Two new flavone glycosides from the leaves of Ochna afzelii Oliv. (Ochnaceae)

Two new glycosylflavones, 6''-O-acetyl-8-C-β-D-galactopyranosylchrysoeriol (1) and 8-C-β-D-galactopyranosylchrysoeriol (2) were isolated from the methanol extract of the leaves of Ochna afzelii Oliv., along with four known compounds namely 8-C-β-D-galactopyranosylapigenin (3), ochnaflavone (4), sitosterol-3-O-β-D-glucopyranoside (5) and D-mannitol (6). Isolation was performed chromatographically and the structures of the purified compounds were elucidated by analyzing their spectroscopic and mass spectrometric data. The antibacterial activity of extract, fractions, and compounds 1 - 4 was evaluated using broth microdilution method against Gram-positive and Gram-negative bacteria while the antioxidant capacity was performed using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) and the ferric reducing antioxidant power (FRAP) methods. The new flavones (1 and 2) displayed moderate antibacterial activities (MIC = 32 - 64 µg/mL) and weak antioxidant properties.

Polyoxygenated Stigmastane-Type Steroids from Vernonia kotschyana Sch. Bip. ex Walp. and Their Chemophenetic Significance

Four polyoxygenated stigmastanes (1-4) alongside known analogues (7-8) and flavonoids (5-6) were isolated from a dichloromethane/methanol (1:1, v/v) extract of the whole plant of Vernonia kotschyana Sch. Bip. ex Walp. (Asteraceae). Their structures were determined by means of spectroscopic and spectrometric analysis. The relative stereochemistry of the new compounds was established and confirmed via biosynthesis evidence and cyclization of 1 under acidic conditions. A plausible biosynthetic pathway to the new compounds and the chemophenetic significance of the isolated constituents were also discussed. The crude extract, fractions, and compounds (1-3) were assessed for their antibacterial activity against five highly prevalent bacterial strains. The fractions and compounds showed low to moderate activity with minimal inhibitory concentrations (MICs) > 125 µg/mL.

Demystifying racemic natural products in the homochiral world

Natural products possess structural complexity, diversity and chirality with attractive functions and biological activities that have significantly impacted drug discovery initiatives. Chiral natural products are abundant in nature but rarely occur as racemates. The occurrence of natural products as racemates is very intriguing from a biosynthetic point of view; as enzymes are chiral molecules, enzymatic reactions generating natural products should be stereospecific and lead to single-enantiomer products. Despite several reports in the literature describing racemic mixtures of stereoisomers isolated from natural sources, there has not been a comprehensive review of these intriguing racemic natural products. The discovery of many more natural racemates and their potential enzymatic sources in recent years allows us to describe the distribution and chemical diversity of this ‘class of natural products’ to enrich discussions on biosynthesis. In this Review, we describe the chemical classes, occurrence and distribution of pairs of enantiomers in nature and provide insights about recent advances in analytical methods used for their characterization. Special emphasis is on the biosynthesis, including plausible enzymatic and non-enzymatic formation of natural racemates, and their pharmacological significance.

Racemic natural products display a wealth of bioactivities and chemical diversity. Their derivation from intriguing racemization processes, through enzymatic or non-enzymatic pathways, are discussed here, as well as their pharmacological properties and the analytical techniques developed for their identification, resolution and characterization.

Insecticidal Activities of Atriplex halimus L., Salvia rosmarinus Spenn. and Cuminum cyminum L. against Dactylopius opuntiae (Cockerell) under Laboratory and Greenhouse Conditions

The wild cochineal Dactylopius opuntiae (Hemiptera: Dactylopiidae) is one of the major insect pests of the prickly pear Opuntia ficus-indica (L.) in Morocco, a well-known fruit and vegetable crop of arid and semi-arid regions around the world. The present study investigated the insecticidal potential of six extracts (three aqueous and three hydroalcoholic (MeOH/H₂O, 20/80 (v/v)) from Atriplex halimus (leaves), Salvia rosmarinus (leaves) and Cuminum cyminum (seeds) to control nymphs and adult females of D. opuntiae under laboratory and greenhouse conditions. Out of the tested samples, A. halimus aqueous extract showed the highest activity, inducing mortality rates of 67.04% (after 4 days) and 85% (after 8 days) on nymphs and adult females of D. opuntiae, respectively, at a concentration of 5% under laboratory conditions. It also showed the highest mortality rate of nymphs with 100% (4 days after application) and 83.75% of adult females (7 days after the second application) at a concentration of 5% when combined with black soap at 10 g/L under greenhouse conditions. The difference in the toxicity of plant species of the study was correlated with their saponin content. A total of 36 of these triterpene glucosides were suggested after a comprehensive LC-MSⁿ profiling of the most active extract, A. halimus, in addition to phytoecdysones and glycosylated phenolic acids and flavonoids. These findings provided evidence that the aqueous leaf extract of A. halimus could be incorporated in the management of the wild cochineal as an alternative to chemical insecticides.

Sesquiterpene Lactones from Vernonia tufnelliae: Structural Characterization and Biological Evaluation

The genus Vernonia is an extremely rich source of biologically active sesquiterpene lactones. The present report describes the spectroscopic structure elucidation and the cytotoxic and antimicrobial properties of five hitherto unknown germacranolide-like sesquiterpenoids and several known compounds. These new derivatives include a compound (1) with an unprecedented 10/5/5/6 tetracyclic framework featuring a hexahydro-1H,3H,7H-furo[3',4':3,4]furo[3,2-c]pyridin-1-one core resulting from an intramolecular cyclization cascade involving a methacrylate substituent and a low molecular weight amine. Furthermore, an elemane-germacranolide hybrid (2) and three amino acid-derived lactones (3-5) were characterized. A plausible biosynthetic pathway to the key alkaloid is presented, while shielding tensor calculations using DFT in combination with the DP4+ method were applied to elucidate its stereostructure. The newly characterized compounds along with ten known sesquiterpene lactones and phenolic compounds have been isolated from Vernonia tufnelliae, a medicinal plant from the western region of Cameroon. Their structures were consistent with spectroscopic and spectrometric data recorded. The present report is the first investigation of the chemistry and biology of V. tufnelliae.

Caper (Capparis spinosa L.): An Updated Review on Its Phytochemistry, Nutritional Value, Traditional Uses, and Therapeutic Potential

Caper (Capparis spinosa L.) is a perennial shrub of the family Capparaceae, endemic to circum-Mediterranean countries. Caper carries a renowned nutritional value, especially in terms of vitamins and antioxidants related to the occurrence of flavonoids, alkaloids, and glucosinolates as main secondary metabolites. Caper extracts have also shown to display antibacterial, antifungal, analgesic, antitumor, hepatoprotective, antioxidant, anti-inflammatory, and neuroprotective effects which correlate the uses of the plant in folk medicine against both metabolic and infectious diseases. The present review aims to provide exhaustive phytochemistry and pharmacological properties survey on Caper constituents. Attention has also been given to the nutritional values and traditional uses of main organs to pinpoint research gaps for future investigations on the plant.

Syzygium jambos L. Alston: An Insight Into its Phytochemistry, Traditional Uses, and Pharmacological Properties

Medicinal plants have been used since ancient times for human healthcare as drugs, spices, and food additives. The progress in technology and medicine observed, the last decades, has improved the quality of life and healthcare but with worrisome drawbacks. Side effects caused by synthetic drugs for instance originate sometimes irreversible health disorders. Natural substances, in contrast, are biologically and environmentally friendly. Syzygium jambos L. (Alston) also known as rose apple conveys a long history as essential traditional medicine with a broad spectrum of application in various cultures. The plant discloses a diverse group of secondary metabolites and extracts that displayed major susceptibilities towards various health concerns especially stress-related and inflammatory diseases. Despite a rich literature about the plant, the chemistry and biology of S. jambos have not been comprehensively reviewed yet. Accordingly, we present herein a literature survey of rose apple which aims to draw the chemical identity of the plant and establish a consistent discussion on the respective biological application of plant extracts and their corresponding traditional uses. The present work could provide a scientific basis for future studies and necessary information for further investigations of new drug discovery.

Toward the Allelopathy of Peganum sp. and Related Chemical Constituents in Agriculture

The genus Peganum constitutes one of the perennial groups of plants of semi-arid regions across the world. It produces diverse classes of metabolites with claimed valuable pharmacological applications. Despite the key chemical and biological properties of the genus, its allelopathy or that of one of its species has not been reviewed yet. Thus, the present survey aims to report the agricultural applications of extracts, fractions, and compounds from the genus Peganum. This work was based on the available literature related to both the Peganum genus and agriculture, which were generated from available high-impact scientific engines. The plants in this genus contain a large group of secondary metabolites including phenolic compounds, terpenes, and N-containing compounds. Alkaloids, as the main components of the extracts from plants in the genus, were identified as the major active principles. The toxicity of Peganum isolates against plants and related pest organisms was also reviewed. Extract preparations from species of Peganum were listed among insecticidal and herbicidal allelochemicals used for crop protection. The review also tried to contextualize natural products in agriculture. Peganum plant extracts and fractions have showed significant potential in weed and crops management, soil health, and biopesticide production.

Alkenylbenzoquinones and other compounds from the fruit of Maesa lanceolata exhibited potent cytotoxic, antibacterial, and antiradical scavenging activities§

A phytochemical study of the methanol extract of the fruit of Maesa lanceolata resulted in the isolation of a new alkenylbenzoquinone (1), alongside the known compounds (Z)-2,5-dihydroxy-6-methyl-3-(pentadec-10'-enyl)-1,4-benzoquinone (2), 2,5-dihydroxy-6-methyl-3-(nonadec-14'-enyl)-1,4-benzoquinone (3), 2,5-dihydroxy-6-methyl-3-(tridecyl)-1,4-benzoquinone (4), (2S,3S,4R,2'R,9E)-[2'-hydroxytetraeicosanoyl]-2-aminooctadec-9-ene-1,3,4-triol (5), monopalmitin (glyceryl palmitate) (6), lupeol (7), and 3-O-(β-D-glucopyranoside)-β-sitosterol (8). The structures of the compounds were established by the means of spectroscopic (1 D- and 2 D-NMR) and spectrometric techniques (MS). The isolated compounds were assessed for their antibacterial, cytotoxic, and antiradical activities. Compound 2 showed moderate activity against Staphylococcus warneri (DSMZ 20036), while the other compounds were inactive. The two quinones 1 and 2 were significantly cytotoxic, with IC₅₀ values of 0.005 µM and 12.5 µM respectively, and were weakly active towards DPPH radical (IC₅₀ >250 µg/mL).

LC-ToF-ESI-MS Patterns of Hirsutinolide-like Sesquiterpenoids Present in the Elephantopus mollis Kunth Extract and Chemophenetic Significance of Its Chemical Constituents

A total of nine sesquiterpenoid lactones together with phenolic compounds and other terpenes were identified from the crude methanol extract of Elephantopus mollis Kunth. Compounds were isolated using different chromatographic techniques and their structures were determined by NMR and IR spectroscopy as well as mass spectrometry. The structures of some detected compounds were assigned based on LC-ToF-ESI-MS screening of main fractions/subfractions from flash chromatography and comparison with isolated analogues as standards. The findings revealed not only the in-source loss of water as the base peak in hirsutinolides but also the in-source loss of corresponding alcohol when the oxygen at position 1 is alkylated. The present study also draws up a complement of data with respect to hirsutinolide-like sesquiterpene lactones whose LC-MS characteristics are not available in the literature. The chemophenetic significance is also discussed. Some of the isolated compounds were reported for the first time to be found in the species, the genus as well as the plant family. The medium-polar fractions of the crude extract, also containing the larger amount of sesquiterpenoid lactones, exhibited activity both against a cancer cell line and bacterial strains. Isolated lactones were also active against the cancer cell line, while the chlorogenic derivatives also valuable in Elephantopus genus showed potent radical scavenging activity. This is the first report of cytotoxic and antibacterial activities of our samples against the tested strains and cell line. The present study follows the ongoing research project dealing with the characterization of taxa with antibacterial and antiparasitic activities from Cameroonian pharmacopeia.

New Alkenylresorcinols with Cytotoxic and Antimicrobial Activities from the Leaves of Embelia schimperi

A phytochemical study of the methanol extract of the leaves of Embelia schimperi resulted in the isolation of three new alkenylresorcinols, 1:  - 3: , together with the known analogs 4:  - 7: . Their structures were established by a combination of spectroscopic techniques. Compounds 1:  - 7: exhibited moderate cytotoxic activity against human cervical cancer cells HeLa-S3 and more pronounced antimicrobial properties towards bacteria and filamentous fungi. The present study falls into an ongoing research project on the characterization of bioactive phenolic lipids from plants of the family Primulaceae.

A new ceramide from the leaves of Lannea schimperi (Hochst. ex A.Rich.) Engl

A new ceramide is being reported herein together with six known compounds from the methanol extract of the leaves of Lannea schimperi (Hochst. ex A.Rich.) Engl. The metabolites were obtained through repeated open column chromatography and were characterized by spectroscopic and spectrometric techniques. The radical-scavenging activity of the crude extract and isolated compounds was evaluated using the DPPH radical. The obtained results suggest the studied species as prominent candidate to fight reactive oxygen species (ROS).

Cytotoxycity and antiplasmodial activity of phenolic derivatives from Albizia zygia (DC.) J.F. Macbr. (Mimosaceae)

Background

The proliferation and resistance of microorganisms area serious threat against humankind and the search for new therapeutics is needed. The present report describes the antiplasmodial and anticancer activities of samples isolated from the methanol extract of Albizia zygia (Mimosaseae).

Material

The plant extract was prepared by maceration in methanol. Standard chromatographic, HPLC and spectroscopic methods were used to isolate and identify six compounds (1–6). The acetylated derivatives (7–10) were prepared by modifying 2-O-β-D-glucopyranosyl-4-hydroxyphenylacetic acid and quercetin 3-O-α-L-rhamnopyranoside, previously isolated from A. zygia (Mimosaceae). A two-fold serial micro-dilution method was used to determine the IC_50s against five tumor cell lines and Plasmodium falciparum.

Results

In general, compounds showed moderate activity against the human pancreatic carcinoma cell line MiaPaca-2 (10 < IC₅₀ < 20 μM) and weak activity against other tumor cell lines such as lung (A-549), hepatocarcinoma (HepG2) and human breast adenocarcinoma (MCF-7and A2058) (IC₅₀ > 20 μM). Additionally, the two semi-synthetic derivatives of quercetin 3-O-α-L-rhamnopyranoside exhibited significant activity against P. falciparum with IC₅₀ of 7.47 ± 0.25 μM for compound 9 and 6.77 ± 0.25 μM for compound 10, higher than that of their natural precursor (IC₅₀ 25.1 ± 0.25 μM).

Conclusion

The results of this study clearly suggest that, the appropriate introduction of acetyl groups into some flavonoids could lead to more useful derivatives for the development of an antiplasmodial agent.

Neo-clerodane diterpenoids from Conyza pyrrhopappa Sch.Bip. ex A.Rich

Two hitherto unknown neo-clerodane-type diterpenoids along with twelve known compounds have been isolated from Conyza pyrrhopappa Sch.Bip. ex A.Rich, a medicinal plant traditionally used across tropical Africa to relieve fever. The structures of isolates have been elucidated by a combination of spectroscopic techniques. The crude extract and the isolated compounds were evaluated in the Hela-S3 cell line and in a panel of microorganisms (bacteria and fungi) at concentrations up to 50 µg/mL. The new compounds were inactive while the pentamethylated flavonoids showed low to significant activity against the cancer cell line used. However, none of the samples showed any activity against the tested microorganisms at this concentration. The present manuscript is the first investigation of the cytotoxicity of phytochemicals and extract from C. pyrrhopappa.

Caffeate and piperidine-3-ol derivatives from the stem bark of Cassia sieberiana

A new caffeate derivative from the ethanol extract of the stem bark of Cassia sieberiana DC. is described herein along with the known secondary metabolites spectaline (2), iso-6-cassine (3), 3-O-methyl-chiro-inositol (4), monobehenin (5), octyl nonadecyloate (6), β-sitosterol (7), stigmasterol (8) and sitosterol 3-O-β-D-glucopyranoside (9). The chemical structures were elucidated by means of various spectroscopic and spectrometric techniques. Extract and isolated compounds were devoid of inhibitory action against the herein selected bacterial strains (MICs > 256 μg/mL) but showed capacities to reduce 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical (EC₅₀ < 3 μg/mL) considerably better than the "gold standard" trolox (EC₅₀ 6.47 ± 0.48 μg/mL).

A new polyketide from the bark of Hypericum roeperianum Schimp. (Hypericaceae)

The isolation and spectroscopic data of a hitherto undescribed polyketide (1) from Hypericum roeperianum Schimp. (Hypericaceae) together with six known compounds (2-7) is herein reported. The structure elucidation is based on extensive 1D- and 2D-NMR, infrared, UV and MS experiments. The structures of the known compounds were confirmed by comparison of their spectroscopic data with those of similar reported compounds in the literature. Some of the isolated compounds had a significant activity against a panel of multidrug-resistant bacterial strains.Supplemental data for this article can be accessed at https://doi.org/10.1080/14786419.2019.1677655.

Saponin with antibacterial activity from the roots of Albizia adianthifolia

An unprecedented saponin is being reported herein together with five known compounds from the methanol extract of the roots of Albizia adianthifolia. The metabolites were obtained over repeated open column chromatography methods and spectroscopic followed by spectrometric techniques. The isolated compounds were tested against eleven Gram-negative bacteria including multidrug resistant strains. The results revealed considerable inhibition of the new saponin against the studied bacteria with MIC values ranging from 16 to 128 μg/mL.

Antibacterial Activity of Flavans from Crinum distichum

The phytochemical study of the ethanol extract from Crinum distichum Herb. was carried out using reversed phase high performance liquid chromatography and afforded a new natural flavan (1), along with (2 S)-4'-hydroxy-7-methoxyflavan (2), (2 R)-4'-hydroxy-5,7-dimethoxyflavan (3), hippadine (4) and hippacine(5). The structure of the new compound was elucidated using a combination of NMR and HRESI-MS analysis while the structures of the known compounds were established by comparison of their spectroscopic data with those of similar reported compounds. Compounds 2–5 also had moderate activity (32> MIC> 16 μg/mL) against methicillin resistant (MRSA) and methicillin sensitive (MSSA) Staphylococcus aureus (both Gram-positive bacteria), whilst compound 1 was inactive against these two bacterial strains (MIC>128μg/mL). None of the compounds was active against the Gram-negative bacterial strains Escherichia coli and Klesbesiella pneumoniae. The research described herein confirms once more that, plants of the Crinum genus continue to be a rich and underexploited source of new small molecules that could lead to the discovery of new bioactive compounds.

Rothtalazepane, A New Azepane from the Wood of Rothmannia talbotii (Rubiaceae)

Rothmannia talbotii, a hitherto chemically unexplored medicinal plant, is used in the Western Region of Cameroon to relieve fever. In our ongoing search for bioactive compounds from Cameroonian medicinal plants, a previously undescribed compound rothtalazepane (1), along with six known compounds, aitchisonide B (2), D-mannitol (3), β-D-glucopyranosyl-(6→1’)-β-D-glucopyranoside (4), monopalmitin (5), stigmasterol (6), and sitosterol 3- O-β-D-glucopyranoside (7) were isolated and characterized from the crude ethanol extract of the wood of R. talbotii. Rothtalazepane (1) exhibits no significant activity against several microbial strains, thus its function likely lies not in antimicrobial defense and it is not the active principle against urinary infections described for Rothmannia.

Antibacterial activity of ethanolic extract and compounds from fruits of Tectona grandis (Verbenaceae)

Background

Well known as teak, Tectona grandis is widely used in African folk medicine for its pharmacological relevance. In Cameroon, this species is a reputed laxative in the Northern Region while in the Western Region, it is used in the treatment of skin diseases and diarrhoea.

Materials and methods

Separation and isolation of compounds were performed using different chromatographic methods while their structures were elucidated by spectroscopic techniques including MS and NMR, and by comparison of data with those reported in the literature. Isolated compounds as well as crude ethanol extract were tested for their antibacterial activities using broth micro-dilution method against four Gram negative bacteria strains Escherichia coli (ATCC 8739), Pseudomonas aeruginosa (PA 01), Klebsiella pneumonia (ATCC 11296) and Escherichia aerogenes (ATCC 13048).

Results

Three known compounds were isolated, including two quinones and one triterpene. They were identified as tectograndone (1), 6-methyl-1,4-dihydroxyanthraquinone (2), and 2β-hydroxyursolic acid (3) respectively. Crude ethanol extract showed good activity against the bacteria strains tested with MIC of 64–256 μg/mL. Among the isolated metabolites, 6-methyl-1,4-dihydroxyanthraquinone exhibited a strong activity against Escherichia aerogenes with MIC of 16 μg/mL, while tectograndone showed a moderate activity against Escherichia coli with MIC of 32 μg/mL. The antibacterial screening of the fruits of this plant as well as that of compounds 1 and 2 is reported herein for the first time.

Conclusion

The research work presented here shows that Tectona grandis fruits possess compounds which could be developed in the treatment of bacterial diseases.