Cytotoxic polyphenolic compounds from Lespedeza bicolor stem bark.

Four new pterocarpans (6aR,11aR)-6a,11a-dihydrolespedezol A2 (2), (6aR,11aR)-2-isoprenyl-6a,11a-dihydrolespedezol A2 (3), (6aR,11aR,3'R)-6a,11a-dihydrolespedezol A3 (4), (6aR,11aR,3'S)-6a,11a-dihydrolespedezol A3 (5) and one new stilbenoid with 1,2-diketone fragment named bicoloketone (6) along with one previously known pterocarpen lespedezol A2 (1) have been isolated from Lespedeza bicolor stem bark using multistage column chromatography on polyamide and silica gel. The structures of the isolated polyphenolic compounds were determined by spectroscopic methods. The absolute configurations of 4 and 5 were determined by comparison of their electronic circular dichroism (ECD) spectra obtained experimentally and the spectra calculated using time-dependent density functional theory (TDDFT). The isolated compounds exhibited a moderate DPPH scavenging effect and ferric reducing power compared to the reference antioxidant quercetin. The cytotoxicity of compounds against three human cancer cell lines, HTB-19, Kyse-30, and HEPG-2, and two normal cell lines, RPE-1 and HEK-293, was tested using the MTT assay. Compound 3 showed the strongest cytotoxic activity against all cell lines (IC50 6.0-19.1 µM) compared with the positive control cisplatin. The other tested compounds possessed moderate cytotoxic activity against cancer cells.

Phenolic compounds from Glycyrrhiza pallidiflora Maxim. and their cytotoxic activity.

Twenty-one phenolic compounds (1-21) including dihydrocinnamic acid, isoflavonoids, flavonoids, coumestans, pterocarpans, chalcones, isoflavan and isoflaven, were isolated from the roots of Glycyrrhiza pallidiflora Maxim. Phloretinic acid (1), chrysin (6), 9-methoxycoumestan (8), isoglycyrol (9), 6″-O-acetylanonin (19) and 6″-O-acetylwistin (21) were isolated from G. pallidiflora for the first time. Isoflavonoid acetylglycosides 19, 21 might be artefacts that could be produced during the EtOAc fractionation process of whole extract. Compounds 2-4, 10, 11, 19 and 21 were evaluated for their cytotoxic activity with respect to model cancer cell lines (CEM-13, MT-4, U-937) using the conventional MTT assays. Isoflavonoid calycosin (4) showed the best potency against human T-cell leukaemia cells MT-4 (CTD50, 2.9 µM). Pterocarpans medicarpin (10) and homopterocarpin (11) exhibit anticancer activity in micromolar range with selectivity on the human monocyte cells U-937. The isoflavan (3R)-vestitol (16) was highly selective on the lymphoblastoid leukaemia cells CEM-13 and was more active than the drug doxorubicin.