Structure-Activity Relationship (SAR) of Phenolics for 2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) Formation in Phenylalanine/Creatinine Reaction Mixtures Including (or Not) Oxygen and Lipid Hydroperoxides

Phenolics can act as either promoters or inhibitors in 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) formation. In an attempt to clarify the structure-activity relationship (SAR) of phenolics for this reaction, the formation of PhIP in mixtures of phenylalanine, creatinine, 13-hydroperoxide of linoleic acid (LOOH) or 4-oxo-2-nonenal, and a wide array of phenolics was studied in the presence and in the absence of oxygen. The obtained results suggested that those phenolics having a high carbonyl scavenging ability inhibited the formation of PhIP. On the other hand, those phenolics that mainly acted as free radical scavengers and, therefore, were easily converted into quinones promoted the formation of PhIP. Phenolics of the first type were m-diphenols and 1,3,5-triphenols. Phenolics of the second type were o- and p-diphenols. Other phenolics, like 1,2,3- and 1,2,4-triphenols, exhibited a behavior either as carbonyl scavengers or as free radical scavengers depending on ring substitutions. Among the studied derivatives, the presence of a carboxylic or a methoxyl group at certain positions inhibited their behavior as carbonyl scavengers and, therefore, promoted the formation of PhIP. A procedure to classify phenolics as either carbonyl or free radical scavengers is proposed.