A new acyclic diterpene acid and bioactive compounds from Knema glauca

Two New Benzoquinone Derivatives from Vietnamese Knema globularia Stems

The chemical investigation of the stems of Knema globularia led to the isolation of two new benzoquinones derivatives, embenones A and B (1 and 2), along with three known compounds (3-5). The structures of the isolated compounds were determined using spectroscopic techniques, including HRESIMS, 1D and 2D NMR, in conjunction with comparison to existing literature data. Compounds 1 and 2 represent new carbon skeletons in nature. Furthermore, all isolated compounds were evaluated for their α-glucosidase inhibitory activity, with compounds 1-3 exhibiting superior potency relative to the positive control (acarbose, IC50 331 μM). Their IC50 values ranged from 1.40 to 96.1 μM.

Three new constituents from the stems of Knema globularia and their α-glucosidase inhibitory activity

Three new metabolites (1-3) were isolated from the stems of Knema globularia, along with five known compounds, including kaempferol (4), quercetin (5), isovanillic acid (6), protocatechuic acid (7), and gallic acid (8). Their structures were deduced using NMR spectroscopic, mass spectrometric analyses, and literature data. The absolute configurations of 1-3 were established by electronic circular dichroism (ECD) spectroscopy. α-Glucosidase inhibitory activities of those compounds were evaluated using a spectrophotometric method, compounds 1-3 showed very strong effects towards α-glucosidase with IC50 values 1.59, 0.58 and 1.37 µM, respectively (the positive control, acarbose, IC50 93.63 µM). Simultaneously, enzyme kinetics study indicated that 2 was a mix-type inhibitor. 2 interacted well in the active site of α-glucosidase enzyme, primarily through hydrogen bonds and hydrophobic interactions.

α-Glucosidase Inhibitors from the Stems of Knema globularia

Six new compounds, globunones A-F (1-6), and two new flavonoids (7 and 8) together with nine known compounds (9-17) were isolated from the stems of Knema globularia. The chemical structures of 1-8 were elucidated by an analysis of their NMR and high-resolution electrospray ionization mass spectrometry data as well as by comparison with literature values. The absolute configurations were determined using time-dependent density functional theory electronic circular dichroism (TD-DFT-ECD). Globunones A-E (1-5) represent the initial combined structures of a flavan-3-ol core and a 1,4-benzoquinone core. Globunone F (6) is the first flavanone-type compound bearing a 2-(2,4-dihydroxyphenyl)-2-oxoethyl group found to date in Nature. Compounds 1-3 and 6-17 were tested for their yeast α-glucosidase inhibitory activity. All compounds tested (except for 13 and 14) showed potent inhibition toward α-glucosidase with IC₅₀ values in the range 0.4-26.6 μM. Calodenin A (15) was the most active compound with an IC₅₀ value of 0.4 μM (the positive control, acarbose, IC₅₀ 93.6 μM). A kinetic analysis of 15 revealed that it is a noncompetitive inhibitor with a K_i value of 3.4 μM.

Nutmegs and wild nutmegs: An update on ethnomedicines, phytochemicals, pharmacology, and toxicity of the Myristicaceae species

Prized medicinal spice true nutmeg is obtained from Myristica fragrans Houtt. Rest species of the family Myristicaceae are known as wild nutmegs. Nutmegs and wild nutmegs are a rich reservoir of bioactive molecules and used in traditional medicines of Europe, Asia, Africa, America against madness, convulsion, cancer, skin infection, malaria, diarrhea, rheumatism, asthma, cough, cold, as stimulant, tonics, and psychotomimetic agents. Nutmegs are cultivated around the tropics for high-value commercial spice, used in global cuisine. A thorough literature survey of peer-reviewed publications, scientific online databases, authentic webpages, and regulatory guidelines found major phytochemicals namely, terpenes, fatty acids, phenylpropanoids, alkanes, lignans, flavonoids, coumarins, and indole alkaloids. Scientific names, synonyms were verified with www.theplantlist.org. Pharmacological evaluation of extracts and isolated biomarkers showed cholinesterase inhibitory, anxiolytic, neuroprotective, anti-inflammatory, immunomodulatory, antinociceptive, anticancer, antimicrobial, antiprotozoal, antidiabetic, antidiarrhoeal activities, and toxicity through in-vitro, in-vivo studies. Human clinical trials were very few. Most of the pharmacological studies were not conducted as per current guidelines of natural products to ensure repeatability, safety, and translational use in human therapeutics. Rigorous pharmacological evaluation and randomized double-blind clinical trials are recommended to analyze the efficacy and therapeutic potential of nutmeg and wild nutmegs in anxiety, Alzheimer's disease, autism, schizophrenia, stroke, cancer, and others.

Lignans of Sesame (Sesamum indicum L.): A Comprehensive Review

Major lignans of sesame sesamin and sesamolin are benzodioxol--substituted furofurans. Sesamol, sesaminol, its epimers, and episesamin are transformation products found in processed products. Synthetic routes to all lignans are known but only sesamol is synthesized industrially. Biosynthesis of furofuran lignans begins with the dimerization of coniferyl alcohol, followed by the formation of dioxoles, oxidation, and glycosylation. Most genes of the lignan pathway in sesame have been identified but the inheritance of lignan content is poorly understood. Health-promoting properties make lignans attractive components of functional food. Lignans enhance the efficiency of insecticides and possess antifeedant activity, but their biological function in plants remains hypothetical. In this work, extensive literature including historical texts is reviewed, controversial issues are critically examined, and errors perpetuated in literature are corrected. The following aspects are covered: chemical properties and transformations of lignans; analysis, purification, and total synthesis; occurrence in Seseamum indicum and related plants; biosynthesis and genetics; biological activities; health-promoting properties; and biological functions. Finally, the improvement of lignan content in sesame seeds by breeding and biotechnology and the potential of hairy roots for manufacturing lignans in vitro are outlined.

A new diarylhexane and two new diarylpropanols from the roots of Knema globularia

A new diarylhexane, kneglobularone B (1) and two new diarylpropanols, kneglobularols A - B (2 - 3) along with seven known compounds (4 - 10) were isolated and characterized from the roots of Knema globularia. It is the first time to find arylpropyl quinone (4) and isoflavone (8) in Myristicaceae family. In addition, 5 was found for the first time in Knema genus. Their structures were elucidated by UV, IR, MS, 1 D and 2 D NMR techniques. Compound 4 exhibited strong cytotoxicity against the NCI - H187 and MCF - 7 cell lines with IC₅₀ values of 3.08 and 6.68 µg/mL, respectively.

Chemical constituents from the Knema globularia fruits and their in vitro cytotoxicity

Two new compounds, designated as knecorticosanones A-B (1-2), along with three known compounds (3-5) were isolated from the fruits of Knema globularia. Their structures were elucidated by extensive spectroscopy analysis, including 1D- and 2D-NMR, UV, IR, and HRESIMS and by comparison with the reported data in the literature. Compounds 1-5 were evaluated for their cytotoxicity. Knecorticosanone B (2) and malabaricone D (5) exhibited moderate cytotoxic effect against Hep-G2, MCF-7 and SK-LU-1 cell lines with IC₅₀ values ranging from 8.76 ± 1.02 to 18.74 ± 1.75 μM while knecorticosanone A (1), virolane (3) and 7-hydroxy-3',4'-methylenedioxyflavan (4) exhibited weak inhibitory effect against these cell lines with IC₅₀ values ranging from 25.85 ± 2.75 to 66.75 ± 2.08 μM.

Chemical investigation and biological activities of the essential oil of Knema kunstleri Warb. from Malaysia

The chemical composition of the essential oil of Knema kunstleri Warb. (Myristicaceae) was investigated for the first time. The essential oil was obtained by hydrodistillation and fully characterized by gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS). In total, 36 components were identified in the essential oil, which made up 91.7% of the total oil. The essential oil is composed mainly of β-caryophyllene (23.2%), bicyclogermacrene (9.6%), δ-cadinene (7.3%), α-humulene (5.7%), and germacrene D (4.3%). The essential oil showed moderate activity towards DPPH free-radical scavenging and lipoxygenase inhibition. To the best of our knowledge, this is the first study of the composition and bioactivities of the essential oil report concerning the genus Knema.

Antimalarial Activity of Plant Metabolites

Malaria, as a major global health problem, continues to affect a large number of people each year, especially those in developing countries. Effective drug discovery is still one of the main efforts to control malaria. As natural products are still considered as a key source for discovery and development of therapeutic agents, we have evaluated more than 2000 plant extracts against Plasmodium falciparum. As a result, we discovered dozens of plant leads that displayed antimalarial activity. Our phytochemical study of some of these plant extracts led to the identification of several potent antimalarial compounds. The prior comprehensive review article entitled “Antimalarial activity of plant metabolites” by Schwikkard and Van Heerden (2002) reported structures of plant-derived compounds with antiplasmodial activity and covered literature up to the year 2000. As a continuation of this effort, the present review covers the antimalarial compounds isolated from plants, including marine plants, reported in the literature from 2001 to the end of 2017. During the span of the last 17 years, 175 antiplasmodial compounds were discovered from plants. These active compounds are organized in our review article according to their plant families. In addition, we also include ethnobotanical information of the antimalarial plants discussed.

Diterpenes as lead molecules against neglected tropical diseases

Nowadays, neglected tropical diseases (NTDs) are reported to be present everywhere. Poor and developing areas in the world have received great attention to NTDs. Drug resistance, safety profile, and various challenges stimulate the search for alternative medications. Plant-based drugs are viewed with great interest, as they are believed to be devoid of side effects. Diterpenes, a family of essential oils, have showed attractive biological effects. A systematic review of the literature was carried out to summarize available evidences of diterpenes against NTDs. For this, databases were searched using specific search terms. Among the 2338 collected reports, a total of 181 articles were included in this review. Of them, 148 dealt with investigations using single organisms, and 33 used multiple organisms. No mechanisms of action were reported in the case of 164 reports. A total of 93.92% were related to nonclinical studies, and 4.42% and 1.66% dealt with preclinical and clinical studies, respectively. The review displays that many diterpenes are effective upon Chagas disease, chikungunya, echinococcosis, dengue, leishmaniasis, leprosy, lymphatic filariasis, malaria, schistosomiasis, and tuberculosis. Indeed, diterpenes are amazing drug candidates against NTDs. Copyright © 2016 John Wiley & Sons, Ltd.

The lignan, (-)-sesamin reveals cytotoxicity toward cancer cells: pharmacogenomic determination of genes associated with sensitivity or resistance

(-)-Sesamin is a lignan present in sesam oil and a number of medicinal plants. It exerts various pharmacological effects, such as prevention of hyperlipidemia, hypertension, and carcinogenesis. Moreover, (-)-sesamin has chemopreventive and anticancer activity in vitro and in vivo. Multidrug resistance (MDR) of tumors leads to fatal treatment outcome in many patients and novel drugs able to kill multidrug-resistant cells are urgently needed. P-glycoprotein (MDR1/ABCB1) is the best known ATP-binding cassette (ABC) drug transporter mediating MDR. ABCB5 is a close relative to ABCB1, which also mediates MDR. We found that the mRNA expressions of ABCB1 and ABCB5 were not related to the 50% inhibition concentrations (IC50) for (-)-sesamin in a panel of 55 cell lines of the National Cancer Institute, USA. Furthermore, (-)-sesamin inhibited ABCB1- or ABCB5-overexpressing cells with similar efficacy than their drug-sensitive parental counterparts. In addition to ABC transporter-mediated MDR, we attempted to identify other molecular determinants of (-)-sesamin resistance. For this reason, we performed COMPARE and hierarchical cluster analyses of the transcriptome-wide microarray-based mRNA expression of the NCI cell panel. Twenty-three genes were identified, whose mRNA expression correlated with the IC50 values for (-)-sesamin. These genes code for proteins of different biological functions, i.e. ribosomal proteins, components of the mitochondrial respiratory chain, proteins involved in RNA metabolism, protein biosynthesis, or glucose and fatty acid metabolism. Subjecting this set of genes to cluster analysis showed that the cell lines were assembled in the resulting dendrogram according to their responsiveness to (-)-sesamin. In conclusion, (-)-sesamin is not involved in MDR mediated by ABCB1 or ABCB5 and may be valuable to bypass chemoresistance of refractory tumors. The microarray expression profile, which predicted sensitivity or resistance of tumor cells to (-)-sesamin consisted of genes, which do not belong to the classical resistance mechanisms to established anticancer drugs.

Myristicyclins A and B: antimalarial procyanidins from Horsfieldia spicata from Papua New Guinea

An antimalarial screen for plants collected from Papua New Guinea identified an extract of Horsfieldia spicata as having activity. Isolation of the active constituents led to the identification of two new compounds: myristicyclins A (1) and B (2). Both compounds are procyanidin-like congeners of myristinins lacking a pendant aromatic ring. Myristicyclin A was found to inhibit the ring, trophozoite, and schizont stages of Plasmodium falciparum at similar concentrations in the mid-μM range.

Antiplasmodial Natural Products

Malaria is a human infectious disease that is caused by four species of Plasmodium. It is responsible for more than 1 million deaths per year. Natural products contain a great variety of chemical structures and have been screened for antiplasmodial activity as potential sources of new antimalarial drugs. This review highlights studies on natural products with antimalarial and antiplasmodial activity reported in the literature from January 2009 to November 2010. A total of 360 antiplasmodial natural products comprised of terpenes, including iridoids, sesquiterpenes, diterpenes, terpenoid benzoquinones, steroids, quassinoids, limonoids, curcubitacins, and lanostanes; flavonoids; alkaloids; peptides; phenylalkanoids; xanthones; naphthopyrones; polyketides, including halenaquinones, peroxides, polyacetylenes, and resorcylic acids; depsidones; benzophenones; macrolides; and miscellaneous compounds, including halogenated compounds and chromenes are listed in this review.

Melidianolic Acid A and B, New Antimalarial Acyclic Diterpenes from Aphanamixis grandifolia

Two new acyclic diterpenes, melidianolic acids A (1) and B (2), have been isolated from the bark of Aphanamixis grandifolia. Their structures were elucidated on the basis of spectroscopic and chemical methods. Melidianolic acids A (1) and B (2) showed antimalarial activity against Plasmodium falciparum 3D7 with IC50 of 6.1 and 7.3 μg/mL, respectively.

In vitro antiplasmodial activity and cytotoxicity of nine plants traditionally used in Gabon

AIM OF THE STUDY

As part of a project to identify new compounds active on malarial parasites, we tested the in vitro antiplasmodial activity of nine plants traditionally used to treat malaria symptoms in Haut-Ogooué Province, South-East Gabon.

MATERIALS AND METHODS

Dichloromethane and methanolic extracts of each plant were tested for their antiplasmodial activity on two chloroquine-resistant strains of Plasmodium falciparum (FCB and W2), based on lactate dehydrogenase activity. Cytotoxicity was assessed with the MTT test on MRC-5 human diploid embryonic lung cells.

RESULTS

The methanolic extract of Staudtia gabonensis and the dichloromethane extract of Adhatoda latibracteata showed high antiplasmodial activity (IC₅₀<1 μg/ml) and low cytotoxicity, with selectivity indexes of about 58.25 and 16.43, respectively. The methanolic extract of Monodora myristica and the dichloromethane extract of Afromomum giganteum also showed promising activity (1<IC₅₀<10 μg/ml) and low cytotoxicity, with selectivity indexes about 15.70 and 12.48, respectively. Dichloromethane extracts of Monodora myristica and Leonotis Africana showed moderate activity (10<IC₅₀<40 μg/ml), with selectivity indexes about 6.07 and 28.89, respectively. Both extracts of Culcasia lancifolia had IC₅₀ values of 10-40 μg/ml but high cytotoxicity (selectivity indexes <2.77). The methanolic extract of Dorstenia klaineana had moderate antiplasmodial activity (IC₅₀ around 17 μg/ml) but strong cytotoxicity (0.43 μg/ml), giving a selectivity index of about 0.03.

CONCLUSIONS

Most extracts of nine selected plants traditionally used to treat malaria in Gabon had interesting antiplasmodial activity in vitro. This supports continued investigations of traditional medicines in the search for new antimalarial agents. The compounds responsible for the observed antiplasmodial effects are under investigation.