Structure--activity relationships in the mutagenicity of quinone methides of 7-hydroxyflavylium salts for Salmonella typhimurium.

Several synthetic 7-hydroxyflavylium salts related to apigeninidin, a natural 3-deoxyanthocyanidin, have been studied in the Ames mutagenicity test using strain TA1537 of Salmonella typhimurium. Under the neutral pH conditions of the test, these flavylium salts are deprotonated through ionization of the C7-OH (pK'a = 4.2-4.4) to form quinone methides. Only the quinone methides of 4-methyl-7-hydroxyflavylium chloride and 4'-methoxy-4-methyl-7-hydroxy-flavylium chloride showed mutagenicity. Responses of 4-8 times the background were observed at the higher doses (1000 micrograms/plate), both with and without metabolic activation. It was concluded that the induction of frameshift mutagenicity by this group of compounds is caused by those quinone methides that have non-ionic, stable polycyclic structures at neutral pH.