Neuroprotective 2-(2-Phenylethyl)chromones of Imperata cylindrica Jeong Seon Yoon, Mi Kyeong Lee, Sang Hyun Sung, and Young Choong Kim* College of Pharmacy and Research Institute of Pharmaceutical Science, Seoul National UniVersity, San 56-1, Sillim-Dong, Gwanak-Gu, Seoul 151-742, Korea ReceiVed September 29, 2005 Bioactivity-guided fractionation of the methanolic extract of the rhizomes of Imperata cylindrica afforded a new compound, 5-hydroxy-2-(2-phenylethyl)chromone (1), together with three known compounds, 5-hydroxy-2-[2-(2- hydroxyphenyl)ethyl]chromone (2), flidersiachromone (3), and 5-hydroxy-2-styrylchromone (4). Among these four compounds, 1 and 2 showed significant neuroprotective activity against glutamate-induced neurotoxicity in primary cultures of rat cortical cells. During our search for neuroprotective compounds from natural products, the MeOH extract of the rhizomes of Imperata cylindrica Beauv. (Gramineae) was found to significantly protect primary cultures of rat cortical cells from the toxicity induced by glutamate, an excitatory neurotransmitter. The rhizomes of I. cylindrica are widely distributed in Asia and have been described as a diuretic, anti-inflammatory, or antipyretic agent in Korean traditional herbal medicine. 1 Previous studies on the rhizomes of I. cylindrica have resulted in the isolation of various compounds such as arundoin, 2 cylindrin, 2 fernenol, 2 cylindol, 3 cylindrene, 4 graminones, 5 and imperarene. 6 To date, however, there has been no report related to neuroprotective constituents of this plant. Thus, we pursued the isolation of neuroprotective constituents from the MeOH extract of I. cylindrica rhizomes by bioactivity-guided fractionation. A new chromone, 5-hydroxy-2-(2-phenylethyl)chromone (1), and three known chromones (2-4) were obtained. Here, we report the isolation and characterization of these chromones and their neuroprotective activity against glutamate-induced neurotoxicity in primary cultures of rat cortical cells. Compound 1 was obtained as a yellow powder. The positive HREIMS of 1 gave a molecular ion at m/z 266.0936, corresponding to the molecular formula C 17 H 14 O 3 (calcd m/z 266.0943). The UV absorption maxima at 344 and 252 nm and the IR absorption at 1655, 1621, and 1477 cm -1 suggested the presence of a chromone ring. 7,8 The 1 H NMR data of 1 indicated the presence of 1,2,3- trisubstituted and monosubstituted aromatic rings from the signals at δ 7.44 (1H, t, J ) 8.4 Hz), 6.80 (1H, dd, J ) 8.4 and 0.9 Hz), and 6.71 (1H, dd, J ) 8.4 and 0.9 Hz) and signals at δ 7.12-7.27 (5H, m), respectively. The presence of two methylene groups was also deduced by the signals at δ 2.99 (2H, t, J ) 7.6 Hz) and 2.86 (2H, t, J ) 7.6 Hz). The other proton signals could be assigned as one hydroxyl group at δ 12.45 (1H, br s) and one olefinic proton at δ 6.00 (1H, s). The 13 C NMR and DEPT spectra of 1 revealed the presence of two methylenes, nine methines, and six quaternary carbons including one carbonyl carbon at δ 183.5 (s). In addition, HMBC correlations were observed between the H-7′ methylene protons at δ 2.99 and C-2′, C-6′, C-8′ and between the H-8′ methylene protons at δ 2.86 and C-3, C-7′. On the basis of these findings, compound 1 was suggested as a 2-(2-phenylethyl)- chromone with one hydroxyl group. The location of the hydroxyl group at δ 12.45 was defined as C-5. Taken together, compound 1 was assigned as the new 5-hydroxy-2-(2-phenylethyl)chromone. Three known compounds were identified from their spectroscopic data by comparison with literature values as 5-hydroxy-2-[2-(2- hydroxyphenyl)ethyl]chromone (2), 10 flidersiachromone (3), 9 and 5-hydroxy-2-styrylchromone (4). 11 Although the synthesis of compound 4 has been described, 11 this is the first time that it has been isolated from natural resources. In addition, compounds 2 and 3 were isolated for the first time from this plant. The neuroprotective activity of compounds 1-4 against glutamate- induced neurotoxicity in primary cultures of rat cortical cells was evaluated by the MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphen- yltetrazolium bromide) assay as described in our previous re- ports. 12,13 As shown in Table 1, compounds 1 and 2 showed significant neuroprotective activity against glutamate-induced neurotoxicity at 10.0 µM concentration. Interestingly, however, * To whom correspondence should be addressed: Tel: 82-2-880-7842. Fax: 82-2-888-2933. E-mail: youngkim@snu.ac.kr. Table 1. Protective Activity of Compounds 1-4 Isolated from I. cylindrica against Glutamate-Induced Neurotoxicity in Primary Cultures of Rat Cortical Cells compound concentration (µM) protection (%) a control 100.0 ( 2.1 glutamate-treated b 0.0 ( 2.2 1 10.0 67.0 ( 5.6*** 2 10.0 63.6 ( 5.6*** 3 10.0 36.1 ( 5.4* 4 10.0 -11.3 ( 4.9 MK-801 c 10.0 82.2 ( 6.9*** a Protection (%) was calculated as 100 × [optical density (OD) of test compound + glutamate-treated culture - OD of glutamate-treated culture]/[OD of control culture - OD of glutamate-treated culture]. The ODs of control and glutamate-injured cultures were 1.00 ( 0.01 and 0.72 ( 0.01, respectively. b Glutamate-treated value differs sig- nificantly from the untreated control at a level of p < 0.001. c MK- 801: dizocipline maleate, a noncompetitive antagonist of NMDA receptor. The values are expressed as mean ( SD of triplicate experiments (*P < 0.05, **P < 0.01, ***P < 0.001). Figure 1. Key HMBC correlations for 1. 290 J. Nat. Prod. 2006, 69, 290-291 10.1021/np0503808 CCC: $33.50 © 2006 American Chemical Society and American Society of Pharmacognosy Published on Web 01/12/2006