Antiproliferative and antiplasmodial dimeric phloroglucinols from Mallotus oppositifolius from the Madagascar Dry Forest (1)

Antiviral and antibacterial properties of phloroglucinols: a review on naturally occurring and (semi)synthetic derivatives with potential therapeutic interest

Phloroglucinol and derived compounds comprise a huge class of secondary metabolites widely distributed in plants and brown algae. A vast array of biological activities, including antioxidant, anti-inflammatory, antimicrobial, and anticancer has been associated to this class of compounds. In this review, the available data on the antiviral and antibacterial capacity of phloroglucinols have been analyzed. Some of these compounds and derivatives show important antimicrobial properties in vitro. Phloroglucinols have been shown to be effective against viruses, such as human immunodeficiency virus (HIV), herpes or enterovirus, and preliminary data through docking analysis suggest that they can be effective against SARS-CoV-19. Also, some phloroglucinols derivatives have shown antibacterial effects against diverse bacteria strains, including Bacillus subtilis and Staphylococcus aureus, and (semi)synthetic development of novel compounds have led to phloroglucinols with a significantly increased biological activity. However, therapeutic use of these compounds is hindered by the absence of in vivo studies and scarcity of information on their mechanisms of action, and hence further research efforts are required. On the basis of this consideration, our work aims to gather data regarding the efficacy of natural-occurring and synthetic phloroglucinol derivatives as antiviral and antibacterial agents against human pathogens, which have been published during the last three decades. The recollection of results reported in this review represents a valuable source of updated information that will potentially help researchers in the development of novel antimicrobial agents.

Recent advances in the synthesis of natural products containing the phloroglucinol motif

Covering: June 2009 to 2021Natural products containing a phloroglucinol motif include simple and oligomeric phloroglucinols, polycyclic polyprenylated acylphloroglucinols, phloroglucinol-terpenes, xanthones, flavonoids, and coumarins. These compounds represent a major class of secondary metabolites which exhibit a wide range of biological activities such as antimicrobial, anti-inflammatory, antioxidant and hypoglycaemic properties. A number of these compounds have been authorized for therapeutic use or are currently being studied in clinical trials. Their structural diversity and utility in both traditional and conventional medicine have made them popular synthetic targets over the years. In this review, we compile and summarise the recent synthetic approaches to the natural products bearing a phloroglucinol motif. Focus has been given on ingenious strategies to functionalize the phloroglucinol moiety at multiple positions. The isolation and bioactivities of the compounds are also provided.

Antimalarial Natural Products

Natural products have made a crucial and unique contribution to human health, and this is especially true in the case of malaria, where the natural products quinine and artemisinin and their derivatives and analogues, have saved millions of lives. The need for new drugs to treat malaria is still urgent, since the most dangerous malaria parasite, Plasmodium falciparum, has become resistant to quinine and most of its derivatives and is becoming resistant to artemisinin and its derivatives. This volume begins with a short history of malaria and follows this with a summary of its biology. It then traces the fascinating history of the discovery of quinine for malaria treatment and then describes quinine's biosynthesis, its mechanism of action, and its clinical use, concluding with a discussion of synthetic antimalarial agents based on quinine's structure. The volume then covers the discovery of artemisinin and its development as the source of the most effective current antimalarial drug, including summaries of its synthesis and biosynthesis, its mechanism of action, and its clinical use and resistance. A short discussion of other clinically used antimalarial natural products leads to a detailed treatment of other natural products with significant antiplasmodial activity, classified by compound type. Although the search for new antimalarial natural products from Nature's combinatorial library is challenging, it is very likely to yield new antimalarial drugs. The chapter thus ends by identifying over ten natural products with development potential as clinical antimalarial agents.

Methylene-bridged dimeric natural products involving one-carbon unit in biosynthesis

This review summarizes the methylene-bridged dimeric natural products involving one-carbon unit in biosynthesis, including their structures, biological activities, synthetic methods, and formation mechanisms.

My 60-Year Love Affair with Natural Products

The author describes his 60-year career in studying the chemistry of natural products, which includes structural, synthetic, and biosynthetic studies of natural products ranging from insect pigments, antibiotics, and fecal mutagens to taxol and other anticancer natural products as well as antimalarial natural products. One of the compounds discussed, napabucasin, is now an anticancer drug in phase III clinical trials.

Flavanones from the Twigs and Barks of Artocarpus lakoocha Having Antiplasmodial and Anti-TB Activities

Chromatographic separation of the acetone extracts from the twigs and barks of Artocarpus lakoocha led to the isolation of the one new flavanone, lakoochanone (1), together with eleven known compounds (2-12). Lakoochanone (1) and moracin C (4) exhibited weak antiplasmodial activity against Plasmodium falciparum Dd2 with IC₅₀ values of 36.7 and 33.9 µM, respectively. Moreover, moracin C (4) and sanggenofuran B (5) showed cytotoxic activity against A2780 cell line with the respective IC₅₀ values of 15.0 and 57.1 µM. In addition, cyclocommunin (7) displayed strong antimycobacterial activity against Mycobacterium tuberculosis H37Ra with the minimum inhibitory concentration (MIC) value of 12.3 µM.

Polymethylated acylphloroglucinols from Rhodomyrtus tomentosa exert acetylcholinesterase inhibitory effects

Chemical investigation of the twigs and leaves of Rhodomyrtus tomentosa led to the isolation and structural identification of a novel polymethylated phloroglucinol meroterpenoid (PPM) featuring a 6/6/6/6 tetracyclic system, rhotomentodione F (1), five new polymethylated polycyclic phloroglucinols (PPPs) with a rare bis-furan framework, rhotomentosones A-E (2-6), and one new adduct composed of an acylphloroglucinol and two β-triketone units, rhotomentosone F (7), as well as five known analogues (8-12). Their structures and absolute configurations were unambiguously determined by comprehensive spectroscopic data and electronic circular dichroism (ECD) calculations. All isolates were evaluated for their anti-inflammatory and acetylcholinesterase (AChE) inhibitory activities. Compound 6 displayed significant AChE inhibitory effect with an IC₅₀ value of 8.68 μM. Further molecular docking studies of 6 revealed that the interactions with AChE residues Ser125, Glu202, and Tyr133 are crucial for AChE inhibitory activity. The current study not only enriches the chemical diversity of phloroglucinols in Myrtaceae species, but also provides potential lead compounds for the further design and development of new AChE inhibitors to treat Alzheimer's disease.

Sc(OTf)3-Catalyzed Synthesis of Symmetrical Dithioacetals and Bisarylmethanes Using Nitromethane as a Methylene Source

Use of nitromethane as an electrophilic methylene source for the synthesis of symmetrical dithioacetals and bisarylmethanes has been showcased using Sc(OTf)₃ as a catalyst. The procedure allows straightforward access to the densely functionalized dithioacetals and bisarylmethanes under mild conditions. Additionally, the method has been applied for the synthesis of antimalarial tetramethyl mellotojaponin C and anticancer dimeric phloroglucinol derivative.

Antibacterial phloroglucinols derivatives from the leaves of Mallotus oppositifolius (Geisler) Müll. Arg. (Euphorbiaceae)

From the ethno-medicinally used leaves of Mallotus oppositifolius, four acylphloroglucinol derivatives, namely Acronyculatin SU (1-3) and Mallotojaponin D (4) were isolated along with seven known compounds (5-11). Structures were elucidated by comprehensive spectroscopic analyses and HRMS data. Absolute configurations were assigned by careful comparison of their specific optical rotation with those of closely related compounds. Compounds 1, 2, 6 and 11 demonstrated inhibitory activity against the bacterial strains E. coli, S. aureus, S. typhi, P. aeruginosa with minimum inhibitory concentration (MIC) values ranging from 3.125 to 50 μg/ml.

Antiplasmodial natural products: an update

Background

Malaria remains a significant public health challenge in regions of the world where it is endemic. An unprecedented decline in malaria incidences was recorded during the last decade due to the availability of effective control interventions, such as the deployment of artemisinin-based combination therapy and insecticide-treated nets. However, according to the World Health Organization, malaria is staging a comeback, in part due to the development of drug resistance. Therefore, there is an urgent need to discover new anti-malarial drugs. This article reviews the literature on natural products with antiplasmodial activity that was reported between 2010 and 2017.

Methods

Relevant literature was sourced by searching the major scientific databases, including Web of Science, ScienceDirect, Scopus, SciFinder, Pubmed, and Google Scholar, using appropriate keyword combinations.

Results and Discussion

A total of 1524 compounds from 397 relevant references, assayed against at least one strain of Plasmodium, were reported in the period under review. Out of these, 39% were described as new natural products, and 29% of the compounds had IC₅₀ ≤ 3.0 µM against at least one strain of Plasmodium. Several of these compounds have the potential to be developed into viable anti-malarial drugs. Also, some of these compounds could play a role in malaria eradication by targeting gametocytes. However, the research into natural products with potential for blocking the transmission of malaria is still in its infancy stage and needs to be vigorously pursued.

Metabolic dependency of chorismate in Plasmodium falciparum suggests an alternative source for the ubiquinone biosynthesis precursor

The shikimate pathway, a metabolic pathway absent in humans, is responsible for the production of chorismate, a branch point metabolite. In the malaria parasite, chorismate is postulated to be a direct precursor in the synthesis of p-aminobenzoic acid (folate biosynthesis), p-hydroxybenzoic acid (ubiquinone biosynthesis), menaquinone, and aromatic amino acids. While the potential value of the shikimate pathway as a drug target is debatable, the metabolic dependency of chorismate in P. falciparum remains unclear. Current evidence suggests that the main role of chorismate is folate biosynthesis despite ubiquinone biosynthesis being active and essential in the malaria parasite. Our goal in the present work was to expand our knowledge of the ubiquinone head group biosynthesis and its potential metabolic dependency on chorismate in P. falciparum. We systematically assessed the development of both asexual and sexual stages of P. falciparum in a defined medium in the absence of an exogenous supply of chorismate end-products and present biochemical evidence suggesting that the benzoquinone ring of ubiquinones in this parasite may be synthesized through a yet unidentified route.

Phloroglucinols from the Roots of Garcinia dauphinensis and Their Antiproliferative and Antiplasmodial Activities

Garcinia dauphinensis is a previously uninvestigated endemic plant species of Madagascar. The new phloroglucinols dauphinols A-F and 3'-methylhyperjovoinol B (1-7) and six known phloroglucinols (8-13) together with tocotrienol 14 and the three triterpenoids 15-17 were isolated from an ethanolic extract of G. dauphinensis roots using various chromatographic techniques. The structures of the isolated compounds were elucidated by NMR, MS, optical rotation, and ECD data. Theoretical ECD spectra and specific rotations for 2 were calculated and compared to experimental data in order to assign its absolute configuration. Among the compounds tested, 1 showed the most promising growth inhibitory activity against A2870 ovarian cancer cells, with IC50 = 4.5 ± 0.9 μM, while 2 had good antiplasmodial activity against the Dd2 drug-resistant strain of Plasmodium falciparum, with IC50 = 0.8 ± 0.1 μM.

Antiplasmodial flavanones and a stilbene from Carpha glomerata

Bioassay-guided fractionation of an extract of Carpha glomerata (Cyperaceae) led to the isolation of seven compounds. Compounds 1 (carphorin A), 3 (carphorin C), 4 (carphorin D), and 5 (carphabene) are new compounds, and compound 2 (8-(3″-hydroxyisoamyl)-naringenin) was isolated for the first time as a natural product. All structures were elucidated based on analyses of their HR-ESIMS and 1D and 2D NMR data. Compounds 1, 2, and 6, which have prenyl or hydroxyprenyl side chains, exhibited antiplasmodial activities with IC₅₀ values of 5.2 ± 0.6, 3.4 ± 0.4, and 6.7 ± 0.8 µM against the drug-resistant Dd2 strain of Plasmodium falciparum. In addition the prenylated stilbene 5 also showed good activity, with IC₅₀ 5.8 ± 0.7 µM.

Novel Bioactive Natural Products Isolated from Madagascar Plants and Marine Organisms (2009-2017)

Madagascar's rain forests and tropical dry forests are home to numerous endemic plant species and the island is considered a biodiversity hotspot. About 80% of the Madagascan (Malagasy) population relies on traditional medicines that have been proven to contain a variety of biologically active compounds. In the search for bioactive compounds from Madagascan biodiversity, we accessed and collected most of the literature dealing with the isolation, structure elucidation, and biological activities of organic small molecules originating from Madagascan plants and marine organisms. Since we published the first review of this work in 2009 (Curr. Med. Chem., 17, 2010, Hou and Harinantenaina), the present paper covers the isolation, structures, and bioactivity of 182 new secondary metabolites isolated from Malagasy higher plants and marine organisms in the last seven years (2009-2017).

An ethnopharmacological survey of medicinal plants traditionally used for cancer treatment in the Ashanti region, Ghana

AIMS

Cancer represents a major health burden and drain on healthcare resources in the world. The majority of the people of Africa still patronize traditional medicine for their health needs, including various forms of cancer. The aim of the following study is the identification of medicinal plants used for cancer treatment by the traditional healers in the Ashanti area of Ghana and to cross-reference the identified plant species with published scientific literature.

METHODOLOGY

Validated questionnaires were administered to 85 traditional healers in 10 communities within Ashanti region. For cross-validation, also 7 healers located outside Ashanti region were investigated to evaluate regional differences. Interviews and structured conversations were used to administer the questionnaires. Selected herbal material dominantly used by the healers was collected and identified.

RESULTS

The ethnopharmacological survey revealed 151 plant species used for cancer treatment. Identified species were classified into different groups according to their frequency of use, resulting in the "top-22" plants. Interestingly group I (very frequent use) contained 5 plant species (Khaya senegalensis, Triplochiton scleroxylon, Azadirachta indica, Entandrophragma angolense, Terminalia superba), three of which belong to the plant family Meliaceae, phytochemically mainly characterized by the presence of limonoids. Cross-referencing of all plants identified by current scientific literature revealed species which have not been documented for cancer therapy until now. Special interest was laid on use of plants for cancer treatment of children.

CONCLUSION

A variety of traditionally used anti-cancer plants from Ghana have been identified and the widespread use within ethnotraditional medicine is obvious. Further in vitro and clinical studies will be performed in the near future to rationalize the phytochemical and functional scientific background of the respective extracts for cancer treatment.

Synthesis and Antimalarial Activity of Mallatojaponin C and Related Compounds

The phloroglucinol mallotojaponin C (1) from Mallotus oppositifolius, which was previously shown by us to have both antiplasmodial and cytocidal activities against the malaria parasite Plasmodium falciparum, was synthesized in three steps from 2',4',6'-trihydroxyacetophenone, and various derivatives were synthesized in an attempt to improve the bioactivity of this class of compounds. Two derivatives, the simple prenylated phloroglucinols 12 and 13, were found to have comparable antiplasmodial activities to that of mallotojaponin C.

Antiplasmodial phloroglucinol derivatives from Syncarpia glomulifera

Bioassay guided fractionation of a MeOH extract of the stem bark of Syncarpia glomulifera (Myrtaceae) led to the isolation of the two new phloroglucinol derivatives (±)-rhodomyrtosone F (1) and (±)-calliviminone I (2), the three known triterpenes, betulinic acid (3), ursolic acid-3-acetate (4), and ursolic acid (5), and 1-(2,4,6-trihydroxyphenyl)-1-hexanone (6). Compound 1 exhibited strong antiplasmodial activity, while compounds 2-4 were moderately active and 5 and 6 were inactive in this assay. The structures of 1 and 2 were elucidated based on analyses of their mass spectrometric data, 1D and 2D NMR spectra, and comparison with related compounds.

New Antiplasmodial Diterpenes from Gutierrezia sarothrae

Bioassay guided fractionation of the MeOH extract of the plant Gutierrezia sarothrae (Asteraceae) using an assay for antiplasmodial activity against the drug-resistant Dd2 strain of Plasmodium falciparum led to the isolation of the two new diterpenes 3α-angeloyloxy-15-hydroxylabda-7,13-dien-16,15-olid-18-oic acid (1) and 3α-angeloyloxy-15-methoxylabda-7,13-dien-16,15-olid-18-oic acid (2). The structures of 1 and 2 were elucidated by interpretation of 1D and 2D NMR spectroscopic data, mass spectrometry, and comparison with the data of related compounds reported in the literature. Compound 1 exhibited moderate antiplasmodial activity with an IC50 values of 10.4 ± 4.3 μM.

New Antiplasmodial Diterpenes from Gutierrezia Sarothrae

Bioassay guided fractionation of the MeOH extract of the plant Gutierrezia sarothrae (Asteraceae) using an assay for antiplasmodial activity against the drug-resistant Dd2 strain of Plasmodium falciparum led to the isolation of the two new diterpenes 3α-angeloyloxy-15-hydroxylabda-7,13-dien-16,15-olid-18-oic acid (1) and 3α-angeloyloxy-15-methoxylabda-7,13-dien-16,15-olid-18-oic acid (2). The structures of 1 and 2 were elucidated by interpretation of ID and 2D NMR spectroscopic data, mass spectrometry, and comparison with the data of related compounds reported in the literature. Compound 1 exhibited moderate antiplasmodial activity with an IC50 values of 10.4 ± 4.3 μM.

Activity of medicinal plants from Ghana against the parasitic gut protist Blastocystis

ETHNOPHARMACOLOGICAL RELEVANCE

The plants tested in this study were examples of plants historically used to treat or alleviate several types of stomach disorders manifested by e.g. stomachache, diarrhoea or dysentery. These plants have been consumed typically as a decoction, sometimes mixed with other flavourings. The aim of this study was to evaluate the anti-Blastocystis activity of 24 plant parts from 21 medicinal plants from Ghana.

MATERIALS AND METHODS

The medicinal plants were collected in the Greater Accra region of Ghana. Every plant part was tested in three different extracts; an ethanolic, a warm, and a cold water extract, at a final concentration of 1 mg/mL for the initial screening, and in a range from 0.0156 to 1mg/mL for determination of inhibitory concentrations. The obligate anaerobic parasitic gut protist Blastocystis (subtype 4) was used as a 48 h old subcultivated isolate in the final concentration of 10(6) cells/mL. Plant extracts inoculated with Blastocystis were incubated at 37 °C for 24 h and 48 h. Both MIC minimum inhibitory concentration (MIC90) assays and minimal lethal concentration (MLC) assays were performed after 24 h and 48 h. The half maximal inhibitory concentration (IC50) was derived after 24 h and 48 h. Antimicrobial activity was tested against two Gram-positive and two Gram-negative bacteria for all 24 plant parts at a final concentration of 1mg/mL.

RESULTS

Screening of the 24 different plant parts showed significant anti-Blastocystis activity of six of the ethanolic extracts: Mallotus oppositifolius, IC50, 24 h 27.8 µg/mL; Vemonia colorata, IC50, 24 h 117.9 µg/mL; Zanthoxylum zanthoxyloides, cortex IC50, 24 h 255.6 µg/mL; Clausena anisata, IC50, 24 h 314.0 µg/mL; Z. zanthoxyloides, radix IC50, 24 h 335.7 µg/mL and Eythrina senegalensis, IC50, 24 h 527.6 µg/mL. The reference anti-protozoal agent metronidazole (MTZ) had an IC50, 24 h of 7.6 µg/mL. Only C. anisata showed antimicrobial activity at a concentration of 800 µg/mL.

CONCLUSION

Six ethanolic plant extracts showed significant anti-parasitic activity against Blastocystis. M. oppositifolius showed nearly as good activity as the reference anti-protozoal drug MTZ. Historically, the active plants found in this study have been used against dysentery, diarrhoea or other stomach disorders. Nowadays they are not used specifically for dysentery, but they are being used as medicinal plants against various stomach disorders.

Neolignans and other metabolites from Ocotea cymosa from the Madagascar rain forest and their biological activities

Ten new neolignans including the 6'-oxo-8.1'-lignans cymosalignans A (1a), B (2), and C (3), an 8.O.6'-neolignan (4a), ococymosin (5a), didymochlaenone C (6a), and the bicyclo[3.2.1]octanoids 7-10 were isolated along with the known compounds 3,4,5,3',5'-pentamethoxy-1'-allyl-8.O.4'-neolignan, 3,4,5,3'-tetramethoxy-1'-allyl-8.O.4'-neolignan, didymochlaenone B, virologin B, ocobullenone, and the unusual 2'-oxo-8.1'-lignan sibyllenone from the stems or bark of the Madagascan plant Ocotea cymosa. The new 8.O.6'-neolignan 4a, dihydrobenzofuranoid 5a, and the bicyclo[3.2.1]octanoid 7a had in vitro activity against Aedes aegypti, while the new compounds 5a, 7a, 8, and 10a and the known virolongin B (4b) and ocobullenone (10b) had antiplasmodial activity. We report herein the structure elucidation of the new compounds on the basis of spectroscopic evidence, including 1D and 2D NMR spectra, electronic circular dichroism, and mass spectrometry, and the biological activities of the new and known compounds.

Methicillin-resistant Staphylococcus aureus, Vancomycin-resistant Enterococcus faecalis and Enterococcus faecium active Dimeric Isobutyrylphloroglucinol from Ivesia gordonii

Bioassay-guided fractionation of the chloroform soluble fraction of stem, leaf, and flower extracts of the American plant Ivesia gordonii led to the isolation of a new dimeric acylphloroglucinol, 3,3′-diisobutyryl-2,6′-dimethoxy-4,6,2′,4′-tetrahydroxy-5,5′dimethyldiphenyl methane (1), to which we have assigned the trivial name of ivesinol (1), together with a known monomeric acylphloroglucinol, 1,5-dihydroxy-2-(2′-methylpropionyl)-3-methoxy-6-methylbenzene (2). The structures of the isolated compounds were characterized using 1D- and 2D- NMR spectroscopy, including COSY, HMQC, HMBC, and ROESY experiments, as well as mass spectrometry. Ivesinol (1) showed potent activity against Staphylococcus aureus (SA) and methicillin-resistant S. aureus (MRSA) with IC50/MIC/MBC values of 0.10/1.25/>20 μg/mL and 0.05/0.31/>20 μg/mL, respectively (vs. IC50/MIC/MBC 0.13/0.5/1.0 μg/mL and 0.13/0.5/1.0 μg/mL of ciprofloxacin), while the corresponding monomer 2 was found to be less active. Compound 1 also demonstrated strong activity against vancomycin-resistant Enteococcus faecium ( VRE) with IC50/MIC/MBC values of 0.22/1.25/>20 μg/mL, whereas the reference standard ciprofloxacin was found to be inactive against this strain. In addition, compound 2 showed moderate activity against two species of Candida and Cryptococcus neoformans, while 1 was inactive against these fungi. In order to evaluate the influence of the acyl group(s) in phloroglucinol (3) as a ligand, the mono- (4) and diacetylphloroglucinol (5) were prepared from 3, and evaluated for their in vitro SA, MRSA, and VRE activities; 2,4-diacetylphloroglucinol (5) showed potent activity, like 1, against SA, MRSA, and VRE (ATCC 700221) with IC50/ MIC values of 0.3/2.5, 0.23/2.5, and 0.86/2.5 μg/mL, respectively, while 4 was inactive.

Methicillin-resistant Staphylococcus aureus, vancomycin-resistant Enterococcus faecalis and Enterococcus faecium active dimeric isobutyrylphloroglucinol from Ivesia gordonii

Bioassay-guided fractionation of the chloroform soluble fraction of stem, leaf, and flower extracts of the American plant Ivesia gordonii led to the isolation of a new dimeric acylphloroglucinol, 3,3'-diisobutyryl-2,6'-dimethoxy-4,6,2',4'-tetrahydroxy-5,5'dimethyldiphenyl methane (1), to which we have assigned the trivial name ofivesinol (1), together with a known monomeric acylphloroglucinol, 1,5-dihydroxy-2-(2'-methylpropionyl)-3-methoxy-6-methylbenzene (2). The structures of the isolated compounds were characterized using 1D- and 2D- NMR spectroscopy, including COSY, HMQC, HMBC, and ROESYexperiments, as well as mass spectrometry. Ivesinol (1) showed potent activity against Staphylococcus aureus (SA) and methicillin-resistant S. aureus (MRSA) with IC50/MIC/MBC values of 0.10/1.25/>20 microg/mL and 0.05/0.31/>20 microg/mL, respectively (vs. IC50/MIC/MBC 0.13/0.5/1.0 microg/mL and 0.13/0.5/1.0 microg/mL of ciprofloxacin), while the corresponding monomer 2 was found to be less active. Compound 1 also demonstrated strong activity against vancomycin-resistant Enterococcus faecium (VRE) with IC50/MlC/MBC values of 0.22/1.25/>20 microg/mL, whereas the reference standard ciprofloxacin was found to be inactive against this strain. In addition, compound 2 showed moderate activity against two species of Candida and Cryptococcus neoformans, while 1 was inactive against these fungi. In order to evaluate the influence of the acyl group(s) in phloroglucinol (3) as a ligand, the mono- (4) and diacetylphloroglucinol (5) were prepared from 3, and evaluated for their in vitro SA, MRSA, and VRE activities; 2,4-diacetylphloroglucinol (5) showed potent activity, like 1, against SA, MRSA, and VRE (ATCC 700221) with IC50/MIC values of 0.3/2.5, 0.23/2.5, and 0.86/2.5 microg/mL, respectively, while 4 was inactive.

Isolation of antiplasmodial anthraquinones from Kniphofia ensifolia, and synthesis and structure-activity relationships of related compounds

Bioassay-guided separation of the South African plant Kniphofia ensifolia for antiplasmodial activity led to the isolation of two new anthraquinones, named kniphofiones A and B (3 and 4), together with three known bioactive anthraquinone monomers (1, 2 and 5), and four known bisanthraquinones (6-9). The structures of the two new compounds were elucidated based on analyses of their 1D and 2D NMR spectra and mass spectrometric data. The dimeric compounds 6 and 7 displayed the strongest antiplasmodial activity among all the isolated compounds, with IC₅₀ values of 0.4 ± 0.1 and 0.2 ± 0.1 μM, respectively. The two new compounds displayed modest activities, with IC₅₀ values of 26 ± 4 and 9 ± 1 μM, respectively. Due to the synthetic accessibility of the new compounds and the increased activity shown by the dimeric compounds, a structure-activity relationship study was conducted. As a result, one analogue of kniphofione B (4), the caffeic acid derivative of aloe-emodin, was found to have the highest activity among all the aloe-emodin derivatives, with an IC50 value of 1.3 ± 0.2 μM.

Antiapicoplast and gametocytocidal screening to identify the mechanisms of action of compounds within the malaria box

Malaria remains a significant infectious disease that causes millions of clinical cases and >800,000 deaths per year. The Malaria Box is a collection of 400 commercially available chemical entities that have antimalarial activity. The collection contains 200 drug-like compounds, based on their oral absorption and the presence of known toxicophores, and 200 probe-like compounds, which are intended to represent a broad structural diversity. These compounds have confirmed activities against the asexual intraerythrocytic stages of Plasmodium falciparum and low cytotoxicities, but their mechanisms of action and their activities in other stages of the parasite's life cycle remain to be determined. The apicoplast is considered to be a promising source of malaria-specific targets, and its main function during intraerythrocytic stages is to provide the isoprenoid precursor isopentenyl diphosphate, which can be used for phenotype-based screens to identify compounds targeting this organelle. We screened 400 compounds from the Malaria Box using apicoplast-targeting phenotypic assays to identify their potential mechanisms of action. We identified one compound that specifically targeted the apicoplast. Further analyses indicated that the molecular target of this compound may differ from those of the current antiapicoplast drugs, such as fosmidomycin. Moreover, in our efforts to elucidate the mechanisms of action of compounds from the Malaria Box, we evaluated their activities against other stages of the life cycle of the parasite. Gametocytes are the transmission stage of the malaria parasite and are recognized as a priority target in efforts to eradicate malaria. We identified 12 compounds that were active against gametocytes with 50% inhibitory concentration values of <1 μM.

Semisynthesis of mallotus B from rottlerin: evaluation of cytotoxicity and apoptosis-inducing activity

Mallotus B (2d) is a prenylated dimeric phloroglucinol compound isolated from Mallotus philippensis. There have been no reports on the synthesis or biological activity of this compound. In the present paper, a semisynthetic preparation of mallotus B is reported via base-mediated intramolecular rearrangement of rottlerin (1), which is one of the major constituents of M. philippensis. The homodimer "rottlerone" was also formed as one of the products of this base-mediated intramolecular reaction. Rottlerin (1), along with rottlerone (2c) and mallotus B (2d), was evaluated for cytotoxicity against a panel of cancer cell lines including HEPG2, Colo205, MIAPaCa-2, PC-3, and HL-60 cells. Mallotus B (2d) displayed cytotoxicity for MIAPaCa-2 and HL-60 cells with IC₅₀ values of 9 and 16 μM, respectively. Microscopic studies in HL-60 cells indicated that mallotus B (2d) induces cell cycle arrest at the G1 phase and causes defective cell division. It also induces apoptosis, as evidenced by distinct changes in cell morphology.

A New Bioactive Diterpene Glycoside from Molinaea Retusa from the Madagascar Dry Forest

In a continuing collaboration in a search for new antiproliferative compounds in Madagascar as part of an International Cooperative Biodiversity Group (ICBG), an ethanol extract of Molinaea retusa Radlk. (Sapindaceae) was investigated on the basis of its moderate antiproliferative activity against the A2780 human ovarian cancer cell line (IC50 16 μg/mL). One new compound, 2″,3″,4″,6′-de- O-acetylcupacinoside (1, IC50 15.4 μM) and two known compounds, cupacinoside (2, IC50 9.5 μM) and 6-de- O-acetylcupacinoside (3, IC50 10.9 μM), were isolated by bioassay-directed fractionation using liquid-liquid partitioning, column chromatography, and HPLC. Compounds 2 and 3 also had moderate antiplasmodial activities, with IC50 values of 4.0 and 6.4 μM, respectively, against Plasmodium falciparum, Dd2 strain. The structures were determined using spectroscopic methods.

A new bioactive diterpene glycoside from Molinaea retusa from the Madagascar dry forest

In a continuing collaboration in a search for new antiproliferative compounds in Madagascar as part of an International Cooperative Biodiversity Group (ICBG), an ethanol extract of Molinaea retusa Radlk. (Sapindaceae) was investigated on the basis of its moderate antiproliferative activity against the A2780 human ovarian cancer cell line (IC50 16 microg/mL). One new compound, 2", 3", 4", 6'-de-O-acetylcupacinoside (1, IC50 15.4 microM) and two known compounds, cupacinoside (2, IC50 9.5 microM) and 6-de-O-acetylcupacinoside (3, IC50 10.9 microM), were isolated by bioassay-directed fractionation using liquid-liquid partitioning, column chromatography, and HPLC. Compounds 2 and 3 also had moderate antiplasmodial activities, with IC50 values of 4.0 and 6.4 microM, respectively, against Plasmodium falciparum, Dd2 strain. The structures were determined using spectroscopic methods.