Starting from 2-(2-aminoethyl)-6-methoxy-1-methylcarbazole, ethyl 9-methoxy-5-methyl-6H-pyrido[4,3-b]carbazole-1-carboxylate was obtained through a three-step sequence. This compound and its 6-methyl derivative react with (dialkylamino)alkylamines to provide various 9-methoxy-5-methyl-6H-pyrido[4,3-b]carbazole-1-(N-substituted carboxamides) whose boron tribromide demethylation afforded corresponding 9-hydroxy-1-(N-substituted carbamoyl)-olivacines. The same pathway but starting from 2-(2-aminoethyl)-6-methoxy-1,4-dimethylcarbazole led to ethyl 9-methoxy-5,11-dimethyl-6H-pyrido[4,3-b]carbazole-1-carboxylate which did not normally react with amines. It provided either the recovered starting material at 120 degrees C or 9-methoxyellipticine resulting from an unexpected decarboethylation in a steel vessel at 180 degrees C. Biological testing of the newly obtained 1-carbamoylolivacine derivatives showed that 9-hydroxylated compounds displayed high cytotoxicity for cultured L1210 and colon 38 cells (IC50 range 5-10 nM) and good antitumor activity in vivo in the P388 leukemia and colon 38 models when administered by the iv route. The most active compound in these series is 9-hydroxy-5,6-dimethyl-1-[N-[2-(dimethylamino)ethyl]carbamoyl]-6H- pyrido[4,3-b]carbazole which was selected for further evaluation on murine solid tumors and for toxicological studies.

A set of disubstituted tetracyclic lactones has been synthesized and tested for potential antitumor activity. Several of them possess a noticeable cytotoxicity against L1210 and HT-29 colon cells in vitro. Relationships between chain nature and biological properties were sought. Lactones with a pentyl or hexyl substituent at C-11 are the most active ones. The introduction of a functional group at the side chain of C-11 modified the potency; carboxylic acid and primary amine decreased the cytotoxicity, whereas a cyano group increased the activity. An extensive structure-activity relationship study of these derivatives, including carbon homologues and bioisosteres has been performed. The synthesis and cytotoxicity of these compounds are discussed. Two lactones are recognized as potential lead compounds.