The tetrahydroprotoberberine alkaloids 5 and 7 possessing a trans-quinolizidine conformation display in vitro KR cytotoxicities in contrast to their corresponding diastereomers 4 and 6 which exist in the cis-quinolizidine conformation and are much less toxic. The DNA-binding parameters of these compounds as well as the protoberberine salts 1, 8, and 9 have been examined by equilibrium dialysis. Only the quaternary salts bind to ...
