Table 12. Sterling biochemical SAR of N-1, C-5 and C-7 substituted 6,8-difluoro analogs.

Compound	R5	R7	R1	topo II DNA cleavage EC50 (µg/ml)a,b
103 WIN 57294	H			2.8
104	H		-CH2CH3	40
105	H			>181
106	-NH2			2.4