Plant antitumor agents. 23. Synthesis and antileukemic activity of camptothecin analogues

Eight optically active and nine racemic ring A modified analogues of 20(S)-camptothecin were prepared and evaluated for antitumor activity in the L-1210 leukemia system. The ring A mono- and disubstituted analogues displayed a wide variance in activity and potency. It was found that monosubstitution by NH2 or OH at positions 9, 10, or 11 yielded compounds with activity much higher than the parent compound, camptothecin, whereas substitution at position 12 greatly reduced activity. In general, disubstitution in ring A greatly reduced antileukemic activity. Replacement of ring A by heterocyclic rings (thiophene or pyridine) leads to analogues with only moderate activity.