First Occurrence of a Furano-glycyrrhetinoate and Its Cytotoxicity.

(18α)-Glycyrrhetinic acid (4) was prepared from (18β)-glycyrrhetinic acid (1), and the cytotoxicity of some derivatives was investigated by photometric SRB assays employing several human tumor cell lines. In summary, (18β)-1 is slightly more cytotoxic than its (18α) epimer 4, but its cytotoxicity is negligible. Higher cytotoxicity was observed for the esters 2 and 5 and for the 3-O-acetylated esters 3 and 6. Cytotoxicity was improved dramatically when the hydroxyl group at position C-3 was replaced by an amino moiety. SeO2 oxidations gave access to a novel furano-glycyrrhetinoate 15. Interestingly, its seleno analog 16 is approximately five to six times less cytotoxic for the tumor cell lines tested, and tumor/non-tumor selectivity is lost upon replacement of the oxygen by a selenium substituent.