Antioxidant activities and flavonoid contents of selected plants belonging to Family Loranthaceae

The methanolic extract of three parasitic plants belonging to family Loranthaceae (Plicosepalus acacia, Plicosepalus curviflorus and Phragmanthera austro arabica) were investigated for their antioxidant activity. The free radical and nitrogen oxide scavenging abilities were evaluated using diphenyl-1-picrylhydrazyl (DPPH), and Griess reagent was used to determine the total antioxidant activity. The three extracts showed comparable activities. The three activities ranged from 18 to 56% of the activity of standard ascorbic. The total flavonoid contents were determined and calculated in terms of quercetin which was detected in all the examined extracts. The quercetin concentration was determined using high performance thin layer chromatography using CHCl3 : MeOH : glacial acetic acid (8.5: 1.5: 0.1) for development. The maximum sensitivity was obtained when the plates were scanned at 360 nm. The concentration of quercetin varied from 0.157 (P. austro arabica) to 0.062 g% (P. acacia) and P. curviflorus contained 0.115 g% w/w quercetin. All validation parameters were found to be satisfactory regarding accuracy, precision, limits of detection and quantitation.Key words: Loranthaceae, antioxidant, spectrophotometry, high performance thin layer chromatography (HPTLC), flavonoids, quercetin, ascorbic acid

Aryloxyalkanoic Acids as Non-Covalent Modifiers of the Allosteric Properties of Hemoglobin

Hemoglobin (Hb) modifiers that stereospecifically inhibit sickle hemoglobin polymer formation and/or allosterically increase Hb affinity for oxygen have been shown to prevent the primary pathophysiology of sickle cell disease (SCD), specifically, Hb polymerization and red blood cell sickling. Several such compounds are currently being clinically studied for the treatment of SCD. Based on the previously reported non-covalent Hb binding characteristics of substituted aryloxyalkanoic acids that exhibited antisickling properties, we designed, synthesized and evaluated 18 new compounds (KAUS II series) for enhanced antisickling activities. Surprisingly, select test compounds showed no antisickling effects or promoted erythrocyte sickling. Additionally, the compounds showed no significant effect on Hb oxygen affinity (or in some cases, even decreased the affinity for oxygen). The X-ray structure of deoxygenated Hb in complex with a prototype compound, KAUS-23, revealed that the effector bound in the central water cavity of the protein, providing atomic level explanations for the observed functional and biological activities. Although the structural modification did not lead to the anticipated biological effects, the findings provide important direction for designing candidate antisickling agents, as well as a framework for novel Hb allosteric effectors that conversely, decrease the protein affinity for oxygen for potential therapeutic use for hypoxic- and/or ischemic-related diseases

1H-Imidazole-2,5-Dicarboxamides as NS4A Peptidomimetics: Identification of a New Approach to Inhibit HCV-NS3 Protease

The nonstructural (NS) protein NS3/4A protease is a critical factor for hepatitis C virus (HCV) maturation that requires activation by NS4A. Synthetic peptide mutants of NS4A were found to inhibit NS3 function. The bridging from peptide inhibitors to heterocyclic peptidomimetics of NS4A has not been considered in the literature and, therefore, we decided to explore this strategy for developing a new class of NS3 inhibitors. In this report, a structure-based design approach was used to convert the bound form of NS4A into 1H-imidazole-2,5-dicarboxamide derivatives as first generation peptidomimetics. This scaffold mimics the buried amino acid sequence Ile-25` to Arg-28` at the core of NS4A21`–33` needed to activate the NS3 protease. Some of the synthesized compounds (Coded MOC) were able to compete with and displace NS4A21`–33` for binding to NS3. For instance, N5-(4-guanidinobutyl)-N2-(n-hexyl)-1H-imidazole-2,5-dicarboxamide (MOC-24) inhibited the binding of NS4A21`–33` with a competition half maximal inhibitory concentration (IC50) of 1.9 ± 0.12 µM in a fluorescence anisotropy assay and stabilized the denaturation of NS3 by increasing the aggregation temperature (40% compared to NS4A21`–33`). MOC-24 also inhibited NS3 protease activity in a fluorometric assay. Molecular dynamics simulations were conducted to rationalize the differences in structure–activity relationship (SAR) between the active MOC-24 and the inactive MOC-26. Our data show that MOC compounds are possibly the first examples of NS4A peptidomimetics that have demonstrated promising activities against NS3 proteins