Meroterpenoids? A historical and critical review of this biogenetic determinant.

In its original definition, meroterpenoids refer to substances of mixed biosynthesis including a terpenoid part. The number of compounds fulfilling this criterion is huge, and almost from the beginning, exclusions were made, more or less, explicitly stated. The concept is well accepted in the microorganism domain, where biosynthetic studies are advanced, while in the plant domain, meroterpenes and meroterpenoids randomly appear. The purpose of this article is to present and discuss miscellaneous categories of products that fulfill the definition and should be considered as meroterpenoids. Our proposal would be to retain the concept to characterize biosynthetic origins and not to consider it as a tool for classification.

Traditional Chinese medicine: saponins, critical micellar concentrations and partition coefficients.

INTRODUCTION: Traditional Chinese medicine (TCM) revolves around complex mixtures bound to specific roles within the formulation, among which saponin-containing plants with alleged properties of harmonising or detoxifying other compounds present in the preparations. OBJECTIVE: This article deals with the study of these interactions with, as a model, the interaction between saponins and selected active principles. METHODS: The measurement of the partition coefficient between water and octanol (logP) was used as an indicator and determined by nuclear magnetic resonance (NMR) for these active principles in the presence of saponins. For each compound, a graph was constructed showing the evolution of logP with increasing concentrations of saponins. RESULTS: Four distinct patterns of interactions were distinguished. Pattern A showed a constant decrease of logP, pattern B showed a decrease followed by a plateau, in pattern C the logP did not vary until the critical micellar concentration (CMC) and decreased afterwards, and pattern D exhibited an increase of logP. These properties were linked to the ability of saponins to form micelles in water once the CMC is reached. The interaction of aconitine and saponins followed pattern D, thus explaining the detoxification of herbal preparations using Aconitum with licorice. The licorice facilitated the extraction of the notoriously water-insoluble artemisinin from Artemisia annua. CONCLUSION: This investigation confirms that the physical properties of micelle forming saponins are intimately linked to a modification of behaviour of the other molecules in solution, as seen with the alteration of logP and the four types of interactions presented.

Phenyl glycosides from the leaves of Flacourtia indica (Burm. f.) Merr (Salicaceae).

Thirteen phenolic glycosides, together with fourteen various known compounds, were isolated from the methanolic extract of leaves of Flacourtia indica. Twelve of these were composed of gentisyl or salicyl alcohols, glycosylated on the phenol and acylated on the primary alcohol with various more or less oxidized forms of pyrocatechuic acid. A number of positions on the glucose or on the acid were further acylated by benzoic or cinnamic acid. In addition to these, a glucoside of a phenyl propanoid was also isolated. The gross structures were elucidated by spectroscopic means including 1D and 2D NMR experiments and HR-ESI-MS analyses. Several of these structures, for example, xylosmin, were previously described but it proved extremely difficult to conclude on their exact identity with the absence of clear data on absolute configuration in the literature.

An easy-to-use and general nuclear magnetic resonance method for the determination of partition coefficients of drugs and natural products.

The lipophilicity of a drug is an important parameter for its eventual development by the pharmaceutical industry. It is usually measured by HPLC following partition of the compound between water and 1-octanol. We present here an alternative, simple, sensitive and quantitative 1 H nuclear magnetic resonance (NMR) method for the experimental measurement of partition coefficients of natural compounds and pharmaceutical drugs. It is based on measuring concentrations in the water phase, before and after partitioning and equilibration between water and octanol, using the ERETIC (Electronic Reference To Access In Vivo Concentration) technique. The signal to noise ratio is improved by a Water Suppression by Excitation Sculpting sequence. Quantification is based on an electronic reference signal and does not need addition of a reference compound. The log P values of 22 natural metabolites and four pharmaceutical drugs were determined and the experimental results are in excellent agreement with literature data. The experiments were run on ~2 mg material. This technique proved to be robust, reproducible and suitable for log P values between -2 and +2.

Quinolizidine Alkaloids from Cylicomorpha solmsii.

Five new quinolizidine alkaloids were isolated from the leaves of Cylicomorpha solmstii (Urb.) Urb. (Caricaceae) and named cylicomorphins A-E (1-5). They all are ester derivatives of the same basic quinolizidine skeleton bearing hydroxy, methyl, and ethanoic acid substituents. Their structures were mainly established by NMR spectroscopy, and the absolute configuration is proposed on the basis of VCD data and Mosher ester derivatization. Compound 5 displayed cytotoxicity in the 10 µM range against an HCT-116 cell line.

Anti-radical flavonol glycosides from the aerial parts of Cleome chelidonii L.f.

Eleven previously undescribed flavonoid glycosides, named cleomesides C-M, along with five known compounds, were isolated from the aerial parts of Cleome chelidonii L.f. (Cleomaceae). All flavonol glycosides were esterified derivatives of 3,7-O-diglycosides of quercetin or kaempferol. Their structures were elucidated by analysis of the 1D and 2D NMR spectra, HR-ESI-MS data, UV spectra, optical rotation and by comparison with literature data. The DPPH radical scavenging properties of the flavonoid glycosides were studied in order to appreciate the effect of the glycoside parts and of the ester groups on this activity compared with the quercetin and kaempferol aglycones. An acetate at position 3 of rhamnose linked to C-7 of flavonol, gave compounds with the strongest antiradical activity. An aromatic ester group at position 6 of terminal glucose of diglycoside chain linked to C-3 of flavonol did not seem to influence the antiradical activity.

Phytochemical components and biological activities of Silene arenarioides Desf.

In this study, six known compounds 1-6 were isolated from the aerial parts of Silene arenarioides Desf. using different chromatographic methods. The structures of these compounds were identified as maltol glycoside (1), soyacerebroside I (2), chrysin (3), apigenin (4), quercetin (5) and stigmasterol glucoside (6). The compounds (1) and (2) are reported for the first time from this genus. The isolated compounds were determined using NMR techniques (1H NMR, 13C NMR, COSY, HSQC and HMBC) and mass spectroscopy (ESI-MS). The antibacterial and antioxidant activities of extracts and of compound (1) have been evaluated. The antioxidant activity was performed by DPPH radical scavenging method, which showed that methanol extract possesses a good antioxidant activity with value of IC50 = 8.064 ± 0.005 µg/mL.

The Iboga Alkaloids.

Iboga alkaloids are a particular class of indolomonoterpenes most often characterized by an isoquinuclidine nucleus. Their first occurrence was detected in the roots of Tabernanthe iboga, a sacred plant to the people of Gabon, which made it cult object. Ibogaine is the main representative of this class of alkaloids and its psychoactive properties are well documented. It has been proposed as a drug cessation treatment and has a wide range of activities in targeting opioids, cocaine, and alcohol. The purpose of this chapter is to provide a background on this molecule and related compounds and to update knowledge on the most recent advances made. Difficulties linked to the status of ibogaine as a drug in several countries have hampered its development, but 18-methoxycoronaridine is currently under evaluation for the same purposes and for the treatment of leishmaniasis. The chapter is divided into six parts: an introduction aiming at defining what is called an iboga alkaloid, and this is followed by current knowledge on their biosynthesis, which unfortunately remains a "black box" as far as the key construction step is concerned. Many of these alkaloids are still being discovered and the third and fourth parts of the chapter discuss the analytical tools in use for this purpose and give lists of new monomeric and dimeric alkaloids belonging to this class. When necessary, the structures are discussed especially with regard to absolute configuration determinations, which remain a point of weakness in their assignments. Part V gives an account of progress made in the synthesis, partial and total, which the authors believe is key to providing solid solutions to the industrial development of the most promising molecules. The last part of the chapter is devoted to the biological properties of iboga alkaloids, with particular emphasis on ibogaine and 18-methoxycoronaridine.

Medicarpin and millepurpan, two flavonoids isolated from Medicago sativa, induce apoptosis and overcome multidrug resistance in leukemia P388 cells.

BACKGROUND: High consumption of flavonoids has been associated with a decrease risk of cancer. Alfalfa (Medicago sativa) leaves have been widely used in traditional medicine and is currently used as a dietary supplement because of their high nutrient content. We previously reported the cytotoxic activity of alfalfa leaf extracts against several sensitive and multidrug resistant tumor cell lines. HYPOTHESIS/PURPOSE: We aimed to determine whether medicarpin and millepurpan, two isoflavonoids isolated from alfalfa leaves, may have pro-apoptotic effects against drug-sensitive (P388) and multidrug resistant P388 leukemia cells (P388/DOX). STUDY DESIGN/METHODS: Cells were incubated with medicarpin or millepurpan for the appropriate time. Cell viability was assessed by the MTT assay. DNA fragmentation was analyzed by agarose gel electrophoresis. Cell cycle analysis was realized by flow cytometry technics. Caspases 3 and 9 activities were measured using Promega caspACE assay kits. Proteins and genes expression were visualized respectively by western-blot using specific antibodies and RT-PCR assay. RESULTS: P-glycoprotein-expressing P388/DOX cells did not show resistance to medicarpin (IC50 ≈ 90 µM for P388 and P388/DOX cells) and millepurpan (IC50 = 54 µM and 69 µM for P388 and P388/DOX cells, respectively). Treatment with medicarpin or millepurpan triggered apoptosis in sensitive as well as multidrug resistant P388 cells. These effects were mediated through the mitochondrial pathway by modifying the balance pro/anti-apoptotic proteins. While 3 µM doxorubicin alone could not induce cell death in P388/DOX cells, concomitant treatment with doxorubicin and subtoxic concentration of medicarpin or millepurpan restored the pro-apoptotic cascade. Each compound increased sensitivity of P388/DOX cells to doxorubicin whereas they had no effect in sensitive P388 cells. Vinblastine cytotoxicity was also enhanced in P388/DOX cells (IC50 = 210 nM to 23 and 25 nM with medicarpin and millepurpan, respectively). This improved sensitivity was mediated by an increased uptake of doxorubicin in P388/DOX cells expressing P-gp. P-gp expression was not altered by exposure to medicarpin and millepurpan. CONCLUSION: These data indicate that medicarpin and millepurpan possess pro-apoptotic properties and potentiate the cytotoxicity of chemotherapy drugs in multidrug resistant P388 leukemia cells by modulating P-gp-mediated efflux of drugs. These flavonoids may be used as chemopreventive agents or as sensitizer to enhance cytotoxicity of chemotherapy drugs in multidrug resistant cancer cells.

Triterpenoid glycosides from the leaves of Meliosma henryi.

Seven triterpenoid glycosides, named meliosmosides A-G, were isolated from the leaves of Meliosma henryi Diels (Sabiaceae). Their structures were elucidated by different spectroscopic methods including 1D and 2D NMR experiments as well as HRESIMS analysis. Isolated compounds were evaluated for their cytotoxic activity against KB cell line.

Triterpenoid saponins from root bark of Zanha golungensis (Sapindaceae).

The chemical investigation of the methanolic extract from root bark of Zanha golungensis Hiern led to the isolation of five new and one known triterpenoid saponins. Their structures were elucidated by full analysis of their spectroscopic data and by partial hydrolysis. These glycosides contain zanhic acid as aglycone, a rare oleanane-type triterpenoid found in species belonging to Sapindaceae, Caryophyllaceae, Asteraceae, and Fabaceae. Two new saponins are esterified saponins by 3,3-dimethylacryloyl and 3-hydroxy-2-methyl-butanoyl residues located on the sugar part. The new compounds were named zanhasaponins D-H following previous isolation of similar compounds from Zanha africana.

Cytotoxicity and apoptosis induced by alfalfa (Medicago sativa) leaf extracts in sensitive and multidrug-resistant tumor cells.

Alfalfa (Medicago sativa) has been used to cure a wide variety of ailments. However, only a few studies have reported its anticancer effects. In this study, extracts were obtained from alfalfa leaves and their cytotoxic effects were assessed on several sensitive and multidrug-resistant tumor cells lines. Using the mouse leukaemia P388 cell line and its doxorubicin-resistant counterpart (P388/DOX), we showed that the inhibition of cell growth induced by alfalfa leaf extracts was mediated through the induction of apoptosis, as evidenced by DNA fragmentation analysis. The execution of programmed cell death was achieved via the activation of caspase-3, leading to PARP cleavage. Fractionation of toluene extract (To-1), the most active extract obtained from crude extract, led to the identification of 3 terpene derivatives and 5 flavonoids. Among them, (-)-medicarpin, (-)-melilotocarpan E, millepurpan, tricin, and chrysoeriol showed cytotoxic effects in P388 as well as P388/DOX cells. These results demonstrate that alfalfa leaf extract may have interesting potential in cancer chemoprevention and therapy.

Triterpene saponins from Antonia ovata leaves.

Six pentacyclic triterpenoid saponins, named antoniosides E-J along with two known alkaloids, were isolated from the leaves of Antonia ovata. Their structures were determined by the extensive use of 1D and 2D-NMR experiments along with HRESIMS analysis and acid hydrolysis. All isolated saponins contained the same pentasaccharide chain: 3-O-[ß-D-glucopyranosyl-(1→2)]-[ß-D-glucopyranosyl-(1→4)]-[ß-D-glucopyranosyl-(1→3)-α-L-arabinopyranosyl(1→6)]-ß-D-glucopyranoside, linked at C-3 of esterified derivatives of polyhydroxyoleanene triterpenoids (theasapogenol A and 15α-hydroxy-theasapogenol A). Isolated compounds were evaluated for their cytotoxic activity against KB cell line by a WST-1 assay, and the IC(50) values ranged from 3.3 to 5.3 µM.

Proteasome inhibitors from Neoboutonia melleri.

Thirty new cycloartane derivatives (1-3, 5-12, 14-32) have been isolated from the leaves of Neoboutonia melleri. Their novelty stems from the loss of one of the C-4 methyl groups (1-3, 5-12, 14-25, and 32) and from the presence of an "extra" carbon atom in the side chain (1-3, 5-12, 14-20, 26-29, and 30-32). Furthermore, compound 32 possesses a rare triterpene skeleton with the cyclopropane ring fused onto C-1 and C-10, instead of C-9 and C-10. The structures were determined by spectrometric means, chemical correlations, and X-ray crystallography of derivative 1c. The substitution pattern in ring A, with a cyclopropyl ring conjugated with an α,ß-unsaturated carbonyl moiety, confers to the molecule a particular reactivity, giving rise to a formal inversion of the stereochemistry of the cyclopropane ring under UV irradiation. These compounds showed an interesting level of activity on the proteasome pathway, thus motivating their evaluation as possible anticancer agents. The large number of isolated compounds permitted a structure-activity relationship analysis, which showed that the presence of the two enone functions was a requirement for the activity.

Intensified extraction of ionized natural products by ion pair centrifugal partition extraction.

The potential of centrifugal partition extraction (CPE) combined with the ion-pair (IP) extraction mode to simultaneously extract and purify natural ionized saponins from licorice is presented in this work. The design of the instrument, a new laboratory-scale Fast Centrifugal Partition Extractor (FCPE300(®)), has evolved from centrifugal partition chromatography (CPC) columns, but with less cells of larger volume. Some hydrodynamic characteristics of the FCPE300(®) were highlighted by investigating the retention of the stationary phase under different flow rate conditions and for different biphasic solvent systems. A method based on the ion-pair extraction mode was developed to extract glycyrrhizin (GL), a biologically active ionic saponin naturally present in licorice (Glycyrrhiza glabra L., Fabaceae) roots. The extraction of GL was performed at a flow rate of 20 mL/min in the descending mode by using the biphasic solvent system ethyl acetate/n-butanol/water in the proportions 3/2/5 (v/v/v). Trioctylmethylammonium with chloride as a counter-ion (Al336(®)) was used as the anion extractant in the organic stationary phase and iodide, with potassium as counter-ion, was used as the displacer in the aqueous mobile phase. From 20 g of a crude extract of licorice roots, 2.2g of GL were recovered after 70 min, for a total process duration of 90 min. The combination of the centrifugal partition extractor with the ion-pair extraction mode (IP-CPE) offers promising perspectives for industrial applications in the field of natural product isolation or for the fractionation of natural complex mixtures.

Steroidal saponins from the leaves of Beaucarnea recurvata.

Thirteen steroidal saponins were isolated from the leaves of Beaucarnea recurvata Lem. Their structures were established using one- and two-dimensional NMR spectroscopy and mass spectrometry. Six of them were identified as: 26-O-ß-D-glucopyranosyl (25S)-furosta-5,20(22)-diene 1ß,3ß,26-triol 1-O-α-L-rhamnopyranosyl-(1→2) ß-D-fucopyranoside, 26-O-ß-D-glucopyranosyl (25S)-furosta-5,20(22)-diene 1ß,3ß,26-triol 1-O-α-L-rhamnopyranosyl-(1→2)-4-O-acetyl-ß-D-fucopyranoside, 26-O-ß-D-glucopyranosyl (25R)-furosta-5,20(22)-diene-23-one-1ß,3ß,26-triol 1-O-α-L-rhamnopyranosyl-(1→2) ß-D-fucopyranoside, 26-O-ß-D-glucopyranosyl (25S)-furosta-5-ene-1ß,3ß,22α,26-tetrol 1-O-α-L-rhamnopyranosyl-(1→4)-6-O-acetyl-ß-D-glucopyranoside, 26-O-ß-D-glucopyranosyl (25S)-furosta-5-ene-1ß,3ß,22α,26-tetrol 1-O-α-L-rhamnopyranosyl-(1→2) ß-D-fucopyranoside, and 24-O-ß-D-glucopyranosyl (25R)-spirost-5-ene-1ß,3ß,24-triol 1-O-α-L-rhamnopyranosyl-(1→2)-4-O-acetyl-ß-D-fucopyranoside. The chemotaxonomic classification of B. recurvata in the family Ruscaceae was discussed.

Inhibition of stromelysin-1 by caffeic acid derivatives from a propolis sample from Algeria.

Stromelysin-1 (matrix metalloproteinase-3: MMP-3) occupies a central position in collagenolytic and elastolytic cascades, leading to cutaneous intrinsic and extrinsic aging. We screened extracts of a propolis sample from Algeria with the aim to isolate compounds able to selectively inhibit this enzyme. A butanolic extract (B (3)) of the investigated propolis sample was found to potently inhibit MMP-3 activity (IC (50) = 0.15 ± 0.03 µg/mL), with no or only weak activity on other MMPs. This fraction also inhibited plasmin amidolytic activity (IC (50) = 0.05 µg/mL) and impeded plasmin-mediated proMMP-3 activation. B (3) was fractionated by HPLC, and one compound, characterized by NMR and mass spectroscopy and not previously identified in propolis, i.e., (+)-chicoric acid, displayed potent IN VITRO MMP-3 inhibitory activity (IC (50) = 6.3 × 10 (-7) M). In addition, both caffeic acid and (+)-chicoric acid methyl ester present in fraction B (3) significantly inhibited UVA-mediated MMP-3 upregulation by fibroblasts.

Triterpenoid saponins from Symplocos lancifolia.

Three new bidesmosidic saponins (1-3) and a new ursane triterpenoid, 2α,3ß,11α,23-tetrahydroxyurs-12-en-28-oic acid (4), along with seven known compounds, were isolated from a methanolic extract of the leaves of Symplocos lancifolia. The bidesmosidic saponins were found to possess the same sugar unit part, composed of two ß-d-glucose moieties and one α-l-rhamnose moiety, linked to maslinic acid, arjunolic acid, and asiatic acid, respectively. Their structures were elucidated by interpretation of their 1D and 2D NMR spectra and completed by analysis of the HRESIMS data. The antibacterial activity of the isolated triterpenoids was evaluated against Staphylococcus aureus, Enterococcus faecalis, Escherichia coli, and Pseudomonas aeruginosa, and several showed activity against Gram-positive bacteria.