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Continuing our interest in the Uncaria genus, the phytochemistry and the in-vitro α-glucosidase inhibitory activities of Malaysian Uncaria cordata var. ferruginea were investigated. The phytochemical study of this plant, which employed various chromatographic techniques including recycling preparative HPLC, led to the isolation of ten compounds with diverse structures comprising three phenolic acids, two coumarins, three flavonoids, a terpene and an iridoid glycoside. These constituents were identified as 2-hydroxybenzoic acid or salicylic acid (1), 2,4-dihydroxybenzoic acid (2), 3,4-dihydroxybenzoic acid (3), scopoletin or 7-hydroxy-6-methoxy-coumarin (4), 3,4-dihydroxy-7-methoxycoumarin (5), quercetin (6), kaempferol (7), taxifolin (8), loganin (9) and β-sitosterol (10). Structure elucidation of the compounds was accomplished with the aid of 1D and 2D Nuclear Magnetic Resonance (NMR) spectral data and Ultraviolet-Visible (UV-Vis), Fourier Transform Infrared (FTIR) spectroscopy and mass spectrometry (MS). In the α-glucosidase inhibitory assay, the crude methanolic extract of the stems of the plant and its acetone fraction exhibited strong α-glucosidase inhibition activity of 87.7% and 89.2%, respectively, while its DCM fraction exhibited only moderate inhibition (75.3%) at a concentration of 1 mg/mL. The IC 50 values of both fractions were found to be significantly lower than the standard acarbose suggesting the presence of potential α-glucosidase inhibitors. Selected compounds isolated from the active fractions were then subjected to α-glucosidase assay in which 2,4-dihydroxybenzoic acid and quercetin showed strong inhibitory effects against the enzyme with IC 50 values of 549 and 556 µg/mL compared to acarbose (IC 50 580 µg/mL) while loganin and scopoletin only showed weak α-glucosidase inhibition of 44.9% and 34.5%, respectively. This is the first report of the isolation of 2-hydroxybenzoic acid, 2,4-dihydroxybenzoic acid and loganin from the genus and the first report of the α-glucosidase inhibitory potential of 2,4-dihydroxybenzoic acid.

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The structure elucidation of three new alkaloids named isoformosaninol (1), formosaninol (2), and longiflorine (3), isolated from the leaves of Uncaria longiflora var. pteropoda (Miq.) Ridsdale, along with their biosynthetic pathways are discussed. Their absolute structures were determined through a combination of physical data interpretation and quantum chemical calculations using the time-dependent density functional theory (TDDFT) method.

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Eleusine indica, locally known as ‘rumput sambau’ is widely used by traditional practitioners in many parts of the world to treat various ailments including sprained muscle, asthma, black jaundice, stomach pain, diarrhea, convulsions, and those related to infection such as malaria, influenza, dysentery as well as pneumonia. The plant has been reported to possess a wide array of biological activities, which were antioxidant, anti-inflammatory, antimicrobial, antidiabetic, antipyretic, antiplasmodial, antiviral, hepatoprotective, and urolithiasis. Despite all the reported traditional uses and biological activities, not many chemical constituents have been isolated from the plant. In this work, E. indica methanolic and hexane extracts were assessed for their anti-proliferative activities against human liver cancer (HepG2) and African green monkey kidney epithelial normal (Vero) cell lines through 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay. Although both extracts were considered to be not active on both cell lines with an IC50 of 91.02 ± 5.74 and 85.30 ± 3.03 µg/mL, and CC50 of >1000 and 639.39 ± 13.97 µg/mL, they were nevertheless more selective towards HepG2 cancer cells compared to the Vero normal cells with selectivity indexes (SI) of 10.99 and 7.50, respectively. Chemical profiling of the extracts on ultra-high performance liquid chromatography (UHPLC) coupled with a diode array detector showed a mixture of different complexity and polarities of compounds. Further isolation and purification on the hexane extract afforded β-sitosterol and stigmasterol, while the methanolic extract yielded loliolide, a benzofuran type of compound. Loliolide has been previously reported to exhibit antitumor activity, which could correlate to the higher antiproliferative selectivity against HepG2 cancer cell line of the methanolic compared to the hexane extracts. This is the first report on the isolation of β-sitosterol, stigmasterol, and loliolide from E. indica.