The Ethnobotany and Chemistry of South African Meliaceae: A Review

New 19(10 → 9)abeo-euphane-type triterpenoids from Trichilia dregeana leaves and NO production inhibitory activities

Phytochemical investigation of the EtOAc soluble fraction from leaves of Trichilia dregeana Sond. (Meliaceae) afforded naturally rare four new pentacyclic triterpenoids (1-4), together with five known pentacyclic analogs (5-8, and 11) and two steroids (9 and 10). Their structures were elucidated by extensive spectroscopic techniques such as 1D and 2D NMR and HRESIMS data analyses. The absolute configuration of 1 was determined by using the single-crystal X-ray diffraction analysis. The nitric oxide (NO) production inhibitory assay indicated that the EtOAc fraction as well as 4 and 7 inhibited the NO production in lipopolysaccharide (LPS)-stimulated RAW264.7 macrophage cells with the IC50 values of 83.53 μg/mL and 81.31 and 85.71 μM, respectively. Compounds 1-4 are rare 19(10 → 9)abeo-euphane-type triterpenoids bearing a 3,10-ether bridge. To the best of our knowledge, this study is the first isolation of triterpenoids with the 3,10-ether bridge in their skeleton from the genus Trichilia, providing new insights into the chemodiversity of the terpenoids in T. dregeana.

Steroids from the Meliaceae family and their biological activities

Steroids are farnesyl diphosphate-derived triterpene derivatives widely distributed in Meliaceae plants that can have several health benefits due to their biological activities. This literature survey on chemical and pharmacological studies of steroids from the Meliaceae plants indicates that 157 distinct steroids classified into six subclasses including (in decreasing number): pregnane-, stigmastane-, ergostane-, cholestane-, androstane- and ecdysterone-type steroids have been reported from a total of 49 plant species. This review aims to provide a reference document compiling information about the occurrence, chemistry and biological activities of meliaceous steroids for the period from 1988 to July 2023. In particular, generalities about the chemistry of steroids with unusual skeletons and underlying biosynthetic pathways are highlighted. In addition, some structural relationships between different compound types and their biological activities are presented. The information used during the writing of this paper was collected from the online libraries PubMed, Google Scholar and Scifinder using the keywords steroids and Meliaceae with no language restriction. This review points out new avenues for further investigations of steroids from plants of the Meliaceae family.

Insights into the Mechanism of Action of the Degraded Limonoid Prieurianin

Limonoids are extremely diversified in plants, with many categories of products bearing an intact, rearranged or fragmented oxygenated scaffold. A specific subgroup of fragmented or degraded limonoids derives from the tetranortriterpenoid prieurianin, initially isolated from the tree Trichilia prieuriana but also found in other plants of the Meliaceae family, including the more abundant species Aphanamixis polystachya. Prieurianin-type limonoids include about seventy compounds, among which are dregeanin and rohitukin. Prieurianin and analogs exhibit insecticidal, antimicrobial, antiadipogenic and/or antiparasitic properties but their mechanism of action remains ill-defined at present. Previous studies have shown that prieurianin, initially known as endosidin 1, stabilizes the actin cytoskeleton in plant and mammalian cells via the modulation of the architecture and dynamic of the actin network, most likely via interference with actin-binding proteins. A new mechanistic hypothesis is advanced here based on the recent discovery of the targeting of the chaperone protein Hsp47 by the fragmented limonoid fraxinellone. Molecular modeling suggested that prieurianin and, to a lesser extent dregeanin, can form very stable complexes with Hsp47 at the protein-collagen interface. Hsp-binding may account for the insecticidal action of the product. The present review draws up a new mechanistic portrait of prieurianin and provides an overview of the pharmacological properties of this atypical limonoid and its chemical family.

Exploring research trends and priorities of genus Melia

The genus Melia is known for its secondary metabolites and recently, this genus is being explored for its timber. There are vast differences among its species. For instance, Melia azedarach is reported to be invasive and while another species, M. dubia, has diverse utility with complex germination and regeneration characteristics. Researchers globally have been working on various aspects of this genus; In this study, using topic modelling and science mapping approach, we attempted to understand research facets on this genus. The literature corpus of the Web of Science database was explored using a single keyword-"Melia" which yielded 1523 publications (1946-2022) and after scrutiny metadata of 1263 publications were used in the study. Although nine individual species were cited in the publications, only three species are accepted viz., M. dubia, M. azedarach, and M. volkensii. This implies taxonomic uncertainty, with potential confusion in assigning scientific findings to particular species. Thus, a taxonomic relook on this genus is warranted for a better assessment of the economic utility in many countries. More importantly, our results indicate that the research interests have recently shifted from the secondary metabolite constituents towards growth, biomass, wood properties, germination, plantation, and green synthesis. The shift in research focus toward wood properties of Melia sp. can impact the wood demand-supply at a global scale owing to its fast growth and the possibility of cultivation over a wider geographical range.

Phytoconstituents from Turraea obtusifolia and their antiplasmodial activity

Three new steroids, turranin M, N and O (1-3), together with four known limonoids, nymania 1 (4), rubralin B (5), aphapolynin C (6) and Trichillia substance Tr B (7), were isolated from the leaves of Turraea obtusifolia. Their chemical structures were elucidated using NMR and MS. Rubralin B (5) displayed good activity against the asexual parasites from the drug sensitive Plasmodium falciparum NF54 strain with an IC50 value of 3.47 µg/mL (4.57 µM), nymania 1 (4) showed a weak activity (IC50 13.36 µg/mL (19.40 µM)) and the rest of compounds had IC50 > 20 µg/mL.

Sesquiterpenoids from Meliaceae Family and Their Biological Activities

Sesquiterpenoids, an important class of natural products possessing three isoprene-derived units, are widely distributed across plants and have a variety of biological activities. All sesquiterpenoids are derived from farnesyl pyrophosphate (FPP), a biosynthesis precursor that can form various carbon skeletons. In order to provide a reference for further research and development of these compounds, this review focused on the increasing number of isolated and volatile sesquiterpenoids found to be produced by plants of the Meliaceae family between 1968 and 2023. The related articles were collected from SciFinder, Google Scholar, and PubMed. According to a literature review, several studies were started for more than 55 years on the plant's stem barks, twigs, leaves, flowers, seeds, and pericarps, where approximately 413 sesquiterpenoid compounds from several groups such as eudesmane, aromadendrane, cadinane, guaiane, bisabolane, furanoeremophilane, humulene, germacrane, and oppositane-type were isolated and identified with some minor products. Additionally, the hypothetical route of sesquiterpenoids biosynthesis from this family was identified, and eudesmane-type was reported to be 27% of the total compounds. The antimicrobial, antidiabetic, antioxidant, antiplasmodial, antiviral, and cytotoxic activities of the isolated compounds and major volatile sesquiterpenoids constituent on essential oil were also evaluated. The result showed the fundamental of using the sesquiterpenoid compounds from the Meliaceae family in traditional medicine and the discovery of new drugs.

The traditional use of Southern African medicinal plants to alleviate fever and their antipyretic activities

ETHNOPHARMACOLOGICAL RELEVANCE

Multiple plant species are used traditionally in southern Africa to treat fever. This review summarises the traditional use, highlights promising plant species and focuses on validation studies to highlight future areas of research.

AIM OF THE STUDY

This study aimed to critically review the use of southern African plants to alleviate fever. Additionally, an examination of research into those plants was undertaken to highlight gaps in the literature with the aim of stimulating further research in this field.

MATERIALS AND METHODS

Ethnobotanical books, reviews and primary research studies were searched to identify plant species traditionally used to treat fever in southern Africa and to summarise the current knowledge and identify areas requiring further research. This study was non-biased and did not have any taxonomic preferences, nor did it favour any southern African healing systems over the others.

RESULTS

The traditional therapeutic uses of 203 southern African plant species to alleviate fever were recorded. Leaves and roots/bulbs/rhizomes were the most commonly used plant part, and they were most commonly prepared as decoctions or infusions and consumed orally. Notably, only twenty-two species (∼11% of the identified species) have been scientifically evaluated for antipyretic properties, with substantially fewer mechanistic studies evident.

CONCLUSIONS

Despite the availability of ethnobotanical records, the antipyretic properties of southern African medicinal plants are poorly reported. Indeed, the efficacy of most plants is yet to be verified and very few mechanistic studies are available.

Evaluation of Wound Healing and Anti-Inflammatory Activities of 80% Methanol Crude Extract and Solvent Fractions of Trichilia dregeana Sond (Meliaceae) Leaves in Mice

Introduction

The leaves of Trichilia dregeana Sond are traditionally used to treat wounds. Even though there have been in vitro studies and claims supporting wound healing, there are no scientific data on in vivo wound healing and anti-inflammatory activities of the leaves of T. dregeana.

Objective

This study aimed to evaluate wound healing and anti-inflammatory activity of 80% methanol crude extract and solvent fractions of T. dregeana in mice.

Method

The leaves of T. dregeana were dried, ground, and macerated with 80% methanol three times successively. The crude extract was fractioned by water, ethyl acetate, and hexane separately. The acute dermal and oral toxicity tests were done by applying 2000 mg/kg of 10% (w/w) crude extract ointment (CEO) topically and 2000 mg/kg of crude extract orally, respectively. The wound healing activity of the crude extract was evaluated on excision, incision, and burn wound models while the fractions were evaluated only on excision wound model. The anti-inflammatory activity of the crude extract was evaluated on xylene-induced ear edema and cotton pellet granuloma tests.

Result

Both acute dermal and oral toxicity tests were found to be safe after topical application of 2000 mg/kg of 10% (w/w) CEO and oral administration of 2000 mg/kg of crude extract suspension, respectively. Both 5% and 10% (w/w) CEO produced significant (p < 0.001) wound contraction and period of epithelialization from day 4 onwards as compared to simple ointment (SO) on both excision and burn wounds. The tensile strength was increased significantly (p < 0.001) for the CEO-treated mice as compared to both untreated and SO groups. The crude extract also showed anti-inflammatory activity at 100, 200, and 400 mg/kg by inhibiting ear edema, exudate, and granuloma formation as compared to the SO group.

Conclusion

The increase in wound contraction, reduction in period of epithelialization, and increase in tensile strength support the traditional claims of T. dregeana for wound healing.

Research progress of meliaceous limonoids from 2011 to 2021

Covering: July 2010 to December 2021Limonoids, a kind of natural tetranortriterpenoids with diverse skeletons and valuable insecticidal and medicinal bioactivities, are the characteristic metabolites of most plants of the Meliaceae family. The chemistry and bioactivities of meliaceous limonoids are a continuing hot area of natural products research; to date, about 2700 meliaceous limonoids have been identified. In particular, more than 1600, including thirty kinds of novel rearranged skeletons, have been isolated and identified in the past decade due to their wide distribution and abundant content in Meliaceae plants and active biosynthetic pathways. In addition to the discovery of new structures, many positive medicinal bioactivities of meliaceous limonoids have been investigated, and extensive achievements regarding the chemical and biological synthesis have been made. This review summarizes the recent research progress in the discovery of new structures, medicinal and agricultural bioactivities, and chem/biosynthesis of limonoids from the plants of the Meliaceae family during the past decade, with an emphasis on the discovery of limonoids with novel skeletons, the medicinal bioactivities and mechanisms, and chemical synthesis. The structures, origins, and bioactivities of other new limonoids were provided as ESI. Studies published from July 2010 to December 2021 are reviewed, and 482 references are cited.