Synthesis and Structure-Activity Relationship Studies of 2,3-Dihydroimidazo[2,1-a]isoquinoline Analogs as Antitumor Agents

5-Aryl-2,3-dihydroimidazo[2,1-a]isoquinolines were reported to have strong antitumor activity and one of the derivatives such as $5-[4^{l}$ -(piperidinomethyl)phenyl]-2,3-dihydroimidazo[2,1-a] isoquinoline (1, SDZ 62-434) was found to be more effective than the clinical cytostatic agent edelfosine (2) in in vitro and in vivo assays. Currently SDZ 62-434 is in clinical trials in Europe. The structure-activity relationship studies of SDZ 62-434 showed that compounds with substitution on ring A were less active than the lead compound. Ring B in SDZ 62-434 was essential for the activity because compounds without B ring had no antitumor activity. Among the 3-arylisoquinolin-1-one derivatives, $3-[4^{I}$-(piperidinomethyl)phenyl] substituted analog had no antitumor activity but simple phenyl substituted compound, such as 4, showed the most potent antitumor activity in various human tumor cell lines.