PULSE-RADIOLYSIS STUDIES ON THE FRAGMENTATION OF ARYLMETHYL QUATERNARY NITROGEN MUSTARDS BY ONE-ELECTRON REDUCTION IN AQUEOUS-SOLUTION

The radical species formed on the reaction of e(aq)(-) with a series o f aryl compounds, all containing a N,N-bis(2-chloroethyl)-N-methylammo niomethyl substituent, have been studied in neutral aqueous solutions by pulse radiolysis using optical absorption spectraphotometry. The be nzene, 1, and 4-methylsulfonylbenzene, 2, derivatives fragmented Immed iately to yield different amounts of benzyl radicals, but the 2-nitrob enzene, 3, and 4-nitrobenzene, 4, derivatives were reduced to long-liv ed radical anions which decayed by bimolecular processes. These nitrob enzene derivatives differed from the corresponding benzyl halides in t hat they did not fragment to benzyl radicals. Similarly, no evidence w as found for the formation of a benzyl-type radical from the radical a nion of the 8-nitronaphthalene derivative, 5. However, benzyl-type rad icals were produced upon intramolecular electron transfer from the ini tially formed radical anions of the 4-nitro-5-imidazole, 6, and the 5- nitro-2-pyrrole, 7, derivatives at rate constants of (8.0 +/- 1.0) x 1 0(3) and (1.0 +/- 0.1) x 10(4) s(-1) respectively; The latter heterocy clic analogues provide an approach for release of cytotoxic tertiary a mines via enzymatic or radiolytic reduction in hypoxic regions of tumo rs.