. I wide range of activity was obtained by varying thr substituents.-\ r in the I? Ia structure from p-methoxyphenyl (100%) inhibition at 100 mg./kg.) to p-chlorophenyl (71% inhibition at 100 mg./kg.) to 2, 1-dichlorophenyl (" 2% inhibition at 100 mg./kg.). These substituents established the same relative order of activity in thr J'IIb series. The markedly increased antitumor activity thus appears to be related to electroil donors on the benzyl group, even ...