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Hydroxybenzylidene hydrazines exhibit a wide spectrum of biological activities. Here, we report synthesis and free radical scavenging activity of nine new N-(hydroxybenzylidene)-N'-[2,6-dinitro-4-(trifluoromethyl)]phenylhydrazines. The chemical structures of these compounds were confirmed by 1H-NMR, 13C-NMR, 19F-NMR, IR spectroscopy, LC-MS, and elemental analysis. The prepared compounds were tested for their activity to scavenge 2,2-diphenyl-1-picrylhydrazyl (DPPH), galvinoxyl radical (GOR), and 2,2'-azino-bis(3-ethylbenzothiazoline)-6-sulphonic acid (ABTS) radicals. The free radical scavenging activity expressed as SC50 values of these compounds varied in a wide range, from a strong to no radical scavenging effect. The most effective radical scavengers were hydroxybenzylidene hydrazines containing three hydroxyl groups in the benzylidene part of their molecules. The prepared compounds were also tested for their activity to inhibit photosynthetic electron transport in spinach chloroplasts. IC50 values of these compounds varied in wide range, from an intermediate to no inhibitory effect., Competing Interests: The authors declare no conflict of interest.

Water infusions of Ligustrum delavayanum and Ligustrum vulgare leaves and eight phenolics isolated therefrom have been assayed in vitro on ofloxacin-induced genotoxicity in the unicellular flagellate Euglena gracilis. The tested compounds luteolin, quercetin, luteolin-7-glucoside, luteolin-7-rutinoside, quercetin-3-rutinoside, apigenin-7-rutinoside, tyrosol and esculetin inhibited the mutagenic activity of ofloxacin (43 microM) in E. gracilis. Water infusions from leaves of L. delavayanum and L. vulgare showed higher antimutagenic effect (p(t) < 0.001). The activity of these samples against ofloxacin (86 microM)-induced genotoxicity was lower, but statistically significant (p(t) < 0.05), excluding the water infusion of L. delavayanum leaves (p(t) < 0.01). Efficacy of quercetin, luteolin-7-rutinoside, apigenin-7-rutinoside was insignificant. The antimutagenic effect of most phenolics we studied could be clearly ascribed to their DPPH scavenging activity, substitution patterns and lipophilicity.

The antioxidant properties of silymarin and its flavanolignan components (silybin, silychristin and silydianin) were tested. Silymarin, silychristin and silydianin exhibit relatively good antioxidant effectiveness against phenylglyoxylic ketyl radicals and DPPH. The most effective scavengers of phenylglyoxylic ketyl radicals were silymarin and silychristin whereas silydianin was ca. 5-times less active than the first two compounds whereas silybin was ineffective. The scavenging properties of the studied compounds against DPPH radicals were in the same sequence: silymarin>silychristin>silydianin>silybin.

The free radical scavenging activity of the water infusions, different organic solvent extracts and some constituents from Ligustrum vulgare and Ligustrum delavayanum leaves was assessed with the aid of DPPH radical. Among the samples screened, water infusions had the strongest free radical scavenging capacity. From the tested compounds scavenging active flavonoid aglycones are present in the most active chloroform fractions from both leaves samples.

Radical scavenging and anti-lipoperoxidative effects of two organic fractions and two aqueous extracts from the leaves of a neglected Andean crop-yacon (Smallanthus sonchifolius Poepp. & Endl., Asteraceae) were determined using various in vitro models. The extracts' total phenolic content was 10.7-24.6%. They exhibited DPPH (IC50 16.14-33.39 microg/mL) and HO* scavenging activities (4.49-6.51 mg/mL). The extracts did not scavenge phenylglyoxylic ketyl radicals, but they retarded their formation. In the xanthine/xanthine oxidase superoxide radical generating system, the extracts' activities were 26.10-37.67 superoxide dismutase equivalents/mg. As one of the extracts displayed xanthine oxidase inhibitory activity, the effect of the extracts on a nonenzymatically generated superoxide was determined (IC50 7.36-21.01 microg/mL). The extracts inhibited t-butyl hydroperoxide-induced lipoperoxidation of microsomal and mitochondrial membranes (IC50 22.15-465.3 microg/mL). These results make yacon leaves a good candidate for use as a food supplement in the prevention of chronic diseases involving oxidative stress.

The antioxidant properties of melatonin were tested in this work by EPR technique. It was found that melatonin scavenges phenylglyoxylic ketyl radicals. Its effectiveness was 10-times lower than that of vitamin C. A new method of generation of phenylglyoxylic ketyl radicals by spontaneous decomposition of D,L-2,3-diphenyltartaric acid in propan-2-ol was used.