Abstract
In this dissertation, I report new and efficient methods for the cleavage of DNA by photolysis of arylhydrazines, diphenyl arylhydrazidophosphates, N - aryl - N - nitrosohydroxylamine ammonium salts and azoxy compounds with UV light. In addition, I also report the cleavage of DNA by thermolysis of N - aryl - N - nitrosohydroxylamine ammonium salts with heat. Thus UV light and heat functioned as the "trigger" to initiate DNA strand scission. In the first part, the photochemical behavior of arylhydrazines was investigated by use of EPR spectroscopy. The new findings suggest that HO．, aryl radicals, arenes and phenols were produced by the photolysis of arylhydrazines, and then a plausible mechanism was proposed. This process was successfully applied to single - strand cleavage of DNA. Furthermore, irradiation of arylhydrazidophosphates with 312 - nm UV light caused single - strand cleavage of DNA. In the second part, a new transformation was developed for the couplⅥing of N - aryl - N - nitrosohydroxylamine ammonium salts to give acyclic and cyclic azoxy compounds. Heating of an ethanolic solution containing N - aryl - N -nitrosohydroxylamine ammonium salts produced the desired azoxy compounds in 80 - 99% yields. Furthermore, irradiation with UV light (□ ≧ 300nm) of ethanolic solutions of those ammonium salts at room temperature also provided the desired azoxy compounds in 51 - 72% yields and NO．. Based on the EPR spectroscopy and isolated products, Two mechanisms were proposed for the transformation under thermal or photolytic conditions. NO．is produced by photolysis and thermolysis N - aryl - N - nitrosohydroxylamine ammonium salts. On the other hand, NO．is suggested as DNA - cleaving species. In the third part, I found that the single - strand cleavage of DNA by use of 312 - nm UV light or heating at 60℃ with various N - aryl - N - nitrosohydroxylamine ammonium salts, which initiate the new and controllable DNA cleavage processes. Azoxy metabolites of procarbazine can damage DNA. In the fourth part, azoxy compounds were examined as photo - induced DNA - cleaving agents. Single - strand cleavage of DNA was accomplished by photolysis of various azoxy compounds with 365 - nm UV light. These DNA - cleaving processes were investigated in control experiments according each requirements: (i) Molecular oxygen was removed from the buffer by bubbling argon gas. (ii) Radical processes were investigated by adding hydroxyl radical scavengers (i. e., ethanol, DMSO, and KI) or general radical scavenger (i. e., cysteine). (iii) Singlet oxygen was removed by adding sodium azide as the scavenger. (iv) H2O was replaced by D2O to increase the lifetime of singlet oxygen. (v) The reactions were treated in the dark. (vi) The reactions were treated at room temperature. (vii) The reactions were treated in different pH values buffer (5.0, 6.0, 7.0, and 8.0). According, the four compounds, arylhydrazines, diphenyl arylhydrazidophosphates, N - aryl - N - nitrosohydroxylamine ammonium salts, and azoxy compounds were applied for DNA cleavage under controllable conditions. The "trigger" of DNA - cleaving processes were successfully found by treating those compounds with DNA. The UV light (312 nm or 365 nm) and heat (60℃) are suggested as the "triggers" for DNA cleavage. And then, HO．, singlet oxygen, NO．, and the oxide moiety of azoxy compounds were proposed as the main DNA - cleaving species for arylhydrazines, diphenyl arylhydrazidophosphates, N -aryl - N - nitroso - hydroxylamine ammonium salts, and azoxy compounds, respectly. Futhermore, although the single - strand cleavage of DNA occurred preferably under acidic conditions, the pH value of the media over the range between 5.0 - 8.0 did not affect the cleaving efficiency of those compounds significantly.