Structure and Synthesis of Vindolicine and Derivatives

This article describes the reaction of vindoline with formaldehyde and trimethyl orthoformate to prepare vindolicine, tris-vindolicinyl methane and higher molecular weight homologues. The synthesis of 10-formyl vindoline as an intermediate allowed further exploration of its chemistry, in particular the reaction with acetone which yielded a symmetrical dimer, which was further reacted with vindoline to give molecules containing three and four vindoline units. These molecules were characterized by NMR and for some of them (vindolicine, 10-formyl vindoline, 10-(1'-(but-1'-en-3'-one))-vindoline) by X-ray crystallography. Depending on the substitution and on the absence of axes of symmetry, the NMR spectra displayed non-equivalent spin systems for the vindoline moieties. The dimer formed from the double condensation of 10-formyl vindoline with acetone showed cytotoxic activity in the micromolar range.

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.

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.

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.

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.

Cytisine-like alkaloids from Ormosia hosiei Hemsl. & E.H. Wilson

Four alkaloids named hosieines A-D were isolated from the root and stem of Ormosia hosiei. Their flat structures were established by mass spectrometry and by a combination of NMR experiments. These molecules probably share a common biosynthetic origin with the lupin alkaloids but they differ in the formation of the last ring, being here part of a rare 2-azabicyclo[3.2.1]octane system. Their absolute configuration was determined by X-ray crystallography using CuKα radiation. As has been described for cytisine, they display a remarkable affinity towards neuronal nicotinic acetylcholine α4β2 receptor.

Constituents of Vigna angularis and their in vitro anti-inflammatory activity

Nine non-phenolic compounds, including four furanylmethyl glycosides, angularides A-D, one ent-kaurane diterpene glycoside, angularin A, and four triterpenoid saponins, angulasaponins A-D, were isolated from seeds of Vigna angularis, together with eight known compounds. Their structures were elucidated on the basis of extensive 1D and 2D NMR spectroscopic analysis as well as chemical methods. Angularin A, angulasaponins A-C, and azukisaponins III and VI showed inhibition of nitric oxide production in LPS-activated RAW264.7 macrophages, with IC50 values ranging from 13μM to 24μM.

Monogagaine, a Novel Dimeric Indole Alkaloid from Tabernaemontana chippii and Tabernaemontana dichotoma [1]

From the rootbark of Tabernaemontana chippii and the stembark of T. dichotoma a novel dimeric indole alkaloid was isolated which was named monogagaine. It was assigned structure 1 on the basis of spectral data. It showed antimicrobial activity against Bacillus subtilis.

Dichapetalins from Dichapetalum species and their cytotoxic properties

Six dichapetalins named dichapetalins N-S were isolated from Dichapetalum mombuttense, Dichapetalum zenkeri and Dichapetalum leucosia. They were accompanied in the same plants by the known dichapetalins A, B, C, I, L and M. The structures of the compounds were elucidated by 1D and 2D NMR experiments and mass spectrometry. They all possessed the dammarane skeleton substituted at position C-3 by a C6-C2 unit forming a 2-phenylpyran moiety. All contained a lactone ring in the side chain except dichapetalins O, Q and R, in which this ring was replaced by a lactol. Dichapetalin Q and R were also the first dichapetalins bearing a tertiary methyl and a double bond instead of the cyclopropane of the dammaranes. All these compounds were assayed against cancer cell lines HCT116 and WM 266-4 and displayed cytotoxic and anti-proliferative activities in the 10(-6) to 10(-8)M range.

Nudicaulins, yellow flower pigments of Papaver nudicaule: revised constitution and assignment of absolute configuration

The constitution of the aglycon of nudicaulin has been revised to be a pentacyclic indole alkaloid. The relative and absolute configurations of the two diastereomers, nudicaulins I (3a) and II (3b), have been assigned by NMR, conformational analyses, and interpretation of the experimental ECD spectra by quantum-chemical calculations.

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,β-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.

Semisynthetic neoboutomellerone derivatives as ubiquitin-proteasome pathway inhibitors

The interesting pharmacological properties of neoboutomellerones 1 and 2 were the basis for the assembly of a small library of analogues consisting of natural products isolated from the plant Neoboutonia melleri and of semisynthetic derivatives. As the two enone systems (C23-C24a and C1-C3) and the two hydroxyls groups (C22 and C26) of neoboutomellerones are required for activity, modifications were focused on these functional groups. Biological evaluation by using a cellular assay for proteasome activity provided clues regarding the mechanism of action of these natural products and synthetic derivatives. Certain neoboutomellerone derivatives inhibited the proliferation of human WM-266-4 melanoma tumor cells at submicromolar concentration and warrant evaluation as anticancer agents.

Four new carvotanacetone derivatives from Sphaeranthus ukambensis, inhibitors of the ubiquitin-proteasome pathway

Six carvotanacetone derivatives (1- 6), amongst which four new compounds (1- 4), were isolated from the aerial parts of Sphaeranthus ukambensis Vatke & O. Hoffm. The structures of the molecules were elucidated by complementary spectroscopic methods, and their biological properties were investigated using human DLD-1 colon cancer cells engineered to stably express a 4 ubiquitin-luciferase (4 Ub-Luc) reporter protein. Five of the isolated carvotanacetone derivatives (2- 6) were found to inhibit the proliferation of the colon cancer cells and interfere with the ubiquitin-proteasome pathway, with potencies in a micromolar range.

Protoflavonoids from ferns impair centrosomal integrity of tumor cells

Six protoflavonoids, including two new compounds, were isolated during a large scale screening of fern extracts for original interaction with mitosis. The new compounds isolated from PHEGOPTERIS decursive-pinnata and EQUISETUM fluviatile were 2',3'-dihydroprotogenkwanone (1) and 2',3'-dihydro-2'-hydroxyprotoapigenone (2). Known compounds were: protoapigenone, protogenkwanone, protoapigenin, and 4'- O- β-D-glucopyranosyl protoapigenin. They showed a cytotoxic activity against HeLa cells at a micromolar level. IC₅₀ values were 2 µM for compound 1 > 10 µM for compound 2, and respectively 2.4, 0.6, > 10 µM for the known compounds. Their cytotoxic effects were associated with phenotypic changes never observed before and characterized by the loss of centrosomal γ-tubulin labelling in both mitotic and interphasic cells.

Pharmacological screening of bryophyte extracts that inhibit growth and induce abnormal phenotypes in human HeLa cancer cells

Antitumor activities of substances from natural sources apart from vascular plants and micro-organisms have been poorly investigated. Here we report on a pharmacological screening of a bryophyte extract library using a phenotypic cell-based assay revealing microtubules, centrosomes and DNA. Among the 219 moss extracts tested, we identified 41 extracts acting on cell division with various combinations of significant effects on interphasic and mitotic cells. Seven extracts were further studied using a cell viability assay, cell cycle analysis and the phenotypic assay. Three distinct pharmacological patterns were identified including two unusual phenotypes.

Meroterpenes from Dichrostachys cinerea inhibit protein farnesyl transferase activity

Eighteen new meroterpene derivatives, dichrostachines A-R (1-18), have been isolated from the root and stem barks of Dichrostachys cinerea, and their structures determined by spectroscopic means and molecular modeling. From a biosynthetic standpoint these compounds arise from a Diels-Alder reaction between a labdane diene of the raimonol type and a flavonoid B-ring-derived quinone. The hypothesis was tested by the partial synthesis of similar compounds by simply mixing methyl communate and a synthetic flavonoid quinone. The hemisynthetic compounds were shown by NMR to have configurations different from those of the natural products, thus allowing a refinement of the biosynthesis hypothesis. Most of the compounds were assayed for their ability to inhibit the enzyme protein farnesyl transferase. The most active compounds exhibited IC50 and cytotoxicity values in the 1 microM range.

Parthenolide inhibits tubulin carboxypeptidase activity

Microtubules are centrally involved in cell division, being the principal components of mitotic spindle. Tubulin, the constituent of microtubules, can be cyclically modified on its alpha-subunit by enzymatic removal of the COOH-terminal tyrosine residue by an ill-defined tubulin carboxypeptidase (TCP) and its readdition by tubulin tyrosine ligase (TTL). We and others have previously shown that suppression of TTL and resulting accumulation of detyrosinated tubulin are frequent in human cancers of poor prognosis. Explanations for the involvement of TTL and detyrosinated tubulin in tumor progression arise from the recent discovery that tubulin detyrosination leads to CAP-Gly protein mislocalization, which correlates with defects in spindle positioning during mitosis. Impaired control of spindle positioning is one factor favoring tumor invasiveness. Thus, TCP could be a target for developing novel therapeutic strategies against advanced stages of cancers. Inhibitors of TCP, by reversing abnormal detyrosinated tubulin accumulation in tumor cells, could impair tumor progression. TCP has never been isolated and this has hampered search of specific inhibitors. In this article, we describe a cell-based assay of TCP activity and its use to screen a library of natural extracts for their inhibitory potency. This led to the isolation of two sesquiterpene lactones. We subsequently found that parthenolide, a structurally related compound, can efficiently inhibit TCP. This inhibitory activity is a new specific property of parthenolide independent of its action on the nuclear factor-kappaB pathway. Parthenolide is also known for its anticancer properties. Thus, TCP inhibition could be one of the underlying mechanisms of these anticancer properties.

High-Throughput Bioluminescence Screening of Ubiquitin-Proteasome Pathway Inhibitors from Chemical and Natural Sources

To discover original inhibitors of the ubiquitin-proteasome pathway, the authors have developed a cell-based bioluminescent assay and used it to screen collections of plant extracts and chemical compounds. They first established a DLD-1 human colon cancer cell line that stably expresses a 4Ubiquitin-Luciferase (4Ub-Luc) reporter protein, efficiently targeted to the ubiquitinproteasome degradation pathway. The assay was then adapted to 96- and 384-well plate formats and calibrated with reference proteasome inhibitors. Assay robustness was carefully assessed, particularly cell toxicity, and the statistical Ź factor value was calculated to 0.83, demonstrating a good performance level of the assay. A total of 18,239 molecules and 15,744 plant extracts and fractions thereof were screened for their capacity to increase the luciferase activity in DLD-1 4Ub-Luc cells, and 21 molecules and 66 extracts inhibiting the ubiquitin-proteasome pathway were identified. The fractionation of an active methanol extract of Physalis angulata L. aerial parts was performed to isolate 2 secosteroids known as physalin B and C. In a cell-based Western blot assay, the ubiquitinated protein accumulation was confirmed after a physalin treatment confirming the accuracy of the screening process. The method reported here thus provides a robust approach to identify novel ubiquitin-proteasome pathway inhibitors in large collections of chemical compounds and natural products.

Acylphloroglucinol derivatives from Mahurea palustris

Five new acylphloroglucinol derivatives, mahureones A-E (1, 3-6), have been isolated from the leaves of Mahurea palustris, and their structures determined by spectroscopic means. During the isolation process, several byproducts (7-9) were formed by reaction of one of the isoprenyl side chains with TFA, water, and acetonitrile. All the compounds were assayed for their ability to inhibit human DNA polymerase beta. The most active compounds, mahureones A (1) and D (5), exhibited IC50 values in the 10 microM range.

Modulation of cellular response to cisplatin by a novel inhibitor of DNA polymerase beta

DNA polymerase beta (Pol beta) is an error-prone enzyme whose up-regulation has been shown to be a genetic instability enhancer as well as a contributor to cisplatin resistance in tumor cells. In this work, we describe the isolation of new Pol beta inhibitors after high throughput screening of 8448 semipurified natural extracts. In vitro, the selected molecules affect specifically Pol beta-mediated DNA synthesis compared with replicative extracts from cell nuclei. One of them, masticadienonic acid (MA), is particularly attractive because it perturbs neither the activity of the purified replicative Pol delta nor that of nuclear HeLa cell extracts. With an IC50 value of 8 microM, MA is the most potent of the Pol beta inhibitors found so far. Docking simulation revealed that this molecule could substitute for single-strand DNA in the binding site of Pol beta by binding Lys35, Lys68, and Lys60, which are the main residues involved in the interaction Pol beta/single-strand DNA. Selected inhibitors also affect the Pol beta-mediated translesion synthesis (TLS) across cisplatin adducts; MA was still the most efficient. Therefore, masticadienonic acid sensitized the cisplatin-resistant 2008C13*5.25 human tumor cells. Our data suggest that molecules such as masticadienonic acid could be suitable in conjunction with cisplatin to enhance anticancer treatments.

Alkylated Isocoumarins fromPituranthos Scoparius

Two isocoumarins have been isolated from the ethyl acetate extract of the root of Pituranthos scoparius: 3-n-propyl-5-methoxy-6-hydroxy-isocoumarin and 3-n-propyl-5,7-dimethoxy-6-hydroxy-isocoumarin. Their structures were assigned by spectral analysis.

Bioactive flavonoids of Tanacetum parthenium revisited

Bio-guided fractionation of an extract from Tanacetum parthenium showing activity as mitotic blocker allowed the isolation and identification of santin 3, jaceidin 2 and centaureidin 1. The latter two closely related flavonols, which, to the best of our knowledge, are isolated here together for the first time, form a mixture difficult to resolve and which is probably the reason for the confusion in the literature regarding their occurrence. Centaureidin 1 had an IC50 of 1 microM while jaceidin 2 and santin 3 were 200 times less active.

Interspecific variation in terpenoid composition of defensive secretions of European Reticulitermes termites

Sixteen terpene compounds were isolated from the soldier defensive secretions of seven European termite taxa of the genus Reticulitermes (Isoptera, Rhinotermitidae). We describe species-specific mixtures of monoterpenes (alpha-pinene, beta-pinene, limonene), sesquiterpenes (germacrene C, germacrene A, germacrene B, beta-selinene, delta-selinene, gamma-selinene, (E)-beta-farnesene, gamma-cadinene, nerolidol), diterpenes (geranyl linalool, geranyl geraniol, geranyl geranial), and one sesterterpene (geranyl farnesol). Compounds were purified by HPLC and their structures determined by means of MS spectrometry, or 1D and 2D NMR spectroscopy. Comparison of two different analytical approaches, CC-MS and HPLC with subsequent NMR spectroscopy, revealed Cope rearrangement of germacrene A, germacrene B, and germacrene C to the respective beta-elemene, gamma-elemene, and delta-elemene under GC conditions, thus demonstrating the limits for this analytical approach. The species-specific compound composition provides insight into taxonomy and species origin of European Reticulitermes. The biological significance of the species-specific composition of Reticulitermes defensive secretions is briefly discussed.

Trypanocidal withanolides and withanolide glycosides from Dunalia brachyacantha

Two new withanolide glycosides, (20R,22R)-O-(3)-alpha-L-rhamnopyranosyl(1-->4)-beta-D-glucopyranosyl-1 alpha,12 beta-diacetoxy-20-hydroxywitha-5,24-dienolide (3) and (20R,22R)-O-(3)-beta-D-xylopyranosyl(1-->3)-[beta-D-xylopyranosyl(1-->4)]-beta-D-glucopyranosyl-1 alpha-acetoxy-12 beta,20-dihydroxywitha-5,24-dienolide (4), were isolated from the leaves and root of Dunalia brachyacantha. Their aglycones, (20R,22R)-1 alpha,12 beta-diacetoxy-3 beta,20-dihydroxywitha-5,24-dienolide (or 1 alpha,12 beta-diacetyldunawithagenine) and (20R,22R)-1 alpha-acetoxy-3 beta,12 beta,20-trihydroxywitha-5,24-dienolide (or 1 alpha-acetyl-12 beta-hydroxydunawithagenine), are novel. The known 18-acetoxywithanolide D (1) and 18-acetoxy-5,6-deoxy-5-withenolide D (2) were also isolated from the leaves. These last two compounds were shown to be responsible for the trypanocidal, leishmanicidal, and bactericidal activities manifested by the crude ethanolic extract. The structures were deduced from spectroscopic data and on the basis of chemical evidence.