Research on the biological activity of enediyne anticancer antibiotics has been at the forefront of cancer research for many decades because of the ability of these molecules to irreversibly cleave double-stranded DNA. The enediynes can intercalate into a double-stranded DNA molecule and undergo Bergman-cyclization to form a carbon-centered biradical intermediate, usually a para-benzyne analog. Because of their short lifetimes, high reactivity, and difficulties in generation, the fundamental chemical properties of para-benzynes have proven challenging to study. Our group has successfully generated and studied unsubstituted para-benzynes in a novel dual-linear quadrupole ion trap mass spectrometer (DLQIT). However, substituent effects on the chemical properties of para-benzynes still remain unexplored.In the present study, the chemical properties of the three CN-substituted isomers of the 2,5-didehydropyridinium cation were examined in the gas phase in the DLQIT. The results were compared with those obtained for the 2,5-didehydropyridinium cation. The 3- and 4-CN-2,5-didehydropyridinium cation mainly showed proton transfer products, suggesting ring opening of parabenzyne. However, the 6-CN-2,5-didehydropyridinium cation was found to undergo mainly radical reactions. Moreover, this CN-substituded para-benzyne exhibited very high reaction efficiencies toward reagents such as cyclohexane and dimethyl disulfide. Calculations suggest that this radical has a triplet ground state rather than a singlet state. The results of proton affinity measurements and experiments using oxygen also support the triplet ground state for this para-benzyne.

Gas phase reactivities of 6-cyano-2, 5-didehydropyridinium radical cation: The first stable and highly reactive charged para-benzyne analogs

248th National Meeting (2014)

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