Synthesis and Antitumor Activity of 20(S)-Camptothecin Derivatives. A-Ring-Substituted 7-Ethylcamptothecins and Their E-Ring-Modified Water-Soluble Derivatives

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Twenty-six novel A-ring-modified 7-ethylcamptothecins (6) were synthesized by Friedlander's condensation of the chiral tricyclic ketone (5) with aminopropiophenones (4). The compounds substituted with fluorine at the 11 position showed strong cytotoxicity to KB and L1210 cells. The 11-fluoro derivatives also exhibited strong inhibitory activity on DNA topoisomerase I. Nine compounds 6 with four to ten times stronger cytotoxicity than that of camptothecin were selected and converted into water-soluble 17-O-acyl amide derivatives (8). Compounds 8e (10-Me, O-COCH₂CH₂SCH₃) and 8f (11-F, O-COC₂H₅) showed activity towards Meth A in mice that was comparable to that of CPT-11, at lower doses than CPT-11.