Screening for bioactive natural products from a 67-compound library of Glycyrrhiza inflata

Licorice shows a variety of pharmacological activities. This work aims to discover bioactive natural products from one botanical source of licorice, Glycyrrhiza inflata. A total of 67 free phenolics were isolated to form a compound library. Based on the bioactivities of licorice, these compounds were screened using cell- or enzyme-based bioassay methods. A total of 11 compounds exhibited potent cytotoxic activities against three human cancer cell lines (HepG2, SW480 and MCF7), while showed little toxicity on human normal cell lines LO2 and HEK293T. A number of chalcones showed remarkable anti-inflammatory activities. Among them, 2 (licochalcone B, IC50 8.78μM), 10 (licoagrochalcone C, IC50 9.35μM) and 13 (licochalcone E, IC50 9.09μM) exhibited the most potent inhibitory activities on LPS-induced NO production, whereas 1, 8, 10, 12 and 13 (IC50 13.9, 7.27, 2.44, 6.67 and 3.83μM) showed potent inhibitory activities on NF-κB transcription. Nine prenylated phenolics were found to be PTP1B inhibitors. Particularly, licoagrochalcone A (4), kanzonol C (7), 2'-hydroxyisolupalbigenin (35), gancaonin Q (45), glisoflavanone (50) and glabrol (53) showed IC50 values of 0.31-0.97μM. Compounds 24 (semilicoisoflavone B, IC50 0.25μM), 26 (allolicoisoflavone B, IC50 0.80μM) and 64 (glabridin, IC50 0.10μM) showed noticeable tyrosinase inhibitory activities. Most of the above bioactive compounds were reported for the first time.