Bromine-, chlorine-, and mixed halogen-substituted 4-methyl-2(5H)-furanones: synthesis and mutagenic effects of halogen and hydroxyl group replacements

The versatility of 4-(hydroxymethyl)-2(5H)-furanone as a starting point for the synthesis of several bromine and mixed halogen analogues of the potent water mutagen 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX) has been demonstrated. However, in some preparations the yields of desired products were lower for bromine- than chlorine-substituted counterparts. A total of 12 bromine-, chlorine-, and mixed halogen-substituted 4-methyl-2(5H)-furanones were tested repeatedly in 10 independent experiments for levels of Salmonella typhimurium (TA100) mutagenicities. The purpose of these experiments was to determine the mutagenic response to changing halogen content, type, and position as well as to learn the measure of these responses in the presence and absence of the C-5 OH group. Mutagenicities reached levels of 10(3) and 10(2) rev/nmol for all trihalo- and dihalo-4-methyl-5-hydroxy-2(5H)-furanones, respectively, notwithstanding substitutions by bromine or chlorine. Trihalides lacking the C-5 hydroxyl group possessed mutagenicities of the order of 10(2) rev/nmol, while hydroxyl group absence in the dihalides resulted in potency levels of slightly less than 10 rev/ nmol. Pairwise comparisons of compound mutagenicities showed that overall the C-5 H-by-OH replacement and, next in importance, increasing the number of C-6 halogens from one to two resulted in the greatest enhancements of mutagenicities. However, in comparing compound pairs within two different sets of four di- and trihalides, it was observed that replacement of a C-5 H by OH enhanced mutagenicity more for the dihalides than the trihalides indicating that increasing the C-6 halogen number simultaneously with replacing C-5 H by OH results in a nonlinear, additive enhancement. For fewer than half of the compound pairs compared, changing the C-6 halogen from chlorine to bromine resulted in small increases in mutagenicity, and for the remaining compound pairs, no increase could be discerned. This result points to the relative unimportance of only C-6 halogen type as a determinant of mutagenicity. Similarly, no impact on mutagenicity was observed for changing only the halogen type attached to C-3.