Four new antioxidant phenylpropanoid glycosides from Microlepia pilosissima

Four new phenylpropanoid glycosides, 9-O-[beta-D-glucopyranosyl-(1 -> 2)-alpha-L-rhamnopyranosyl]-3,4-dimethoxy-cinnamic acid (1), 9-O-[beta-D-glucopyranosyl-(1 -> 2)-alpha-L-rhamnopyranosyl]-4-methoxycinnamic acid (2), 9-O-alpha-L-rhamnopyranosyl-3,4-dimethoxy-cinnamic acid (3), and 9-O-[6-Oacetyl-beta-D-glucopyranosyl]-4-methoxy-cinnamic acid (4), together with three known compounds 9-O-alpha-L-rhamnopyranosyl-4-hydroxy-cinnamic acid (5), 9-O-beta-D-glucopyranosyl-4-methoxycinnamic acid (6), and 9-O-beta-D-glucopyranosyl-3,4-dimethoxy-cinnamic acid (7) were isolated from the 70% EtOH extract of the dry fronds of Microlepia pilosissima. Their chemical structures were elucidated by spectroscopic analysis. Moreover, 1 and 2 exhibited comparable scavenging activities with (+/-)-alpha-tocopherol against DPPH radicals, while compounds 3-7 displayed moderate antioxidant activities.