Structure-activity relationship and MM2 energy minimized conformational analysis of quercetin and its derivatives in the DPPH• radical scavenging capacity

Antioxidant activity of quercetin (1) and its derivatives (2-15) was evaluated by using DPPH assay and IC50 values were calculated. Dihedral angles α of C3-C2-C1’-C6’ chain and β of O1-C2-C-1’-C2’ chain between AC and B rings of these flavones were determined by using MM2 energy minimized structures. Structure-activity relationship study revealed that quercetin (1), quercetin-5-methyl ether (2), quercetin-3’-methyl ether (3) and quercetin-3’,5-dimethyl ether (4) displaying a high antioxidant activity (IC50 = 47.20-119.27 μM) possess similar dihedral angles (α 11.1-11.5º and β 6.3-6.6º). Mono- and/or di-methoxy substituent(s) at 3’ and 5 positions of the flavone are most suitable for the preservation of the antioxidant capacity while retaining conformational geometry. BIBECHANA 17 (2020) 19-2

Structure-activity relationship and MM2 energy minimized conformational analysis of quercetin and its derivatives in the DPPH• radical scavenging capacity

Antioxidant activity of quercetin (1) and its derivatives (2-15) was evaluated by using DPPH assay and IC50 values were calculated. Dihedral angles α of C3-C2-C1’-C6’ chain and β of O1-C2-C-1’-C2’ chain between AC and B rings of these flavones were determined by using MM2 energy minimized structures. Structure-activity relationship study revealed that quercetin (1), quercetin-5-methyl ether (2), quercetin-3’-methyl ether (3) and quercetin-3’,5-dimethyl ether (4) displaying a high antioxidant activity (IC50 = 47.20-119.27 μM) possess similar dihedral angles (α 11.1-11.5º and β 6.3-6.6º). Mono- and/or di-methoxy substituent(s) at 3’ and 5 positions of the flavone are most suitable for the preservation of the antioxidant capacity while retaining conformational geometry. BIBECHANA 17 (2020) 19-2

Triconoids A–D, Four Limonoids Possess Two Rearranged Carbon Skeletons from Trichilia connaroides

Four limonoids, triconoids A–C (<b>1</b>–<b>3</b>) possessing a new rearranged mexicanolide skeleton and triconoid D (<b>4</b>) furnishing a new rearranged 1,2-seco-phragmalin skeleton, were isolated from the Nepalese plant Trichilia connaroides. Two rearranged limonoid skeletons sharing an F ring of methyl 5-oxotetrahydrofuran-2-carboxylate were postulated to be formed biosynthetically via a very unique chemical cascade. Their structures were fully accomplished by spectroscopic data, single-crystal X-ray diffraction, and electrostatic circular dichroism analysis

Hydroxylated <i>Daphniphyllum</i> Alkaloids from <i>Daphniphyllum himalense</i>

Thirteen new hydroxylated calyciphylline A-type <i>Daphniphyllum</i> alkaloids (<b>1</b>–<b>13</b>) were isolated from an ethanolic extract of <i>Daphniphyllum himalense</i>. These structures were characterized on the basis of spectroscopic data analysis, especially from their 2D NMR spectra. Oxidation at the C-3, C-9, C-11, and C-12 positions is reported for the first time for this class of compounds. Selective compounds showed low inhibitory rates against three kinase enzymes, PTP1B, aurora A, and IKK-β, at a concentration of 20 μg/mL

Himalensines A and B, Alkaloids from <i>Daphniphyllum himalense</i>

Chemical investigation into the alkaloidal constituents of the Nepalese <i>Daphniphyllum himalense</i> has returned two new compounds, himalensines A (<b>1</b>) and B (<b>2</b>), with unprecedented carbon skeletons. Structures of the two alkaloids have been characterized on the basis of spectroscopic methods, especially via 2D NMR data analysis. Himalensine B (<b>2</b>) showed marginal inhibitory activities against two kinases, PTP1B and IKK-β

Antileishmanial diterpenoid alkaloids from <i>Aconitum spicatum</i> (Bruhl) Stapf

<p>The crude extracts of tubers of <i>Aconitum spicatum</i> (Bruhl) Stapf were investigated for <i>in vitro</i> antileishmanial activity against <i>Leishmania major</i>. The dichloromethane extract at pH 2.5 showed antileishmanial activity with IC₅₀ value of 27.10 ± 0.0 μg/mL. Chromatographic purification of the dichloromethane extract led to isolation of three C-19 norditerpenoid alkaloids indaconitine (<b>1</b>), chasmaconitine (<b>2</b>) and ludaconitine (<b>3</b>). Compounds <b>3</b> and <b>2</b> showed antileishmanial activity with IC₅₀ = 36.10 ± 3.4 and 56.30 ± 2.1 μg/mL, respectively. Compound <b>1</b> was less effective (IC₅₀ > 100 μg/mL). The cytotoxicity of compounds <b>1</b>, <b>2</b> and <b>3</b> studied against MCF7, HeLa and PC3 cancer cell lines and 3T3 normal fibroblast cell line did not show cytotoxicity at 30 μM.</p