Examination of the Phenolic Profile and Antioxidant Activity of the Leaves of the Australian Native Plant Smilax glyciphylla

Together with the sweet principle component glycyphyllin A (3), seven phenolic compounds including two new dihydrochalcone rhamnopyranosides, glycyphyllin B (1) and glycyphyllin C (2), and five known flavonoids, catechin (4), kaempferol-3-O-beta-D-glucopyranoside (5), quercetin-3-O-beta-D-glucopyranoside (6), kaempferol-3-O-beta-neohesperidoside (7), and 2R,3R-dihydrokaempferol-3-O-beta-D-glucopyranoside (8), have been isolated from the ethanolic extract of the leaves of Smilax glyciphylla for the first time. The structures of these compounds were characterized by spectroscopic methods including UV, MS, and ID and 2D NMR In vitro antioxidant capacity tests employing FRAP and DPPH assays indicated that 1, 4, and 6 exhibited potent antioxidant activity and are the key phenolics responsible for the antioxidant activity of the leaf extract of S. glyciphylla.