Daltonkins A and B, Two New Carboxyethylflavanones from the Heartwood ofDalbergia tonkinensis

Vietnamese Dalbergia tonkinensis: A Promising Source of Mono- and Bifunctional Vasodilators

Hypertension is a risk factor for cardiovascular diseases, which are the main cause of morbidity and mortality in the world. In the search for new molecules capable of targeting K_Ca1.1 and Ca_V1.2 channels, the expression of which is altered in hypertension, the in vitro vascular effects of a series of flavonoids extracted from the heartwoods, roots, and leaves of Dalbergia tonkinensis Prain, widely used in traditional medicine, were assessed. Rat aorta rings, tail artery myocytes, and docking and molecular dynamics simulations were used to analyse their effect on these channels. Formononetin, orobol, pinocembrin, and biochanin A showed a marked myorelaxant activity, particularly in rings stimulated by moderate rather than high KCl concentrations. Ba²⁺ currents through Ca_V1.2 channels (I_Ba1.2) were blocked in a concentration-dependent manner by sativanone, 3′-O-methylviolanone, pinocembrin, and biochanin A, while it was stimulated by ambocin. Sativanone, dalsissooside, and eriodictyol inhibited, while tectorigenin 7-O-[β-D-apiofuranosyl-(1→6)-β-D-glucopyranoside], ambocin, butin, and biochanin A increased I_KCa1.1. In silico analyses showed that biochanin A, sativanone, and pinocembrin bound with high affinity in target-sensing regions of both channels, providing insight into their potential mechanism of action. In conclusion, Dalbergia tonkinensis is a valuable source of mono- and bifunctional, vasoactive scaffolds for the development of novel antihypertensive drugs.

Essential oils of Uvaria boniana - chemical composition, in vitro bioactivity, docking, and in silico ADMET profiling of selective major compounds

Phytochemical investigation applying GC (gas chromatography)-MS (mass spectrometry)/GC-FID (flame ionization detection) on the hydro-distilled essential oils of the Vietnamese medicinal plant Uvaria boniana leaf and twig lead to the detection of 35 constituents (97.36%) in the leaf oil and 52 constituents (98.75%) in the twig oil. Monoterpenes, monoterpenoids, sesquiterpenes, and sesquiterpenoids were characteristic of U. boniana essential oils. The leaf oil was represented by major components (E)-caryophyllene (16.90%), bicyclogermacrene (15.95%), α-humulene (14.96%), and linalool (12.40%), whereas four compounds α-cadinol (16.16%), epi-α-muurolol (10.19%), α-pinene (11.01%), and β-pinene (8.08%) were the main ones in the twig oil. As compared with the leaf oil, the twig oil was better in antimicrobial activity. With the same MIC value of 40 mg/mL, the twig oil successfully controlled the growth of Gram (+) bacterium Bacillus subtilis, Gram (-) bacterium Escherichia coli, fungus Aspergillus niger, and yeast Saccharomyces cerevisiae. In addition, both two oil samples have induced antiinflammatory activity with the IC₅₀ values of 223.7-240.6 mg/mL in NO productive inhibition when BV2 cells had been stimulated by LPS. Docking simulations of four major compounds of U. boniana twig oil on eight relevant antibacterial targets revealed that epi-α-muurolol and α-cadinol are moderate inhibitors of E. coli DNA gyrase subunit B, penicillin binding protein 2X and penicillin binding protein 3 of Pseudomonas aeruginosa with similar free binding energies of -30.1, -29.3, and -29.3 kJ/mol, respectively. Furthermore, in silico ADMET studies indicated that all four docked compounds have acceptable oral absorption, low metabolism, and appropriated toxicological profile to be considered further as drug candidates.

Essential Oils of the Leaf and Stem of Polyalthia viridis Craib and Their Biological Activities

Plants of the genus Polyalthia can be seen as a rich resource of essential oils type terpenoids. In this study, the essential oils obtained by hydro-distillation from the leaf and stem of Polyalthia viridis were analysed by gas chromatography/mass spectrometry–flame ionization detection. Thirty-nine constituents (95.3%) were identified in the leaf oils and 42 constituents (90.9%) in the stem oils. Sesquiterpene hydrocarbons and oxygenated sesquiterpenes were the main constituents of both oils, in which 2 sesquiterpene hydrocarbons, germacrene D (45.1%-47.4%) and bicyclogermacrene (8.2%-17.1%), were the 2 major compounds. The stem oils inhibited the growth of 3 cancer cell lines, HepG2, MCF7, and A549, with half inhibitory concentration (IC50) values of 56.7 to 68.4 μg/mL. The stem oils also successfully suppressed the growth of the filamentous fungus Aspergillus niger and the yeast Candida albicans with minimum inhibitory concentration values of 50 μg/mL. P viridis oils suppressed NO production in lipopolysaccharide-stimulated BV2 microglial cells, with IC50 values of 57.6 to 76.7 μg/mL.

Essential Oils of Polyalthia suberosa Leaf and Twig and Their Cytotoxic and Antimicrobial Activities

Essential oils from the leaf and twig of Polyalthia suberosa (Roxb.) Thwaites were analyzed using GC/MS/FID. A total of sixty-three constituents were namely identified accounting for 96.03 and 94.12 % in the hydrodistilled oils of the leaf and twig, respectively. Monoterpenes, monoterpenoids, sesquiterpenes, and sesquiterpenoids were characteristic derivatives of P. suberosa essential oils. Sesquiterpenes bicyclogermacrene (26.26 %) and (E)-caryophyllene (7.79 %), and monoterpene β-pinene (12.71 %) were the major constituents of the leaf oil. Sesquiterpenes (E)-caryophyllene (17.17 %) and α-humulene (9.55 %), sesquiterpenoid caryophyllene oxide (9.41 %), and monoterpenes camphene (8.16 %) and tricyclene (6.35 %) were to be main components in the twig oil. The leaf oil indicated cytotoxic activity against three cancer cell lines HepG2, MCF7 and A549 with the IC₅₀ values of 60.96-69.93 μg/mL, while the twig oil inhibited MCF7 with the IC₅₀ value of 66.70 μg/mL. Additionally, the twig oil successfully suppressed the growth of the negative Gram bacterium Pseudomonas aeruginosa, fungus Aspergillus niger, and yeast Candida albicans with the same MIC value of 50 μg/mL, whereas the leaf oil had the same result on the negative Gram bacterium Escherichia coli.

Antimicrobial flavonoids as a potential substitute for overcoming antimicrobial resistance

BACKGROUND

Infectious diseases are the leading cause of death in 21^st century due to antimicrobial resistance and scarcity of new molecules to undertake rising infections. There could be a multiple reasons behind antimicrobial resistance whether it is increased drug metabolism or bacterial endotoxins. The demand of effective medication is increasing day by day to treat microbial infections and combat antimicrobial resistance. In recent years most of the synthetic antimicrobials developed resistance so natural products could provide better options to fulfill this demand. There has been increasing interest in the research on flavonoids because various flavonoids were found to be effective against pathogenic microorganisms.

OBJECTIVE

The objective of this article will be to explore antimicrobial activity of flavonoids with special focus on their possible mechanism of action.

METHODS

The article reviewed recent literature related to flavonoids with antimicrobial activity, which were isolated from various sources and the compounds showing fairly good activity against tested microbial species were discussed.

RESULTS

By throughout literature review it has been found that flavonoids show antimicrobial effect by inhibiting virulence factors, efflux pump, biofilm formation, membrane disruption, cell envelop synthesis, nucleic acid synthesis, and bacterial motility inhibition.

CONCLUSION

Most of the antimicrobial drugs available now a days are ineffective due to development of resistance to them. Flavonoids have the potential to overcome this emerging crisis as this class of natural products showed the antimicrobial activity by different mechanisms than those of conventional drugs, so flavonoid could be an effective treatment of pathogenic infections.

Fatty Acids, Tocopherols, and Phytosterol Composition of Seed Oil and Phenolic Compounds and Antioxidant Activity of Fresh Seeds from Three Dalbergia Species Grown in Vietnam

This research aimed to investigate the chemical composition of seed oils extracted from three Vietnamese Dalbergia species (D. tonkinensis, D. mammosa, and D. entadoides). The fatty acid profiles and contents of tocopherols and sterols of the seed oils, and total phenolic compounds extracted from the fresh seeds were characterized using different methods. Among the examined samples, D. tonkinensis seed oils showed high contents of linoleic acid (64.7%), whereas in D. mammosa, oleic acid (51.2%) was predominant. In addition, α- and γ-tocopherol and β-sitosterol were major ingredients in the seed oils, whereas ferulic acid and rosmarinic acid are usually predominant in the seeds of these species. Regarding sterol composition, the D. entadoides seed oil figured for remarkably high content of Δ5,23-stigmastadienol (1735 mg/kg) and Δ7-stigmastenol (1298 mg/kg). In addition, extracts with methanol/water (80:20, v/v) of seeds displayed significant in vitro antioxidant activity which was determined by DPPH free radical scavenging assay.

Ethnobotanical study on medicinal plants used by local Van Kieu ethnic people of Bac Huong Hoa nature reserve, Vietnam

ETHNOPHARMACOLOGICAL RELEVANCE

The ethnobotanical survey was carried out in the Bac Huong Hoa Nature Reserve (BHHNR), Vietnam. The Van Kieu ethnic group, the inhabitant of Nature Reserve, is rich in knowledge about the medicinal plants found in the Nature Reserve. However, their knowledge is less documented.

AIM OF THE STUDY

The present study was conducted to document the use of medicinal plants, plant parts used, mode of preparation and delivery by the ethnic group of Van Kieu. The study also aimed at comparing the information generated by this study with the previously published Dictionary of Vietnam Medicinal plants (DVM).

MATERIALS AND METHODS

The information was collected through semi-structured and unstructured interviews. The interviews were conducted from April 2016 to March 2017. The number of informants involved in the survey was 93 belonging to age group of 20-81. Species Use-Reports (UR) were analyzed to determine the plant importance in the local and the Informant Consensus Factor (FIC). Local plant uses were listed and compared with the previously published data from Vietnam.

RESULTS

Comprehensively 355 Use-Reports were documented in this study. A total of 111 medicinal plant species belonging to 102 genera and 46 families were reported. Out of 46 families, Euphorbiaceae (10 species), Compositae and Leguminosae (9 species each), Apocynaceae (7 species), Rutaceae and Rubiaceae (5 species each) were the dominant families. Leaves were the most frequently used plant part (43.1%) in the preparation of medicines. The most frequent preparation method was decoction (49%) while the oral route of administration (51%) was the most commonly mentioned mode of administration. Artocarpus heterophyllus Lam., Chromolaena odorata (L.) R.M.King & H.Rob., Blumea balsamifera (L.) DC., Psidium guajava L. and Catunaregam spinosa (Thunb.) Tirveng. were shown to be the most useful plants as indicated by their relatively high UR. Eight medicinal plants (7.21%) used by Van Kieu ethnic people have not been previously reported in DVM.

CONCLUSION

The Van Kieu ethnic group holds valuable knowledge about uses of medicinal plant resources which is inherited through generations however this knowledge was not documented. The study highlights the need for documenting and publicizing the traditional medicinal knowledge which will provide basic data for further research and conservation.

New Records of Potent In-Vitro Antidiabetic Properties of Dalbergia tonkinensis Heartwood and the Bioactivity-Guided Isolation of Active Compounds

Alpha-glucosidase inhibitory activity has been commonly used for the evaluation of antidiabetic property in vitro. The aim of this study is to investigate and characterize Dalbergia tonkinensis as a potential source of antidiabetic compounds. The screening of the active parts used, such as trunk bark, heartwood, and the leaves of Dalbergia tonkinensis indicated that all these extracted parts used with methanol demonstrated potent α-glucosidase inhibitory activity. The in vitro antidiabetic property of Dalbergia tonkinensis was notably recorded for the first time and showed activity (EC₅₀ = 0.17–0.78 mg/mL) comparable to those of reported potent herbal extracts (EC₅₀ = 0.25–4.0 mg/mL) and higher activity than that of acarbose, a commercial antidiabetic drug (EC₅₀ = 1.21 mg/mL). The stability tests revealed that the heartwood of Dalbergia tonkinensis extract (HDT) possesses high pH stability with relative activity in the range of 80–98%. Further bioassay-guided purification led to the isolation of 2 active compounds identified as sativanone and formononetin from the ethyl acetate fraction and water fraction of HDT, respectively. These α-glucosidase inhibitors (aGIs) show promising inhibition against various types of α-glucosidases. Remarkably, these inhibitors were determined as new mammalian aGIs, showing good effect on rat α-glucosidase. The results suggest that Dalbergia tonkinensis is a potent source of aGIs and suggest promise in being developed as functional food with antidiabetic efficacy. The results of this study also enrich our knowledge concerning current biological activity and constituents of Dalbergia tonkinensis species.

Antimicrobial Activity of the Constituents of Dalbergia tonkinensis and Structural-Bioactive Highlights

The vulnerable plant Dalbergia tonkinensis Prain, is a rare species, native to Vietnam. Phytochemical investigations and biological evaluations of this species are quite limited. Antimicrobial screening has suggested that, at the low dose of 1.0 mg/mL, the methanol extracts of the leaf, stem bark, and root, as well as chloroform fraction of heartwood can serve as useful sources against seven gram-positive skin microbacteria, Bacillus cereus (ATCC27522), Escherichia coli (JM109), Staphylococcus aureus (ATCC25923), Staphylococcus epidermidis (ATCC14990), Streptococcus pneumonia (ATCC49619), Streptococcus pyogenes (ATCC12344), and Vibrio parahaemolyticus (RIMD2210010), and four oral gram-positive microbacteria Streptococcus mutans (ATCC 25175), Streptococcus mitis (ATCC903), Streptococcus sobrinus (ATCC 33478), and Porphyromonas gingivalis (ATCC33277), with an inhibitory percentage of 60-80% growth for several strains Bacillus cereus, Escherichia coli, and Streptococcus pneumonia. We further assessed antimicrobial activities of the enriched diverse flavonoids from chloroform fraction of its heartwood. Extensive structural activity relationship studies showed structure function closely related to the antimicrobial activity, in which methoxylation at C-2’, and 4’ in isoflavanones, hydroxylation at C-3’ in flavones, substitution at C-5 in isoflavones, and lactone opened ring in neoflavonoids were found to increase the effective inhibitions. In the second antimicrobial assessment, the isolated flavonoid liquiritigenin showed the MIC values of 50, and 100 μg/mL against the microbacterial strains Staphylococcus aureus subsp. aureus (ATCC 11632), and Aspergillus niger (439), respectively, whereas the MIC value of 100 μg/mL was assignable to biochanin A against microbacterium Staphylococcus aureus subsp. aureus.