Three new phenanthrenes, a new stilbenoid isolated from the roots ofStemona tuberosaLour. and their cytotoxicity

Search for Snail Repellents: Antimollusc Activities from Stemona parviflora and Six Other Chinese Stemona Species

Snails are important agricultural pests difficult to control, but data regarding molluscicidal assays are scant. Stemona alkaloids are typical secondary metabolites for the taxa and have been broadly investigated for their pharmacological and toxicological effects. This makes it possible for us to further develop the toxicities of these compounds to snails. In this work, we tested the antifeedant properties of leaves from seven Chinese Stemona species against the land snail species Bradybaena ravida in choice and non-choice feeding assays. The tested leaves Stemona parviflora exhibited the most deterrent effects, and a further phytochemical investigation of aerial parts led to the identification of 16 alkaloids. Among them, three novel alkaloids could be identified. The alkaloidal fraction and single alkaloids were further assayed against this snail species, and the results suggest a cocktail effect because the impact of the alkaloidal fraction was higher than the effects caused by single alkaloids. The study can promote the search process of natural antimollusc products from plants to control snails.

Bioactive small-molecule constituents of Lao plants

Laos has a rich plant diversity, and medicinal plants are used extensively in Lao traditional medicine for the treatment of a variety of human diseases. However, only a relatively small number of these plants have been investigated for their major components with potential antitumor, anti-infective, and other types of bioactivities. These species include Asparagus cochinchinensis, Diospyros quaesita, Gongronema napalense, Marsypopetalum modestum, Nauclea orientalis, Rourea minor, Stemona pierrei, and Stemona tuberosa. Thus far, the bioactive compounds isolated from these Lao plants include alkaloids, glycerol esters, phenolic compounds such as lignans and stilbenoids, steroids, and triterpenoids. Of these, the norlignan, nyasol (1b), the triterpenes, pyracrenic acid [3β-O-trans-caffeoylbetulinic acid (3)] and betulinic acid (3b), and the dimeric thiopyridine, dipyrithione (5), were found to show both cancer cell cytotoxicity and anti-infective activity. The present review focuses on examples of promising lead compounds isolated from Lao plants, with their possible development as potential therapeutic agents being discussed. It is hoped that this contribution will provide useful information on higher plants growing in Laos to help stimulate future discoveries of potential agents for the treatment of cancer, infections, and other diseases.

FT-ICR-MS-based metabolomics: A deep dive into plant metabolism

Metabolomics involves the identification and quantification of metabolites to unravel the chemical footprints behind cellular regulatory processes and to decipher metabolic networks, opening new insights to understand the correlation between genes and metabolites. In plants, it is estimated the existence of hundreds of thousands of metabolites and the majority is still unknown. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) is a powerful analytical technique to tackle such challenges. The resolving power and sensitivity of this ultrahigh mass accuracy mass analyzer is such that a complex mixture, such as plant extracts, can be analyzed and thousands of metabolite signals can be detected simultaneously and distinguished based on the naturally abundant elemental isotopes. In this review, FT-ICR-MS-based plant metabolomics studies are described, emphasizing FT-ICR-MS increasing applications in plant science through targeted and untargeted approaches, allowing for a better understanding of plant development, responses to biotic and abiotic stresses, and the discovery of new natural nutraceutical compounds. Improved metabolite extraction protocols compatible with FT-ICR-MS, metabolite analysis methods and metabolite identification platforms are also explored as well as new in silico approaches. Most recent advances in MS imaging are also discussed.

The traditional uses, phytochemistry, and pharmacology of Stemona species: A review

ETHNOPHARMACOLOGICAL RELEVANCE

Plants of genus Stemona (Stemonaceae) have been long used locally and traditionally in many South and East Asian counties to relieve cough, dispel phlegm, prevent asthma, control pests, diminish inflammation, decrease pain, and treat some cutaneous diseases.

AIM OF STUDY

This review provided comprehensive and up-to-date information about botanic characterization and distribution, ethnopharmacology, secondary metabolites, pharmacological activities, and toxicology of plants of genus Stemona to explore the scientific potential and future therapeutic potential of the plants.

MATERIALS AND METHODS

This article conducted a literature review on information about the Stemona species in multiple electronic databases, including PubMed, Web of Science, Wiley, Science Direct, Elsevier, Google Scholar, ACS publications, SpringerLink, and China National Knowledge Internet. Information was also derived from other literature sources (e.g. Chinese Pharmacopoeia, 2015 edition, Chinese herbal classic books, PhD and MSc thesis). Plant names were validated by "The Plant List" (www.theplantlist.org). All studies of the genus Stemona were included in this review until March 2020.

RESULTS

Our comprehensive analysis of the scientific literatures indicated that many Stemona species are popular and valuable herbal medicines with therapeutic potentials to treat various ailments. Phytochemical analyses identified alkaloids and stilbenoids as the major bioactive substances of Stemona species. Numerous studies have shown that the extracts and secondary metabolites isolated from these plants have a wide range of pharmacological activities, including insecticidal and antifeedant, antitussive, anti-inflammatory, anticancer, antimicrobial, and antivirus activities.

CONCLUSION

Though plants of genus Stemona have been put to enormous traditional uses, the pharmacological studies conducted were insufficient. Therefore, more secondary metabolites need to be studied for more detailed pharmacological studies. Further studies are also required to establish the mechanisms which mediate the plants' bioactivities in relation to the medicinal uses as well as investigate any potential toxicity for future clinical studies.

Stilbenoids from the roots of Stemona tuberosa

Two new stilbenoids, stemobenoids A (1) and B (2), together with three known compounds were obtained from the roots of Stemona tuberosa. The structures of the new compounds were established by extensive spectroscopic analysis, including HRMS, 1D and 2D NMR data. Compounds 1 and 2 displayed potent quinone reductase inducing activity in Hepa 1c1c7 cells.

Cytotoxic and larvicidal activities of Stemona alkaloids from the aerial parts and roots of Stemona curtisii Hook.f

A new Stemona alkaloid glycoside derivative, 6-hydroxy-5,6-seco-stemocurtisinoside (4), was isolated from the ethanolic extract of the aerial parts of Stemona curtisii Hook.f., together with stemocurtisine (1), (11Z)-1',2'-didehydrostemofoline (2) and 6-hydroxy-5,6-seco-stemocurtisine (3). Whereas, stemocurtisine (1), stemocurtisinol (5) and oxyprotostemonine (6) were isolated from the roots. Their structures were elucidated using 1D and 2D NMR spectroscopy as well as MS experiments. The extract and the pure isolated compounds were evaluated for their cytotoxicities and their larvicidal activities against the dengue vector, Aedes aegypti. The alkaloid 2 showed the strongest larvicidal activity with a LC₅₀ value of 2.44 µM. While the alkaloid 3 exhibited cytotoxicity against MCF-7 and KB cells (IC₅₀ values of 62.52 and 18.82 µM, respectively) and showed no significant cytotoxicity against Vero cells. Additionally, quantitative analysis of the most active compounds; 2 and 3 in the crude extracts was also performed by HPLC.

Phenanthrenes: A Promising Group of Plant Secondary Metabolites

Although phenanthrenes are considered to constitute a relatively small group of natural products, discovering new phenanthrene derivatives and evaluating their prospective biological activities have become of great interest to many research groups worldwide. Based on 160 references, this review covers the phytochemistry and pharmacology of 213 naturally occurring phenanthrenes that have been isolated between 2008 and 2016. More than 40% of the 450 currently known naturally occurring phenanthrenes were identified during this period. The family Orchidaceae is the most abundant source of these compounds, although several new plant families and genera have been involved in the search for phenanthrenes. The presence of certain substituent patterns may be restricted to specific families; vinyl-substituted phenanthrenes were reported only from Juncaceae plants, and prenylated derivatives occur mainly in Euphorbiaceae species. Therefore, these compounds also can serve as chemotaxonomic markers. Almost all of the newly isolated compounds have been studied for their biological activities (e.g., potential cytotoxic, antimicrobial, anti-inflammatory, and antioxidant effects), and many of them showed multiple activities. According to the accumulated data, denbinobin, with a novel mechanism of action, has great potential as a lead compound for the development of a new anticancer agent.

A new 9,10-dihydrophenanthrene and cell proliferative 3,4-δ-dehydrotocopherols from Stemona tuberosa

A new compound, 9,10-dihydro-5-methoxy-8-methyl-2,7-phenanthrenediol (1), was isolated from the roots of Stemona tuberosa Lour. (Stemonaceae) together with two new optically active compounds, (2S,4'R,8'R)-3,4-δ-dehydrotocopherol (2) and (2R,4'R,8'R)-3,4-δ-dehydrotocopherol (3). The structures of compounds 1-3 were determined on the basis of spectroscopic data analysis. Compounds 2 and 3 were each purified from a stereoisomeric mixture of 2 and 3 by preparative HPLC using a chiral column for the first time. The absolute configurations at C-2 of 2 and 3 were determined by Circular Dichroism (CD) experiments. As a part of the research to find natural wound healing agents, all isolates and the mixture of 2 and 3 were evaluated for their cell proliferative effects using a mouse fibroblast NIH3T3 and a HeLa human cervical cancer cell line. As a result, 1, 2, 3, or the mixture of 2 and 3 showed 41.6%, 78.4%, 118.6%, 38.2% increases of cell proliferation in the mouse fibroblast NIH3T3 respectively, compared to 28.4% increase of δ-tocopherol. Moreover, none of them induced cancer cell proliferation. Therefore, 3,4-δ-dehydrotocopherols, especially pure isomers 2 and 3 can be suggested as potential wound healing agents.

Stemofurans X-Y from the Roots of Stemona Species from Laos

Two new phenylbenzofuran-type stilbenoids named stemofurans X and Y (1, 2) were isolated from the roots of Stemona pierrei and S. tuberosa, respectively, together with ten known compounds. These compounds were stemanthrenes B-C (3, 4), (+)-syringaresinol (5), maistemonine (6), isomaistemonine (7) and sesamin (8) from S. pierrei, and stemophenanthrenes A-C (9–11) and isopinosylvin A (12) from S. tuberosa. Stemofurans X-Y (1, 2) showed moderate cytotoxicity against the four cancer cell lines KB (human epidermal carcinoma), MCF7 (human breast carcinoma), SK-LU-1 (human lung carcinoma), and Hep-G2 (hepatocellular carcinoma).

Cytotoxic and antimicrobial activities of substituted phenanthrenes from the roots of Combretum adenogonium Steud Ex A. Rich (Combretaceae)

Aim:

The aim of this study was to isolate the bioactive compounds from the roots of Combretum adenogonium and assess for its antibacterial and cytotoxic properties.

Materials and Methods:

The extract was obtained using 20% aqueous ethanol and further subjected to fractionation with 1:1 n-butanol/water. Chromatographic analyses of the n-butanol fraction led to the isolation of compounds (1-3). The compounds (1-3) were assayed for antibacterial activities using two-fold microdilution methods and cytotoxicity using brine shrimps lethality assay.

Results:

Following spectroscopic analyses the compounds were established as 2,3,8-trihydroxy-4,6-dimethoxyphenanthrene (1a) and 2,3,8-trihydroxy-4,6-dimethoxy-9,10-dihydrophenanthrene (1β). Compound 2 was derived from 2,3,8-trihydroxy-4,6-dimethoxyphenanthrene condensation with methyl acetate while Compound 3 was derived from 2,3,8-trihydroxy-4,6-dimethoxy-9,10-dihydrophenanthrene condensation with methyl propionate. These compounds (1-3) were active against Pseudomonas aeruginosa with minimal inhibitory concentration-value of 0.16 mg/ml. The compounds (1-3) also exhibited significant toxicity with LC₅₀ (95% confidence interval [CI]) of 12.11 (7.32-20.05) µg/ml compared to standard anticancer drug, cyclophosphamide which had LC₅₀ (95% CI) value of 16.37 (12.01-22.31) µg/ml.

Conclusion:

These compounds add for a novel structure that can be synthesized, further screened for in vitro and in vivo models and clinical trials in order to evaluate its potential for further development as new anticancer agent.