The coupling of acetylated piperazinylamide spacered triterpenoic oleanolic acid and ursolic acid with meta or para substituted carboxylated malachite green analogs gave conjugates 10, 11, 15, and 16 that were cytotoxic for several human tumor cell lines. Especially, an oleanolic acid-derived compound 10 was cytotoxic for MCF-7 human breast carcinoma cells (EC 50 = 0.7 μM). These derivatives represent first examples of triterpenoic acid derivatives holding a cationic scaffold derived from malachite green. Graphical Abstract

Pentacyclic triterpenoids oleanolic acid, ursolic acid, betulinic acid, and platanic acid were acetylated and converted into several amides 9–31; the cytotoxicity of which has been determined in sulforhodamine B assays employing seral human tumor cell lines and nonmalignant fibroblasts. Thereby, a betulinic acid/trans-1,4-cyclohexyldiamine amide showed excellent cytotoxicity (for example, EC50 = 0.6 μM for HT29 colon adenocarcinoma cells).

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