Synthesis and antitumor activity of duocarmycin derivatives: A-ring pyrrole analogues of duocarmycin B2.

A series of the eight-substituted A-ring pyrrole derivatives of duocarmycin B2 were synthesized, and evaluated for in vitro anticellular activity against HeLa S3 cells and in vivo antitumor activity against murine sarcoma 180 in mice. In addition, the stability of the analogues in aqueous solution was examined. The 8-H and the 8-CN compounds which cannot structurally release the cyclopropane compound (DU-86), exhibited extremely diminished anticellular activity compared with duocarmycin A (1a) or DU-86. The ethers and the sulfonates which were not converted to DU-86 under usual conditions (35 degrees C, pH 7), showed almost equal in vivo activities to that of 1a. However, their optimal doses were significantly higher than that for 1a. Most of the A-ring pyrrole analogues which can be chemically or enzymatically converted to DU-86, displayed remarkably superior in vivo antitumor activity to 1a. These results suggest that the A-ring pyrrole analogues need to chemically or enzymatically release DU-86 as an active metabolite to exhibit potent in vivo antitumor activity.