Krishnagranatins A–I: New limonoids from the mangrove, Xylocarpus granatum, and NF-κB inhibitory activity

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.

Naming of new natural products: Standard, pitfalls and tips-and-tricks

Naming a newly discovered natural product (NP) is a pleasant but difficult exercise. In most cases, the NP name will be given with reference to the species of origin, be it a plant, a marine organism, a mammalian or microbial species. For a long time, the use of biologically-based trivial names has been recommended to identify the parental linkage between the product and the originating genus or species. But the recommendation is not always followed and a multiplicity of trivial names have been attributed to NP, based on locations (country, region, city), foods, music, animals, forenames, etc. Tips-and-tricks associated with the naming of NP are underlined here. Usually, NP are differentiated across a homogeneous chemical series with a letter (from the Latin or Greek alphabet), followed or not with a number. In other cases, the change of a single letter distinguishes a series of NP. Common pitfalls associated with the naming of NP are enumerated, including the complexity of names, use of synonyms, duplicated names, confusing names and inappropriate terminology. The difficulties regularly encountered with the naming of NP are discussed. Four essential recommendations are recalled: (i) a thorough analysis of the existing products to avoid duplicated names and confusion, (ii) the use of a biologically-based trivial name to retrace the origin of the product, (iii) the strict adherence to the codes of chemical nomenclature, and (iv) the preference for simple names to facilitate transmission. Naming a new NP is a rewarding task, which shall be performed with all due skill, care and diligence.

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.

Exploring the Mangrove Fruit: From the Phytochemicals to Functional Food Development and the Current Progress in the Middle East

Nowadays, the logarithmic production of existing well-known food materials is unable to keep up with the demand caused by the exponential growth of the human population in terms of the equality of access to food materials. Famous local food materials with treasury properties such as mangrove fruits are an excellent source to be listed as emerging food candidates with ethnomedicinal properties. Thus, this study reviews the nutrition content of several edible mangrove fruits and the innovation to improve the fruit into a highly economic food product. Within the mangrove fruit, the levels of primary metabolites such as carbohydrates, protein, and fat are acceptable for daily intake. The mangrove fruits, seeds, and endophytic fungi are rich in phenolic compounds, limonoids, and their derivatives as the compounds present a multitude of bioactivities such as antimicrobial, anticancer, and antioxidant. In the intermediary process, the flour of mangrove fruit stands as a supplementation for the existing flour with antidiabetic or antioxidant properties. The mangrove fruit is successfully transformed into many processed food products. However, limited fruits from species such as Bruguiera gymnorrhiza, Rhizophora mucronata, Sonneratia caseolaris, and Avicennia marina are commonly upgraded into traditional food, though many more species demonstrate ethnomedicinal properties. In the Middle East, A. marina is the dominant species, and the study of the phytochemicals and fruit development is limited. Therefore, studies on the development of mangrove fruits to functional for other mangrove species are demanding. The locally accepted mangrove fruit is coveted as an alternate food material to support the sustainable development goal of eliminating world hunger in sustainable ways.

Concise syntheses and anti-inflammatory effects of isocorniculatolide B and corniculatolide B and C

The first total syntheses of isocorniculatolide B, corniculatolide B, and corniculatolide C, consisting of isomeric corniculatolide skeletons, have been accomplished in a divergent manner. The key features of the synthesis involve the construction of diaryl ether linkages by nucleophilic aromatic substitution, installation of a C14-substituted alkyl side chain via a sequence of Baeyer-Villiger reaction and Claisen rearrangement, and efficient construction of corniculatolide and isocorniculatolide frameworks, including 17-membered (exterior) macrolactone skeletons from a versatile diaryl ether intermediate by Mitsunobu macrolactonization. Moreover, we prepared the structural congeners of isomeric corniculatolides via diverted total synthesis approach including desmethyl analogues and related dimeric macrolides. The anti-inflammatory activities of the synthesized natural products, analogues and synthetic intermediates were also investigated. In particular, corniculatolide B significantly inhibited the protein expression of COX-2 and the mRNA expressions of TNF-α, IL-1β and IL-6 by inhibiting of NF-κB signaling in intestinal epithelial cells induced by lipopolysaccharide treatment. It also significantly inhibited the promoter activity and the phosphorylation of subunits p50 and p65 of NF-κB to the same extent as Bay 11-7082, a potent IκB kinase inhibitor. These results suggest that corniculatolide B might have therapeutic potential in inflammatory bowel disease via NF-κB signaling pathway.

Ethnomedicinal Use, Phytochemistry, and Pharmacology of Xylocarpus granatum J. Koenig

The mangrove plants are the potential sources of foods and remedies for people living in the forests and nearby communities. Xylocarpus granatum J. Koenig is traditionally used to treat various diseases including diarrhea, cholera, dysentery, fever, malaria, and viral infections, among others. To summarize critically the taxonomy, ethnomedicinal, phytochemistry, and pharmacological activities of X. granatum, information was collected from different databases. An up-to-date search (till June 2020) was carried out with the help of various scientific web resources from databases such as PubMed, Science Direct, Google Scholar, and various patent offices (e.g., WIPO, CIPO, and USPTO) using the keywords “Xylocarpus granatum” and then paired with ethnomedicinal use and phytochemical, phytochemistry, and pharmacological activity (in vitro, ex vivo, and in vivo studies). Findings revealed that seeds, fruits, stem bark, leaf, and twigs of X. granatum exhibited a wide range of key phytochemicals including limonoids, phragmalin, limonoid-based alkaloids, mexicanolides, protolimonoids, flavonols, and lactones. The plant possessed potent antioxidant, anticancer, antidiabetic, antimicrobial, antimalarial, antifeedant, and neuroprotective activities. No clinical studies have been reported in the databases. Ethnomedicinal assessment indicated the application of X. granatum in various fields of medical science specially to treat various human ailments, and this was attributed to the presence of enormous alkaloids as confirmed by pharmacological studies. However, to understand the mechanism of action in-depth studies are required. In view of these findings, more research is necessary to explore and characterize the chemical compounds and toxicological aspects of this medicinal mangrove plant. Overall, it can be stated that X. granatum may be one of the hopeful medicinal herbs for the treatment of various diseases in human beings.

Marine natural products

This review covers the literature published between January and December in 2018 for marine natural products (MNPs), with 717 citations (706 for the period January to December 2018) referring to compounds isolated from marine microorganisms and phytoplankton, green, brown and red algae, sponges, cnidarians, bryozoans, molluscs, tunicates, echinoderms, mangroves and other intertidal plants and microorganisms. The emphasis is on new compounds (1554 in 469 papers for 2018), together with the relevant biological activities, source organisms and country of origin. Reviews, biosynthetic studies, first syntheses, and syntheses that led to the revision of structures or stereochemistries, have been included. The proportion of MNPs assigned absolute configuration over the last decade is also surveyed.

Krishnolides E-K: New limonoids from the Krishna mangrove Xylocarpus moluccensis

Seven new limonoids, named krishnolides E-K (1-7), including three khayanolides, two mexicanolides, a derivative of trangmolin A, and an andirobin, were isolated from seeds of the Indian Krishna mangrove, Xylocarpus moluccensis. The structures of these limonoids were established by HRESIMS, extensive NMR investigations, and X-ray crystallography. Most notably, the absolute configurations of 1, 5, 6, and 7 were unequivocally determined by single-crystal X-ray diffraction analyses (Cu Kα). Krishnolide F (2) exhibited significant agonistic effects on human pregnane-X-receptor (hPXR) at the concentration of 10.0 μM. Molecular docking revealed that 2 could bind a helix near the region of the Helix 12 of hPXR. Polar contribution could be electrostatic effects from the formation of two stable protein-ligand hydrogen bonds between Gln285/1-OH and His407/1-OH, respectively. This is the first report of agonistic effects of a khayanolide-type limonoid on hPXR.

Limonoids from fruiting bodies of the wood-rot basidiomycete Fulvifomes xylocarpicola associated with the mangrove tree Xylocarpus granatum

Three previously undescribed limonoids, fulvifomins A-C, together with two known compounds, 6-deoxydetigloyl-swietenine acetate and methyl angolensate, were isolated from fruiting bodies of the wood-rot fungus Fulvifomes xylocarpicola (Hymenochaetaceae), growing on the mangrove tree Xylocarpus granatum (Meliaceae). The structures were elucidated on the basis of NMR spectroscopic and mass spectrometry data, and X-ray crystallographic analysis (for fulvifomin A). A number of similar limonoids have been isolated from higher plants of the family Meliaceae, including X. granatum. The present study represents a unique evidence that the associated basidiomycete also contains these limonoids. Fulvifomin B exhibited moderate antimalarial and antitubercular activites.

α-Glucosidase Inhibitory Isomeric Corniculatolides from the Stems of the Indian Mangrove Plant, Xylocarpus granatum

Three new isomeric corniculatolides (1, 2, and 3) with an unusual caffrane and isocorniculane framework, and five known metabolites were isolated from the chloroform extract of the stems of Xylocarpus granatum. The structures of the new metabolites were deduced as corniculatolide B (1), isocorniculatolide B (2), and corniculatolide C (3) by spectroscopic data analysis and a combination of chemical transformations and supported by single-crystal X-ray crystallographic data of 1 and 3. The isolated compounds were evaluated for their in vitro cytotoxicity and α-glucosidase (Saccharomyces cerevisiae) inhibitory potential. Compound 3 possessed α-glucosidase inhibitory activity with an IC₅₀ value of 24.8 μM, whereas these rare macrolides showed no effect on the mammalian cancer cell lines MIAPaCa-2, DU145, MCF-7, and HTC-116.

TDDFT-ECD and DFT-NMR studies of thaigranatins A–E and granatumin L isolated from Xylocarpus granatum

TDDFT-ECD calculations were utilized to explain the mirror image or different ECD spectra of thaigranatins A–E and granatumin L.

Limonoids Containing a C₁⁻O⁻C29 Moiety: Isolation, Structural Modification, and Antiviral Activity

Five new limonoids named thaigranatins A⁻E (1⁻5), containing a C₁⁻O⁻C₂₉ moiety, were isolated from seeds of the Thai Xylocarpus granatum, collected at the mangrove swamp of Trang Province, together with the known limonoid, granatumin L (6). The structures of these compounds were established by HR-ESIMS and extensive NMR spectroscopic data. The absolute configuration of 1 was unequivocally determined by single-crystal X-ray diffraction analysis, conducted with Cu Kα radiation; whereas that of 2 or 6 was established to be the same as that of 1 by the similarity of their electronic circular dichroism (ECD) spectra. In view of the marked antiviral activity of 6, its structure was modified via hydrolysis with alkaline KOH, esterification with diazomethane and various organic acids, and oximization with hydroxyamine. Finally, 18 derivatives, viz. 7⁻10, 8a⁻8i, 9a⁻9b, and 10a⁻10c, were obtained. In vitro antiviral activities of these derivatives against human immunodeficiency virus 1 (HIV-1) and influenza A virus (IAV) were evaluated. Most notably, 8i exhibited marked inhibitory activity against HIV-1 with an IC₅₀ value of 15.98 ± 6.87 μM and a CC₅₀ value greater than 100.0 μM; whereas 10b showed significant inhibitory activity against IAV with an IC₅₀ value of 14.02 ± 3.54 μM and a CC₅₀ value greater than 100.0 μM.