstract Six prenylated benzoic acid derivatives and three chalcones have been isolated from the dichloromethane extract of the leaves of Piper dilatatum (Piperaceae). Their structures were elucidated by means of mass spectrometry, UV and NMR spectroscopy. Four of the benzoic acid derivatives displayed antifungal properties against Cladosporium cucumerinum in direct bioautography on TLC plates. Taboganic acid has been obtained for the first time from plant origin.

Structure revision of a furanocoumarin from Dorstenia contrajerva

Abstract Two furanocoumarins have been isolated from Dorstenia contrajerva L.: bergapten and 4-[[3-(4,5-dihydro-5,5-dimethyl-4-oxo-2-furanyl)-butyl]oxy]-7H-furo[3,2-g][1]benzopyran-7-one. The structures were established by UV, NMR and mass spectrometry. The structure of the second compound, an unusual furanocoumarin, was confirmed by X-ray analysis. This substance has already been isolated from D. contrajerva, but the structure was incorrectly elucidated.

Lignans from Mosla scabra

Two new cyclobutane-type lignans, named moslolignans A and B, together with two known ones, andamanicin and magnosalin, were isolated from the whole plant of Mosla scabra. Their structures were established as 1beta*,2beta*,3alpha*,4alpha*-1,2-dimethyl-3-(3- methoxy-4,5-methylene-dioxyphenyl)-4-(2,4,5-trimethoxyphenyl)-cycl obutane and 1beta*,2beta*,3alpha*,4alpha*-1,2-dimethyl-3-(2, 5-dimethoxy-3,4-methylenedioxyphenyl)-4-(2,4,5-trimethoxyphenyl)-cyclobu tane by spectroscopic methods. This is the first report of naturally-occurring cyclobutane-type lignans with asymmetrical substitutions.

In vitro cytotoxicity of 11 Panamanian plants.

Thirty-five crude extracts from 11 Panamanian plants, distributed in 10 genera and five families, were evaluated for their in vitro cytotoxicity. Four extracts exhibited an inhibition of cellular growth at IC(50) values lower than 25 microg/ml which was considered a significant activity.