SECONDARY RADICAL ATTACK ON DNA NUCLEOTIDES - REACTION BY ADDITION TODNA BASES AND ABSTRACTION FROM SUGARS

In this work radicals generated by dissociative electron attachment to iodoacetamide (H2NCOCH2.) and 6-chloromethyluracil ((UCH2.)-C-6) are suggested to react with DNA nucleotides in frozen aqueous solutions vi a either hydrogen abstraction or addition to the double bonds of the b ases. Methyl hydrogens of TMP are the preferential sites of the attack by H2NCOCH2. radical. For dCMP the Cl' site on the sugar group is fou nd to be the preferred site of hydrogen abstraction by H2NCOCH2. while for dGMP and to a lesser extent dAMP attack al the C8 position of the purine ring is found to be competitive with sugar attack. In general allylic (UCH2.)-C-6 and (UCH2.)-C-5 radicals are found to be poor hydr ogen abstractors and the only reaction pathway found is the addition t o double bonds at C6 in thymine and C8 in adenine and guanine. Whereas , the cytosine 5,6 double bond appears to be unreactive towards additi on at low temperatures. Some evidence is found for sugar radical addit ion to the adenine C8 position.