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A series of new derivatives of 1,2,4-triazoles have been synthesized and their antioxidant properties have been studied. It was established that the obtained compounds exhibit a stabilizing effect on cell membranes and demonstrate antioxidant activity with respect to erythrocytes under oxidative stress conditions.

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New 1,2,4-triazole-3-thiols were synthesized by reactions of the corresponding carboxylic acid hydrazides with isothiocyanates and subsequent cyclization of intermediate 1,4-substituted thiosemicarbazides. Alkylation of 1,2,4-triazole-3-thiols with benzyl chlorides and bromacetophenones gave only S-substituted derivatives. † Deceased.Biological studies on synthetic analogs of naturally occurring heterocyclic compounds showed that most of them exhibit a broad spectrum of biological activity. Among compounds of this series, of particular interest are 1,2,4-triazoles which are mostly of synthetic origin. Some 1,2,4-triazole derivatives exhibit hypotensive effect [1] and possess antitumor [2], fungicidal [3], antibacterial [4], and other kinds of biological activity.While searching for new useful properties in the series of 1,2,4-triazoles we synthesized their new derivatives. Reactions of carboxylic acid hydrazides Ia-Id with allyl, phenyl, and furfurylmethyl isothiocyanates gave 1,4-disubstituted thiosemicarbazides IIa-IIe. Optimal conditions for this reaction were found. The best results were obtained by heating the initial reactants in ethanol for a short time [5]. Compounds IIa-IIe underwent intramolecular cyclization in alkaline medium to form targeted 3,4-disubstituted 1,2,4-triazole-3-thiols IIIa-IIIe. It is advisable to carry out this reaction with the use of 10% aqueous sodium or potassium hydroxide. The cyclization was complete in 4 h, and compounds IIIa-IIIe were formed in high yield [6] (Scheme 1).From the viewpoint of biological activity, synthesis of 1,2,4-triazole-3-thiol derivatives substituted at the sulfur atom seemed to be promising. For instance, biological effects of compounds possessing free and substituted thiol groups could be compared. 3,4-Disubstituted 1,2,4-triazole-3-thiols IIIa-IIIe were subjected to alkylation with various halogen derivatives, specifically with substituted benzyl chlorides and bromoacetophenones (Scheme 2). The optimal conditions for the alkylation with benzyl chlorides included the use of anhydrous acetone as solvent and anhydrous potassium carbonate as base and prolonged heating (10 h). The reactions of III with bromoacetophenones were complete in 2 h in the absence of a base.