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

4-Mercaptoimidazoles derived from the naturally occurring family of antioxidants, the ovothiols, were assayed for their antioxidant properties. These compounds are powerful HOCl 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 x 10(10) 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 hearing an electron-withdrawing group on position 2 of the imidazole ring are the most potent antioxidant molecules in this series.