Chinese Journal of Natural Medicines 2018, 16(8):

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1 Chinese Journal of Natural Medicines 2018, 16(8): Chinese Journal of Natural Medicines New flavonoids and methylchromone isolated from the aerial parts of Baeckea frutescens and their inhibitory activities against cyclooxygenases-1 and -2 ZHOU Jun-Neng 1Δ, YAN Ming 2Δ, GAO Peng 2, HOU Ji-Qin 1, PHAM Thi-Anh 1, WANG Hao 1* 1 State Key Laboratory of Natural Medicines, Department of Natural Medicinal Chemistry, China Pharmaceutical University, Nanjing , China; 2 Jiangsu Key Laboratory of Drug Screening, China Pharmaceutical University, Nanjing , China Available online 20 Aug., 2018 [ABSTRACT] In the present study, we carried out a phytochemical investigation of the ethanol extract of the aerial parts of Baeckea frutescens, which resulted in the isolation of two new flavonoid glycosides, myricetin 3-O-(5''-O-galloyl)-α-L-arabinofuranoside (1), 6-methylquercetin 7-O-β-D-glucopyranoside (2), one new methylchromone glycoside, 7-O-(4', 6'-digalloyl)-β-D-glucopyranosyl-5- hydroxy-2-methylchromone (3), together with three known compounds (4 6). The structures of these isolated compounds were established on the basis of 1D and 2D NMR techniques and chemical methods. The anti-inflammatory activities of the compounds 1 6 were evaluated for their inhibitory effects against cyclooxygenases-1 and -2 in vitro. Compounds 1 6 showed potent COX-1 and COX-2 inhibiting activities in vitro with IC 50 values ranging from 1.95 to 5.54 μmol L 1 and ranging from 1.01 to 2.27 μmol L 1, respectively. [KEY WORDS] Baeckea frutescens; Flavonoid; Methylchromone; Cyclooxygenase-1; Cyclooxygenase-2 [CLC Number] R284.1 [Document code] A [Article ID] (2018) Introduction Baeckea frutescens L. (Myrtaceae) is mainly distributed in south and southeast China, and has been used as folk herbal medicine for the treatment of inflammatory diseases, including traumatic injury, cystitis urocystitis, and inflammatory diarrhea [1]. B. frutescens has been shown to possess antiinflammatory [2], antioxidant [3-4], and cytotoxic activities [5-6]. From the aerial parts or roots of Baeckea frutescens, several classes of compounds, such as sesquiterpenes [7], phloroglucinols [8-9], chromones [10-11], flavonoids [12-15], cyclopentenones and furanones [16], and essential oil [17], have been isolated. In our continuing investigation of anti-inflammatory constituents from the aerial parts of B. frutescens, the n-buoh portion from the ethanol extract of this plant was [Received on] 13-Sep [Research funding] This work was supported by the National Natural Science Foundation of China (No ). [ * Corresponding author] Tel: , Fax: , wanghao@cpu.edu.cn Δ These authors contributed equally to this work. These authors have no conflict of interest to declare. Published by Elsevier B.V. All rights reserved found to inhibit cyclooxygenases-1 and -2 (COX-1 and -2) in vitro, with the concentration exhibiting 50% inhibition (IC 50 ) being and μg ml 1, respectively. This paper describes the isolation and structure elucidation of two new flavonoid glycosides, myricetin 3-O-(5''-O-galloyl)-α-L-arabinofuranoside (1), 6-methylquercetin 7-O-β-D-glucopyranoside (2), and one new methylchromone glycoside, 7-O-(4', 6'-digalloyl)-β-D-glu-copyranosyl-5-hydroxy-2-methylchromone (3), together with three known compounds (4 6), obtained from this plant. In addition, the anti-inflammatory activities of these compounds were evaluated for their inhibitory effects against both COX-1 and COX-2 in vitro. Results and Discussion The ethanol extract of B. frutescens was suspended in water and then partitioned successively with petroleum ether (60 90 C), chloroform, and n-buoh. The n-buoh extract was chromatographed on MCI gel, ODS, and semi-preparative HPLC to afford compounds 1 6. The other three known compounds were identified as 6-methylquercetin (4) [14], quercetin 3-O-(5''-O-galloyl)-α-L-arabinofuranoside (5) [20], 6-methylquercetin 4'-O-β-D-glucopyranoside (6) [14] (Fig. 1), by comparison of their 1 H- and 13 C NMR data with literature data. 615

2 Fig. 1 Chemical structures of compounds 1 6 from Baeckea frutescens Compound 1 was obtained as a yellow amorphous powder. The HR-ESI-MS of 1 exhibited a quasi-molecular ion [M + H] + at m/z , consistent with a molecular formula of C 27 H 22 O 16. Its IR (KBr) spectrum suggested absorption bands of hydroxyl group at 3486 cm 1, carbonyl group at 1720, 1670 cm 1, and aromatic group at 1596, 1528 cm 1. The 13 C NMR and DEPT spectra of 1 displayed 27 carbon signals, of which 15 were assigned to the flavone aglycone moiety, and the remaining 12 signals corresponded to a pentose moiety and a galloyl residues. The 1 H NMR spectrum of 1 showed a pair of meta-coupled aromatic proton signals [δ H 6.18 (1H, d, J = 1.5 Hz, H-6), 6.37 (1H, d, J = 1.5 Hz, H-8)], two pairs of aromatic proton signals [δ H 7.06 (2H, s, H-2', 6'), 6.88 (2H, s, H-2''', 6''')], and one anomeric proton [δ H 5.49 (1H, d, J = 1.2 Hz, H-1''of Ara)], correlated with the carbon signal at δ C (C-1 ) in the HSQC spectrum. All these NMR signals suggested that compound 1 might be a galloyl flavonoid glycoside with a skeleton of myricetin-3-o-α-arabinofuranoside [18]. Acid hydrolysis of 1 with 2 mol L 1 HCl yielded L-arabinose, identified by reversed-phase HPLC after conversion of the sugar to thiocarbamoyl thiazolidine derivatives [19]. The small coupling constant (J = 1.2 Hz) of the anomeric proton at δ H 5.49 indicated the α-configuration of the L-arabinofuranosyl moiety and its coupling constant was close to that (J = 1.4 Hz) of quercetin 3-O-(5''-O-galloyl)- α-l-arabinofuranoside [20]. Compared with those of myricetin- 3-O-αarabinofuranoside [18], the upfield shift of δ C 81.8 (C-4'') and the downfield shift of δ C 62.4 (C-5'') indicated that the galloyl moiety was attached at C-5'' of the arabinose, further confirmed by comparison of the NMR data with those of quercetin 3-O-(5''-O-galloyl)-α-L-arabinofuranoside [20]. The location of the oligosaccharide moiety linked to C-3 of the aglycone was determined by the HMBC correlation between H-1'' (δ H 5.49) and C-3 (δ C 133.1). With the aid of the 1 H- 1 H COSY, HSQC and HMBC experiments (Fig. 2), all the 1 H- and 13 C NMR signals of 1 were assigned as shown in Table 1. Hence, the structure of compound 1 was established to be myricetin 3-O- (5''-O-galloyl)-α-L-arabinofuranoside. Compound 2 was obtained as a yellow amorphous powder. The HR-ESI-MS of 2 showed a quasi-molecular ion [M + H] + at m/z , corresponding to the molecular formula of C 22 H 22 O 12. The IR (KBr) spectrum showed bands for hydroxyl (3473 cm 1 ), carbonyl (1652 cm 1 ) and phenyl (1599, 1520 cm 1 ). The 13 C NMR spectrum showed 22 carbon signals attributable to a C-methylated flavonoid aglycone moiety and a hexose residue. The 1 H NMR spectrum of 2 displayed signals assignable to a C-methylated flavonol moiety, including a characteristic ABX coupling system of B ring [δ H 7.72 (1H, d, J = 1.8 Hz, H-2'), 7.56 (1H, dd, J = 1.8, 8.5 Hz, H-6'), 6.91 (1H, d, J = 8.5 Hz, H-5')], a methyl signal at δ H 2.09 (3H, s, 6-CH 3 ), as well as a single aromatic proton signal at δ H 6.87 (1H, s, H-8). The 1 H NMR of 2 also showed one anomeric proton [δ H 5.08 (1H, d, J = 7.1 Hz, H-1''of Glc)], correlated with the carbon signal at δ C (C-1 ) in the HSQC spectrum. Acid hydrolysis of 2 with 2 mol L 1 HCl afforded D-glucose, as identified by HPLC analysis, compared with authentic sample. The coupling constant (J = 7.1 Hz) of the anomeric proton (δ H 5.08) indicated the β-configuration of the glucopyranosyl moiety. The location of methyl group at C-6 position was supported by the HMBC correlations between 6-CH 3 (δ H 2.09) and C-5 (δ C 156.9), C-6 (δ C 107.8) and C-7 (δ C 160.7). In addition, the HMBC correlation from H-1'' (δ H 5.08) to C-7 (δ C 160.7) indicated that the glucopyranosyl moiety was attached at C-7. With the aid of the 1 H- 1 H COSY, HSQC 616

3 Fig. 2 The key HMBC and 1 H- 1 H COSY correlations of compounds 1 and 3 Table 1 1 H NMR and 13 C NMR data of compounds 1 3 in DMSO-d 6 Position 1 a 2 a 3 b δ H (J in Hz) δ c δ H (J in Hz) δ c δ H (J in Hz) δ c s d (1.5) d (2.1) d (1.5) s d (2.1) CH s CH s O-β-D-Glc 1' d (7.8) ' 7.06 s d (1.8) t (8.4) ' t (9.0) ' t (9.6) ' d (8.5) m ' 7.06 s dd (1.8, 8.5) dd (6.0, 12.0), 4.33 d (12.0) O-α-L-Ara 7-O-β-D-Glc 4'-galloyl 1'' 5.49 d (1.2) d (7.1) '' 4.19 m m c s '' 3.84 m c m c '' 3.83 m c m c

4 Continued Position 1 a 2 a 3 b δ H (J in Hz) δ c δ H (J in Hz) δ c δ H (J in Hz) δ c 5'' 4.08 m m c '' 3.74 m, 3.53 m c s C=O ''-galloyl 6'-galloyl 1''' ''', 6''' 6.88 s s ''', 5''' ''' C=O a 1 H and 13 C NMR data were measured at 500 MHz and 125 MHz, respectively; b 1 H and 13 C NMR data were measured at 300 MHz and 75 MHz, respectively; c Overlapping signals were assigned from 1 H- 1 H COSY, HSQC and HMBC experiments and HMBC experiments (Fig. 2), all the 1 H and 13 C NMR signals of 2 were assigned as shown in Table 1. Thus, 2 was elucidated as 6-methylquercetin 7-O-β-D-glucopyranoside. Compound 3 was obtained as a pale yellow amorphous powder. The molecular formula of 3 was determined as C 30 H 26 O 17 by HR-ESI-MS (m/z [M + H] + ). Its IR spectrum exhibited hydroxyl (3450 cm 1 ), carbonyl (1708, 1660 cm 1 ) and phenyl (1619, 1508 cm 1 ) groups. The 1 H- NMR spectrum of 3 displayed signals of a phenolic hydroxyl proton at δ H (1H, s, OH-5), two pairs of aromatic protons at δ H 6.99 (2H, s) and δ H 6.92 (2H, s), two meta-coupled aromatic protons at δ H 6.42 (1H, d, J = 2.1 Hz, H-6), 6.67 (1H, d, J = 2.1 Hz, H-8), a single olefinic proton at δ H 6.21 (1H, s, H-3), as well as methyl protons at δ H 2.27 (3H, s). The 1 H NMR spectrum also displayed protons at δ H 5.30 (1H, d, J = 7.8 Hz, H-1'), 4.33 (1H, d, J = 12.0 Hz, H-6'a), 4.06 (1H, dd, J = 6.0, 12.0 Hz, H-6'b), indicating the presence of one glucopyranosyl residues. The 13 C NMR spectrum showed 26 carbon signals attributable to one C-methylated chromone, two galloyl groups and a hexose residue. Comparing the NMR data of 3 with the literature values indicated that Compound 3 possessed the aglycone structure of 5, 7-dihydroxy- 2-methylchromone [21]. The methyl group was positioned at C-2, supported by the HMBC correlations from 2-CH 3 (δ H 2.27, 3H, s) to C-2 (δ C 168.5) and C-3 (δ C 108.2). In addition, acid hydrolysis of 3 afforded D-glucose, as confirmed by HPLC analysis compared with authentic sample. The coupling constant (J = 7.8 Hz) of the anomeric proton (δ H 5.30) suggested the β-configuration of the glucopyranosyl substituent. Substitution of the glucopyranosyl moiety at C-7 hydroxyl group was confirmed by the HMBC correlation from H-1' (δ H 5.30) to C-7 (δ C 162.4). The two galloyl groups were deduced to be located at C-4' and C-6', as evidenced from the key HMBC correlations from H-4' (δ H 4.96) to C=O (δ C 165.5), also from H-6'a (δ H 4.33), H-6'b (δ H 4.06) to C=O (δ C 165.1). With the aid of the 1 H- 1 H COSY, HSQC and HMBC experiments (Fig. 2), all the 1 H and 13 C NMR signals of 3 were assigned as shown in Table 1. On the basis of above data, the structure of compound 3 was determined to be 7-O-(4',6'- digalloyl)-β-d-glucopyranosyl-5-hydroxy-2-methyl chromone. Compounds 1 6 were isolated from the active n-buoh fraction of the ethanol extract of the aerial parts of B. frutescens. The in vitro inhibitory activities were evaluated against both COX-1 and COX-2 for the isolates obtained in the present study and the results are summarized in Table 2. Compounds 1 6 showed potent COX-1 inhibiting activities in vitro with IC 50 values ranging from 1.95 to 5.54 μmol L 1. All the tested compounds also displayed obvious COX-2 inhibitory activities with IC 50 values ranging from 1.01 to 2.27 μmol L 1. These findings suggested that the anti-inflammatory activities of B. frutescens were partly attributed to these flavonoids and methylchromones. Table 2 Inhibitory activities of compounds 1 6 against COX-1 and COX-2 in vitro Compounds COX-1 IC 50 (μmol L 1 ) COX ± ± ± ± ± ± ± ± ± ± ± ± 0.40 SC-560 a ± DuP-697 a ± a SC-560 and DuP-697 were used as the positive control Experimental General experimental procedures Optical rotations were measured with a Rudolph Autopol IV polarimeter (Rudolph Research Analytical, Hackettstown, America). UV spectra were obtained on a Shimadzu UV-2450 spectrophotometer (Shimadzu Corp., Kyoto, Japan). IR spectra were recorded on a FT-IR spectrometer (Bruker, Bremerhaven, Germany). The HR-ESI-MS spectra were measured 618

5 with an Agilent 6210 Q-TOF mass spectrometer equipped with an electrospray ionization (ESI) source (Agilent Technologies Co., Ltd., Santa Clara, America). NMR spectra were obtained on Bruker Avance 500 or 300 MHz spectrometer (500 or 300 MHz for 1 H NMR, 125 or 75 MHz for 13 C NMR) (Bruker, Bremerhaven, Germany) with TMS as internal standard. Column chromatography was performed on macroporous absorption resin of HPD-100 ( mm, Nankai Resin Technology Ltd., Tianjin China), MCI gel (CHP20P, μm, Mitsubishi Chemical Company, Tokyo, Japan), Sephadex LH-20 (Pharmacia, Uppsala, Sweden), and RP-C 18 (YMC Gel ODS-A 12 nm, S-50 μm, YMC, Tokyo, Japan). Semi-preparative HPLC was carried out on Shimadzu LC-8A pump, Shimadzu SPD-20A detector, and Shim-Pack Prep-ODS (15 µm, 20 mm 250 mm) column for separation (Shimadzu Corp., Kyoto, Japan). Plant materials The aerial parts of Baeckea frutescens (Myrtaceae) were collected from Guangxi Province of China in October of 2014 and authenticated by Prof. QIN Min-Jian (Department of Medicinal Plants, College of traditional Chinese medicine, China Pharmaceutical University, Nanjing, China). A voucher specimen (No. BF201410) was deposited in the Department of Natural Medicinal Chemistry, China Pharmaceutical University. Extraction and isolation The dry aerial parts of B. frutescens (18 kg) were extracted with 95% ethanol (100 L) under reflux (4 3 h) at 83 C. The combined extracts were concentrated under reduced pressure to afford a dark green residue extract (2.0 kg). The extract was suspended in water (3 L) and successively extracted with petroleum ether (60 90 C) (4 3 L), chloroform (3 3 L), and n-buoh (4 3 L). The n-buoh crude extract (900 g) was first fractionated by macroporous adsorptive resin of HPD-100 (10 cm 120 cm), eluted with EtOH H 2 O (0 : 100, 30 : 70, 60 : 40, 85 : 15, V/V) to afford four fractions. The 60% EtOH portion (200 g) was then subjected to MCI gel (6 cm 70 cm) column chromatography, eluted with MeOH H 2 O (10 : 90 to 100:0, V/V) to obtain ten fractions (Fr. A J). Fraction D (11.5 g) was then subjected to Sephadex LH-20 column (3.2 cm 120 cm) with MeOH as eluents to obtain seven fractions (Frs. D1 D7). Fraction D6 (0.98 g) was further separated by RP-C 18 column (2.5 cm 60 cm) with MeOH H 2 O (30 : 70 to 100 : 0) to obtain a mixture of Compounds 1 and 5. The mixture was subjected to reversed phase semi-preparative HPLC (MeOH H 2 O/0.1% formic acid 47 : 53, flow rate 15 ml min 1 ) to yield compounds 1 (34.2 mg, t R = 9.7 min) and 5 (32.3 mg, t R = 16.5 min). Fraction D3 (1.2 g) was repeatedly chromatographed over a RP-C 18 column (2.5 cm 60 cm, MeOH H 2 O, 30 : 70 to 100 : 0) to obtain a mixture of compounds 2, 4, and 6. The mixture was subjected to semi-preparative HPLC (CH 3 CN H 2 O/0.1% formic acid 20 : 80, flow rate 15 ml min 1 ) to yield compounds 2 (14.5 mg, t R = 18.7 min), 4 (36.2 mg, t R = 32.3 min), and 6 (9.2 mg, t R = 21.3 min). Fraction I (10.3 g) was then subjected to Sephadex LH-20 column (3.2 cm 120 cm) eluted with MeOH to obtain seven fractions (Frs. I1 I7). Fraction I4 (1.0 g) was subjected to RP-C 18 column eluted with MeOH H 2 O (30 : 70 to 100 : 0) to give a mixture of compound 3. The mixture was purified with semi-preparative HPLC (CH 3 CN H 2 O/0.1% formic acid 20 : 80, flow rate 15 ml min 1 ) to yield compound 3 (40.0 mg, t R = 14.8 min). Identification of new compounds Myricetin 3-O-(5''-O-galloyl)-α-L-arabinofuranoside (1) Yellow amorphous powder; [α] 20 D (c 0.10, MeOH); UV (MeOH) λ max (log ε): 265 (4.29), 355 (4.22) nm; IR (KBr) ν max : 3486, 1720, 1670, 1596, 1528 cm 1 ; ESI-MS m/z 601 [M H] ; HR-ESI-MS m/z [M + H] + (Calcd. for C 27 H 23 O 16, ); 1 H- (500 MHz in DMSO-d 6 ) and 13 C NMR (125 MHz in DMSO-d 6 ) spectral data are listed in Table 1. 6-Methylquercetin 7-O-β-D-glucopyranoside (2) Yellow amorphous powder; [α] 20 D 63.0 (c 0.10, MeOH); UV (MeOH) λ max (log ε): 257 (4.41), 372 (4.19) nm; IR (KBr) ν max : 3473, 1652, 1599, 1520, 1487 cm 1 ; ESI-MS m/z [M H] ; HR-ESI-MS m/z [M + H] + (Calcd. for C 22 H 23 O 12, ); 1 H- (500 MHz in DMSO-d 6 ) and 13 C- NMR (125 MHz in DMSO-d 6 ) spectral data are listed in Table 1. 7-O-(4',6'-digalloyl)-β-D-glucopyranosyl-5-hydroxy-2- methylchromone (3) Pale yellow amorphous powder; [α] 20 D 42.9 (c 0.11, MeOH); UV (MeOH) λ max (log ε): 256 (4.33), 277 (4.34) nm; IR (KBr) ν max : 3450, 1708, 1660, 1619, 1508 cm 1 ; ESI-MS m/z [M H] ; HR-ESI-MS m/z [M + H] + (Calcd. for C 30 H 27 O 17, ); 1 H- (300 MHz in DMSO-d 6 ) and 13 C NMR (75 MHz in DMSO-d 6 ) spectral data are listed in Table 1. Acid hydrolysis of compounds 1 3 and HPLC analysis Each compound (1, 2, and 3; 2.0 mg each) was hydrolyzed in 2 mol L 1 hydrochloric acid (2 ml) in water bath at 100 C for 2 h, respectively. The hydrolysates were evaporated to dryness respectively, and the residues were diluted with 2 ml of H 2 O and extracted with 2 ml of ethyl acetate. The aqueous layer was concentrated under reduced pressure to give a residue. Then 1 ml of pyridine and 2 mg of L-cysteine methyl ester hydrochloride were added to the residue and the mixtures were heated at 60 C for 1 h. Ten μl of O-Tolyl isothiocyanate was then added, and the mixtures were heated at 60 C for an additional 1 h. After dried under vacuum, the reaction mixtures were dissolved in MeOH and analyzed by reversed-phase HPLC [column: Shim-Pack VP-ODS (5 μm, 4.6 mm 150 mm), mobile phase: 20% CH 3 CN in 0.1% formic acid, column temperature: 35 C, flow rate: 0.8 ml/min, UV detection λ max : 250 nm]. The absolute configuration of the monosaccharide was confirmed to be D-glucose and L-arabinose, by comparison of the retention times of monosaccharide derivatives with those of standard samples, D-glucose (27.7 min) and L-arabinose (31.0 min). Assay for inhibition of COX-1 and COX-2 activity Inhibitory activity of all the compounds on the enzymes COX-1 and COX-2 was assayed using Colorimetric COX 619

6 (ovine) Inhibitory Screening Assay Kit purchased from Cayman Chemical (Ann. Arbor, MI, U.S.A., Catalog No ) according to the protocol recommended by the supplier. Tested compounds were dissolved in DMSO at a concentration of mol L 1 as stock solution, and then diluted into appropriate concentrations (100, 25, 6.25, 1.56, 0.39, 0.10, and 0.02 μmol L 1 ) with assay buffer. SC-560 and DuP-697 (Cayman Chemical, Michigan, USA) were used as positive controls for screening COX-1 and COX-2 inhibitors, respectively. Results were expressed as means ± SD of three independent experiments, with each experiment including triplicate sets. References [1] Chen JY, Ya QK, Lu WJ, et al. Study on the chemical constituents of Baeckea frutescens [J]. Nat Prod Res Dev, 2008, 20(5): [2] Jia BX, Zeng XL, Ren FX, et al. Baeckeins F-I, four novel C-methylated biflavonoids from the roots of Baeckea frutescens and their anti-inflammatory activities [J]. Food Chem, 2014, 155: [3] Quang TH, Cuong NX, Van MC, et al. New flavonoids from Baeckea frutescens and their antioxidant activity [J]. Nat Prod Commun, 2008, 3(5): [4] Navanesan S, Wahab NA, Manickam S, et al. Evaluation of selected biological capacities of Baeckea frutescens [J]. BMC Complem Altern M, 2015, 15(1): 1. [5] Ito T, Nisa K, Rakainsa SK, et al. New phloroglucinol derivatives from Indonesian Baeckea frutescens [J]. Tetrahedron, 2017, 73(8): [6] Makino M, Fujimoto Y. Flavanones from Baeckea frutescens [J]. Phytochemistry, 1999, 50(2): [7] Tsui WY, Brown GD. Sesquiterpenes from Baeckea frutescens [J]. J Nat Prod, 1996, 59(11): [8] Fujimoto Y, Usui S, Makino M, et al. Phloroglucinols from Baeckea frutescens [J]. Phytochemistry, 1996, 41(3): [9] Hou JQ, Guo C, Zhao JJ, et al. Frutescone A G, tasmanonebased meroterpenoids from the aerial parts of Baeckea frutescens [J]. J Org Chem, 2017, 82(3): [10] Tsui WY, Brown GD. Chromones and chromanones from Baeckea frutescens [J]. Phytochemistry, 1996, 43(4): [11] Satake T, Kamiya K, Saiki Y, et al. Chromone C-glycosides from Baeckea frutescens [J]. Phytochemistry, 1999, 50(2): [12] Jia BX, Yang J, Chen XQ, et al. Baeckeins A and B, two novel 6-methylflavonoids from the roots of Baeckea frutescens [J]. Helv Chim Acta, 2011, 94(12): [13] Jia BX, Zhou YX, Chen XQ, et al. Structure determination of baeckeins C and D from the roots of Baeckea frutescens [J]. Magn Reson Chem, 2011, 49(11): [14] Jia BX, Ren FX, Jia L, et al. Baeckein E, a new bioactive C- methylated biflavonoid from the roots of Baeckea frutescens [J]. Nat Prod Res, 2013, 27(22): [15] Tsui WY, Brown GD. Unusual metabolites of Baeckea frutescens [J]. Tetrahedron, 1996, 52(29): [16] Ito T, Nisa K, Kodama T, et al. Two new cyclopentenones and a new furanone from Baeckea frutescens and their cytotoxicities [J]. Fitoterapia, 2016, 112: [17] Dai DN, Thang TD, Olayiwola TO, et al. Chemical composition of essential oil of Baeckea frutescens L. [J]. Int Res J Pure Appl Chem, 2015, 1(8): [18] Abd El-kader AM, El-Readi MZ, Ahmed AS, et al. Polyphenols from aerial parts of Polygonum bellardii and their biological activities [J]. Pharm Biol, 2013, 51(8): [19] Wang GC, Li T, Deng FY, et al. Five new phenolic glycosides from Hedyotis scandens [J]. Bioorg Med Chem Let, 2013, 23(5): [20] Matsuzaki K, Ishii R, Kobiyama K, et al. New benzophenone and quercetin galloyl glycosides from Psidium guajava L. [J]. J Nat Med, 2010, 64(3): [21] Tane P, Ayafor JF, Sondengam BL, et al. Chromone glycosides from Schumanniophyton magnificum [J]. Phytochemistry, 1990, 29(3): Cite this article as: ZHOU Jun-Neng, YAN Ming, GAO Peng, HOU Ji-Qin, PHAM Thi-Anh, WANG Hao. New flavonoids and methylchromone isolated from the aerial parts of Baeckea frutescens and their inhibitory activities against cyclooxygenases-1 and -2 [J]. Chin J Nat Med, 2018, 16(8):