Antioxidant activity of some organosulfur compounds in vitro

The medicinal properties of many natural plant products are related with the antioxidant action of their constituents- oligosulfides and polyphenols. To increase the effectiveness of the antioxidant effect in lipid peroxidation and for reducing of undesirable toxic effects the combination in one molecule of several functional groups that act by various mechanisms seems one profitable. The goal of present study was to determine the antioxidant properties of synthetic sterically hindered 2,6-di-tert-butyl-4-mercaptophenol (1), bis(3,5-di-tert-butyl-4-hydroxyphenyl)disulfide (2) in comparison with disulfides containing in plant products: diphenyl disulfide (3), dibenzyl disulfide (4), dibutyl disulfide (5), di-tert-butyl disulfide (6), diallyl disulfide (7), methyl propyl trisulfide (8). Antioxidant properties were investigated by various assays including DPPH radical scavenging, Cu2+ ion reduction (CUPRAC-test), model reactions of peroxidation of cis-9-octadecenoic (oleic) acid and lipids from the liver of Russian sturgeon in vitro as well as metal chelating activity. It was found that bis(3,5-di-tert-butyl-4-hydroxyphenyl) disulfide demonstrated both high DPPH radical scavenging activity and TEACCUPRAC value and significantly decreased the level of primary products of lipid peroxidation (LPO) - lipid hydroperoxides (LOOH) as well as secondary products - carbonyl compounds which form colored complexes with thiobarbituric acid (TBARS). All sulfur compounds demonstrated the inhibitory activity in oleic acid peroxidation except dibutyl disulfide. The maximum decrease of LOOH and TBARS in lipid peroxidation was detected for bis(3,5-di-tert-butyl-4-hydroxyphenyl) disulfide. In the case of long-term LPO of liver lipids the antioxidant activity of all sulfur-containing compounds except diphenyl disulfide that exhibit pro-oxidant activity was ascertained. The efficiency of the antioxidant action of most compounds was decreased with time. Compound 2 was the only exception for which the increase in the efficiency of antioxidant action over time was discovered due to the presence of both 2,6-di-tert-butylphenol- and -S-S- fragments providing the prolonged antioxidant action. The high antioxidant efficiency let one to consider compound 2 for practical use as an effective inhibitor of lipid peroxidation in biological substrates and cytoprotector.