Isolation and characterisation of secondary metabolites from Trifolium vesiculosum Savi and their antiproliferative activities.

One unreported flavonol namely morin-7-O-methyl ether (1) along with seven known compounds were isolated from the aerial parts of Trifolium vesiculosum Savi which were elucidated by using extensive spectroscopic methods such as 1D and 2D NMR and HR-MS. According to the cell viability assay (MTS) on the purified compounds (1-8), quercetin-3-O-(6''-trans-p-coumaroyl)-ß-galactoside (4) revealed remarkable antiproliferative activity most particularly against breast cancer cells (IC50 = 2.90 ± 0.25 µM in HCC1937 and 7.98 ± 0.57 µM in MCF7) while moderate inhibitory activity (IC50 = 17.96 ± 0.51-51.70 ± 2.69 µM) on prostate, colorectal and liver cancer cell viability was observed. Further mechanistic examinations (Annexin V/PI staining, DNA content and detection of reactive oxygen species analyses) showed that compound 4 significantly induced apoptosis, enhanced mitochondrial reactive oxygen species (ROS) accumulation, and caused cell cycle arrest in cancer cells by increasing accumulation of cells at G0/G1 and/or G2/M phases of the cell cycle.

Portobelamides A and B and Caciqueamide, Cytotoxic Peptidic Natural Products from a Caldora sp. Marine Cyanobacterium.

Three new compounds, portobelamides A and B (1 and 2), 3-amino-2-methyl-7-octynoic acid (AMOYA) and hydroxyisovaleric acid (Hiva) containing cyclic depsipeptides, and one long chain lipopeptide caciqueamide (3), were isolated from a field-collection of a Caldora sp. marine cyanobacterium obtained from Panama as part of the Panama International Cooperative Biodiversity Group Program. Their planar structures were elucidated through analysis of 2D NMR and MS data, especially high resolution (HR) MS2/MS3 fragmentation methods. The absolute configurations of compounds 1 and 2 were deduced by traditional hydrolysis, derivative formation, and chromatographic analyses compared with standards. Portobelamide A (1) showed good cytotoxicity against H-460 human lung cancer cells (33% survival at 0.9 µM).

Kalkipyrone B, a marine cyanobacterial γ-pyrone possessing cytotoxic and anti-fungal activities.

Bioassay-guided fractionation of two marine cyanobacterial extracts using the H-460 human lung cancer cell line and the OVC-5 human ovarian cancer cell line led to the isolation of three related α-methoxy-ß, ß'-dimethyl-γ-pyrones each containing a modified alkyl chain, one of which was identified as the previously reported kalkipyrone and designated kalkipyrone A. The second compound was an analog designated kalkipyrone B. The third was identified as the recently reported yoshinone A, also isolated from a marine cyanobacterium. Kalkipyrone A and B were obtained from a field-collection of the cyanobacterium Leptolyngbya sp. from Fagasa Bay, American Samoa, while yoshinone A was isolated from a field-collection of cyanobacteria (cf. Schizothrix sp.) from Panama. One-dimensional and two-dimensional NMR experiments were used to determine the overall structures and relative configurations of the kalkipyrones, and the absolute configuration of kalkipyrone B was determined by (1)H NMR analysis of diastereomeric Mosher's esters. Kalkipyrone A showed good cytotoxicity to H-460 human lung cancer cells (EC50=0.9µM), while kalkipyrone B and yoshinone A were less active (EC50=9.0µM and >10µM, respectively). Both kalkipyrone A and B showed moderate toxicity to Saccharomyces cerevisiae ABC16-Monster strain (IC50=14.6 and 13.4µM, respectively), whereas yoshinone A was of low toxicity to this yeast strain (IC50=63.8µM).

Antioxidant and tyrosinase inhibitory activities of flavonoids from Trifolium nigrescens Subsp. petrisavi.

Trifolium nigrescens was researched for its chemical constituents for the first time. Bioassay-guided isolation of the EtOAc extract from the leaves of T. nigrescens resulted in the purification of a new biflavone, 4''',5,5″,7,7″-pentahydroxy-3',3'''-dimethoxy-3-O-ß-d-glucosyl-3″,4'-O-biflavone (1) along with eleven known compounds consisting of three phenolics (2-4), and eight flavonoid glycosides (5-12). Their structures were determined by extensive 1D and 2D NMR, and MS data analyses. The isolated compounds were evaluated for their antioxidant activity and inhibitory activity on mushroom tyrosinase. Highly potent inhibitions were found by compounds 7 (IC50 = 0.38 mM), 8 (IC50 = 0.19 mM), and 12 (IC50 = 0.26 mM) when compared with standard tyrosinase inhibitors kojic acid (IC50 = 0.67 mM) and l-mimosine (IC50 = 0.64 mM). The antioxidative effect of the isolated compounds and the extracts were determined by using ß-carotene-linoleic acid, DPPH(•) scavenging, ABTS(+•) scavenging, superoxide scavenging, and CUPRAC assays. The experimental findings indicated that all the compounds demonstrated activity in all antioxidant activity tests employed except for the compounds 2-6. Compounds 2-6 showed moderate activity only in ABTS(+•) scavenging assay. The new compound 1 exhibited better activity than standard α-tocopherol in DPPH(•) scavenging, and ABTS(+•) scavenging assays. The results show that T. nigrescens can be regarded as a potential source of antioxidant compounds and tyrosinase inhibitors of significance in both the pharmaceutical and food industries.

Phenolic compounds from Trifolium echinatum Bieb. and investigation of their tyrosinase inhibitory and antioxidant activities.

Two bischromones, 3,3'-dimethoxy-2'-oxychromone (1), 3,3'-dihydroxy-2,2'-oxychromone (2) and a biflavone, 5,7,4',5″,3'",4″″-hexahydroxy-3″-O-ß-glucosyl-3',7″-O-biflavone (3) have been isolated from whole plant of Trifolium echinatum Bieb. together with five known flavonoids. The structures of the compounds were elucidated by 1D and 2D NMR analysis as well as HRESIMS. The isolated compounds were investigated for their antioxidant activity and tyrosinase inhibitory activity. Highly potent inhibition was found for compounds 1 (IC50=0.41 mM), 5 (IC50=0.47 mM) and 8 (IC50=0.45 mM) compared to those of standard tyrosinase inhibitors kojic acid (IC50=0.67 mM) and l-mimosine (IC50=0.64 mM). The antioxidative effect of the extracts was determined by using ß-carotene-linoleic acid, DPPH scavenging, ABTS(+) scavenging, and CUPRAC assays. The experimental findings indicated that the compounds 2 and 8 were found to be active in radical scavenging and CUPRAC assays.

Structure elucidation of two new unusual monoterpene glycosides from Euphorbia decipiens, by 1D and 2D NMR experiments.

Two new unusual monoterpene glycosides, (Z)-3,6-dimethyl-3-(ß-D-O-glucosylmethylene)cyclohept-4-ene-1-one (1) and 3,6-dimethyl-3-(ß-D-O-glucosylmethylene)cycloheptanone (2) have been isolated along with five known compounds, 3-hydroxy-4-methoxybenzoic acid, 6,7-dihydroxycoumarin, luteolin, apigenin 5-O-αl-L-rhamnoside, and pinocembrin-7-O-rutinoside from ethyl acetate extract of Euphorbia decipiens. The structures of the isolated compounds were elucidated by extensive 1D- and 2D-NMR, and mass spectroscopic analyses.

7',8'-Dihydroobolactone, a typanocidal alpha-pyrone from the rainforest tree Cryptocarya obovata.

Mass-directed isolation of the CH(2)Cl(2)/MeOH extract from the leaves of Cryptocarya obovata resulted in the purification of a new trypanocidal alpha-pyrone, 7',8'-dihydroobolactone (1). The chemical structure of 1 was determined by 1D/2D NMR, MS and CD data analysis. 7',8'-Dihydroobolactone was shown to inhibit Trypanosoma brucei brucei with an IC(50) of 2.8 microM.

Cellular reactive oxygen species inhibitory constituents of Hypericum thasium Griseb.

The phytochemical investigation of the ethyl acetate extract of Hypericum thasium has led to the characterization of four benzophenone derivatives 1-4, a known benzophenone 5 and four known flavonoids, quercetin (6), quercitrin (7), isoquercetin (8), and 3, 8''-biapigenin (9). Lucigenin- and luminal-based chemiluminescence assays were employed to monitor the inhibitory activity of these compounds towards the production of reactive oxygen species (ROS) by human polymorphoneutrophils (PMNs). The assay results showed that benzophenones 1 and 3 are extracellular inhibitors of ROS production, while flavonoids 6, 8, and 9 can modulate intracellular ROS production.