Hydroxycinnamoylmalated flavone C-glycosides from Lemna japonica

Three previously undescribed flavone C-glycosides (1-3), along with seven known ones (4-10), were isolated and characterized from the smallest flowering aquatic plant, Lemna japonica. On the basis of spectroscopic analysis and alkaline hydrolysis, compounds 1-3 were identified to be luteolin 6-C-(2 ''-O-trans-caffeoyl-D-malate)-beta-glucoside (1), apigenin 6-C-(2 ''-O-trans-caffeoyl-D-malate)-beta-glucoside (2), and luteolin 6-C-(2 ''-O-trans-coumaroyl-D-malate)-beta-glucoside (3). Compounds 1-3 are characteristic of a trans-coumaroyl-D-malate or trans-caffeoyl-D-malate linked to C-2 '' of the glucose, which was reported for the first time. Compounds 1-3 exhibited weak cytotoxicity against HepG-2, SW-620, and A-549 cell lines, with IC50 values between 42.5 and 19.2 mu g/ml, and moderate antioxidant activity. Meanwhile compound 3 displayed moderate nematocidal activity with an EC50 value of 1.56 mg/ml.