In vitro antioxidant properties of potential biotransformaton products of salicylate, sulphasalazine and aminodypyrine

2,3- and 2,5-dihydroxybenzonate (formed from salicylate by nonenzymatic or enzymatic hydroxylation), and 5-aminosalicylate (a prime metabolite of sulphasalazine) are highly effecient quenchers of the chemiluminescence (CL) produced by an oxyl radical flux. Monohydric phenols (including salicylate) and meta-dihydric phenols are virtually inactive. These findings suggest that the para- o3 ortho-configuration of hydroxy/amino groups is important for this activity. These differences in activity between 2,3- and 2,5-dihydroxybenzonate, 5-aminosaalicylate and monohydric phenols/2,4-, 2,6-dihydroxybenzoate were not seen in assays monitoring hydroxyl radicals. 4-aminophenazone (an oxidation product of both amidopyrine/aminopyrine and isopyrine), 4-hydroxyphenazone and some dietary catechols (and ascorbate), are also potent quenchers of oxy radical-associated CL.