Meliaceous Limonoids: Chemistry and Biological Activities

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.

Limonoids from the fruits of Chisocheton erythrocarpus and their mosquito larvicidal activities

Phytochemical study of the fruits of Chisocheton erythrocarpus (Hiern) allowed the identification of eight undescribed limonoids, namely erythrocarpines O - V (1-6, 7a and 7b), along with seven known compounds. The structures of these compounds were elucidated based on spectroscopic and HRMS data, along with electronic circular dichroism to configure the absolute configuration. Erythrocarpines O and P are γ-hydroxybutenolide analogs of mexicanolide-type limonoids while erythrocarpine Q - V are phragmalin-type limonoids possessing a 1,29-oxymethylene bridge with either benzoyl or cinnamoyl moiety in their structures. Mosquito larvicidal activity revealed that crude DCM extract of C. erythrocarpus possessed a good larvicidal effect against Aedes aegypti larvae in 48 h (LC50 = 153.0 ppm). Subsequent larvicidal activity of isolated compounds indicated that erythrocarpine G (10) and 14-deoxyxyloccensin K (11) were responsible for the enhanced larvicidal effect of the extract, reporting LC50 values of 18.55 ppm and 41.16 ppm, respectively. Moreover, residual activity testing of the crude DCM extract revealed that the duration of its larvicidal effects is up to 14 days, where it maintained a 98 % larval mortality throughout the test period, under laboratory conditions.

Computational Binding Study Hints at Ecdysone 20-Mono-Oxygenase as the Hitherto Unknown Target for Ring C-Seco Limonoid-Type Insecticides

The insecticidal property of ring C-seco limonoids has been discovered empirically and the target protein identified, but, to date, the molecular mechanism of action has not been described at the atomic scale. We elucidate on computational grounds whether nine C-seco limonoids present sufficiently high affinity to bind specifically with the putative target enzyme of the insects (ecdysone 20-monooxygenase). To this end, 3D models of ligands and the receptor target were generated and their interaction energies estimated by docking simulations. As a proof of concept, the tetrahydro-isoquinolinyl propenamide derivative QHC is the reference ligand bound to aldosterone synthase in the complex with PDB entry 4ZGX. It served as the 3D template for target modeling via homology. QHC was successfully docked back to its crystal pose in a one-digit nanomolar range. The reported experimental binding affinities span over the nanomolar to lower micromolar range. All nine limonoids were found with strong affinities in the range of -9 < ΔG < -13 kcal/mol. The molt hormone ecdysone showed a comparable ΔG energy of -12 kcal/mol, whereas -11 kcal/mol was the back docking result for the liganded crystal 4ZGX. In conclusion, the nine C-seco limonoids were strong binders on theoretical grounds in an activity range between a ten-fold lower to a ten-fold higher concentration level than insecticide ecdysone with its known target receptor. The comparable or even stronger binding hints at ecdysone 20-monooxygenase as their target biomolecule. Our assumption, however, is in need of future experimental confirmation before conclusions with certainty can be drawn about the true molecular mechanism of action for the C-seco limonoids under scrutiny.

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.

Swieteliacates S-U, phragmalin limonoids, from the leaves of Swietenia macrophylla

Three novel phragmalin-type limonoids, swieteliacates S-U (1-3), were isolated from Swietenia macrophylla leaves, alongside four previously identified limonoids (4-7). The structures, encompassing absolute configurations, were delineated through 1D and 2D NMR analyses, high-resolution mass spectrometry (HR-MS), and NMR and ECD calculations. Swieteliacate S (1) is a distinctive cryptate comprising a tricyclo[4.2.110,30.11,4]decane fragment and an additional five-membered oxygen ring. Compounds 3 and 5 exhibited inhibition rates of 26.08 ± 2.26% and 15.42 ± 3.66%, respectively, on triglyceride (TG) production in Hep G2 cells at 40 μM.

Erythrocarpines IN, new limonoids from the barks of Chisocheton erythrocarpus and their neuroprotective effects against hydrogen peroxide in NG108-15 cells

A phytochemical study on the bark of Chisocheton erythrocarpus Hiern (Meliaceae) has led to the isolation of six new phragmalin-type limonoids named erythrocarpines I - N (1-6) along with one known limonoid, erythrocarpine F (7). Their structures were fully characterized by spectroscopic methods. The pre-treatment of NG108-15 cells with 1-5, 7 (2 h) demonstrated low to good protective effects against H2O2 exposure; 1 (83.77% ± 1.84 at 12.5 μM), 2 (69.07 ± 2.01 at 12.5 μM), 3 (80.38 ± 2.1 at 12.5 μM), 4 (62.33 ± 1.95 at 25 μM),5 (58.67 ± 1.85 at 50 μM) and 7 (66.07 ± 2.03 at 12.5 μM). Interestingly, 1 and 3 demonstrated comparable protective effects to positive control epigallocatechin gallate (EGCG) with similar cell viability capacity (≈ 80%), having achieved that at lower concentration (12.5 μM) than EGCG (50 μM). Collectively, the results suggested the promising use of 1 and 3 as potential neuroprotective agents against hydrogen peroxide-induced cytotoxicity in neuronal model.

Limonoids from neem (Azadirachta indica A. Juss.) are potential anticancer drug candidates

Neem (Azadirachta indica A. Juss.), a versatile evergreen tree recognized for its ethnopharmacological value, is a rich source of limonoids of the triterpenoid class, endowed with potent medicinal properties. Extracts of neem have been documented to display anticancer effects in diverse malignant cell lines as well as in preclinical animal models that has largely been attributed to the constituent limonoids. Of late, neem limonoids have become the cynosure of research attention as potential candidate agents for cancer prevention and therapy. Among the various limonoids found in neem, azadirachtin, epoxyazadiradione, gedunin, and nimbolide, have been extensively investigated for anticancer activity. Azadirachtin, a potent biodegradable pesticide, exhibits profound antiproliferative effects by preventing mitotic spindle formation and cell division. The antiproliferative activity of gedunin has been demonstrated to be mediated primarily via inhibition of heat shock protein90 and its client proteins. Epoxyazadiradione inhibits pro-inflammatory and kinase-driven signaling pathways to block tumorigenesis. Nimbolide, the most potent cytotoxic neem limonoid, inhibits the growth of cancer cells by regulating the phosphorylation of keystone kinases that drive oncogenic signaling besides modulating the epigenome. There is overwhelming evidence to indicate that neem limonoids exert anticancer effects by preventing the acquisition of hallmark traits of cancer, such as cell proliferation, apoptosis evasion, inflammation, invasion, angiogenesis, and drug resistance. Neem limonoids are value additions to the armamentarium of natural compounds that target aberrant oncogenic signaling to inhibit cancer development and progression.

Progress Toward the Asymmetric De Novo Synthesis of Limonoids

Asymmetric de novo construction of limonoids remains a challenging problem in stereoselective synthesis due to the diverse and complex structures associated with this class of natural products. Here, a unique synthetic pathway to an "intact" limonoid system is described. The synthetic route is based on exploiting an oxidative rearrangement reaction of a densely functionalized late-stage intermediate to simultaneously establish the stereodefined C10 quaternary center and an allylic acetate at C12. This is a unique example of a complex rearrangement reaction that proceeds on a system whose presumed intermediate allyl cation is highly hindered and lacks neighboring protons that are otherwise required for cation termination.

Limonoids from the roots of Melia azedarach and their anti-inflammatory activity

Twelve undescribed limonoids, meliazedarines J-U (1-12), along with a known one, were isolated from the roots of Melia azedarach. Their structures were elucidated by extensive spectroscopic investigations, X-ray diffraction analyses, and ECD calculations. Compounds 1-8 were identified as ring intact limonoids, while compounds 9-12 were established as ring C-seco ones. The anti-inflammatory potential of compounds 1-4, 6, 8, 9, and 11-13 was evaluated on macrophages. Compounds 1, 3, 4, 6, and 9 significantly suppressed nitric oxide production in lipopolysaccharide (LPS)-induced RAW 264.7 macrophages, among them compound 3 showed the best inhibitory effect with an IC50 value of 7.07 ± 0.48 μΜ. Furthermore, compound 3 effectively reduced interleukin-1β secretion in LPS plus nigericin-induced THP-1 macrophages by inhibiting NLRP3 inflammasome activation. The results strongly suggested that limonoids from the roots of M. azedarach might be candidates for treating inflammation-related diseases.

Molecular Docking of Nimbolide Extracted from Leaves of Azadirachta indica with Protein Targets to Confirm the Antifungal, Antibacterial and Insecticidal Activity

Nimbolide, a tetranortriterpenoid (limonoid) compound isolated from the leaves of Azadirachta indica, was screened both in vitro and in silico for its antimicrobial activity against Fusarium oxysporum f. sp. cubense, Macrophomina phaseolina, Pythium aphanidermatum, Xanthomonas oryzae pv. oryzae, and insecticidal activity against Plutella xylostella. Nimbolide exhibited a concentration-dependent, broad spectrum of antimicrobial and insecticidal activity. P. aphanidermatum (82.77%) was more highly inhibited than F. oxysporum f. sp. cubense (64.46%) and M. phaseolina (43.33%). The bacterium X. oryzae pv. oryzae forms an inhibition zone of about 20.20 mm, and P. xylostella showed about 66.66% mortality against nimbolide. The affinity of nimbolide for different protein targets in bacteria, fungi, and insects was validated by in silico approaches. The 3D structure of chosen protein molecules was built by homology modelling in the SWISS-MODEL server, and molecular docking was performed with the SwissDock server. Docking of homology-modelled protein structures shows most of the chosen target proteins have a higher affinity for the furan ring of nimbolide. Additionally, the stability of the best-docked protein-ligand complex was confirmed using molecular dynamic simulation. Thus, the present in vitro and in silico studies confirm the bioactivity of nimbolide and provide a strong basis for the formulation of nimbolide-based biological pesticides.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12088-023-01104-6.

Triterpenoids from the fruits of Aphanamixis polystachya and their inhibitory activities on nitric oxide production

Nineteen triterpenoids, including five previously unknown (four triucallane-type derivatives and one highly oxidized A, B-seco limonoids), together with fourteen known triterpenoids, were isolated from the fruits of Aphanamixis polystachya. Their structures were elucidated by extensive spectroscopic analysis. All isolates were evaluated their anti-inflammatory activities. The result showed that all compounds inhibit LPS-induced nitric oxide production in RAW264.7 macrophages with their IC50 value ranging from 95 to 1332 uM, and compound 6 exhibited obvious anti-inflammatory activity comparable to that of the positive control, with IC50 values of 94.96 uM.

Azadiradione, a Component of Neem Oil, Behaves as a Superoxide Dismutase Mimic When Scavenging the Superoxide Radical, as Shown Using DFT and Hydrodynamic Voltammetry

The neem tree, Azadirachta indica, belongs to the Meliaceae family, and its use in the treatment of medical disorders from ancient times to the present in the traditional medical practices of Asia, Africa and the Middle East is well-documented. Neem oil, extracted from the seeds of the fruit, is widely used, with promising medicinal benefits. Azadiradione, a principal antioxidant component of the seeds of A. indica, is known to reduce oxidative stress and has anti-inflammatory effects. To directly measure the antioxidant ability of neem oil, we used Rotating Ring Disk Electrode (RRDE) hydrodynamic voltammetry to quantify how it can scavenge superoxide radical anions. The results of these experiments show that neem oil is approximately 26 times stronger than other natural products, such as olive oil, propolis and black seed oil, which were previously measured using this method. Next, computational Density Functional Theory (DFT) methods were used to arrive at a mechanism for the scavenging of superoxide radical anions with azadiradione. Our work indicates that azadiradione is an effective antioxidant and, according to our DFT study, its scavenging of the superoxide radical anion occurs through a reaction mechanism in which azadiradione mimics the antioxidant action of superoxide dismutase (SOD). In this mechanism, analogous to the SOD enzymatic reaction, azadiradione is regenerated, along with the production of two products: hydrogen peroxide and molecular oxygen. This antioxidant process provides an explanation for azadiradione's more general and protective biochemical effects.

Putative Identification of New Phragmaline-Type Limonoids from the Leaves of Swietenia macrophylla King: A Case Study Using Mass Spectrometry-Based Molecular Networking

Swietenia macrophylla King is a plant commonly known as Brazilian mahogany. The wood from its stem is highly prized for its exceptional quality, while its leaves are valued for their high content of phragmalin-type limonoids, a subclass of compounds known for their significant biological activities, including antimalarial, antitumor, antiviral, and anti-inflammatory properties. In this context, twelve isolated limonoids from S. macrophylla leaves were employed as standards in mass spectrometry-based molecular networking to unveil new potential mass spectrometry signatures for phragmalin-type limonoids. Consequently, ultra-performance liquid chromatography coupled with high-resolution mass spectrometry was utilized for data acquisition. Subsequently, the obtained data were analyzed using the Global Natural Products Social Molecular Networking platform based on spectral similarity. In summary, this study identified 24 new putative phragmalin-type limonoids for the first time in S. macrophylla. These compounds may prove valuable in guiding future drug development efforts, leveraging the already established biological activities associated with limonoids.

An overview of limonoid synthetic derivatives as promising bioactive molecules

Limonoids, a class of abundant natural tetracyclic triterpenoids, present diverse biological activity and provide a versatile platform amenable by chemical modifications for clinical use. Among all of the limonoids isolated from natural sources, obacunone, nomilin, and limonin are the primary hub of limonoid-based chemical modification research. To date, more than 800 limonoids analogs have been synthesized, some of which possess promising biological activities. This review not only discusses the synthesis of limonoid derivatives as promising therapeutic candidates and details the pharmacological studies of their underlying mechanisms from 2002 to 2022, but also proposes a preliminary limonoid synthetic structure-activity relationship (SAR) and provides future direction of limonoid derivatization research.

Medicinal plants of the upper Aswa River catchment of northern Uganda - a cultural crossroads

BACKGROUND

This paper presents a comparative inventory of medicinal plant taxa and their uses by smallholder farming communities of four cultures in the Aswa River catchment of northern Uganda, situated in the eastern Sudanian savanna parkland ecotype of sub-Saharan Africa. The purpose of the study was to document the ethnobotanical use of medicinal plants by the Lango, Acholi, Teso (Atesot) and Ethur (jo Abwor), in an historical moment before civil conflict and mass displacement of the respondent communities disrupted the inter-generational transmission of traditional technical knowledge within the study area.

METHODS

Following community consultations in four districts of northern Uganda during 1999-2000, interviews were conducted with holders of specialist knowledge on plants used as medicine on basis of a plant specimen allocated a voucher number and identified by the national herbarium. Use reports reflecting specific medicinal applications were compiled in aggregate to obtain a Relative Importance Index ranking. The commonality of medicinal taxa cited between each cultural interface was assessed by the Jaccard Index of Similarity, and the similarity of specific medicinal usage by taxon using Rahman's Similarity Index.

RESULTS

The data collected from 112 respondents comprise 280 medicinal use reports describing 263 applications for 62 medical conditions, citing 108 taxa from 44 botanical families of which Fabaceae comprised 20% of all use reports. No earlier mention could be found to corroborate 72 use reports (27% of the total), representing medicinal indications as yet undocumented, and potentially worthy of investigation. The RI values ranged between 15 and 94%, with 13 taxa having RI values above 50%. The JI ratios indicate the highest degree of similarity in the plant taxa used as medicine (21%) between the Lango and Teso cultures who share a common origin; however, Rahman's Similarity Index indicates the highest similarity of specific medicinal usage by taxon between the Lango and Acholi, who share a common language group through cultural assimilation over time.

CONCLUSIONS

As a comparative study, the results imply that cultural exchange and assimilation may be a greater driver of inter-cultural similarity of ethnopharmacological use of a given taxon, as compared to shared historical origins.

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.

Chukrasia tabularis limonoid plays anti-inflammatory role by regulating NF-κB signaling pathway in lipopolysaccharide-induced macrophages

Background

Chukrasia tabularisis, a well-known tropical tree native to southeastern China, has anti-inflammatory and antioxidant activities, and contains large amounts of limonoids and triterpenoids.

Objective

The aim of this study was to investigate the potential anti-inflammatory activity of limonoids from C. tabularis on lipopolysaccharide (LPS)-mediated RAW264.7 cells.

Methods and results

Using a bioassay-guided approach, the chemical fraction with high anti-inflammatory activity was found and its chemical constituents were investigated. Phytochemical studies on active extracts resulted in the separation of three novel phragmalin limonoids (1-3), together with two known limonoids (4-5) and 11 tirucallane triterpenes (6-16). The activity of these isolated compounds in the production of nitric oxide (NO) on LPS-reated macrophages was evaluated. Limonoid 2 indicated significant anti-inflammatory activities with IC50 value of 4.58 μM. Limonoid 2 notably inhibited the production of NO, interleukin- 6 and tumor necrosis factor-α on macrophage. Signal transduction and activation of STAT and NF-κB activators were effectively blocked by limonoid 2.

Conclusions

These results indicate that limonoid 2 has an anti-inflammatory effect by the inhibiting JAK2/STAT3, iNOS/eNOS, and NF-κB signaling pathways and regulating inflammatory mediators.

Phragmalin-Type Limonoids from the Fruits of Chukrasia tabularis and Their Anti-Inflammatory Activity

Phytochemical investigation on the fruits of C. tabularis led to the isolation of five new phragmalin-type limonoids (1-5) and four known ones (6-9). The structures of the new compounds 1-5, named chuktabamalins A-E, were elucidated via spectroscopic techniques (HRESIMS, 1D and 2D NMR) and were comparable with the literature data of known compounds. In addition, new compounds were evaluated for in vitro anti-inflammatory activity. Compounds 1, 2, 3 and 5 showed moderate anti-inflammatory activity with IC₅₀ values of 21.72 ± 2.79, 23.29 ± 1.00, 47.08 ± 3.47 and 66.67 ± 2.89 μM, respectively.

The anti-melanogenic properties of Swietenia macrophylla king

Fair flawless skin is the goal for some cultures and the development of irregular skin pigmentation is considered an indication of premature skin aging. Hence, there is a rising demand for skin whitening cosmetics. Thus, this research will be focusing on discovering the anti-pigmentation properties of Swietenia macrophylla seeds. Firstly, the seeds were extracted with ethanol and further fractionate based on their polarity before testing them on zebrafish embryos. The ethanolic extract of the seed demonstrated significant inhibition of both tyrosinase activity and melanin production in the embryos. However, after fractionation, the anti-melanogenic ability was observed to have decreased, signifying that the phytocompounds may be synergistic in nature. Still in the proteomic studies the ethanolic extract and its hexane fraction both induced the downregulation of cathepsin LB and cytoskeletal proteins that have connections to the melanogenic pathway, confirming that S. macrophylla seeds do indeed have anti-pigmentation properties that can be exploited for cosmetic use. Next, limonoids (tetranortriterpenoids found in the seed) were tested for their inhibitory effect against human tyrosinase related protein 1 (TYRP-1) via molecular docking. It was found that limonoids have a stronger binding affinity to TYRP-1 than kojic acid, suggesting that these phytocompounds may have the potential in inhibiting pigmentation. However, this still needs further confirmation before these phytocompounds can be developed into a skin whitening agent. Other assays like ex-vivo or 3D human skin culture can also be used to better study the seeds anti-pigmentation effect on humans.

Post-Cyclization Skeletal Rearrangements in Plant Triterpenoid Biosynthesis by a Pair of Branchpoint Isomerases

Triterpenoids possess potent biological activities, but their polycyclic skeletons are challenging to synthesize. The skeletal diversity of triterpenoids in plants is generated by oxidosqualene cyclases based on epoxide-triggered cationic rearrangement cascades. Normally, triterpenoid skeletons then remain unaltered during subsequent tailoring steps. In contrast, the highly modified triterpenoids found in Sapindales plants imply the existence of post-cyclization skeletal rearrangement enzymes that have not yet been found. We report here a biosynthetic pathway in Sapindales plants for the modification of already cyclized tirucallane triterpenoids, controlling the pathway bifurcation between different plant triterpenoid classes. Using a combination of bioinformatics, heterologous expression in plants and chemical analyses, we identified a cytochrome P450 monooxygenase and two isomerases which harness the epoxidation-rearrangement biosynthetic logic of triterpene cyclizations for modifying the tirucallane scaffold. The two isomerases share the same epoxide substrate made by the cytochrome P450 monooxygenase CYP88A154, but generate two different rearrangement products, one containing a cyclopropane ring. Our findings reveal a process for skeletal rearrangements of triterpenoids in nature that expands their scaffold diversity after the initial cyclization. In addition, the enzymes described here are crucial for the biotechnological production of limonoid, quassinoid, apoprotolimonoid, and glabretane triterpenoids.

Meliaceae genomes provide insights into wood development and limonoids biosynthesis

Meliaceae is a useful plant family owing to its high-quality timber and its many limonoids that have pharmacological and biological activities. Although some genomes of Meliaceae species have been reported, many questions regarding their unique family features, namely wood quality and natural products, have not been answered. In this study, we provide the whole-genome sequence of Melia azedarach comprising 237.16 Mb with a contig N50 of 8.07 Mb, and an improved genome sequence of Azadirachta indica comprising 223.66 Mb with a contig N50 of 8.91 Mb. Moreover, genome skimming data, transcriptomes and other published genomes were comprehensively analysed to determine the genes and proteins that produce superior wood and valuable limonoids. Phylogenetic analysis of chloroplast genomes, single-copy gene families and single-nucleotide polymorphisms revealed that Meliaceae should be classified into two subfamilies: Cedreloideae and Melioideae. Although the Meliaceae species did not undergo additional whole-genome duplication events, the secondary wall biosynthetic genes of the woody Cedreloideae species, Toona sinensis, expanded significantly compared to those of A. indica and M. azedarach, especially in downstream transcription factors and cellulose/hemicellulose biosynthesis-related genes. Moreover, expanded special oxidosqualene cyclase catalogues can help diversify Sapindales skeletons, and the clustered genes that regulate terpene chain elongation, cyclization and modification would support their roles in limonoid biosynthesis. The expanded clans of terpene synthase, O-methyltransferase and cytochrome P450, which are mainly derived from tandem duplication, are responsible for the different limonoid classes among the species. These results are beneficial for further investigations of wood development and limonoid biosynthesis.

LC-MS Analysis, Computational Investigation, and Antimalarial Studies of Azadirachta indica Fruit

Malaria is a deadly disease that continues to pose a threat to children and maternal well-being. This study was designed to identify the chemical constituents in the ethanolic fruit extract of Azadirachta indica, elucidate the pharmacological potentials of identified phytochemicals through the density functional theory method and carry out the antimalarial activity of extract using chemosuppression and curative models. The liquid chromatography-mass spectrometry (LC-MS) analysis of the ethanolic extract was carried out, followed by the density functional theory studies of the identified phytochemicals using B3LYP and 6-31G (d, p) basis set. The antimalarial assays were performed using the chemosuppression (4 days) and curative models. The LC-MS fingerprint of the extract led to the identification of desacetylnimbinolide, nimbidiol, O-methylazadironolide, nimbidic acid, and desfurano-6α-hydroxyazadiradione. Also, the frontier molecular orbital properties, molecular electrostatic potential, and dipole moment studies revealed the identified phytochemicals as possible antimalarial agents. The ethanolic extract of A indica fruit gave 83% suppression at 800 mg/kg, while 84% parasitaemia clearance was obtained in the curative study. The study provided information about the phytochemicals and background pharmacological evidences of the antimalarial ethnomedicinal claim of A indica fruit. Thus, isolation and structure elucidation of the identified phytochemicals from the active ethanolic extract and extensive antimalarial studies towards the discovery of new therapeutic agents is recommended for further studies.

Five new limonoids isolated from Walsura robusta

Five new toosendanin limonoids with highly oxidative furan ring walsurobustones A-D (1-4), and one new furan ring degraded limonoid walsurobustone E (5) together with one known compound toonapubesic acid B (6) were isolated from the leaves of Walsura robusta. Their structures were elucidated by NMR and MS data. Especially, the absolute configuration of toonapubesic acid B (6) was confirmed by X-ray diffraction study. Compounds 1-6 exhibited good cytotoxicity against the cancer cell lines HL-60, SMMC-7721, A-549, MCF-7, and SW480.

Constituents of the Stem Bark of Trichilia monadelpha (Thonn.) J. J. De Wilde (Meliaceae) and Their Antibacterial and Antiplasmodial Activities

The chemical investigation of the EtOH extract from the stem bark of Trichilia monadelpha (Thonn.) J. J. De Wilde afforded two new limonoids (1 and 2): 24-acetoxy-21,25-dihydroxy-21,23-epoxytirucall-7-en-3-one (1) and (6R)-1-O-deacetylkhayanolide E (2), together with eleven known compounds (3-13), including additional limonoids, flavonoids, triterpenoids, steroids, and fatty acid. Their structures were determined using 1D- and 2D-NMR experiments, ESI mass spectrometry, and single crystal X-ray diffraction analysis. The antibacterial and antiplasmodial activities of the extracts, sub-extracts, fractions, and some of the isolated compounds were evaluated in known pathogenic strains, including Staphylococcus aureus and Plasmodium falciparum. Fraction E (n-Hex/EtOAc 30:70, v/v) showed significant activity against S. aureus ATCC 25923 with a MIC value of 3.90 µg/mL, while one of its constituents (epicatechin (9)) exhibited significant activity with MIC values of 7.80 µg/mL. Interestingly, grandifotane A (6) (IC₅₀ = 1.37 µM) and khayanolide D (5) (IC₅₀ = 1.68 µM) were highly active against the chloroquine-sensitive/sulfadoxine-resistant plasmodium falciparum 3D7 strain, unlike their corresponding plant extract and fractions.

UV light-driven late-stage skeletal reorganization to diverse limonoid frameworks: A proof of concept for photobiosynthesis

Late-stage skeletal reorganization (LSSR) is a type of fascinating organic transformation processes in natural product total synthesis. However, few facile and effective LSSR methodologies have hitherto been developed. Here, LSSR of limonoid natural products via photochemical cascades is first reported. Starting from xyloelves A and B, nine distinct limonoid products with five unprecedented scaffolds are generated. The photocascade pathways of these natural products and mechanistic rationale via intramolecular triplet energy transfer are revealed by quantum mechanical calculations. Most notably, ultraviolet light-driven transannular and stereoselective C → C 1,4-acyl migration is first found as a photochemical approach, particularly for LSSR of natural products. This approach holds promise for designing LSSR strategies to access bioactive cage-like molecules. Besides that, our findings provide a clear proof of concept for natural product photobiosynthesis. Xyloelf A, substantially ameliorating concanavalin A-induced liver injury in mice, could be used as a unique molecular template for hepatoprotective drug discovery.

Complex scaffold remodeling in plant triterpene biosynthesis

Triterpenes with complex scaffold modifications are widespread in the plant kingdom. Limonoids are an exemplary family that are responsible for the bitter taste in citrus (e.g., limonin) and the active constituents of neem oil, a widely used bioinsecticide (e.g., azadirachtin). Despite the commercial value of limonoids, a complete biosynthetic route has not been described. We report the discovery of 22 enzymes, including a pair of neofunctionalized sterol isomerases, that catalyze 12 distinct reactions in the total biosynthesis of kihadalactone A and azadirone, products that bear the signature limonoid furan. These results enable access to valuable limonoids and provide a template for discovery and reconstitution of triterpene biosynthetic pathways in plants that require multiple skeletal rearrangements and oxidations.

Munronin V with 7/7/6 tricarbocyclic framework from Munronia henryi harms inhibits tau pathology by activating autophagy

Munronin V (1), isolated from Munronia henryi Harms, is the first example, to the best of our knowledge, of an unprecedented 7/7/6 tricarbocyclic framework featuring an unusual A,B-seco-limonoid ring. The structures of munronin V were established from extensive spectroscopic and electronic circular dichroism (ECD) analyses. The novel A,B-seco with two seven-membered lactones was formed as a result of Baeyer-Villiger oxidation. Compound 1 activated autophagy and inhibited Tau pathology as revealed by flow cytometric analyses, confocal imaging analysis and western blotting, and this effect was mediated by transcription factor EB (TFEB). These findings suggested that 1 might have potential as a compound for combating Alzheimer's disease.

Limonoids from the fruits of Chisocheton lasiocarpus (Meliaceae)

Two new azadirone-type limonoids, namely lasiocarpine A (1) and lasiocarpine B (2) were isolated from the fruit of Chisocheton lasiocarpus along with three known limonoids (3-5). UV, IR, one- and two- dimensional NMR, and mass spectrometry were used to determine the chemical structure of the isolated compounds. Furthermore, their cytotoxic activity against breast cancer cell line MCF-7 was evaluated using PrestoBlue reagent. From these compounds, lasiocarpine A (1) showed the strongest activity with an IC₅₀ value of 43.38 μM.

Secotrijugins A-D, four highly oxidized and rearranged limonoids from Trichilia sinensis and their anti-inflammatory activity

Four undescribed highly oxidized and rearranged limonoids, secotrijugins A-D, were purified from the leaves and twigs of Trichilia sinensis. Within them, secotrijugin A was characterized as a rare 30-nortrijugin-type limonoid with an unusual cleavage of 1,14-ether bond, secotrijugins B and C represented new examples with the cleavage of δ-lactone ring D, and secotrijugin D was a rare trijugin-type limonoid with an unusual 2,6-oxygen bridge. The structures of limonoids were characterized by means of spectroscopic analysis and ECD calculations. The cellular screening revealed that secotrijugin B was the most active against LPS-stimulated NO production in BV-2 cells, which played an anti-inflammatory role by downregulating COX-2 and iNOS protein expression. The further in vivo experiments confirmed that secotrijugin B had strong in vivo anti-inflammatory effect via suppressing NO and ROS generation.

Phytochemistry and Biological Activities of Guarea Genus (Meliaceae)

Guarea is one of the largest genera of the American Meliaceae family, consisting of over 69 species which are widely distributed in Mexico, Argentina, and Africa and are used in traditional medicine for several diseases. Previous studies reported that the Guarea species produce secondary metabolites such as sesquiterpenoid, diterpenoid, triterpenoid, limonoid, steroid, and aromatic compounds. The preliminary chemical investigation commenced by isolating the limonoid compound, dihydrogedunin, in 1962; then, 240 compounds were obtained from the isolation and hydrodistillation process. Meanwhile, sesquiterpenoid is a significant compound with 52% of Guarea species. The extract and compounds were evaluated for their anti-inflammation, antimalarial, antiparasitic, antiprotozoal, antiviral, antimicrobial, insecticidal, antioxidant, phosphorylation inhibitor, and cytotoxic biological activities. The Guarea genus has also been reported as one of the sources of active compounds for medicinal chemistry. This review summarizes some descriptions regarding the types of Guarea species, especially ethnobotany and ethnopharmacology, such as the compounds isolated from the part of this genus, various isolation methods, and their bioactivities. The information can be used in further investigations to obtain more bioactive compounds and their reaction mechanisms.

Limonoids with anti-inflammatory activity: A review

The natural limonoids distributed mainly in the Meliaceae and Rutaceae plants are known for their unique and complex structure with high degree oxidation and cyclic rearrangement. However, these compounds exhibit a broad range of biological activities such as insecticidal, antibacterial, antifungal, antimalarial, antioxidant, anticancer, antiviral, and anti-inflammatory. There is still limited report about the biological activity of the anti-inflammatory effect of limonoids isolated from plants. Therefore, this study aimed to examine the effect of intact, deformed and rearranged limonoids as anti-inflammatory agents. The majority of anti-inflammatory investigations were evaluated by in vitro and in vivo assays of the isolated pure compounds and their derivatives. For the in vitro study, intact and C-ring seco limonoids showed a potent inhibitory effect against NO production. The in vivo analysis of Intact, C-seco, and AD-seco limonoids showed a potent effect based on the inhibition of pro-inflammatory cytokines expression, indicating their potency as anti-inflammatory agents.

Bioactivity-guided isolation of anti-inflammatory limonins from Chukrasia tabularis

Chukrasia tabularis is an economically important tree and widely cultured in the southeast of China. Its barks, leaves, and fruits are consumed as a traditional medicine and perceived as a valuable source for bioactive limonin compounds. The extracts from root barks of C. tabularis showed significant anti-inflammatory effect. The aim of this research was to explore the material basis of C. tabularis anti-inflammatory activity, and to purify and identify anti-inflammatory active ingredients. By a bioassay-guided isolation of dichloromethane fraction obtained two novel phragmalin limonins, Chukrasitin D and E (1 and 2), together with 12 known limonins (3-14). The chemical structure of these compounds is determined on the basis of extensive spectral analysis and chemical reactivity. In addition, the activities of these isolated limonins on the production of nitric oxide (NO), tumor necrosis factor alpha (TNF-α), and nuclear factor kappa B (NF-κB) in RAW264.7 cells induced by lipopolysaccharide (LPS) were evaluated. Limonins 1 and 2 indicated significant anti-inflammatory activity with IC50 values of 6.24 and 6.13 μM. Compound 1 notably inhibited the production of NF-κB, TNF-α and interleukin 6 (IL-6) in macrophages. The present results suggest that the root barks of C. tabularis exhibited anti-inflammatory effect and the limonins may be responsible for this activity.

Research Progress on Small Molecular Inhibitors of the Type 3 Secretion System

The overuse of antibiotics has led to severe bacterial drug resistance. Blocking pathogen virulence devices is a highly effective approach to combating bacterial resistance worldwide. Type three secretion systems (T3SSs) are significant virulence factors in Gram-negative pathogens. Inhibition of these systems can effectively weaken infection whilst having no significant effect on bacterial growth. Therefore, T3SS inhibitors may be a powerful weapon against resistance in Gram-negative bacteria, and there has been increasing interest in the research and development of T3SS inhibitors. This review outlines several reported small-molecule inhibitors of the T3SS, covering those of synthetic and natural origin, including their sources, structures, and mechanisms of action.

Waste Citrus reticulata Assisted Preparation of Cobalt Oxide Nanoparticles for Supercapacitors

The green, sustainable, and inexpensive creation of novel materials, primarily nanoparticles, with effective energy-storing properties, is key to addressing both the rising demand for energy storage and the mounting environmental concerns throughout the world. Here, an orange peel extract is used to make cobalt oxide nanoparticles from cobalt nitrate hexahydrate. The orange peel extract has Citrus reticulata, which is a key biological component that acts as a ligand and a reducing agent during the formation of nanoparticles. Additionally, the same nanoparticles were also obtained from various precursors for phase and electrochemical behavior comparisons. The prepared Co-nanoparticles were also sulfurized and phosphorized to enhance the electrochemical properties. The synthesized samples were characterized using scanning electron microscopic and X-ray diffraction techniques. The cobalt oxide nanoparticle showed a specific capacitance of 90 F/g at 1 A/g, whereas the cobalt sulfide and phosphide samples delivered an improved specific capacitance of 98 F/g and 185 F/g at 1 A/g. The phosphide-based nanoparticles offer more than 85% capacitance retention after 5000 cycles. This study offers a green strategy to prepare nanostructured materials for energy applications.

Insecticidal Activities and GC-MS Analysis of the Selected Family Members of Meliaceae Used Traditionally as Insecticides

The environmental and health risks associated with synthetic pesticides have increased the demand for botanical insecticides as safer and biodegradable alternatives to control insect pests in agriculture. Hence in this study, five Meliaceae species were evaluated for their insecticidal activities against the Spodoptera frugiperda and the Plutella xylostella larvae, as well as their chemical constituents. Repellence, feeding deterrence, and topical application bioassays were employed to evaluate their insecticidal activities. GC-MS analysis was performed to identify chemical compounds present in each plant. The repellence bioassay indicated that Melia azedarach extracts exhibited the highest repellence percentage against S. frugiperda (95%) and P. xylostella (90%). The feeding deterrence bioassay showed that M. azedarach and Trichilia dregeana extracts displayed excellent antifeeding activity against the S. frugiperda (deterrent coefficient, 83.95) and P. xylostella (deterrent coefficient, 112.25), respectively. The topical application bioassay demonstrated that Ekebergia capensis extracts had the highest larval mortality against S. frugiperda (LD₅₀ 0.14 mg/kg). Conversely, M. azedarach extracts showed the highest larval mortality against P. xylostella (LD₅₀ 0.14 mg/kg). GC-MS analysis revealed that all plant extracts had compounds belonging to the two noteworthy groups (phenols and terpenes), which possess insecticidal properties. Overall, this study lends scientific credence to the folkloric use of Meliaceae species as potential biocontrol agents against insect pests.

Mexicanolide limonoids from the seeds of Khaya ivorensis with antimicrobial activity

The methanol extract of the seeds of Khaya ivorensis afforded two new mexicanolide limonoids, ivorensines A and B (1 and 2), together with one known compound, ruageanin D (3). The structures of the isolated compounds were established based on 1 D and 2 D (¹H-¹H COSY, HMQC, and HMBC) NMR spectroscopy, in addition to high resolution mass spectrometry. The isolated limonoids were tested in vitro for antimicrobial potentials against 5 pathogenic microorganisms. As a result, compounds 1-3 exhibited antimicrobial activity against the tested Gram negative bacteria at the minimum inhibitory concentration values less than 50 μg/ml.

Unified Total Synthesis of the Limonoid Alkaloids: Strategies for the De Novo Synthesis of Highly Substituted Pyridine Scaffolds

Highly substituted pyridine scaffolds are found in many biologically active natural products and therapeutics. Accordingly, numerous complementary de novo approaches to obtain differentially substituted pyridines have been disclosed. This article delineates the evolution of the synthetic strategies designed to assemble the demanding tetrasubstituted pyridine core present in the limonoid alkaloids isolated from Xylocarpus granatum, including xylogranatopyridine B, granatumine A and related congeners. In addition, NMR calculations suggested structural misassignment of several limonoid alkaloids, and predicted their C3-epimers as the correct structures, which was further validated unequivocally through chemical synthesis. The materials produced in this study were evaluated for cytotoxicity, anti-oxidant effects, anti-inflammatory action, PTP1B and Nlrp3 inflammasome inhibition, which led to compelling anti-inflammatory activity and anti-oxidant effects being discovered.

Concise Chemoenzymatic Synthesis of Gedunin

The limonoids have attracted significant attention from the synthetic community owing to their striking structural complexity and medicinal potential. Recent efforts notwithstanding, synthetic access to many intact or ring D-seco limonoids still remains elusive. Here, we report the first de novo synthesis of gedunin, a ring D-seco limonoid with HSP90 inhibitory activity, that proceeds in 13 steps. Two enabling features in our strategy are the application of modern catalytic transformations to set the key quaternary centers in the carbocyclic core and the use of biocatalytic oxidation at C3 to establish a chemical handle to access the A-ring enone motif. The strategy presented herein may provide an entry point to a wider range of oxidized limonoids.

Toward the Asymmetric Synthesis of Cardenolides and Related Steroidal Systems: syn-SN2' of Organometallics with C14-C17 Vinylepoxides

In a program aimed at establishing a common sequence of C-C bond-forming reactions for asymmetric construction of tetracyclic triterpenoid natural products and related synthetic systems, effort has been directed toward introducing C17β-substitution by late-stage functionalization of stereodefined "steroidal" D-ring vinylepoxides (spanning C14-C17). It has been found that cyanocuprates participate in syn-SN2' reactions that result in products bearing various C17β-substituents and containing a β-OH at C14.

Phytochemistry and biological activity of Lansium domesticum Corr. species: a review

OBJECTIVES

This study aims to review and describe the ethnobotanical, phytochemical and biological activity of various extracts and compounds isolated from Lansium domesticum Corr. from 1967 to 2022 and to study the opportunities that can be developed in the future in the pharmaceutical and pharmacology fields. The related articles, followed by the classification of L. domesticum Corr. according to ethnobotanical, biological and phytochemical properties, were collected from SciFinder, Google Scholar and PubMed.

KEY FINDINGS

More than 80 compounds have been isolated and identified from L. domesticum Corr., including terpenoids and their glycosides. Furthermore, the pharmacological activity of the extracts and pure compounds of L. domesticum Corr. tested in vitro and in vivo were mainly confirmed to include antifeedant, antimalarial, antimicrobial, antibacterial, and radical scavenging activity, antimutagenic, and anticancer.

SUMMARY

In conclusion, based on this review, all data on the phytochemical and biological activity of L. domesticum Corr. can be used to support scientists in further research aim to determine the reaction mechanism of the extracts or compounds and need to be further validated using in vivo models together with toxicological analysis to establish their maximum tolerated dose.

Chemical constituents of Entandrophragma angolense and their anti-inflammatory activity

From the stem bark of Entandrophragma angolense, six undescribed compounds were isolated, including seco-tirucallane type triterpenoids, limonoids, and a catechin glucoside, along with nineteen known structures. All structures were determined by interpretation of spectroscopic and HRMS data, and absolute configuration was confirmed with the aid of electronic circular dichroism. The isolated compounds were tested for LPS-induced NO inhibition in RAW 264.7 macrophages and EC₅₀ values for moluccensin O and (-)-catechin were 81 μM and 137 μM, respectively.

Unusual Secondary Metabolites from the Mangrove Ecosystems: Structures, Bioactivities, Chemical, and Bio-Syntheses

Mangrove ecosystems are widely distributed in the intertidal zone of tropical and subtropical estuaries or coasts, containing abundant biological communities, for example, mangrove plants and diverse groups of microorganisms, featuring various bioactive secondary metabolites. We surveyed the literature from 2010 to 2022, resulting in a collection of 134 secondary metabolites, and classified them into two major families in terms of the biological sources and 15 subfamilies according to the chemical structures. To highlight the structural diversity and bioactivities of the mangrove ecosystem-associated secondary metabolites, we presented the chemical structures, bioactivities, biosynthesis, and chemical syntheses.

Naturally occurring dimeric triterpenoids: Occurrence, chemistry and bioactivities

The triterpenes represent one of the most reported subclasses of specialized metabolites from the plant kingdom. They play a key role in the protection of plants and their metabolism in addition to displaying a high structural diversity and large scale of biological activities. The scaffold can undergo several reactions like oxidation or substitution at different positions of the skeleton leading to the formation of several types of compounds. More specifically, triterpene dimer is a small group of compounds found in nature (from plants precisely). Until 2021, the chemical and pharmacological works reported in the literature indicated the identification of 90 natural dimeric triterpenes and 11 synthetic derivatives from 19 plants species and very few of them have been biologically evaluated for their antibacterial, antioxidant, antiproliferative or molluscicide activities. This review aims to compile the literature on the occurrence, chemistry and biological activities of the triterpenoid dimers. To attend this goal, a literature survey has been done in a number of online libraries including Scifinder, PubMed, Web of Science and Google Scholar using keywords terpene, triterpene, dimer, celastroloid without language restriction. This paper provides the easiest access to the information on triterpene dimers for readers and researchers in view to enhancing the continuity of research works on this topic.

Antimicrobial mexicanolide limonoids from the seeds of Khaya senegalensis

Three new mexicanolide limonoids were obtained from the 90% ethanol extract of the seeds of Khaya senegalensis. Their structures were elucidated as senegalenines A-C (1-3) by analysing their 1D/2D NMR and MS spectroscopic analysis. In addition, the isolated limonoids were tested in vitro for antimicrobial potentials against 5 pathogenic microorganisms. Consequently, compounds 1-3 exhibited antimicrobial activity against the tested Gram negative bacteria at the minimum inhibitory concentration values less than 40 μg/ml.

Chemotaxonomic investigation of plant terpenoids with an established database (TeroMOL)

Terpenoids constitute the biggest class of plant-derived natural products with diverse chemical structures and extensive biological activities. Interpreting enzyme functions and mining new structures of terpenoids could be inspired by the cheminformatic and chemotaxonomic analysis, whereas it is hampered by the incompleteness of available data for terpenoids. Here a dedicated terpenoids database, TeroMOL, is developed to collect more than 170 000 terpenoids and their derivatives annotated with reported biological sources, along with a user-friendly and freely accessible webserver to visualise and analyse the terpenoids skeletons and organism sources. The quantitative distributions as well as the qualitative trends between terpenoid skeletons and organism sources in plant kingdom are revealed from a chemotaxonomic view, while no comparisons are attempted due to the inherent data biases. Nevertheless, the terpenoid chemomarkers in several organisms are discussed based on the available data with highly enriched and exclusive carbon skeletons. We believe that the TeroMOL database and its accessory computational tools will be very promising for exploring the chemical space and biological sources of terpenoids, and assisting the terpenoid research community in the future.

Ultra-high performance liquid chromatography Q-Orbitrap MS/MS-based profiling and quantification of limonoids in Meliaceae plants

Meliaceae plants have been extensively used in agriculture, folklore, and traditional medicine. They are the major storehouses for structurally diverse limonoids (meliacins) possessing various bioactivities like antifeedant, insecticidal, antimicrobial, etc. However accurate detection of these tetranortriterpenes from the vast pool of metabolites in plant tissue extracts or biological sample is a crucial challenge. Though the mass spectrum (MS) provides the molecular mass and the corresponding elemental composition, it cannot be relied precisely. The exact identification of a specific metabolite demands the MS/MS spectrum containing the signature product ions. In the present study, we have developed the UHPLC Q-Orbitrap-based method for identification, quantification, and characterization of limonoids in different plant tissue extracts requiring minimum plant material. Using this method, we carried out the limonoid profiling in different tissue extracts of sixteen Meliaceae plants and the identification of limonoids was performed by comparing the retention time (RT), ESI-( +)-MS spectrum, and HCD-MS/MS of the purified fifteen limonoids used as reference standards. Our results revealed that early intermediates of the limonoid biosynthetic pathway such as azadiradione, epoxyazadiradione, and gedunin occurred more commonly in Meliaceae plants. The MS/MS spectrum library of the fifteen limonoids generated in this study can be utilized for identification of these limonoids in other plant tissue extracts, botanical fertilizers, agrochemical formulations, and bio pesticides.

Inhibition of the P2X7/NLRP3 Inflammasome Signaling Pathway by Deacetylgedunin from Toona sinensis

Limonoids are considered the effective part in Meliaceae plants that exert anti-inflammatory effects. Gedunin-type limonoids specifically have anti-inflammatory effects. However, the role of gedunin-type limonoids in the inflammatory diseases mediated by NLRP3 inflammasome remains to be explored. We found that deacetylgudunin (DAG), a gedunin-type limonoid from Toona sinensis, had similar anti-inflammatory effects and lower toxicity than gedunin. Further studies showed that DAG down-regulated the NF-κB pathway, inhibited K⁺ efflux and ROS release, inhibited ASC oligomerization, and significantly weakened the interaction of NLRP3 with ASC and NEK7. Furthermore, DAG could not further inhibit IL-1β secretion and K⁺ efflux when combined with the P2X7 inhibitor A438079. In conclusion, our research revealed that DAG exerted an anti-inflammatory effect by inhibiting the P2X7/NLRP3 signaling pathway and enriched the application of gedunin-type limonoids in inflammatory diseases driven by the NLRP3 inflammasome.

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.

Insecticidal Triterpenes in Meliaceae: Plant Species, Molecules, and Activities: Part II (Cipadessa, Melia)

Plant-originated triterpenes are important insecticidal molecules. Research on the insecticidal activity of molecules from Meliaceae plants has always been a hotspot due to the molecules from this family showing a variety of insecticidal activities with diverse mechanisms of action. In this paper, we discussed 116 triterpenoid molecules with insecticidal activity from 22 plant species of five genera (Cipadessa, Entandrophragma, Guarea, Khaya, and Melia) in Meliaceae. In these genera, the insecticidal activities of plants from Entandrophragma and Melia have attracted substantial research attention in recent years. Specifically, the insecticidal activities of plants from Melia have been systemically studied for several decades. In total, the 116 insecticidal chemicals consisted of 34 ring-intact limonoids, 31 ring-seco limonoids, 48 rearranged limonoids, and 3 tetracyclic triterpenes. Furthermore, the 34 ring-intact limonoids included 29 trichilin-class chemicals, 3 azadirone-class chemicals, and 1 cedrelone-class and 1 havanensin-class limonoid. The 31 ring-seco limonoids consisted of 16 C-seco group chemicals, 8 B,D-seco group chemicals, 4 A,B-seco group chemicals, and 3 D-seco group chemicals. Furthermore, among the 48 rearranged limonoids, 46 were 2,30-linkage group chemicals and 2 were 10,11-linkage group chemicals. Specifically, the 46 chemicals belonging to the 2,30-linkage group could be subdivided into 24 mexicanolide-class chemicals and 22 phragmalin-class chemicals. Additionally, the three tetracyclic triterpenes were three protolimonoids. To sum up, 80 chemicals isolated from 19 plant species exhibited antifeedant activity toward 14 insect species; 18 chemicals isolated from 17 plant species exhibited poisonous activity toward 10 insect species; 16 chemicals isolated from 11 plant species possessed growth-regulatory activity toward 8 insect species. In particular, toosendanin was the most effective antifeedant and insect growth-regulatory agent. The antifeedant activity of toosendanin was significant. Owing to its high effect, toosendanin has been commercially applied. Three other molecules, 1,3-dicinnamoyl-11-hydroxymeliacarpin, 1-cinnamoyl-3-methacryl-11-hydroxymeliacarpin, and 1-cinnamoyl-3-acetyl-11-hydroxymeliacarpin, isolated from Meliaazedarach, exhibited a highly poisonous effect on Spodoptera littoralis; thus, they deserve further attention.