New rearranged limonoids from Harrisonia perforata. III

Haperforatones A-M, thirteen undescribed limonoids from Harrisonia perforata with anti-inflammatory activity

UPLC-Q-TOF-MS combined with mass defect filtering strategies were applied for the phytochemical investigation of Harrisonia perforata, leading to the isolation of thirteen undescribed limonoids named haperforatones A-M (1-13) and seventeen known compounds (14-30). Particularly, haperforatones D-E (4-5) have an unprecedented A, B, C, D-seco-6, 7-nor-C-24-limonoid skeleton, structurally stripped of the five-membered lactone ring B and formed a double bond at the C-5 and C-10 positions. Their 2D structures and relative configurations were identified using spectroscopic data. The absolute configurations of 1, 4, and 6 were established via X-ray diffraction crystallography. All 30 compounds were evaluated for anti-inflammatory potential in LPS-induced Raw 264.7 cell lines. Among those tested compounds, the most potent activity against LPS-induced NO generation was demonstrated by haperforatone F (6), with the IC50 value of inhibition NO production of 7.2 µM. Additionally, 6 could significantly inhibit IL-1β and IL-6 release and markedly downregulate the protein expression level of iNOS in the LPS-stimulated RAW264.7 cells at 10 µM. The possible mechanism of NO inhibition of 6 was also investigated using molecular docking, which revealed the interaction of compound 6 with the iNOS protein.

Navigating the Pauson-Khand Reaction in Total Syntheses of Complex Natural Products

"Total synthesis endeavors provide wonderful opportunities to discover and invent new synthetic reactions as a means to advance organic synthesis in general. Such discoveries and inventions can occur when the practitioner faces intransigent problems that cannot be solved by known methods and/or when method improvements are desired in terms of elegance, efficiency, cost-effectiveness, practicality, or environmental friendliness" (K. C. Nicolaou et al. from their review in CCS Chem. 2019, 1, 3-37). To date tens of thousands of bioactive compounds have been isolated from plants, microbes, marine invertebrates, and other sources. These chemical structures have been studied by chemists who scanned the breadth of natural diversity toward drug discovery efforts. Drug-likeness of natural products often possesses common features including molecular complexity, protein-binding ability, structural rigidity, and three-dimensionality. Considering certain biologically important natural products are scarce from natural supply, total synthesis may provide an alternative solution to generating these compounds and their derivatives for the purpose of probing their biological functions. Natural products bearing quaternary carbon stereocenters represent a group of biologically important natural entities that are lead compounds in the development of pharmacological agents and biological probes. However, the stereocontrolled introduction of quaternary carbons, with vicinal patterns that substantially expand the complexity of molecular architectures and chemical space in particular, presents distinct challenges because of the high steric repulsion between substituents. Though remarkable advance has been seen for quaternary carbon stereocenter generation, the process remains a daunting challenge given that the formation of highly congested stereocenters increases the difficulty in achieving orbital overlap.In the past two decades, our group has initiated a program to develop synthetic strategies and methods with the aim of advancing the frontiers of the total syntheses of biologically important complex natural products bearing all-carbon quaternary stereogenic centers. Typical endeavors have involved the use of a Pauson-Khand (PK) reaction as a key step in constructing core structures with all-carbon quaternary stereogenic center(s), with the aid of well-orchestrated thiourea-Co- and thiourea-Pd-catalyzed PK reactions. These methodological advances have enabled us to achieve total syntheses of a series of topologically complex natural products with diverse structural features. These methods will enable the assembly of molecules with improved biological functions and provide tool compounds for elucidation of mechanism of action or identification of potential cellular targets.

Recent progress in the synthesis of limonoids and limonoid-like natural products

Recent progress in syntheses of limonoids and limonoid-like natural products is reviewed. The current “state-of-art” advance on novel synthetic strategy are summarized and future outlook will be presented.

12β-Acetyloxyperforatin, a New Limonoid from Harrisonia Perforata

A new A, D-seco limonoid, named 12-acetyloxyperforatin (1), along with three known ones, were isolated from the leaves of Harrisonia perforata. Their structures were elucidated on the basis of spectroscopic analysis, including extensive NMR techniques and computational modelling. These compounds showed no inhibitory activity against the 11β-HSD1 enzyme.

(±)-Perforison A, A Pair of New Chromone Enantiomers from Harrisonia perforata

(+)-Perforison A and (-)-perforison A, a new pair of chromone enantiomers, along with four known compounds, were isolated from the leaves and stems of Harrisonia perforata. Their structures and absolute configurations were determined on the basis of extensive analysis of spectroscopic data and electronic circular dichroism (ECD) calculations. The cytotoxic activities in vitro of these compounds were evaluated, but none showed significant activity.

Isolation and Asymmetric Total Synthesis of Perforanoid A

A novel limonoid, perforanoid A, was isolated, and an asymmetric total synthesis was achieved in 10 steps. The key steps are chiral tertiary aminonaphthol mediated enantioselective alkenylation of an aldehyde to an allylic alcohol, Pd-catalyzed coupling of the allylic alcohol with vinyl ether to form the γ-lactone ring, and cyclopentenone ring formation through a Rh-catalyzed Pauson-Khand reaction. Preliminary studies show that perforanoid A is cytotoxic towards HEL, K562, and CB3 tumor cell lines.

Inhibitory Effect on β -Hexosaminidase Release from RBL-2H3 Cells of Extracts and Some Pure Constituents of Benchalokawichian, a Thai Herbal Remedy, Used for Allergic Disorders

Introduction. Benchalokawichian (BCW), a Thai traditional herbal formulation, has long been used as antipyretic and to treat skin disorders. It comprises roots from five herbs: Ficus racemosa, Capparis micracantha, Clerodendrum petasites, Harrisonia perforata, and Tiliacora triandra. This polyherbal remedy has recently been included in the Thailand National List of Essential Medicines (Herbal Products list). Methodology. A Bioassay-guided fractionation technique was used to evaluate antiallergy activities of crude extracts, and those obtained by the multistep column chromatography isolation of pure compounds. Inhibitory effect on the release of β-hexosaminidase from RBL-2H3 cells was used to determine antiallergic activity. Results. Two pure compounds from BCW formulation showed higher antiallergic activity than crude or semipure extracts. Pectolinarigenin showed the highest antiallergic activity, followed by O-methylalloptaeroxylin, with IC50 values of 6.3 μg/mL and 14.16 μg/mL, respectively. Moreover, the highest activities of pure compounds were significantly higher than chlorpheniramine (16.2 μg/mL). Conclusions. This study provides some support for the use of BCW in reducing itching and treatment of other skin allergic disorders. The two isolated constituents exhibited high antiallergic activity and it is necessary to determine their mechanism of action. Further phytochemical and safety studies of pure compounds are required before development of these as antiallergy commercial remedies.

Chemical constituents from fruits of Harrisonia perforata

Eight limonoids (1-8) including three A, B and D-seco-16-nor-type ones, 5,6-dehydrodesepoxyharperforin C2 (1), harrpernoid B (2), and its C-9S epimer, harrpernoid C (3), along with six known compounds (9-14), were isolated from fruits of Harrisonia perforata. Extensive spectroscopic analysis was used to elucidate their structures and stereochemistries. Further confirmation of structures of 1 and 2 were obtained by single-crystal X-ray diffraction. Limonoids (1-8) were evaluated for their anti-tobacco mosaic virus activity and in vitro cytotoxicity against A549 and HL60 cell lines; only compound 2 showed weak activity.

Botanical repellents and pesticides traditionally used against hematophagous invertebrates in Lao People's Democratic Republic: a comparative study of plants used in 66 villages

Hematophagous parasites such as leeches, ticks, mites, lice, bedbugs, mosquitoes, and myiasis-producing fly larvae are common health problems in Lao People's Democratic Republic. Several arthropod-borne infections, e.g., malaria, dengue fever, and Japanese encephalitis, are endemic there. Effective vector control methods including the use of pesticides, insecticide-treated bed nets, and synthetic and plant-based repellents are important means of control against such invertebrates and the pathogens they may transmit or directly cause. In this study, we documented traditional knowledge on plants that are used to repel or kill hematophagous arthropods, including mosquitoes, bedbugs, human lice, mites and ticks, fly larvae, and blood-sucking leeches. Structured interviews were carried out in 66 villages comprising 17 ethnic groups, covering a range of cultures, throughout Lao People's Democratic Republic. A total of 92 plant species was recorded as traditional repellents (including plants for pesticidal usages) in 123 different plant-ectoparasite combinations. The number and species of plants, and animal taxa repelled (or killed) per plant species differed per region, village, and ethnic group. Traditional use was confirmed in the scientific literature for 74 of these plant species, and for an additional 13 species using literature on closely related species. The use of botanical repellents and pesticides from many plant species is common and widespread in the Lao countryside. In the future, the identification of the active components in certain plants to develop more optimal, inexpensive repellents, insecticides, acaricides, or antileech compounds as alternatives to synthetic repellents/pesticides against blood-feeding insects, ticks, mites, and leeches is warranted.

Antimalarial and cytotoxic activities of ethnopharmacologically selected medicinal plants from South Vietnam

Malaria is a major global public health problem and the alarming spread of drug resistance and limited number of effective drugs now available underline how important it is to discover new antimalarial compounds. An ethnopharmacological investigation was undertaken of medicinal plants traditionally used to treat malaria in the South Vietnam. Forty-nine plants were identified, 228 extracts were prepared and tested for their in vitro activity against Plasmodium falciparum, and assessed for any cytotoxicity against the human cancer cell line HeLa and the embryonic lung MRC5 cell line. In a first screening at a concentration of 10 microg/ml, 92 extracts from 46 plants showed antiplasmodial activity (parasite growth inhibition >30%). The IC(50) values of the most active extracts were determined as well as their selectivity towards Plasmodium falciparum in comparison to their cytotoxic effects against the human cell lines. Six plants showed interesting antiplasmodial activity (IC(50) ranging from 0.4 to 8.6 microg/ml) with a good selectivity: two Menispermaceae, Arcangelisia flava (L.) Merr. and Fibraurea tinctoria Lour., and also Harrisonia perforata (Blanco) Merr. (Simaroubaceae), Irvingia malayana Oliv. ex Benn. (Irvingiaceae), Elaeocarpus kontumensis Gagn. (Elaeocarpaceae) and Anneslea fragrans Wall. (Theaceae).

Limonoids: overview of significant bioactive triterpenes distributed in plants kingdom

The search for limonoids started long back when scientists started looking for the factor responsible for bitterness in citrus which has negative impact on citrus fruit and juice industry worldwide. The term limonoids was derived from limonin, the first tetranortriterpenoid obtained from citrus bitter principles. Compounds belonging to this group have exhibited a range of biological activities like insecticidal, insect antifeedant and growth regulating activity on insects as well as antibacterial, antifungal, antimalarial, anticancer, antiviral and a number of other pharmacological activities on humans. Although hundreds of limonoids have been isolated from various plants but, their occurrence in the plant kingdom is confined to only plant families of order Rutales and that too more abundantly in Meliaceae and Rutaceae, and less frequently in Cneoraceae and Harrisonia sp. of Simaroubaceae. Limonoids are highly oxygenated, modified terpenoids with a prototypical structure either containing or derived from a precursor with a 4,4,8-trimethyl-17-furanylsteroid skeleton. All naturally occurring citrus limonoids contain a furan ring attached to the D-ring, at C-17, as well as oxygen containing functional groups at C-3, C-4, C-7, C-16 and C-17. The structural variations of limonoids found in Rutaceae are less than in Meliaceae and are generally limited to the modification of A and B rings, the limonoids of Meliaceae are more complex with very high degree of oxidation and rearrangement exhibited in the parent limonoid structure. To counter the problem of bitterness in citrus juice and products genetic engineering of citrus to maximize the formation of limonoid glucosides for reducing limonoid bitterness is the focus of recent and future research. Regarding the biological activities of limonoids the investigations are to be directed towards detailed characterization, quantification, and designing a simple as well as versatile synthetic route of apparently important limonoids. Extraction methods too should be optimized; evaluation and establishment of pharmaco-dynamic and kinetic principles, and structure activity relationships should be a key goal associated with limonoids so that they can be safely introduced in our arsenal of pharmaceuticals to safeguard the humanity from the wrath of disease and its discomfort.

Mexicanolide limonoids from the Madagascan Meliaceae Quivisia papinae

An investigation of the seeds of the Madagascan Meliaceae Quivisia papinae has yielded five mexicanolide group limonoids, together with two known mexicanolide limonoids and two known triterpenoids. Quivisianolide A 9 possesses a hitherto unreported 9alpha,11alpha-epoxide ring, quivisianolide B 10 the corresponding delta(9(11)) double bond, and quivisianone 11 is a 17-keto seco-ring D compound.