Radical cations of benzo[α]pyrene (BP) and 6-substituted derivatives were generated by one-electron oxidation with 2 equiv of Mn(OAc)3.2H2O. Some of the properties of these radical cations were investigated by nucleophilic trapping with acetate ion. BP produced predominantly 6-OAcBP and small amounts of BP 1,6-, 3,6-, and 6,12-dione. 6-FBP yielded 6-OAcBP, a mixture of l,6-(OAc)2BP and 3,6-(OAc)2BP, and BP diones. In the case of 6-C1BP and 6-BrBP the major products obtained were a mixture of the 1-OAc and 3-OAc derivatives, and BP diones, while substantial starting material remained unreacted. 6-CH3BP afforded mostly 6-OAcCH2BP, a mixture of 1-OAc and 3-OAc derivatives of 6-CH3BP, and a mixture of 1-OAc and 3-OAc derivatives of 6-OAcCH2BP. These results indicate that nucleophilic substitution of BP,+and 6-FBP.+occurs exclusively at C-6. For 6-ClBP-+and 6-BrBP*+substitution at C-l and C-3, which are the positions of second highest charge density in their radical cations after C-6, compete successfully for nucleophilic substitution. For 6-CH3BP'+charge localization at C-6 activates the methyl group rendering it the most reactive toward nucleophilic attack. Competitive acetoxylation of 6-CH3BP.+ also occurs to a minor extent at C-l and C-3. These mechanistic studies have been useful in clarifying some aspects of the metabolism of BP and its halogeno derivatives by cytochrome P-450 and peroxidases. Furthermore, this chemistry can provide some guidance in understanding the mechanism of tumor initiation by these compounds.
ASJC Scopus subject areas
- Organic Chemistry