A new diarylhexane and two new diarylpropanols from the roots of Knema globularia

Chemical composition, acetylcholinesterase inhibition and molecular docking studies of essential oil from Knema hookeriana Warb. (Myristicaceae)

The genus Knema Lour. is distributed mainly in Southeast Asian and widely used in folk medicine for treating diseases such as jaundice, chronic fever, and inflammation. The chemical composition, acetylcholinesterase inhibition, and molecular docking studies of essential oil from Knema hookeriana Warb. were investigated in this study. The essential oil was achieved through hydrodistillation and was characterised using gas chromatography (GC-FID) and gas chromatography-mass spectrometry (GC-MS). The acetylcholinesterase inhibitory activity was evaluated using Ellman method while molecular docking studies were carried out using Autodock v.4.3.2. The results revealed that the essential oil examined consisted mainly of β-caryophyllene (26.2%), germacrene D (12.5%), δ-cadinene (9.2%), germacrene B (8.8%) and bicyclogermacrene (5.5%). The essential oil showed acetylcholinesterase activity with IC50 value of 70.5 µg/mL. The enzyme-ligand molecular docking study showed that β-caryophyllene and δ-cadinene exhibited good binding affinities towards AChE with docking scores -8.1 kcal/mol and -8.3 kcal/mol, respectively.

Globunoids A-D, undescribed bichalconoid and biflavanoids with α-glucosidase and α-amylase inhibitory activities from Knema globularia stems

A bichalconoid, globunoid A (1) and three biflavanones, globunoids B-D (2-4), previously undescribed, were isolated from the stems of Knema globularia, along with fourteen known analogues 5-18. The chemical structures of 1-4 were elucidated by the comprehensive spectroscopic analysis including UV, IR, HRESIMS, and NMR; the absolute configurations were determined based on their NOESY data, DP4+ statistical analysis, and ECD calculation. Up to now, compounds 2 and 3 represent the first 3,3″-linked biflavanone structures. Among the isolated compounds, 2, 3, and 2,3-dihydrocalodenin B (6) potently inhibited α-glucosidase and α-amylase activities, with IC50 values in the range 1.1-7.5 μM. Furthermore, the most active compound 6 was found to be a non-competitive inhibitor against these two enzymes.

Three new constituents from the stems of Knema globularia and their α-glucosidase inhibitory activity

Three new metabolites (1-3) were isolated from the stems of Knema globularia, along with five known compounds, including kaempferol (4), quercetin (5), isovanillic acid (6), protocatechuic acid (7), and gallic acid (8). Their structures were deduced using NMR spectroscopic, mass spectrometric analyses, and literature data. The absolute configurations of 1-3 were established by electronic circular dichroism (ECD) spectroscopy. α-Glucosidase inhibitory activities of those compounds were evaluated using a spectrophotometric method, compounds 1-3 showed very strong effects towards α-glucosidase with IC50 values 1.59, 0.58 and 1.37 µM, respectively (the positive control, acarbose, IC50 93.63 µM). Simultaneously, enzyme kinetics study indicated that 2 was a mix-type inhibitor. 2 interacted well in the active site of α-glucosidase enzyme, primarily through hydrogen bonds and hydrophobic interactions.

Ru(II)-Catalyzed Asymmetric Transfer Hydrogenation of Chalcones in Water: Application to the Enantioselective Synthesis of Flavans BW683C and Tephrowatsin E

The oxo-tethered-Ru(II) precatalyst promoted the one-pot C═C/C═O reduction of chalcones using sodium formate as the hydrogen source in water through asymmetric transfer hydrogenation. Twenty-seven 1,3-diarylpropan-1-ols were obtained in good to excellent yields (up to 96%) and enantiomeric purities (up to 98:2). Our data suggested that the enones are first reduced to the corresponding dihydrochalcones (1,4-selectivity) and then into 1,3-diarylpropan-1-ols (C═O reduction). The stereoelectronic effects of electron-donating and electron-withdrawing groups at the ortho, meta and para positions of both aromatic rings were evaluated. The 2-OH group at the B ring was well tolerated, allowing a straightforward enantioselective synthesis of two flavans through the Mitsunobu cyclization, the antiviral (S)-BW683C and the natural flavan (S)-tephrowatsin E.

Chemical composition of essential oil and antioxidant activity of the essential oil and methanol extracts of Knema globularia (Lam.) Warb. from Vietnam

This study is the first to investigate the chemical composition of essential oil and antioxidant activity of the essential oil and methanol extracts from the leaves of Knema globularia (Lam.) Warb. from Vietnam. According to gas chromatography and gas chromatography-mass spectrometry analysis, the major constituents of K. globularia essential oil were β-elemene (25.48%), α-copaene (17.05%), β-caryophyllene (9.37%), and α-humulene (8.42%). The antioxidant activity of the samples was determined using DPPH and ABTS methods. In both assays, the polar subfraction of the methanolic extract showed better antioxidative capacity than the nonpolar subfraction and the essential oil. In addition, the amounts of total phenol value in the polar subfraction and the nonpolar subfraction were determined to be 113.84 μg/mg and 47.52 μg/mg, respectively. The findings demonstrate that the essential oil and methanol extracts of K. globularia possess significant antioxidant activities and may be a new potential source of natural antioxidants.

α-Glucosidase Inhibitors from the Stems of Knema globularia

Six new compounds, globunones A-F (1-6), and two new flavonoids (7 and 8) together with nine known compounds (9-17) were isolated from the stems of Knema globularia. The chemical structures of 1-8 were elucidated by an analysis of their NMR and high-resolution electrospray ionization mass spectrometry data as well as by comparison with literature values. The absolute configurations were determined using time-dependent density functional theory electronic circular dichroism (TD-DFT-ECD). Globunones A-E (1-5) represent the initial combined structures of a flavan-3-ol core and a 1,4-benzoquinone core. Globunone F (6) is the first flavanone-type compound bearing a 2-(2,4-dihydroxyphenyl)-2-oxoethyl group found to date in Nature. Compounds 1-3 and 6-17 were tested for their yeast α-glucosidase inhibitory activity. All compounds tested (except for 13 and 14) showed potent inhibition toward α-glucosidase with IC₅₀ values in the range 0.4-26.6 μM. Calodenin A (15) was the most active compound with an IC₅₀ value of 0.4 μM (the positive control, acarbose, IC₅₀ 93.6 μM). A kinetic analysis of 15 revealed that it is a noncompetitive inhibitor with a K_i value of 3.4 μM.

Ethnomedicinal Plants in Herbal Remedies Used for Treatment of Skin Diseases by Traditional Healers in Songkhla Province, Thailand

Skin disorders are a worldwide health problem that normally affect human life. A traditional healer is an important expert in researching notable medicinal plants for skin disease treatment. This study aimed to determine the traditional knowledge and the use of medicinal plants for the treatment of skin diseases among traditional healers in the Songkhla province, Thailand. The ethnobotanical information was collected from experienced traditional healers by semi-structured interviews and participant observations. Plant specimens were also collected and identified using the standard taxonomic method. The data were analyzed by interpretation and descriptive statistics. Twenty-five polyherbal formulations for the treatment of skin diseases were obtained from traditional healers with at least 10 years of experience. A total of 66 plant species in 38 families were documented. Leaves and trees were the most commonly employed plant parts and plant habits included in the herbal remedies, respectively. Fabaceae, Rubiaceae, and Zingiberaceae were the majority of the cited families. Oryza sativa L. and Zingiber montanum (J. Koenig) Link ex A.Dietr. were the most preferred plants combined in the prescriptions, which had the highest use value (UV = 0.83). The highest relative frequency of citation was represented by Curcuma longa L., Eurycoma longifolia Jack, Knema globularia (Lamk.) Warb, and Senna siamea (Lam.) Irwin & Barneby. (0.55 each). This research suggests the importance of traditional healers in the healing of skin diseases with herbal remedies. A variety of medicinal plants are used in the prescriptions for the treatment of skin disorders in the Songkhla province, in the south of Thailand. Pharmacological and toxicological activities as well as phytochemical constituents of polyherbal remedies should be further investigated to scientifically verify further applications of widely practiced herbal medicines.

Knecorticosanones C-H from the fruits of Knema globularia (Lam.) warb

Six undescribed polyketides, 1-6, were discovered from the fruits of Knema globularia (Lam.) warb. Two known polyketides and three known lignans were also isolated. Cytotoxicities against HepG2 and KKU-M156 cells of all polyketides were evaluated. Compound 1 displayed the most cytotoxic activity against HepG2 and KKU-M156 cell lines with IC50 values of 1.57 ± 0.37 and 1.78 ± 0.14 μg mL-1, respectively. The structure of all isolates was identified using spectroscopic methods including NMR, IR, MS and ECD.