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)-β-glucoside (1), apigenin 6-C-(2″-O-trans-caffeoyl-d-malate)-β-glucoside (2), and luteolin 6-C-(2″-O-trans-coumaroyl-d-malate)-β-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 19.2μg/ml, and moderate antioxidant activity. Meanwhile compound 3 displayed moderate nematocidal activity with an EC₅₀ value of 1.56mg/ml.