Isolation of flavonoids and triterpenoids from the fruits of Alphitonia neocaledonica and evaluation of their anti-oxidant, anti-tyrosinase and cytotoxic activities

A concise update on the synthetic transformation of aurones via asymmetric cycloaddition, annulation, and Michael/Mannich reactions

This review provides a comprehensive overview of the significance of aurone cores in organic chemistry, highlighting their crucial role as synthetic intermediates. With their innate electrophilic reactivity and convenient accessibility, aurone cores play a vital role in catalysing the development of novel methodologies and facilitating the creation of intricate compounds. The objective of this review is to present a current and insightful compilation that summarizes the progress in aurone synthetic transformations, focusing on diverse cycloaddition ([3 + 2], [4 + 2], [4 + 3], [10 + 2]) and annulation reactions.

The Cytotoxic Activity of Dammarane-Type Triterpenoids Isolated from the Stem Bark of Aglaia cucullata (Meliaceae)

The Aglaia genus, a member of the Meliaceae family, is generally recognized to include a number of secondary metabolite compounds with diverse structures and biological activities, including triterpenoids. Among the members of this genus, Aglaia cucullata has been reported to have unique properties and thrives exclusively in mangrove ecosystems. This plant is also known to contain various metabolites, such as flavaglines, bisamides, and diterpenoids, but there are limited reports on the isolation of triterpenoid compounds from its stem bark. Therefore, this research attempted to isolate and elucidate seven triterpenoids belonging to dammarane-type (1-7) from the stem bark of Aglaia cucullata. The isolated compounds included 20S,24S-epoxy-3α,25-dihydroxy-dammarane (1), dammaradienone (2), 20S-hydroxy-dammar-24-en-3-on (3), eichlerianic acid (4), (20S,24RS)-23,24-epoxy-24-methoxy-25,26,27-tris-nor dammar-3-one (5), 3α-acetyl-cabraleahydroxy lactone (6), and 3α-acetyl-20S,24S-epoxy-3α,25-dihydroxydammarane (7). Employing spectroscopic techniques, the chemical structures of the triterpenoids were identified using FTIR, NMR, and HRESITOF-MS. The cytotoxic activity of compounds 1-7 was tested with the PrestoBlue cell viability reagent against MCF-7 breast cancer, B16-F10 melanoma, and CV-1 normal kidney fibroblast cell lines. The results displayed that compound 5 had the highest level of bioactivity compared to the others. Furthermore, the IC₅₀ values obtained were more than 100 μM, indicating the low potential of natural dammarane-type triterpenoids as anticancer agents. These findings provided opportunities for further studies aiming to increase their cytotoxic activities through semi-synthetic methods.

The genus Alphitonia Reissek ex Endl. (Rhamnaceae): A review of its customary uses, phytochemistry and biological activities

ETHNOPHARMACOLOGICAL RELEVANCE

Alphitonia Reissek ex Endl. is a relatively small genus of the family Rhamnaceae. Plants of this genus are found predominantly in the tropical regions of Southeast Asia, Australia and the Pacific, with some species being widely distributed and others endemic to a region. Almost half of the species of the Alphitonia genus have been reported for their customary (traditional and contemporary) medicinal uses. This includes for the treatment of skin conditions, headache, stomachache, inflammation, and body pain such as joint pain and childbirth.

AIM OF THE REVIEW

The aim of this review is to provide the first comprehensive account on the customary uses including ethnomedicinal uses, and phytochemistry and biological activities of the Alphitonia genus, and to identify gaps in current knowledge and scope for future research of plants of this genus.

MATERIALS AND METHODS

Information relevant to the genus Alphitonia was collected by searching the scientific databases (SciFinder, Google Scholar, ACS publications, PubMed, Wiley Online Library and International Plant name Index). Species names were validated using the World Flora Online database (www.worldfloraonline.org).

RESULTS

Eight plants from the Alphitonia genus have been reported to be used as customary medicines, i.e. A. excelsa, A. ferruginea, A. franguloides, A. incana, A. neocaledonica, A. petriei, A. philippinensis and A. zizyphoides. A. excelsa, A. petriei, A. philippinensis and A. zizyphoides, have been shown to have biological activities that align with their customary uses, including antimicrobial, antioxidant and anti-inflammatory activities. Only five Alphitonia species reported for their medicinal customary uses have been explored for their phytochemistry, i.e. A. excelsa, A. neocaledonica, A. petriei, A. philippinensis and A. zizyphoides. Compounds identified from these plants include those that are well known for their medicinal importance. A. macrocarpa, A. whitei and A. xerocarpus have also been examined for their phytochemistry and have been found to have the same or similar bioactive compounds to those found in customarily used Alphitonia species. No biological activities or phytochemistry studies have been reported for the known customarily used medicinal plants A. ferruginea, A. franguloides and A. incana.

CONCLUSIONS

This review highlights the customary uses, biological activities and phytochemistry of plants of the Alphitonia Reissek ex Endl. genus and highlights the significance of the knowledge systems of Indigenous peoples. Of the plants that have been researched for their biological activities and phytochemistry, there is good correlation with these properties and their customary medicinal uses. However, over half of the plants of the Alphitonia genus, including those that are already reported in the public domain for their customary medicinal uses, have had none or limited biological activities or phytochemistry studies conducted. While only eight species of the Alphitonia genus have been reported as customary medicines, other Alphitonia species also possess medicinally important compounds, and it is possible that they are customary medicines but their uses have not been shared publicly by the Indigenous knowledge custodians. There is clearly much scope for further investigation of this genus with regards to their ethnomedicinal uses and therapeutic potential.

Medicinal Plants and Phytochemicals for the Treatment of Pulmonary Hypertension

Background

Pulmonary hypertension (PH) is a progressive disease that is associated with pulmonary arteries remodeling, right ventricle hypertrophy, right ventricular failure and finally death. The present study aims to review the medicinal plants and phytochemicals used for PH treatment in the period of 1994 – 2019.

Methods

PubMed, Cochrane and Scopus were searched based on pulmonary hypertension, plant and phytochemical keywords from August 23, 2019. All articles that matched the study based on title and abstract were collected, non-English, repetitive and review studies were excluded.

Results

Finally 41 studies remained from a total of 1290. The results show that many chemical treatments considered to this disease are ineffective in the long period because they have a controlling role, not a therapeutic one. On the other hand, plants and phytochemicals could be more effective due to their action on many mechanisms that cause the progression of PH.

Conclusion

Studies have shown that herbs and phytochemicals used to treat PH do their effects from six mechanisms. These mechanisms include antiproliferative, antioxidant, antivascular remodeling, anti-inflammatory, vasodilatory and apoptosis inducing actions. According to the present study, many of these medicinal plants and phytochemicals can have effects that are more therapeutic than chemical drugs if used appropriately.

Activity of catechins and their applications

Background

Catechins, which are polyphenol compounds found in many plants and are an important component of tea leaves, are strong anti-oxidants.

Research

Many studies seek to enhance the effects of catechins on the human body and boost their protective power against UV radiation. There are many examples of the positive anti-microbial, anti-viral, anti-inflammatory, anti-allergenic, and anti-cancer effects of catechins. Catechins increase the penetration and absorption of healthy functional foods and bio cosmetics into the body and the skin, thus improving their utility. High value-added anti-oxidant substances have been extracted from food and plant sludge, and experiments have shown that catechins are safe when applied to the human body. The stability of catechins is very important for their absorption into the human body and the effectiveness of their anti-oxidant properties.

Conclusion

Continued research on the strong anti-oxidant effects of catechins is expected to result in many advances in the food, cosmetics, and pharmaceutical industries.

A comprehensive review on tyrosinase inhibitors

Tyrosinase is a multi-copper enzyme which is widely distributed in different organisms and plays an important role in the melanogenesis and enzymatic browning. Therefore, its inhibitors can be attractive in cosmetics and medicinal industries as depigmentation agents and also in food and agriculture industries as antibrowning compounds. For this purpose, many natural, semi-synthetic and synthetic inhibitors have been developed by different screening methods to date. This review has focused on the tyrosinase inhibitors discovered from all sources and biochemically characterised in the last four decades.

DFT Studies on the Antioxidant Activity of Naringenin and Its Derivatives: Effects of the Substituents at C3

The radical scavenging activity of a flavonoid is largely influenced by its structure. The effects of the substituents at C3 position on the antioxidant activity of naringenin were carried out using the density functional theory (DFT) method. The reaction enthalpies related with the three well-established mechanisms were analyzed. Excellent correlations were found between the reaction enthalpies and Hammett sigma constants. Equations obtained from the linear regression can be helpful in the selection of suitable candidates for the synthesis of novel naringenin derivatives with enhanced antioxidant properties. In the gas and benzene phases, the antioxidant activity of naringenin was enhanced by the electron-donating substituents via weakening the bond dissociation enthalpy (BDE). In the water phase, it was strengthened by electron-withdrawing groups—via lowering the proton affinity (PA). The electronic effect of the substituent on the BDE of naringenin is mainly governed by the resonance effect, while that on the ionization potential (IP) and PA of naringenin is mainly controlled by the field/inductive effect.

FPOA induces the apoptosis of HepG2 cells

The triterpenoid 3-acetoxylanosta-8,24-dien-21-oic acid (FPOA) is isolated from the fruiting body of Fomitopsis pinicola. The present study reports that FPOA exerts cytotoxic activity and describes the molecular mechanism of FPOA-induced apoptosis on human HepG2 hepatoma cells. FPOA exhibited significant cytotoxic effects against HepG2, MCF-7 and HeLa cells. However, FPOA was particularly cytotoxic towards HepG2 cells, with a half maximal inhibitory concentration value of 42.10 µM, thus these cells were taken forward for further analysis. Flow cytometry results demonstrated that FPOA significantly increased the apoptotic rate of HepG2 cells in a dose-dependent manner, explaining its potent cytotoxicity. In addition, western blot analysis revealed that FPOA significantly increased the B-cell lymphoma 2 (Bcl-2)-associated X/Bcl-2 ratio, and cytochrome c, caspase-9 and caspase-3 release, in addition to significantly decreasing poly(ADP) ribose polymerase levels. These observations indicate that FPOA induces the apoptosis of HepG2 cells by activating members of the caspase protein family and triggering the mitochondrial apoptosis signaling pathway. Based on these results, FPOA is a potential agent for the treatment of cancer.

Rubiarbonone C inhibits platelet-derived growth factor-induced proliferation and migration of vascular smooth muscle cells through the focal adhesion kinase, MAPK and STAT3 Tyr705 signalling pathways

BACKGROUND AND PURPOSE

The proliferation and migration of vascular smooth muscle cells (VSMCs) induced by platelet-derived growth factor (PDGF) are important steps in cardiovascular diseases, including neointimal lesion formation, myocardial infarction and atherosclerosis. Here, we evaluated the rubiarbonone C-mediated signalling pathways that regulate PDGF-induced VSMC proliferation and migration.

EXPERIMENTAL APPROACH

Cell proliferation and migration were measured in cells treated with rubiarbonone C followed by PDGF BB using the MTT assay, [³ H]-thymidine incorporation, flow cytometry and wound-healing migration assay, MMP gelatin zymography, a fluorescence assay for F-actin. Western blotting of molecules including MAPK, focal adhesion kinase (FAK) and STAT3 and an immunofluorescence assay using anti-PCNA and -STAT3 antibodies were performed to evaluate rubiarbonone C signalling pathway(s). The medial thickness of the carotid artery was evaluated using a mouse carotid ligation model.

KEY RESULTS

Rubiarbonone C inhibited PDGF-induced VSMC proliferation and migration and diminished the ligation-induced increase in medial thickness of the carotid artery. In PDGF-stimulated VSMCs rubiarbonone C decreased the following: (i) levels of cyclin-dependent kinases, cyclins, PCNA and hyperphosphorylated retinoblastoma protein; (ii) levels and activity of MMP2 and MMP9; (iii) activation of MAPK; (iv) F-actin reorganization, by reducing FAK activation; (v) activation of STAT3.

CONCLUSIONS AND IMPLICATIONS

These findings suggest that rubiarbonone C inhibits the proliferation and migration of VSMCs by inhibiting the FAK, MAPK and STAT3 signalling pathways. Therefore, rubiarbonone C could be a good candidate for the treatment of cardiovascular disease.

Triterpenoid saponins and other glycosides from the stems and bark of Jaffrea xerocarpa and their biological activity

Six previously undescribed triterpenoid saponins and two previously undescribed norlupane triterpenes were isolated with five known saponins, three known lupane derivatives, 17,20-didehydro-20-deoxyjujubogenin, rutin, (±) 3α-O-β-d-glucopyranosyl-lyoniresinol, (±) 4-O-β-d-glucopyranosyl-maesopsin, three phenol glycosides, and uridine from the stems and bark of Jaffrea xerocarpa (Baill.) H. C. Hopkins & Pillon (= Basionym Alphitonia xerocarpus Baill.) (Rhamnaceae), an endemic tree of New Caledonia. The chemical structures of the purified compounds were identified by nuclear magnetic resonance and mass spectrometry. The isolated compounds were tested for their antioxidant, antityrosinase, antibacterial and cytotoxic activities. The aqueous methanol extract showed antioxidant activity (DPPH assay) due to the presence of rutin and other phenolic compounds. Three lupane triterpenes showed good cytotoxic activities against KB cells line (IC₅₀ from 7.7 to 8.5 μM). The previously undescribed 2α-formyl-A(1)norlup-20(29)-en-28-oic acid showed antibacterial activity against Staphylococcus aureus and Enterococcus faecalis with both MIC values of 4 μg/mL.

Ferulic Acid and Naturally Occurring Compounds Bearing a Feruloyl Moiety: A Review on Their Structures, Occurrence, and Potential Health Benefits

The ubiquitous compound 4-hydroxy-3-methoxycinnamic acid, also known as ferulic acid (FA), constitutes a bioactive ingredient of many foods that may offer beneficial effects against disorders related to oxidative stress, including cancer, diabetes, and neurodegenerative diseases. This review discusses the antioxidant properties of FA, establishing relationships to several biological activities already described for this natural product. Next, 387 naturally occurring compounds, all isolated from plants and published between 1990 and 2015, the structures of which bear 1 or more feruloyl moieties, are covered in this review along with their structural formulas, botanical sources, and bioactivities. The compounds' distribution, structural patterns, bioactivities, and perspectives on food research are also succinctly discussed.

Bioactive alkaloids from the aerial parts of Houttuynia cordata

ETHNOPHARMACOLOGICAL RELEVANCE

Houttuynia cordata is an important traditional Chinese medicine used in heat-clearing and detoxifying, swelling and discharging pus, promoting diuresis and relieving stranguria which recorded in Pharmacopoeia of the people's Republic of China (2015 Edition). H. cordata has been recorded in the book Bencaogangmu which was written by Shizhen Li for the treatment of pyretic toxicity, carbuncle swelling, haemorrhoids, and rectocele diseases.

AIM OF THE STUDY

Phytochemical investigation of the aerial parts of H. cordata and evaluation of their PTP1B inhibitory activities and hepatoprotective activities.

MATERIALS AND METHODS

The dried aerial parts of H. cordata were fractionated by liquid-liquid extraction to obtain CHCl₃, ethyl acetate, and n-butanolic fractions. The CHCl₃ fraction was confirmed active fraction by the bioactivity-guided investigation, which was isolated and purified by chromatographing over silica gel, Sephadex LH-20, MPLC, and preparative HPLC. The chemical structures of the purified compounds were identified by their spectroscopic data and references.

RESULTS

Eight new compounds (1-8), together with fourteen known compounds (9-22) were isolated from the aerial parts of H. cordata. The known compounds (9-22) were obtained from this plant for the first time. Among them, some compounds exhibited moderate bioactivities.

CONCLUSION

Compounds (1-8) were identified as new alkaloids, and the known alkaloids (9-22) were isolated from this plant for the first time. Compounds 1, 4, 14, and 19 showed significant PTP1B inhibitory activities with IC₅₀ values of 1.254, 2.016, 2.672, and 1.862µm, respectively. Compounds 1, 3, 6, 11, 17, and 20 (10µm) exhibited moderate hepatoprotective activities against D-galactosamine-induced WB-F344 cells damage.

Triterpenoids from the leaves of Alphitonia xerocarpus Baill and their biological activity

Ten previously undescribed triterpenoid saponins and a previously undescribed norlupane triterpenoid were isolated, with three known saponins, four known flavonoids, two known lupane derivatives, sitosterol and 6'-heptadecanoyl-3-O-β-d-glucopyranosylsitosterol from the leaves of Alphitonia xerocarpus (Rhamnaceae), an endemic tree of New Caledonia. The chemical structures of the purified compounds were identified by nuclear magnetic resonance and mass spectrometry. The isolated compounds were tested for their antioxidant, antityrosinase, antibacterial and cytotoxic activity. The aqueous methanol extract showed antioxidant activity (DPPH assay) due to the presence of rutin. Ceanothenic acid showed good cytotoxic activity against a KB cell line (IC50 = 2.6 μM) and antibacterial activity against Staphylococcus aureus and Enterococcus faecalis with MIC values of 8 and 16 μg/mL, respectively. The previously undescribed 29-hydroxyceanothenic acid exhibited moderate cytotoxic activity (IC50 = 10 μM), good antibacterial activity against S. aureus (MIC = 4 μg/mL) and moderate antibacterial activity against E. faecalis (MIC = 16 μg/mL).

Optimization of Extraction Condition of Bee Pollen Using Response Surface Methodology: Correlation between Anti-Melanogenesis, Antioxidant Activity, and Phenolic Content

Bee pollen is flower pollen with nectar and salivary substances of bees and rich in essential components. Bee pollen showed antioxidant and tyrosinase inhibitory activity in our assay system. To maximize the antioxidant and tyrosinase inhibitory activity of bee pollen, extraction conditions, such as extraction solvent, extraction time, and extraction temperature, were optimized using response surface methodology. Regression analysis showed a good fit of this model and yielded the second-order polynomial regression for tyrosinase inhibition and antioxidant activity. Among the extraction variables, extraction solvent greatly affected the activity. The optimal condition was determined as EtOAc concentration in MeOH, 69.6%; temperature, 10.0 °C; and extraction time, 24.2 h, and the tyrosinase inhibitory and antioxidant activity under optimal condition were found to be 57.9% and 49.3%, respectively. Further analysis showed the close correlation between activities and phenolic content, which suggested phenolic compounds are active constituents of bee pollen for tyrosinase inhibition and antioxidant activity. Taken together, these results provide useful information about bee pollen as cosmetic therapeutics to reduce oxidative stress and hyperpigmentation.