Three New Compounds, Licopyranol A–C, Together with Eighteen Known Compounds Isolated from Glycyrrhiza glabra L. and Their Antitumor Activities

Glycyrrhiza glabra L., known as licorice, is one of the most famous herbs in the world. In this study, we investigated the phytochemical and antitumor activities of G. glabra, especially its anti-colorectal cancer activities. G. glabra was extracted with 70% methanol, and the ethyl acetate layer was separated by silica gel, ODS, LH-20 column chromatography, and semi-preparative HPLC to obtain the compounds. The structures were determined by NMR and MS methods. Three new compounds named licopyranol A–C (1–3), and eighteen known compounds (4–21) were isolated. Compounds with an isoprenyl group or dimethylpyran ring showed better antitumor activities. Licopyranol A (1) and glycyrol (5) both inhibited the proliferation, reduced clone formation and promoted apoptosis of RKO cells. The Western blotting assays showed that glycyrol significantly reduced the expression of E-cadherin, β-catenin, c-Myc, and GSK-3β proteins in RKO cells, suggesting that glycyrol may inhibit the growth of colorectal cancer RKO cells via the Wnt/β-catenin signaling pathway.