8-AZAPSORALEN DERIVATIVES - ISOLATION AND CHARACTERIZATION OF THE FURAN-SIDE CYCLOADDUCTS WITH DNA

The formation of C-4-cycloadducts by photoreaction of eight methyl der ivatives of 8-azapsoralen with DNA was studied. The main reaction invo lves the furan ring of the compounds and the 5,6 double bond of thymin e giving cis-syn adducts, although a minor amount of a cycloadduct wit h cytosine was also isolated for 4,4'-dimethylazapsoralen. The role of the nitrogen atom appears to depend on the electronic effect, leading to a decrease in the reactivity of the pyrone ring. As with psoralens , the methyl groups increase both the lipophilicity and, with the exce ption of the 5,4',5'-trimethyl derivative, the photoreactivity. Howeve r, methyl groups do not appear to influence the chemistry of the photo addition.