Studies On The Chemical Constituents Of Hop Cones And Their Antitumor Activity

The hop plant, Humulus lupulus L. (Moraceae), is a dioecious twining perennial, which is cultivated widely throughout the temperate zones of the world. The female inflorescences of the hop plant, so-called hop cones or hops, are used in folk medicine as a tranquilizer, bitter stomachic and antituberculosis drugs. Hop cones which have characteristic flavour and aroma are also widely used in the brewing industry. During our screening for antitumor materials from plants used in Chinese traditional medicine by MTT method using K562 cells, we found that the crude extract of hop cones showed strong inhibitory effect on the proliferation of K562 cells. Thus, a chemical investigation on the hop cones was undertaken in the present dissertation focusing on its antitumor constituents.In a pilot experiment, little amounts (10 g) of powdered hop cones were extracted with EtOAc, alcohol and 60% alcohol successively to give EtOAc extract (E), alcohol extract and 60% alcohol extract respectively. The EtOAc extract (E) was further extracted with hexane and then Et2O to divided into three parts, the hexane extract (E-1), Et2O extract (E-2) and insoluble part (E-3). In a bioassay using K562 cells, E-1 and E-3 showed the strong antitumor activity that corresponded to the effect of the crude extract of hop cones observed in our preliminary screening test. Thus the large amounts (5.2 kg) of powdered hop cones were extracted with EtOAc and the EtOAc extract (1029.6 g) obtained was extracted in turn with hexane and then Et2O to obtained E-1 (455.1 g) and E-3 (140.0 g).Compounds 1~7 were isolated from E-1 and E-3 by a separation procedure using various column chromatography, PTLC and PHPLC. Structures of the compounds obtained were investigated by spectroscopic methods (MS, UV, 1D NMR and 2D NMR) to identify them as xanthohumol (1), xanthohumolⅠ(2), xanthohumol B (3), kaempferol 3-O-α-L-rhamnopyranosyl-(1→6)-β-D-glucopyranoside (4), pinocembrin (5), naringenin (6) andβ-sitosterol (7), respectively. The antitumor activity for 1~7 was assayed by MTT method using human leukemia carcinoma K562 cells, accompanied with the morphological observation of the cells under light microscope.Among the compounds obtained, 1~6 showed the antitumor effect on the K562 cells to a different extent. Among them, 1 showed the highest activity on the proliferation of K562 cells with the IC50 value of 7.2μg/mL; 2, 3 and 5 moderately inhibited the proliferation of K562 cells with the IC50 values of 62.0, 28.9 and 89.1μg/mL respectively; while the others had weak effect towards K562 cells (IC50>100μg/mL). The activities of those compounds appeared to a certain extent some relations to their structures.In conclusion, 5 and 6 were isolated from the genus Humulus for the first time, and the antitumor activity for 2 and the inhibitory effect of 1 and 3~6 on the proliferation K562 cells were reported for the first time in the present study.