Antiproliferative limonoids of a Malleastrum sp. from the Madagascar rainforest

Fascinating Furanosteroids and Their Pharmacological Profile

This review article delves into the realm of furanosteroids and related isoprenoid lipids derived from diverse terrestrial and marine sources, exploring their wide array of biological activities and potential pharmacological applications. Fungi, fungal endophytes, plants, and various marine organisms, including sponges, corals, molluscs, and other invertebrates, have proven to be abundant reservoirs of these compounds. The biological activities exhibited by furanosteroids and related lipids encompass anticancer, cytotoxic effects against various cancer cell lines, antiviral, and antifungal effects. Notably, the discovery of exceptional compounds such as nakiterpiosin, malabaricol, dysideasterols, and cortistatins has revealed their potent anti-tuberculosis, antibacterial, and anti-hepatitis C attributes. These compounds also exhibit activity in inhibiting protein kinase C, phospholipase A2, and eliciting cytotoxicity against cancer cells. This comprehensive study emphasizes the significance of furanosteroids and related lipids as valuable natural products with promising therapeutic potential. The remarkable biodiversity found in both terrestrial and marine ecosystems offers an extensive resource for unearthing novel biologically active compounds, paving the way for future drug development and advancements in biomedical research. This review presents a compilation of data obtained from various studies conducted by different authors who employed the PASS software 9.1 to evaluate the biological activity of natural furanosteroids and compounds closely related to them. The utilization of the PASS software in this context offers valuable advantages, such as screening large chemical libraries, identifying compounds for subsequent experimental investigations, and gaining insights into potential biological activities based on their structural features. Nevertheless, it is crucial to emphasize that experimental validation remains indispensable for confirming the predicted activities.

Isolation of the New Antiplasmodial Butanolide, Malleastrumolide A, from Malleastrum sp. (Meliaceae) from Madagascar

An extract of Malleastrum sp. (Meliaceae) collected in Madagascar by the Madagascar International Cooperative Biodiversity Group was found to have antimalarial activity, with an IC₅₀ value between 2.5 and 5 μg ml^-1 . After purification by liquid-liquid partition, chromatography on a Diaion open column, C₁₈ SPE and C₁₈ reversed phase HPLC, the new butanolide, malleastrumolide A, was isolated. The structure of malleastrumolide A was determined by mass spectrometry, NMR, and ECD. The double bond position was determined by cross-metathesis and mass spectrometry. The compound has antiproliferative activity against the A2780 ovarian cancer cell line with an IC₅₀ value of 17.4 μm and antiplasmodial activity against the drug-resistant Dd2 strain of Plasmodium falciparum with an IC₅₀ value of 2.74 μm.

Recent progress in the chemistry and biology of limonoids

Significant limonoids: new isolated limonoids, and recent developments in the total chemical synthesis, and structural modifications of limonoids regarding the bioactivities have been summarised.

Antiproliferative Diterpenes from a Malleastrum sp. from the Madagascar dry forest

An ethanol extract of leaves of the plant species Malleastrum sp. collected in northern Madagascar afforded the new clerodane diterpene 18-oxo-cleroda-3,13-dien-16,15-olide (1), together with the three known clerodane diterpenes 16,18-dihydroxykolavenic acid lactone (2), solidagolactone (3) and (-)-kolavenol (4), and the known labdane diterpene 3-oxo-ent-Iabda-8(17),13-dien-15,16-olide (5). Compounds 1, 3, and 4 showed moderate antiproliferative activities against the A2780 ovarian cancer cell line, with the IC50 values of 3.01 ± 0.8, 7.84 ± 0.2, and 17.9 ± 3 µM, respectively. The structure elucidations of all compounds were carried out based on analysis of NMR and mass spectroscopic data. The relative stereochemistry of compound 1 was determined by NOESY NMR spectrum.

An overview on chemical aspects and potential health benefits of limonoids and their derivatives

Limonoids are heavily oxygenated, modified triterpenes dominant in Meliaceae and Rutaceae plant families. The term 'limonoid' is derived from limonin, which was first identified as the bitter constituent of Citrus seeds in 1841. This group of secondary metabolites exhibits a wide range of biological properties, including anticancer, antibacterial, antifungal, antimalarial, and antiviral activities. Significant progress on the role of limonoids as promising candidates for cancer chemoprevention and/or therapy has been achieved in particular in recent years. The aim of this review article is to discuss the recent developments on limonoids chemical aspects and biological activities with the relationship between structure and activity, supporting the new possibilities for the medicinal and/or nutraceutical use of these compounds.

Antiproliferative homoscalarane sesterterpenes from two Madagascan sponges

Dereplication of the antiproliferative ethyl acetate fraction of the Madagascan sponge Carteriospongia sp. led to the detection and isolation of the two known homoscalarane-type sesterterpenes 1 and 2. Investigation of a similar sponge containing closely related compounds afforded the four new antiproliferative homoscalarane sesterterpenes (3 and 5-7). The structures of all isolated compounds were elucidated by spectroscopic methods, including UV, IR and 1D and 2D NMR. Compounds 1, 3 and 5 displayed submicromolar antiproliferative activity against the A2780 ovarian cell line with IC50 values of 0.65, 0.26 and 0.28 μM, respectively, while compounds 6 and 7 showed moderate activity (4.5 and 8.7 μM, respectively). Compounds 3 and 5 also displayed anti-proliferative activity against the H522-T1 non-small cell lung and A2058 human melanoma cancer cell lines.

Astrotricoumarin, an antiproliferative 4′-hydroxy-2′,3′-dihydroprenylated methylcoumarin from an Astrotrichilia sp. from the Madagascar dry forest[1]

Bioassay guided fractionation of the ethanol extract of a new endemic species of the genus Astrotrichilia led to the isolation of the new antiproliferative 3-(4′-hydroxy-2′,3′-dihydroprenyl)-4,6-dimethoxy-5-methylcoumarin, named astrotricoumarin (8) with an IC50 value of 6.8 μM against the A2780 cell line. The structure of compound 8 was elucidated on the basis of its physical and spectroscopic data, including extensive 1D- and 2D-NMR analysis.

Astrotricoumarin, an antiproliferative 4'-hydroxy-2',3'-dihydroprenylated methylcoumarin from an Astrotrichilia sp. from the Madagascar dry forest

Bioassay guided fractionation of the ethanol extract of a new endemic species of the genus Astrotrichilia led to the isolation of the new antiproliferative 3-(4'-hydroxy-2',3'-dihydroprenyl)-4,6-dimethoxy-5-methylcoumarin, named astrotricoumarin (8) with an IC50 value of 6.8 microM against the A2780 cell line. The structure of compound 8 was elucidated on the basis of its physical and spectroscopic data, including extensive 1D- and 2D-NMR analysis.

Antiproliferative compounds of Cyphostemma greveana from a Madagascar dry forest

Bioassay-guided fractionation of the EtOH extracts obtained from a plant identified as Cyphostemma greveana Desc. (Vitaceae) led to the identification of one macrolide, lasiodiplodin (1), three sesquiterpenoids, 12-hydroxy-15-oxoselina-4,11-diene (2), 1β,6α-dihydroxyeudesm-4(15)-ene (3), and (7R*)-opposit-4(15)-ene-1β,7-diol (5), and a new diterpenoid, 16,18-dihydroxykolavenic acid lactone (4). All the isolates were tested against the A2780 human ovarian cancer cell line, and compound 4 and a fraction containing 5 as the major constituent showed antiproliferative activities with IC(50) values of 0.44 μM (0.14 μg/ml) and 0.045 μg/ml, respectively. A partial synthesis of compound 5 was carried out, but the pure synthetic compound was inactive, indicating that the activity of the fraction containing it must be due to a very minor and as yet unidentified substance.

Antiproliferative compounds from Pongamiopsis pervilleana from the Madagascar Dry Forest

Bioassay-guided fractionation of an ethanol extract of the roots of the endemic Malagasy plant Pongamiopsis pervilleana led to the isolation of the three new compounds (2'R)-4'-hydroxyemoroidocarpan (1), pongavilleanine (3), and epipervilline (4) together with two known compounds, identified as emoroidocarpan (2) and rotenolone (5). The structures of all compounds were determined by physical, chemical, and spectroscopic evidence. The stereochemistry at C-2' of the previously reported compound emoroidocarpan was determined to be R by the observation of a negative Cotton effect at 474 nm in the CD spectrum of its osmate ester derivative. Compounds 2-5 displayed moderate antiproliferative activity against the A2780 human ovarian cancer cell line, and rotenolone also showed micromolar antiproliferative activity toward the breast cancer BT-549, prostate cancer DU 145, NSCLC NCI-H460, and colon cancer HCC-2998 cell lines.

Triterpenoids

This review covers the isolation and structure determination of triterpenoids including squalene derivatives, protostanes, lanostanes, holostanes, cycloartanes, dammaranes, euphanes, tirucallanes, tetranortriterpenoids, lupanes, oleananes, friedelanes, ursanes, hopanes, isomalabaricanes and saponins; 574 references are cited.

Biodiversity conservation and drug discovery: Can they be combined? The Suriname and Madagascar experiences

The approach to new drugs through natural products has proved to be the single most successful strategy for the discovery of new drugs, but in recent years its use has been deemphasized by many pharmaceutical companies in favor of approaches based on combinatorial chemistry and genomics, among others.Drug discovery from natural sources requires continued access to plant, marine, and microbial biomass, and so the preservation of tropical rainforests is an important part of our drug discovery program. Sadly, many of the tropical forests of the world are under severe environmental pressure, and deforestation is a serious problem in most tropical countries. One way to combat this loss is to demonstrate their value as potential sources of new pharmaceutical or agrochemical products.As part of an effort to integrate biodiversity conservation and drug discovery with economic development, we initiated an International Cooperative biodiversity Group (ICBG) to discover potential pharmaceuticals from the plant biodiversity of Suriname and Madagascar. The Group, established with funding from agencies of the United States government, involved participants from the USA, Suriname, and Madagascar. The basic approach was to search for bioactive plants in the Suriname and Malagasy flora, and to isolate their bioactive constituents by the best available methods, but the work included capacity building as well as research. Progress on this project will be reported, drawing on results obtained from the isolation of bioactive natural products from Suriname and Madagascar. The benefits of this general approach to biodiversity and drug discovery will also be discussed.

A natural love of natural products

Recent research on the chemistry of natural products from the author’s group that led to the receipt of the ACS Ernest Guenther Award in the Chemistry of Natural Products is reviewed. REDOR NMR and synthetic studies established the T-taxol conformation as the bioactive tubulin-binding conformation, and these results were confirmed by the synthesis of compounds which clearly owed their activity or lack of activity to whether or not they could adopt the T-taxol conformation. Similar studies with the epothilones suggest that the current tubulin-binding model needs to be modified. Examples of natural products discovery and biodiversity conservation in Suriname and Madagascar are also presented, and it is concluded that natural products chemistry will continue to make significant contributions to drug discovery.