Phenolic Compounds in the Leaves of Populus ussuriensis and their Antioxidant Activities

Two new phenolic glucosides [isograndidentatin A (1) and isograndidentatin B (2)], 5 known phenolic glucosides [grandidentatin (3), salireposide (4), populoside (5), populoside A (6), and salicortin (7)], and 2 known phenolic acids [p-coumaric acid (8) and caffeic acid (9)] were isolated from the leaves of Populus ussuriensis. Structure elucidation of 1 and 2 was achieved through extensive spectroscopic techniques. Compounds 1-6 and 9 showed significant antioxidant activities, which were evaluated by the DPPH radical-scavenging method (IC50 values of 6.68, 6.61, 6.75, 6.84, 6.76, 6.79, and 5.92 mu M, respectively) and the ABTS(.+) radical-scavenging system (TEAC values of 1.21, 1.28, 1.26, 1.05, 1.69, 1.60, and 2.00 mM, respectively).