63019-41-0Relevant academic research and scientific papers
Charge delocalization in persistent benz[a]anthracenium cations bah+ and related α-carbocations/carboxonium ions: modeling epoxide ring opening in potent carcinogens
Laali, Kenneth K.,Tanaka, Mutsuo
, p. 7280 - 7285 (1998)
Parent BA 1 protonates at C-7/C-12 to give 1H+ and laH+ in 3:1 ratio which remains unaffected by variation in temperature and the superacid system. Increasing steric crowding at the bayregion by introduction of a methyl at C-l (1-MBA) changes the ratio of C-7/C-12 protonated arenium ions 2H+/2aH+ to 10:1. The highly potent 7,12-dimethylbenz[a]anthracene, 7,12-DMBA, gives a 1:1 mixture of the two ipso-protonated cations 3aH+/3H+ whose composition changes to 50:1 overtime in favor of 3aH+ (ipso-attack at bay-region), showing it to be the thermodynamic cation. 3-Methylcholanthrene, 3MC, is exclusively protonated at C-6 (→4aH+). Cation 5+ (a simplified model for bay-region epoxide ring opening) is cleanly formed via its carbinol 5-OH with FSO3H/ SO2C1F. Ketone 6 is O-protonated in TFAH and in TFAH/H2SO4 to give the bay-region carboxonium ion 6H+; its diprotonation in FSO3H·SbFs (4:1)/SO2C1F gave the first example of the oxoniumarenium dication 6H22+. α-BA-substituted secondary carbocation 7+ and the carboxonium ion 8H+ were generated to probe charge delocalization into the α-BA moiety via C-7. To gauge the importance of the benz[α] ring and for comparison, the anthracene-substituted carbocations 9+ and carboxonium ion 10H+ were generated and studied. Charge delocalization pathways into the PAH periphery are evaluated on the basis of Δδ13C values. AMI was used as a complementary tool for qualitative comparison with experiment. The resulting arenium ions and benzylic carbocations exhibit strong anthracenium ion character emphasizing the importance of an electrondeficient anthracene moiety. The present study constitutes the first direct investigation of carbocations in the BA series, whose bay-region and K-region diol epoxides are considered the ultimate carcinogens en route to PAH-DNA adduct formation.
