Xanthine oxidase inhibitory activity of natural and hemisynthetic flavonoids from Gardenia oudiepe (Rubiaceae) in vitro and molecular docking studies.

Xanthine oxidase (XO), an enzyme widely distributed among mammalian tissues, is associated with the oxidation of xanthine and hypoxanthine to form uric acid. Reactive oxygen species are also released during this process, leading to oxidative damages and to the pathology called gout. Available treatments mainly based on allopurinol cause serious side effects. Natural products such as flavonoids may represent an alternative. Thus, a series of polymethoxyflavones isolated and hemisynthesized from the bud exudates of Gardenia oudiepe has been evaluated for in vitro XO inhibitory activity. Compounds 1, 2 and 3 were more active than the reference inhibitor, Allopurinol (IC50 = 0.25 ± 0.004 µM) with IC50 values of (0.004 ± 0.001) µM, (0.05 ± 0.01) µM and (0.09 ± 0.003) µM, respectively. Structure-activity relationships were established. Additionally, a molecular docking study using MOE™ tool was carried out to establish the binding mode of the most active flavones with the enzyme, showing important interactions with its catalytic residues. These promising results, suggest the use of these compounds as potential leads for the design and development of novel XO inhibitors.

From meiogynin A to the synthesis of dual inhibitors of Bcl-xL and Mcl-1 anti-apoptotic proteins.

The synthesis of one of the most potent dual inhibitors of the anti-apoptotic proteins Bcl-xL and Mcl-1 is reported. This analogue of a natural sesquiterpenoid dimer meiogynin A was elaborated by a convergent asymmetric synthesis with 36% yield in ten steps.

Foliar manganese accumulation by Maytenus founieri (Celastraceae) in its native New Caledonian habitats: populational variation and localization by X-ray microanalysis.

Hyperaccumulation by plants is a rare phenomenon that has potential practical benefits. The majority of manganese (Mn) hyperaccumulators discovered to date occur in New Caledonia, and little is known about their ecophysiology. This study reports on natural populations of one such species, the endemic shrub Maytenus founieri. Mean foliar Mn concentrations of two populations growing on ultramafic substrates with varying soil pHs were obtained. Leaf anatomies were examined by light microscopy, while the spatial distributions of foliar Mn in both populations were examined by qualitative scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS). Plants growing on two different substrates were found to have very different mean dry weight (DW) foliar Mn concentrations. Light microscopy showed that the leaves had very distinct thick dermal structures, consisting of multiple layers of large cells in the hypodermis. In vivo X-ray microprobe analyses revealed that, in both populations, Mn sequestration occurred primarily in these dermal tissues. The finding here that foliar Mn is most highly localized in the nonphotosynthetic tissues of M. founieri contrasts with results from similar studies on other woody species that accumulate high Mn concentrations in their shoots.

Cytotoxicity of Rhamnosylanthraquinones and Rhamnosylanthrones from Rhamnus nepalensis.

An extract of the fruits of Rhamnus nepalensis collected in Hoa Binh Province, Vietnam, was cytotoxic to KB cells. A bioassay-guided fractionation led to the isolation of a series of known anthraquinones and anthrones, one new rhamnosylanthraquinone, 3'-O-acetylfrangulin A (8), several new rhamnosylanthrones, the prinoidin-emodin bianthrones (9A-D), the prinoidin bianthrones (10A,B), and the rhamnepalins (11A-C). A structure-cytotoxic activity relationship study was performed on these isolates and some semisynthetic derivatives.

Cytotoxic prenylxanthones from Garcinia bracteata.

Bioassay-guided fractionation of a leaf extract of G. bracteata has yielded six new prenylxanthones, bractatin (1), isobractatin (2), 1-O-methylbractatin (3), 1-O-methylisobractatin (4), 1-O-methyl-8-methoxy-8,8a-dihydrobractatin (5), and 1-O-methylneobractatin (6). The structures of these compounds have been elucidated by spectroscopic means (NMR, MS), literature data, and X-ray crystallographic analysis of 2. These compounds possess significant cytotoxicity against the KB cell line.

Rubiginoside, a farnesyl glycoside from Lepisanthes rubiginosa.

Chemical investigation of the methanolic fraction of Lepisanthes rubiginosa bark has led to the isolation and characterisation of a new tetrasaccharide derivative of farnesol named rubiginoside along with known triterpenoid saponins.

Six triterpenoid saponins from Mmaesa laxiflora.

Six new triterpenoid saponins, maelaxins A-F (1-6), were isolated from a n-BuOH extract of the leaves of Maesa laxiflora. They possess 22-O-angeloyl-camelliagenin A, 16-O-acetyl, 22-O-angeloyl-camelliagenin A, or 22-O-(2Z)-hexenoyl-camelliagenin A as the aglycon. The pentasaccharide moiety linked to C-3 of the aglycon consists of D-glucuronic acid, L-rhamnose, D-glucose, and/or D-galactose. Their structures were elucidated by extensive NMR experiments including 1H-1H (COSY, 2D HOHAHA, NOESY) and 1H-13C (HMQC and HMBC) spectroscopy and chemical evidence.