Two Novel Antioxidative Stilbene Tetramers from Parthenocissus laetevirens by Shan He, Liyan Jiang, Bin Wu, Jing Zhou, and Yuan-Jiang Pan* Department of Chemistry, Zhejiang University, Hangzhou 310027, P.R. China (phone: þ 86-571-87951264; fax: þ 86-571-87951629; e-mail: cheyjpan@zju.edu.cn) Laetevirenols F (1) and G (2), two novel stilbene tetramers with an unprecedented skeleton, were isolated from Parthenocissus laetevirens . Their structures were elucidated by spectroscopic analysis, including 1D- and 2D-NMR experiments, and their possible biogenetic pathway was discussed. In addition, both compounds were determined to be potent singlet-oxygen quenchers by electron paramagnetic resonance (EPR) experiments, which highlights their potential pharmacological applica- tions in singlet oxygen mediated diseases. Introduction. – Stilbenes and their oligomers are naturally occurring polyphenols mainly distributed in particular families of plants including Vitaceae, Dipterocarpa- ceae, Gnetaceae, Cyperaceae, and Leguminosae [1]. They have received considerable chemical and biological attention owing to their structural complexity as well as diverse bioactivities [2][3], such as antioxidant [4], cancer-chemopreventive [5], anti- inflammatory [6], anti-HIV [7], antifungal [8], antimutagenic [9], cytotoxic [10], and hepatoprotective [11] activities. They are, therefore, potentially useful lead compounds for drug development. Plants of the genus Parthenocissus (Vitaceae) are known to be rich sources of stilbenes and their oligomers, especially resveratrol oligomers [12 – 15]. P. laetevirens Rehd. is usually planted as a cover crop in east China and traditionally used as folk medicine for the treatment of rheumatism, furuncle, and chronic ulcer [16] . Recently, we have reported the isolation of five new resveratrol oligomers together with three known ones from P. laetevirens [17]. Shortly after, further phytochemical studies led to the first occurrence of stilbene tetramers in this genus with a novel skeleton. Considering the structural relationship between these tetramers 1 1 ) 2 ) and 2 1 ) 2 ) and other oligomers found previously from this species, this report is of biosynthetic significance. Furthermore, the new stilbene tetramers showed strong quenching activities against singlet oxygen, which may highlight their potential pharmacological applications. Results and Discussion. – Compound 1 was isolated as a colorless amorphous powder, and its molecular formula was established as C 56 H 42 O 12 , on the basis of NMR and HR-ESI-MS data, which suggested that 1 was a resveratrol tetramer (resveratrol ¼ 5-[(1E)-2-(4-hydroxyphenyl)ethenyl]benzene-1,3-diol). The 1 H-NMR and 1 H, 1 H- Helvetica Chimica Acta – Vol. 92 (2009) 1260  2009 Verlag Helvetica Chimica Acta AG, Zürich 1 ) Tentative assignment: structures 1 and 2 may be reversed. 2 ) Arbitrary atom numbering; for systematic names, see Exper. Part.