Research progress of meliaceous limonoids from 2011 to 2021

Alliaxylines A-E: five new mexicanolides from the stem barks of Dysoxylum alliaceum (Blume) Blume ex A.Juss

A total of five new mexicanolides (1-5), namely alliaxylines A-E, together with two known limonoids 6 and 7, were isolated and identified from Dysoxylum alliaceum (Blume) Blume ex. A.Juss. (Meliaceae). The structures of these compounds were elucidated based on extensive spectroscopic analyses, including HR-ESI-MS, UV, IR, 1D, and 2D NMR, as well as theoretical stimulation of NMR shifts with the DP4 + algorithm. Consequently, this study aimed to examine cytotoxic activities of these compounds against MCF-7 and A549 cell lines. The results implied that compound 2 was the most potent against the two tested cells, with IC50 values of 34.95 ± 0.21 and 44.39 ± 1.03 µM.

Toonanoronoids A-E, five new limonoids from Toona ciliata var. yunnanensis

Five new B-seco-limonoids, namely toonanoronoids A-E (1-5), in conjunction with three previously reported compounds, were isolated from the EtOAc extract of the twigs and leaves of Toona ciliata var. yunnanensis. Their structures were elucidated through comprehensive spectroscopic and X-ray crystallographic analysis. The cytotoxic activities of new compounds against five human tumor cell lines (HL-60, SMMC-7721, A549, MCF-7, and SW480) were screened, Compounds 4 and 5 exerted inhibition toward two tumor cell lines (HL-60, SW-480) with IC50 values between 1.7 and 5.9 μM.

Limonoids isolated from Chisocheton ceramicus Miq. and the antiadipogenic mechanism of action of ceramicine B

Different types of limonoids have been isolated from plants of the Chisocheton genus, notably from the species Chisocheton ceramicus  Miq. which is largely distributed in the Indonesian archipelago and Malaysia region. A variety of natural products have been found in the bark of the tree and characterized as antimicrobial and/or antiproliferative agents. The isolated limonoids include chisomicines A-E, proceranolide, and a few other compounds. A focus is made on a large series of limonoids designated ceramicines A to Z including derivatives with antiparasitic activities, antioxidant, antimelanogenic, and antiproliferative effects and/or acting as regulators of lipogenesis. The lead compound in the series is ceramicine B functioning as a potent inhibitor of lipid droplet accumulation (LDA). Extracts from Chisocheton ceramicus and ceramicines have shown anti-LDA effects, with little or no cytotoxic effects. Ceramicine B is the most active compound functioning as a regulator of lipid storage in cells and tissues. Ceramicine B is a transcriptional repressor of peroxisome proliferator-activated receptor γ (PPARγ) and an inhibitor of phosphorylation of the transcription factor FoxO1, acting via an upstream molecular target. Targeting of glycogen synthase kinase-3β is proposed, based on the analogy with structurally related limonoids known to target this enzyme, and supported by a molecular docking analysis. The target and pathway implicated in ceramicine B activity are discussed. The analysis shed light on ceramicine B as a natural product precursor for the design of novel compounds capable of reducing LDA in cells and of potential interest for the treatment of obesity, liver diseases, and other pathologies.

Study on the Performance Test of Fe-Ce-Al/MMT Catalysts with Different Fe/Ce Molar Ratios for Coking Wastewater Treatment

It is very important to choose a suitable method and catalyst to treat coking wastewater. In this study, Fe-Ce-Al/MMT catalysts with different Fe/Ce molar ratios were prepared, characterized by XRD, SEM, and N2 adsorption/desorption, and treated with coking wastewater. The results showed that the optimal Fe-Ce-Al/MMT catalyst with a molar ratio of Fe/Ce of 7/3 has larger interlayer spacing, specific surface area, and pore volume. Based on the composition analysis of real coking wastewater and the study of phenol simulated wastewater, the response surface test of the best catalyst for real coking wastewater was carried out, and the results are as follows: initial pH 3.46, H2O2 dosage 19.02 mL/L, Fe2+ dosage 5475.39 mL/L, reaction temperature 60 °C, and reaction time 248.14 min. Under these conditions, the COD removal rate was 86.23%.

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.

Unusual Vilasinin-Class Limonoids from Trichilia rubescens

Eight vilasinin-class limonoids, including the unusually chlorinated rubescins K-M (1-3), the 2,3-epoxylated rubescin N (4), and rubescins O-R (5-8), were newly isolated from Trichilia rubescens. The structures of the isolated compounds were determined through spectroscopic and spectrometric analyses, as well as ECD calculations. The natural occurrence of chlorinated limonoids 1-3 was confirmed by chemical methods and HPLC analysis of a roughly fractionated portion of the plant extract. Eight selected limonoids, including previously known and new compounds, were evaluated for antiproliferative activity against five human tumor cell lines. All tested limonoids, except 8, exhibited significant potency, with IC50 values of <10 μM; in particular, limonoid 14 strongly inhibited tumor cell growth, with IC50 values of 0.54-2.06 μM against all tumor cell lines, including multi-drug-resistant cells.

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.

Unusual triterpenoids and steroids from Cipadessa baccifera and their biological activities

Five undescribed triterpenoids and steroids (1-5), as well as ten known compounds, were purified from the branches and leaves of Cipadessa baccifera. Notably, 1 and 2 are rare cipadesin-type limonoids with an unusual 8,30-epoxide ring and 1,8-ether linkage, respectively. Compound 5 possessed pregnane steroid skeleton with an uncommon 5/6/6/6/5-fused ring system. Their structures were constructed by extensive spectroscopic analysis (NMR, IR, UV, and HRESIMS), and their absolute configurations were confirmed by ECD calculations and quantum chemical calculations. All the isolates were in vitro assayed for their antimicrobial potentials against 6 pathogenic microorganisms and antiproliferation activities against five human cancer cell lines. As a result, compounds 5, 12, 13, and 14 exhibited moderate antibacterial activities (MIC: 25-50 μg/mL). Moreover, 5 showed cytotoxicity against five cancer cell lines with IC50 values ranging from 8.0 to 19.9 μM.

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.

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.

Nomilin and its analogue obacunone alleviate NASH and hepatic fibrosis in mice via enhancing antioxidant and anti-inflammation capacity

Nonalcoholic steatohepatitis (NASH) and hepatic fibrosis are leading causes of cirrhosis with rising morbidity and mortality worldwide. Currently, there is no appropriate treatment for NASH and hepatic fibrosis. Many studies have shown that oxidative stress is a main factor inducing NASH. Nomilin (NML) and obacunone (OBA) are limonoid compounds naturally occurring in citrus fruits with various biological properties. However, whether OBA and NML have beneficial effects on NASH remains unclear. Here, we demonstrated that OBA and NML inhibited hepatic tissue necrosis, inflammatory infiltration and liver fibrosis progression in methionine and choline-deficient (MCD) diet, carbon tetrachloride (CCl4 )-treated and bile duct ligation (BDL) NASH and hepatic fibrosis mouse models. Mechanistic studies showed that NML and OBA enhanced anti-oxidative effects, including reduction of malondialdehyde (MDA) level, increase of catalase (CAT) activity and the gene expression of glutathione S-transferases (GSTs) and Nrf2-keap1 signaling. Additional, NML and OBA inhibited the expression of inflammatory gene interleukin 6 (Il-6), and regulated the bile acid metabolism genes Cyp3a11, Cyp7a1, multidrug resistance-associated protein 3 (Mrp3). Overall, these findings indicate that NML and OBA may alleviate NASH and liver fibrosis in mice via enhancing antioxidant and anti-inflammation capacity. Our study proposed that NML and OBA may be potential strategies for NASH treatment.

Flindissone, a Limonoid Isolated from Trichilia prieuriana, Is an LXR Agonist

In this study, the ability of six limonoids from Trichilia prieuriana (Meliaceae) to activate the liver X receptor (LXR) was assessed. One of these limonoids, flindissone, was shown to activate LXR by reporter-gene assays. Flindissone is a ring-intact limonoid, structurally similar to sterol-like LXR ligands. In endogenous cellular settings, flindissone showed an activity profile that is characteristic of LXR agonists. It induced cholesterol efflux in THP-1 macrophages by increasing the cholesterol transporter ABCA1 and ABCG1 gene expression. In HepG2 cells, flindissone induced the expression of IDOL, an LXR-target gene that is associated with the downregulation of the LDL receptor. However, unlike synthetic and similarly to sterol-based LXR agonists, flindissone did not induce the expression of the SREBP1c gene, a major transcription factor regulating de novo lipogenesis. Additionally, flindissone also appeared to be able to inhibit post-translational activation of SREBP1c. The results presented here reveal a natural product as a new LXR agonist and point to an additional property of T. prieuriana and other plant extracts containing flindissone.

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.

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.

d-chiro-Inositol Derivatives with Multidrug Resistance Reversal Activities from the Fruits of Chisocheton siamensis

Chisosiamols A-K (1-11), 11 new d-chiro-inositol derivatives, along with a known analogue (12) were isolated from the fruits of Chisocheton siamensis. Their planar structures and relative configurations were elucidated by the comprehensive application of spectroscopic methods, especially from the characteristic coupling constants, and ¹H-¹H COSY spectra. The absolute configurations of the d-chiro-inositol core were determined using the ECD exciton chirality and X-ray diffraction crystallographic analytical methods. This is the first crystallographic data reported for the d-chiro-inositol derivatives. A structural elucidation strategy mainly combining ¹H-¹H COSY correlations and ECD exciton chirality for determining the structure of d-chiro-inositol derivatives was developed, which also led to the revisions of previously reported structures. Bioactivity evaluation indicated that chisosiamols A, B, and J can reverse multidrug resistance in MCF-7/DOX cells in the IC₅₀ range of 3.4-6.5 μM (RF: 3.6-7.0).

Hainanxylogranolides A-F: New Limonoids isolated from the seeds of Hainan mangrove plant Xylocarpus granatum

Six new limonoids, named hainanxylogranolides A-F (1-6), together with nineteen known ones (7-25) were isolated from the seeds of a Hainan mangrove Xylocarpus granatum. The structures of the new compounds were established by extensive NMR spectroscopic data combined with the DFT and TDDFT calculated electronic circular dichroism spectra. Hainanxylogranolide A (1) is the aromatic B-ring limonoid containing a central pyridine ring and a C-17 substituted γ(21)-hydroxybutenolide moiety. Hainanxylogranolide B (2) belongs to the small group of mexicanolides containing a C₃-O-C₈ bridge, whereas hainanxylogranolides C and D (3 and 4) are mexicanolides comprising a C₁-O-C₈ bridge. Compounds 9 and 25 posed obvious inhibition effect on the tube formation of HUVECs. There are only about 25% tube-like structures were observed at the concentration of 40.0 μM of compound 25. The antiviral activities of the isolates against herpes simplex virus-1 (HSV-1) and severe fever with thrombocytopenia syndrome virus (SFTSV) were tested in vitro. Compound 23 exhibited moderate anti-SFTSV activity with the IC₅₀ value of 29.58 ± 0.73 μM. This is the first report of anti-angiogenic effect and anti-SFTSV activity of limonoids from the genus Xylocarpus.

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.

Rare noreudesmane sesquiterpenoids from the fruits of Dysoxylum densiflorum

Seven rare noreudesmane sesquiterpenoids (dysoxydenones M-S, 1-7), including three 11,12,13-trinoreudesmanes, three 13-noreudesmanes and one spirovetivane-type sesquiterpenoid, along with two known analogues were isolated from the fruits of Dysoxylum densiflorum. The planar structures were elucidated by a combination of 1D, 2D NMR and HRESIMS analyses. Their absolute configurations were determined by combination of single-crystal X-ray diffraction, CD exciton chirality method and ECD calculation. All compounds were screened for anti-inflammatory activity on LPS-induced RAW 264.7 cells and IL-1β inhibitory activity.

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.

Bioactive limonoids from Carapa guianensis seeds oil and the sustainable use of its by-products

Carapa guianensis (Andiroba, Meliaceae) is considered a multipurpose tree. In Brazil, Indigenous people have used it as insect repellent and in the treatment of various diseases. Most biological activities and popular uses are attributed to limonoids, which are highly oxygenated tetranortriterpenoids. More than 300 limonoids have been described in Meliaceae family. Limonoids from Andiroba oil have shown high anti-inflammatory and anti-allergic activities in vivo, by inhibiting platelet activating factors and many inflammatory mediators such as IL-5, IL-1β and TNF-α. It also reduced T lymphocytes, eosinophils and mast cells. In corroboration with the wide popular use of Andiroba oil, no significant cytotoxicity or genotoxicity in vivo was reported. This oil promotes apoptosis in a gastric cancer cell line (ACP02) at high concentrations, without showing mutagenic effects, and is suggested to increase the body's nonspecific resistance and adaptive capacity to stressors, exhibit some antioxidant activity, and protect against oxidative DNA damages. Recently, new methodologies of toxicological assays have been applied. They include in chemico, in vitro, in silico and ex vivo procedures, and take place to substitute the use of laboratory animals. Andiroba by-products have been used in sustainable oil production processes and as fertilizers and soil conditioners, raw material for soap production, biodegradable surfactants and an alternative natural source of biodegradable polymer in order to reduce environmental impacts. This review reinforces the relevance of Andiroba and highlights its ability to add value to its by-products and to minimize possible risks to the health of the Amazonian population.

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.

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.