Introduction Alzheimer's disease (AD) is one of the major neurodegenerative diseases. Extensive studies have shown that amyloid b protein (Ab), the major component of senile plaques, plays a key role in the pathogenesis of AD [1]. Ab participates in the induction of neuronal cell death and neuritic changes [2], [3]. Neurotoxic ef- fectsmaybeattributabletodisturbancesincalciumhomeostasis and the resulting accumulation of reactive oxygen species (ROS). ROScausemembranedamagetherebycompromisingmembrane integrityandincreasingthepermeabilityforions.Thisinturnin- creases calcium influx and leads to the generation of more ROS [4], [5]. Therefore, increasing antioxidant concentrations at the cellular level could provide considerable protection against ROS. Flavonoids occur very widely in food plants and herbal medi- cines. They not only exert antioxidative and antiproliferative ac- tivity but also bind to the estrogen receptor thereby reducing ROS production [3], [6], [7]. Flemingia macrophylla L. (Leguminosae) is a popular traditional remedy used in Taiwan [8]. The stems have been used in tradi- tional medicine as an antirheumatic and anti-inflammatory agent and for increasing blood circulation. A flavanone [9] and an isoflavone [10] were isolated from the stems, but there have been no previous studies examining its biological activity. In this study, primary cultures of neonatal cortical neurons from thecerebralcortexofHarlanSprague-Dawleyratpupsatpostna- tal day 1 were used as target cells. The effects of F. macrophylla extracts or isolated pure compounds on Ab 25-35 -induced cell apoptosis were determined using the MTT assay for evaluating neuroprotective activity. Herein, we report the isolation and structureelucidationofthreenewflavonoids(1±3)andtheinhi- bitory activity of the bioactive components on Ab-induced neu- rotoxicity. Materials and Methods General experimental procedures Melting points were determined on a Yanagimoto micromelting point apparatus and are uncorrected. Optical rotations were measured on a JASCO DIP-370 polarimeter. IR spectra were re- NeuroprotectiveFlavonoidsfrom Flemingia macrophylla Young-JiShiao Chuen-NeuWang Wan-YuWang Yun-LianLin Affiliation National Research Institute of Chinese Medicine, Taipei, Taiwan, Republic of China Correspondence Yun-Lian Lin ´ ´ 155±1 Li-Nong Street, Sec.2 ´ Shih-Pai ´ Taipei 112 ´ Taiwan ´ Republic of China ´ Phone: +886-2-2820-1999 ext. 6531 ´ Fax: +886-2-2825-0743 ´ E-mail: yllin@nricm.edu.tw Received November 2, 2004 ´ Accepted April 22, 2005 Bibliography Planta Med 2005; 71: 835±840 ´  Georg Thieme Verlag KG Stuttgart ´ New York DOI 10.1055/s-2005-871297 ´ Published online August 19, 2005 ISSN 0032-0943 Abstract Using an Ab-induced neurotoxicity blocking assay to direct frac- tionation, three new flavonoids, fleminginin (1), flemingichro- mone (2), and flemingichalcone (3), and twenty known com- pounds were isolated from the active fractions of the aerial parts of Flemingia macrophylla. The structures of 1 ± 3 were elucidated on the basis of spectroscopic data. When tested for neuroprotec- tive activity, compound 2, osajin (4), 5,7,4¢-trihydroxy-6,8-dipre- nylisoflavone (5), 5,7,4¢-trihydroxy-6,3¢-diprenylisoflavone (6), and aureole (7) protected neuronal cells from Ab-induced dam- age with EC 50 values of 31.43  3.16, 5.01  1.28,11.25 1.51, 4.47 0.65,12.092.55 mM, respectively. Key words Flemingia macrophylla ´ Leguminosae ´ flavonoids ´ neuroprotec- tion Original Paper 835