Résumé : The isomer (9H-quino[4,3,2-de][1,7]phenanthroline-9-one) (2) of the marine alkaloid ascididemin (9H-quino[4,3,2-de][1,10]phenanthroline-9-one) (1) has been synthesized in six steps from 1,4-dimethoxyacridine (10) with an overall yield of 12%. Different related compounds were prepared and tested in vitro at six different concentrations on 12 different human cancer cell lines of various histopathological types (glioblastomas and breast, colon, lung, prostate and bladder cancers). Almost all the compounds present cytotoxic activity of micromolar order.