4-Mercaptoimidazoles derived from the naturally occurring antioxidant ovothiols 1. Antioxidant properties

Abstract

4-Mercaptoimidazoles derived from the naturally occurring family of antioxidants, the ovothiols, were assayed for their antioxidant properties. These compounds are powerful HOCI scavengers, more potent than the aliphatic thiol N-acetylcysteine. They react slowly with hydrogen peroxide with second order rate constants of 0.13–0.89 M^-1 s^-1. Scavenging of hydroxyl radical occurs at a diffusion-controlled rate (k = 2.0–5.0 × 10¹⁰ M^-1 s^-1) for the most active compounds, which are also able to inhibit copper-induced LDL peroxidation. The combination of radical scavenging and copper chelating properties may explain the inhibitory effects on LDL peroxidation. Two molecules of mercaptoimidazole can chelate a copper ion and form a square planar complex detected by EPR. Compounds bearing an electron-withdrawing group on position 2 of the imidazole ring are the most potent antioxidant molecules in this series.

Keywords:

• 4-Mercaptoimidazoles
• hypochlorous acid
• hydrogen peroxide
• hydroxyl radical
• lipid peroxidation