Design, synthesis, and evaluation of N-aroyloxy-2-thiopyridones as DNA photocleaving reagents.

N-Benzoyloxy-2-thiopyridone (12) was shown to induce single-strand nicks in duplex DNA upon irradiation with visible light (lambda&350 nm). This finding led to the design of a series of compounds, in which an acridinyl nucleus was covalently linked to the N-benzoyloxy-2-thiopyridone unit. These conjugates (15, 16, 17 and 18) were synthesized and evaluated as novel DNA photocleaving reagents. Optimal photocleaving activity was observed for conjugate 16, in which a flexible polymethylene spacer of 4 carbons was used to connect the aminoacridine entity to the thiopyridone. This compound was shown to cleave DNA at low microM concentrations and was approximately two-orders of magnitude more efficient than the parent N-benzoyloxy-2-thiopyridone (12). Furthermore, the DNA cleavage ladders induced by 16 and 12 were found to be identical and of no significant sequence selectivity. These data suggest that the N-aroyloxy-2-thiopyridones can be used for the design of new DNA photocleaving reagents with potential use as 'photofootprinting agents' or as 'site-directed photonucleases'.