Synthesis and cytotoxicity of 3-amino-glycyrrhetinic acid derivatives

The aim of this study was to prepare 3-hydroximino- and 3-amino derivatives of glycyrrhetinic acid and derivatives to evaluate their in vitro cytotoxicity for a panel of human tumor cell lines. Thus, commercially available glycyrrhetinic acid (1) was acetylated or oxidized at position C-3 and transformed into a variety of different esters and amides followed by their conversion to 3-oximes and amines. While the parent compound was not cytotoxic at all, the 3-amino esters are highly cytotoxic. Interestingly, 3-amino amides were significantly less cytotoxic than 3-amino esters. The (3b, 18b, 20b) Benzyl 3-amino-11-oxoolean-12-en-30-oate was the most cytotoxic compound of this series showing an EC50 = 1.3 mM for 518A2 melanoma cells.