Isolation and structure elucidation of new antioxidants from leaves of Populus ussuriensis

Populus ussuriensis Kom. (Salicaceae) leaves have been widely used in folk medicines to treat various diseases [1–2]. A 70% acetone extract of P. ussuriensis leaves was analyzed for antioxidant activity by ABTS ^·+ and DPPH free radical scavenging assays. After partitioning with several solvents, the EtOAc soluble fraction, which showed strong antioxidant activity, was further purified by Sephadex LH-20 column chromatography. The known phenolic acids ρ-coumaric acid (I) and caffeic acid (II), 5 known phenolic glucosides, salireposide (III), populoside (IV), suwonpopuloside (V), salicortin (VI) and grandidentatin (VII), and 2 new phenolic glucosides, 2-hydroxycyclohexyl-4'-O-p-coumaroyl-β-D-glucopyranoside (VIII) and 2-hydroxycyclohexyl-6'-O-p-coumaroyl-β-D-glucopyranoside (IX) were isolated as the active principles and their structures were elucidated on the basis of physicochemical and spectroscopic methods. This is the first report of the chemical composition of P. ussuriensis. Compounds I-VI and IX showed significant antioxidant activities (DPPH IC₅₀ values of 6.68, 6.61, 6.75, 6.84, 6.76, 6.79 and 5.92 µM, respectively; ABTS ^·+ TEAC values of 1.21, 1.28, 1.26, 1.05, 1.69, 1.60, and 2.00 mM, respectively), suggesting they may be exploited as biopreservatives in food applications and health supplements in functional food, to alleviate oxidative stress.

R₁=p-coumaroyl, R₂=H (VIII); R₂=p-coumaroyl, R₁=H (IX) (p-coumaroyl)

Acknowledgement s: Financial support from Natural Science Foundation of Tianjin City (09JCYBJC15800, 09JCZDJC21800).

References: [1] Zhang, XF. et al. (2006)J. Nat. Prod. 69:1370-1373.

[2] Lin, M. et al. (1993) Acta Pharm. Sinic. 28:437-441.