Cembranolides from the leaves of Croton gratissimus

Anti-HIV crotocascarin ω from Kenyan Croton dichogamus

An anti-HIV methanol-soluble fraction of a 1:1 CH2Cl2:CH3OH extract of twigs of a Kenyan Croton dichogamus yielded seven compounds, the new crotocascarin ω (1), the known β-oplopanone (2), dihydroconiferyl acetate (3), 3'(4''-hydroxyphenyl)-propyl benzoate (4), lupeol, sitosterol and stigmasterol. Crotocascarin ω (90%) inhibited HIV-1 replication with an IC50 value of 5.3 nM, and the compound was cytotoxic towards MT-4 cells presenting an IC50 value of 84 µM. In silico modelling showed that the anti-HIV activity for compound 1 could be through the HIV-1 protease inhibition.

Histochemical Analysis and Ultrastructure of Trichomes and Laticifers of Croton gratissimus Burch. var. gratissimus (Euphorbiaceae)

Croton gratissimus (Lavender croton) possesses three distinct secretory structures. These include lepidote and glandular trichomes and non-articulated unbranched laticifers. The lepidote trichomes form a dense indumentum on the abaxial surface of the leaves and canopy the glandular trichomes. Although assumed to be non-glandular, transmission electron microscopy (TEM) indicated high metabolic activity within the stalk and radial cells. Glandular trichomes are embedded in the epidermal layer and consist of a single cell which forms a prominent stalk and dilated head. Laticifers occur on the mid-vein of leaves and are predominantly associated with vascular tissue. In the stems, laticifers are associated with the phloem and pith. Both trichome types and laticifers stained positive for alkaloids, phenolic compounds, and lipids. Positive staining for these compounds in lepidote trichomes suggests their involvement in the production and accumulation of secondary metabolites. These metabolites could provide chemical defense for the plant and potentially be useful for traditional medicine.

Cyclooxygenase Enzyme and Lipid Peroxidation Inhibitory Terpenoids and Steroidal compounds as Major Constituents in Cleome viscosa Leaves

Bioassay guided study of Cleome viscosa Linn. (Cleomaceae) leaves led to the isolation of a new cembrenoid diterpene (1: ) and three known compounds (2:  - 4: ) from the hexane extract. The chemical structures of these compounds were elucidated by spectroscopic methods such as NMR (1D and 2D), HRMS and IR and identified and afforded compound 1: , malabaric acid (2: ), stigmast-4-en-3-one (3: ) and stigmast-4-ene-3,6-dione (4: ). This is the first report of compounds 1: and 2: from C. viscosa Linn. Isolates were evaluated for anti-inflammatory activity using in vitro cyclooxygenase enzyme (COX-1 and -2) inhibitory assays. The novel cembrenoid diterpene (1: ) exhibited IC₅₀ values of 8.4 µM for COX-1 enzyme and 45.2 µM for COX-2 enzyme, respectively. Similarly, malabaric acid (2: ) exhibited IC₅₀ values of 11.5 µM for COX-1 enzyme and 46.9 µM for COX-2 enzyme, respectively. Their inhibitory activities were in par with non-steroidal anti-inflammatory drugs aspirin, ibuprofen and naproxen. Sterols 3: and 4: gave IC₅₀ values of 62.6 and 67.9 µM, respectively for COX-1 enzyme while indicating weak COX-2 enzyme inhibition. Lipid peroxidation inhibitory (LPO) and MTT assays were used to determine antioxidant activity of these compounds. Compounds 1:  - 4: showed LPO inhibition with IC₅₀ values between 82 and 100 µM and moderate antioxidant activity in the MTT assay. Biological activities reported for these compounds are for the first time and it support anecdotal medicinal claims of C. viscosa Linn. leaves.

Anti-HIV Ermiasolides from Croton megalocarpus

In recent years, elucidation of novel anti-HIV bioactive compounds from natural products is gaining importance rapidly, not only from the research and publications, but also from controlled clinical studies. Here we report three new anti-HIV eudesmane-type sesquiterpenes, 5β-Hydroxy-8α-methoxy eudesm-7(11)-en-12,8-olide (1), 5β,8α-Dihydroxy eudesm-7(11)-en-12,8-olide (2) and 5β-Hydroxy-8H-β-eudesm-7(11)-en-12,8-olide (3). These are trivially named ermiasolide A-C and were isolated from the bark of Croton megalocarpus. 5β-Hydroxy-8α-methoxy eudesm-7(11)-en-12,8-olide (1), showed the highest anti-HIV activity by inhibiting 93% of the viral replication with an IC₅₀ = 0.002 µg/mL. On the other hand, 5β-Hydroxy-8H-β-eudesm-7(11)-en-12,8-olide (3) and 5β,8α-dihydroxy eudesm-7(11)-en-12,8-olide (2), inhibited viral replication by 77.5% at IC₅₀ = 0.04 µg/mL and 69.5% at IC₅₀ = 0.002 µg/mL, respectively. Molecular docking studies showed that the proposed mechanism of action leading to these results is through the inhibition of HIV-protease.

Constituents of Croton megalocarpus with Potential Anti-HIV Activity

Reported herein is an anti-HIV monochlorinated compound, 1β-acetoxy-3β-chloro-5α,6α-dihydroxycrotocascarin L (1), of the rare crotofolane diterpenoid class. Compound 1, a suspected artifact of extraction, along with the previously undescribed 11β-acetoxycrotocascarin L (2) and a known compound, crotocascarin K (3), were isolated from the bark of Croton megalocarpus, a Kenyan oil-producing seed crop. Compounds 1 and 3 inhibited HIV-1 replication with IC₅₀ values of 28 and 5.5 nM, respectively. Furthermore, both compounds lacked cytotoxicity toward MT-4 cells and FM-55-M1 cells at concentrations of up to 50 μM. Compounds 1 and 3 were both found to inhibit HIV-1 protease.

Study on South African Indigenous Teas-Antioxidant Potential, Nutritional Content, and Hypoxia-Induced Cyclooxygenase Inhibition on U87 MG Cell Line

Background: This study comparatively assessed seven indigenous traditional tea plants on several attributes that included antioxidant, nutritional, caffeine contents, and cyclooxygenase activity. Methodology: Nutritional content of all tea plants were determined for energy, fat, carbohydrates, total sugars, dietary fiber and amino acids. Antioxidant potential and the antioxidant potentiating secondary metabolites were also measured and compared. Further, we investigated the tea plants for any role they would have on cyclooxygenase (COX) activity on cobalt chloride (CoCl₂) induced human glioma cell lines (U87MG). Results: The tea plants were found non-cytotoxic at concentrations tested against the human Chang liver and HeK 293 kidney cells and were found to be naturally caffeine free. The lowest and highest extraction yield among the tea plants was 7.1% for B. saligna and 15.48% for L. scaberrimma respectively. On average, the flavonol content was 12 to 8 QE/g, ORAC 800 µmol TE/g, TEAC 150 µmol TE/g, FRAP 155 µmol AAE/g, polyphenols 40 mg GAE/g, flavanols 0.35 mg CE/g, flavonols 12 mg QE/g and total flavonoid content (TFC) 180 µg QE/mg. The COX activity has been found to be inhibited by a dose-dependent manner by L. scaberrimma, B. saligna and L. javanica. Conclusion: The results further support competitive value of tea plants and need for improved and further development.

Phylogeny, Phytomedicines, Phytochemistry, Pharmacological Properties, and Toxicity of Croton gratissimus Burch (Euphorbiaceae)

Croton gratissimus is an important plant in Africa setup and across the globe for its ethnomedicinal uses in managing a wide range of diseases. Its phylogeny, pharmacological properties, ethnomedicinal uses, phytochemistry, and cytotoxicity have been highlighted in various articles and journals. This review article aims to give a comprehensively overviewed literature about Croton gratissimus genus. Authentic literature sources such as books, peer reviewed articles, journals, theses, Google Scholar, Science Direct, and any other validated internet source have been used to develop this review. Croton gratissimus is richly found across different climatic zones because of its ability to adapt to various climatic conditions. It is mainly found in rocky hills as a scrub that is about 12–15 m tall. Its leaves are glossy, green on the top, and silvery underneath. Some of the leaves may look brick red rusty. Croton gratissimus has been explored traditionally to manage a number of diseases among the human race since time immemorial. It has been used to treat different ailments ranging from respiratory tract infections, urinary tract infections, malaria, diabetes, hypertension, dermatological conditions, arthritis, gastrointestinal disorders, fever, sexually transmitted diseases, and infertility. Studies have shown that parts of this plant have antioxidative, antimicrobial, anticholinesterases inhibitory, antidiabetic, antihyperlipidemic, anticonvulsant, antiulcer, antihypertensive, antiproliferative, antiplasmodial, and anti-inflammatory activities. Terpenoids and flavonoids have shown to be the major classes of compounds in this plant. Its toxicity has not been well established; some studies have suggested that Croton gratissimus can cause hepatotoxicity and genotoxicity. More studies are needed to elucidate the compounds and their structures giving this plant a wide range of pharmacological activities, efficacy, safety, and toxicity levels, since the plant has greater ethnomedicinal uses. This would give a great indication of discovering new novelties that can give a breakthrough in drug discovery.

Exploring four South African Croton species for potential anti-inflammatory properties: in vitro activity and toxicity risk assessment

ETHNOPHARMACOLOGICAL RELEVANCE

The African Continent harbours approximately 26 Croton species. Many Croton species are used in traditional medicine in southern Africa to treat a variety of ailments including malaria, tuberculosis, microbial infection and inflammation. Considering the high diversity of the genus Croton, the ethnopharmacological information available on southern African species is rather limited. Furthermore, the potential for novel anti-inflammatory drug scaffolds has not previously been investigated.

AIM OF THE STUDY

The aim of the study was to evaluate the potential of four South African Croton species extracts (Croton gratissimus, Croton pseudopulchellus, Croton sylvaticus, and Croton steenkampianus) for anti-inflammatory activity targeting the TLR4 signalling pathway and to assess the potential risk for hepatotoxicity and genotoxicity using an in vitro cellomics approach.

MATERIAL AND METHODS

Leaf extracts of C. gratissimus, C. pseudopulchellus, C. sylvaticus and C. steenkampianus were prepared using methanol and chloroform (1:1, v/v). The anti-inflammatory activity was determined using LPS induced nitric oxide production in RAW 264.7 macrophages, while the hepatotoxicity and genotoxicity was evaluated using multi-parameter end point analysis in C3A and Vero cells, respectively. Mitochondrial membrane potential, mitochondrial mass, oxidative stress, lysosomal content and lipid accumulation were used as markers to assess the risk for hepatotoxicity.

RESULTS

All four species attenuated nitric oxide production with negligible cytotoxicity. However, C. gratissimus yielded the most favorable profile. Cell density was significantly reduced in both C3A and Vero cells with the C. gratissimus extract providing a suitable toxicity profile amenable to further high content analysis. While there was no meaningful effect on mitochondrial dynamics, a strong dose dependent increase in lipid content, paralleled by an expansion of the lysosomal compartment, identifies a potential risk for steatosis. Risk for genotoxicity was investigated using the micronucleus assay which revealed a dose dependent increase in micronuclei formation. Changes in nuclear morphology and cell ploidy further strengthens the associated risk for genotoxicity and suggests the extract from C. gratissimus may function as an aneugen. Collectively, the data demonstrates that although the selected species possess anti-inflammatory components, the risk for possible hepatotoxic and genotoxic side effects may negate their prospect towards further drug development.

A review of biological activities and phytochemistry of six ethnomedicinally important South African Croton species

ETHNOPHARMACOLOGICAL RELEVANCE

The genus Croton (Euphorbiaceae) encompasses 1300 species, which consist of a variety of trees and shrubs distributed across the world. About 26 species are harboured on the African continent. This genus plays an essential role in African folk medicine. Croton species are traditionally used for the treatment of many diverse conditions such as diabetes, malaria, sexually transmitted diseases, cancer, inflammation, fever, digestive problems and fungal infections.

AIM OF THE REVIEW

To provide a comprehensive overview of the ethnobotany, traditional uses, phytochemistry and biological activities of six selected southern Africa Croton species; C.gratissimus Burch., C. megalobotrys Müll.-Arg., C. menyhartii Gȕrke, C. pseudopulchellus Pax, C. steenkampianus Gerstner and C. sylvaticus Schltdl.).

MATERIALS AND METHODS

Various electronic databases, namely Google, Google Scholar, Scopus, ScienceDirect, Biomed Central and Pubmed, were used to search for information related to the traditional uses, chemistry and pharmacology of Croton species. Books were also consulted to collect all pertinent information.

RESULTS AND DISCUSSION

The ethnopharmacology, phytochemistry and biological activities of southern African Croton species are reviewed. The literature revealed that Croton species are trusted traditional medicines for the treatment of microbial infections and malaria. The non-volatile components of Croton species include flavonoids, terpenoids and alkaloids, while the volatile constituents comprise mainly of monoterpenes (α-phellandrene, α-pinene and 1,8-cineole) and sesquiterpenes (caryophyllene oxide). Most of the reported biological activities (anti-oxidant, antimicrobial, anticancer and antimalarial) were based on in vitro assays and were accredited to various extracts. However, both in vitro and in vivo studies, linking the reported activities to specific compounds, are still lacking.

CONCLUSIONS

Croton species are used in traditional medicine to treat a range of ailments, and various in vitro biological activities have been investigated, with some extracts exhibiting good activity that could be considered for further investigation. The in vitro activities obtained seem to justify the use of Croton species in traditional medicine. Data on in vivo studies are scarce and studies usually focused on a single collection. The need to establish a quality control protocols for the standardisation of these herbal drugs is also important.

Ent-clerodane and ent-trachylobane diterpenoids from Croton dictyophlebodes

The stem bark and root bark extracts of Croton dictyophlebodes (Euphorbiaceae) yielded seven undescribed ent-clerodanes: 15,16-epoxy-17,12(S)-olide-ent-cleroda-1,3,13(16),14-tetraen-18-oic acid methyl ester (crotodictyo A), 3β,4β:15,16-diepoxy-ent-cleroda-13(16),14-dien-20-al (crotodictyo B), 3β,4β:15,16-diepoxy-ent-cleroda-13(16),14-dien-19,20-dioic acid (crotodictyo C), 3β,4β:15,16-diepoxy-ent-cleroda-13(16),14-dien-20,19-olide (crotodictyo D), 3β,4β:15,16-diepoxy-20,12(R)-olide ent-cleroda-13(16),14-dien-19-oic acid methyl ester (crotodictyo E), 15,16-epoxy-ent-cleroda-3,13(16),14-trien-12-oxo-18-oic acid (crotodictyo F) and 15,16-epoxy-ent-cleroda-1,3,13(16),14-tetraen-12-oxo-18-oic acid (crotodictyo G), in addition to 15,16-epoxy- ent-cleroda-3,13(16),14-trien-12-oxo-18-oic acid methyl ester (crotodictyo H), reported previously as a synthetic derivative, and acetyl aleuritolic acid. The root extract yielded two ent-trachylobanes, ent-trachylobane-18,19-diol, the undescribed ent-trachylobane-2α,19-diol, along with ent-kaur-16-en-19-oic acid and 2-methoxybenzyl benzoate. Compounds were evaluated against the NCI 60 panel of human tumour cell lines at a single dose of 10^-5 M, but showed no significant activity.

Cytotoxic diterpenoids from the leaves and stem bark of Croton haumanianus (Euphorbiaceae)

The leaf extract of Croton haumanianus J. Léonard (Euphorbiaceae) yielded twenty-six compounds, including eight previously reported ent-kauranes and an ent-labdane and eight undescribed ent-kauranes, ent-16R-kauran-17-al, ent-3β-hydroxy-16R-kauran-17-al, ent-16S,17-epoxykauran-19-ol, ent-16S,17-epoxykauran-3β-ol, ent-17-palmityloxykaurane-3β,16β-diol, ent-17-palmityloxykauran-16β-ol, ent-3α,18-cyclokaurane-16β,17-diol and 19-nor-16α,17-dihydroxy-ent-kaur-4(18)-ene and three undescribed ent-clerodanes, dimethyl ent-15,16-epoxy-6β-hydroxy-1,3,13(16),14-clerodatetraen-20,12S-olide-18,19-dioate (saniolide A), dimethyl ent-15,16-epoxy-6β-hydroxy-1,3,13(16),14-clerodatetraen-20,12R-olide-18,19-dioate (12-epi-saniolide A), methyl ent-15,16-epoxy-1,3,13(16),14-clerodatetraen-18,6R:20,12S-diolide-19-oate (saniolide B). The stem bark extract yielded the ent-clerodane crotocorylifuran, and five undescribed ent-isopimaranes, ent-isopimara-8(14),15-dien-18-al, ent-18-hydroxyisopimara-8(14),15-dien-7-one, ent-isopimara-7,15-dien-18-oic acid, ent-isopimara-7,15-dien-18-ol and ent-isopimara-8,15-dien-7-oxo-18-oic acid. Three compounds, ent-kaurane-3β,16β,17-triol, ent-17-palmityloxykaurane-3β,16β-diol and ent-17-palmityloxykauran-16β-ol, showed selective activity against three of the NCI 60 cancer cell lines, the colon (HCT-116), the melanoma (M14) and the renal (786-0) cancer cell lines at a concentration of 10^-5 M.

HPLC-Based Activity Profiling for Antiprotozoal Compounds in Croton gratissimus and Cuscuta hyalina

In a screening of Sudanese medicinal plants for antiprotozoal activity, the chloroform fractions obtained by liquid-liquid partitioning from ethanolic extracts of fruits of Croton gratissimus var. gratissimus and stems of Cuscuta hyalina Roth ex Schult. exhibited in vitro activity against axenically grown Leishmania donovani amastigotes. This antileishmanial activity was localized by HPLC-based activity profiling. Targeted preparative isolation afforded flavonoids 1–6, 3-methoxy-4-hydroxybenzoic acid (7), and benzyltetrahydroisoquinoline alkaloids laudanine (8) and laudanosine (9) from C. gratissimus, and pinoresinol (10), isorhamnetin (11), (-)-pseudosemiglabrin (12), and kaempferol (13) from C. hyalina. The antiprotozoal activity of 1–13 against L. donovani (axenic and intracellular amastigotes), Trypanosoma brucei rhodesiense (bloodstream forms), and Plasmodium falciparum (erythrocytic stages), and the cytotoxicity in L6 murine myoblast cells were determined in vitro. Quercetin-3,7-dimethylether (6) showed the highest activity against axenic L. donovani (IC_50, 4.5 µM; selectivity index [SI], 12.3), P. falciparum (IC_50, 7.3 µM; SI, 7.6), and T. b. rhodesiense (IC₅₀, 2.4 µM; SI, 23.2). The congener ayanin (2) exhibited moderate antileishmanial (IC₅₀, 8.2 µM; SI, 12.2), antiplasmodial (IC₅₀, 7.8 µM; SI, 12.9), and antitrypanosomal activity (IC₅₀, 11.2 µM; SI, 8.9). None of the compounds showed notable activity against the intramacrophage form of L. donovani.

Ent-abietane and ent-pimarane diterpenoids from Croton mubango (Euphorbiaceae)

Twelve ent-abietane and two ent-pimarane diterpenoids were isolated from the leaves of Croton mubango Müll. Arg. (Euphorbiaceae) collected in the Democratic Republic of the Congo. 2β-Hydroxy-ent-abieta-7,13-dien-3-one, 15-hydroxy-ent-abieta-7,13-dien-3-one, 13α,15-dihydroxy-ent-abieta-8(14)-en-3-one, 2β,9,13-trihydroxy-ent-abieta-7-en-3-one, 2β,7β-dihydroxy-ent-abieta-8,11,13-trien-3-one, 15-hydroxy-ent-abieta-8,11,13-trien-3-one and ent-pimara-8(14),15-dien-3-one and the ent-forms of the previously reported normal series diterpenoids, ent-abieta-8,11,13-trien-3-one, 7β-hydroxy-ent-abieta-8,11,13-trien-3-one, 3α-hydroxy-ent-abieta-8,11,13-triene, 15-hydroxy-ent-abieta-8,11,13-triene and 6β-hydroxy-ent-abieta-8,11,13-triene are reported here for the first time. Structures were established using HRESIMS, FTIR, NMR, DP4+ probability calculations and by comparison of the experimental and calculated electronic circular dichroism (ECD) spectra. Ent-pimara-8(14), 15-dien-3-one, showed antiproliferative activity against melanoma (MALME-3M), renal (UO-31) and ovarian cancer cell lines (IGROV1) at a concentration of 10^-5 M in the NCI 60 screen.

Bioactive terpenoids from Croton laui

Two new highly-oxygenated neo-clerodane diterpenoids, 3S-acetoxyl-mollotucin D dilactone ester (1) and 6S-crotoeurin C (2), and a new lupane-type triterpene, 16β-hydroxyl-3β-O-trans-coumaroyl-betulin (6), as well as three known analogues (3-5) were obtained from the leaves of Croton laui. The structures of the new compounds were determined by extensive spectroscopic methods, and their absolute configurations were determined by combination of single-crystal X-ray diffraction analysis, electronic circular dichroism (ECD) spectra, and literature data. Compounds 2 and 3 exhibited inhibitory activities of lipopolysaccharide (LPS)-induced nitric oxide (NO) production in RAW 264.7 macrophages with IC₅₀ values of 1.2 and 1.6 μM, respectively. Additionally, compound 6 exhibited activity against Col205 and HepG2 cell lines with IC₅₀ values of 12.9 and 17.7 μM, respectively.

Rapid Construction of the Scaffold of Quorumolide A Enabled by a Tandem ROM/RCM Strategy and a Tandem Oxidative Cyclization Strategy

A synthetically challenging framework in the plant-derived cembranoid quorumolide A was established in a seven-step sequence featuring a ring-opening/-closing metathesis cascade reaction to construct the fused butenolide ring and the 14-membered macroring in a single step. The utilization of a tandem oxidative cyclization strategy is the key to build the tetrahydro-2H-pyran moiety.

Supercritical CO2 fluid extraction of croton crassifolius Geisel root: Chemical composition and anti-proliferative, autophagic, apoptosis-inducing, and related molecular effects on A549 tumour cells

BACKGROUND

The use of plant essential oils as pharmaceuticals is a fast-growing market especially in China. Throughout the 20th century, a rapid increase took place in the use of many essential oil-derived products in the medicinal industry as nutraceuticals, medicinal supplements, and pharmaceuticals.

PURPOSE

The objective of this study was to explore the chemical composition of Croton crassifolius essential oil as well as its potential anti-tumour properties and related anti-proliferative, autophagic, and apoptosis-inducing effects.

METHODS

Supercritical CO₂ fluid extraction technology was used to extract CCEO and the chemical constituents of the essential oil were identified by comparing the retention indices and mass spectra data taken from the NIST library with those calculated based on the C7-C40 n-alkanes standard. The cytotoxic activity and anti-proliferative effects of CCEO were evaluated against five cancer cell lines and one normal human cell line via CCK-8 assays. In addition, flow cytometry was used to detect cell cycle arrest. The efficacy of CCEO treatments in controlling cancer cell proliferation was assessed by cell cycle analysis, clonal formation assays, RT-qPCR, and western blot analysis. Autophagic and apoptosis-inducing effects of oils and the associated molecular mechanisms were assessed by flow cytometry, cell staining, reactive oxygen species assays, RT-qPCR, and western blot analysis.

CONCLUSION

Forty compounds representing 92.90% of the total oil were identified in CCEO. The results showed that CCEO exerted a measurable selectivity for cancer cell lines, especially for A549 with the lowest IC₅₀ value of 25.00 ± 1.62 μg/mL. Assessment of the anti-proliferative effects of CCEO on A549 cells showed that the oil inhibited cell proliferation and colony formation in a dose- and time-dependent manner. Investigation of the molecular mechanisms of cell cycle regulation confirmed that the oil arrested A549 cells in G2/M phase by decreasing the expression of cyclin B1-CDK1 and cyclin A-CDK1 and increasing the expression of cyclin-dependent kinase inhibitor (CKI) P21 at both the transcriptional and translational levels. Autophagy staining assays and western blot analysis revealed that CCEO promoted the formation of autophagic vacuoles in A549 cells and increased the expression of autophagy-related proteins beclin-1 and LC3-II in a dose-dependent manner. A series of apoptosis analyses indicated that CCEO induces apoptosis through a mitochondria-mediated intrinsic pathway. This study revealed that CCEO is a promising candidate for development into an anti-tumour drug of the future.

Croton gratissimus leaf extracts inhibit cancer cell growth by inducing caspase 3/7 activation with additional anti-inflammatory and antioxidant activities

BACKGROUND

Croton species (Euphorbiaceae) are distributed in different parts of the world, and are used in traditional medicine to treat various ailments including cancer, inflammation, parasitic infections and oxidative stress related diseases. The present study aimed to evaluate the antioxidant, anti-inflammatory and cytotoxic properties of different extracts from three Croton species.

METHODS

Acetone, ethanol and water leaf extracts from C. gratissimus, C. pseudopulchellus, and C. sylvaticus were tested for their free radical scavenging activity. Anti-inflammatory activity was determined via the nitric oxide (NO) inhibitory assay on lipopolysaccharide (LPS)-stimulated RAW 264.7 macrophages, and the 15-lipoxygenase inhibitory assay using the ferrous oxidation-xylenol orange assay. The cytotoxicity of the extracts was determined on four cancerous cell lines (A549, Caco-2, HeLa, MCF-7), and a non-cancerous African green monkey (Vero) kidney cells using the tetrazolium-based colorimetric (MTT) assay. The potential mechanism of action of the active extracts was explored by quantifying the caspase-3/- 7 activity with the Caspase-Glo® 3/7 assay kit (Promega).

RESULTS

The acetone and ethanol leaf extracts of C. pseudopulchellus and C. sylvaticus were highly cytotoxic to the non-cancerous cells with LC₅₀ varying between 7.86 and 48.19 μg/mL. In contrast, the acetone and ethanol extracts of C. gratissimus were less cytotoxic to non-cancerous cells and more selective with LC₅₀ varying between 152.30 and 462.88 μg/mL, and selectivity index (SI) ranging between 1.56 and 11.64. Regarding the anti-inflammatory activity, the acetone leaf extract of C. pseudopulchellus had the highest NO inhibitory potency with an IC₅₀ of 34.64 μg/mL, while the ethanol leaf extract of the same plant was very active against 15-lipoxygenase with an IC₅₀ of 0.57 μg/mL. A linear correlation (r<0.5) was found between phytochemical contents, antioxidant, anti-inflammatory and cytotoxic activities of active extracts. These extracts induced differentially the activation of caspases - 3 and - 7 enzymes in all the four cancerous cells with the highest induction (1.83-fold change) obtained on HeLa cells with the acetone leaf extract of C. gratissimus.

CONCLUSION

Based on their selective toxicity, good antioxidant and anti-inflammatory activities, the acetone and ethanol leaf extracts of C. gratissimus represent promising alternative sources of compounds against cancer and other oxidative stress related diseases.

Chemical Constituents from Croton Species and Their Biological Activities

The genus Croton belongs to the Euphorbiaceae family, which comprises approximately 1300 species. Many Croton species have been used as folk medicines. This review focuses on the chemical constituents from Croton species and their relevant biological activities, covering the period from 2006 to 2018. A total of 399 new compounds, including 339 diterpenoids, were reported. Diterpenoids are characteristic components of the Croton species. These isolated compounds exhibited a broad spectrum of bioactivities, including cytotoxic, anti-inflammatory, antifungal, acetylcholinesterase inhibitory, and neurite outgrowth-promoting properties. The present review provides a significant clue for further research of the chemical constituents from the Croton species as potential medicines.

Diterpenoids from the roots of Croton dichogamus Pax

Four previously undescribed diterpenoids including two crotofolanes, crotodichogamoin A and B, and two halimanes, crothalimene A and B, a new sesquiterpenoid, and fifteen previously reported compounds, including the crotofolane, crotohaumanoxide, the casbane, depressin, a further seven furanohalimane diterpenoids, three patchoulane and two further cadinane sesquiterpenoids and aleuritolic acid were isolated from the root of Croton dichogamus. Crotodichogamoin B is an important biosynthetic intermediate of the crotofolane class and this is the first report of patchoulene sesquiterpenoids from the genus. Compounds were tested at one concentration, 1 × 10^-5 M, in the NCI59 cell one-dose screen but did not show significant activity snd were also evaluated for their cytotoxicity against Caco-2 cell lines using the neutral red assay. 10-epi-Maninsigin D reduced Caco-2 cell viability at 10, 30 and 100 μM, with values of decreased viability of 28%, 48% and 43% respectively. None of the other tested compounds showed significant activity.

Deheiculatins A-L, 20-oxygenated cembranoids from Macaranga deheiculata

Twelve cembranoids, deheiculatins A-L, were isolated from the leaves and twigs of Macaranga deheiculata. Their structures were elucidated on the basis of spectroscopic data. Five of these compounds displayed moderate inhibitory activity against human and/or mouse 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1). 20-Oxygenated cembranes are rare.

Crassins A-H, Diterpenoids from the Roots of Croton crassifolius

Phytochemical investigation of the 70% acetone extract of Croton crassifolius roots afforded eight new diterpenoids, crassins A-H (1-8), and 19 known compounds. The structures of the new compounds were determined by spectroscopic methods, and their absolute configurations were determined by electronic circular dichroism, single-crystal X-ray diffraction analysis, comparison with literature data, and biogenetic considerations. Crassins A (1) and B (2) are new ring B-rearranged diterpenoids, whereas crassin C (3) is a new ring A-rearranged diterpenoid. Crassin H (8) exhibited selective cytotoxicity against A549 cells (IC₅₀ 5.2 μM) compared with HL-60 cells (IC₅₀ 11.8 μM). The known compound chettaphanin-II exhibited moderate activity against the A549 and HL-60 cell lines (IC₅₀ 8.4 and 10.5 μM, respectively).

Diterpenoids from Croton laui and their cytotoxic and antimicrobial activities

Fourteen new diterpenoids including clerodane (1-12), labdane (13), and norlabdane (14) types, as well as nine known analogues were isolated from the aerial parts of Croton laui. Their structures were established on the basis of spectroscopic analysis, and that of crotonolide H (11) was confirmed by single-crystal X-ray crystallography. Crotonolide A (1) exhibited moderate cytotoxicity against two tumor cell lines, HL-60 (human premyelocytic leukemia, IC50 9.42 μM) and P-388 (murine leukemia, IC50 7.45 μM), and crotonolide G (10) displayed significant antibacterial activity against a panel of Gram-positive bacteria.

The uniqueness and therapeutic value of natural products from West African medicinal plants, part II: terpenoids, geographical distribution and drug discovery

In this review series, an attempt has been made to give indepth coverage of natural products derived from West African medicinal plants with diverse biological activities.

Anti-oxidative and cholinesterase inhibitory effects of leaf extracts and their isolated compounds from two closely related Croton species

A comparative evaluation of the antioxidant and acetylcholinesterase inhibitory activity of the leaf extracts of Croton gratissimus and Croton zambesicus (subgratissimus) and compounds isolated from the extracts was carried out to determine their potential and suitability or otherwise as a substitute for each other in the management of oxidative and neurodegenerative conditions. Different antioxidant assays (DPPH, FRAP, β-carotene-linoleic and the lipid peroxidation models) and the microplate assay for acetylcholinesterase (AChE) inhibition were carried out separately to study the activities of the crude leaf extracts and four solvent fractions from each of the two Croton species. Bioassay guided fractionation was used to target antioxidant constituents of the crude extracts and ethyl acetate fractions of 20% aqueous methanol extract of C. gratissimus on silica gel and Sephadex LH-20 columns resulted in the isolation of kaempferol-3-O-β-6’’(p-coumaroyl) glucopyranoside (tiliroside, 2), apigenin-6-C-glucoside (isovitexin, 3) and kampferol (4). The extract of C. zambesicus yielded quercetin-3-O-β-6’’(p-coumaroyl) glucopyranoside-3’-methyl ether (helichrysoside-3’-methyl ether, 1), kaempferol-3-O-β-6’’(p-coumaroyl) glucopyranoside (tiliroside, 2) and apigenin-6-C-glucoside (isovitexin, 3). Three of the isolated compounds and their different combinations were also included in the bioassays. In all the assays performed, the antioxidant capacity and AChE inhibitory effects of C. zambesicus extracts were weaker than those of C. gratissimus. This suggests that C. gratissimus may not be substituted by C. zambesicus, despite the similarity in some of their constituents. Generally, the combinations made from the isolated compounds showed better activities in most of the assays compared to the individual isolated compounds. This suggests mechanisms such as synergism and/or additive effects to be taking place. This study established low, moderate and high antioxidant activities as well as AChE inhibitory effects by the crude extracts, fractions, compounds and compound combinations. This means some of the extracts, isolated compounds and compound combinations could be useful in the management of neurodegenerative conditions and serve as sources of natural neurodegenerative agents.