Chemical Constituents and Derivatization of Melodorinol from the 633 - 636 Roots of Melodorum Fruticosum

2015 NPC Natural Product Communications Vol. 10

No. 4 Chemical Constituents and Derivatization of Melodorinol from the 633 - 636 Roots of Melodorum fruticosum

Siriwat Hongnaka, Jongkolnee Jongaramruongb, Suttira Khumkratokc, Pongpun Siriphongd and Santi Tip-pyanga,* aNatural Products Research Unit, Department of Chemistry, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand bDepartment of Chemistry, Faculty of Science, Burapha University, Chonburi 20321, Thailand c Walai Rukhavej Botanical Research Institute, Mahasarakham University, Mahasarakham 44000, Thailand dNatural Products Research Section, Research Division, National Cancer Institute, Bangkok 10400, Thailand

[email protected]

Received: November 24th, 2014; Accepted: January 5th, 2015

Chemical investigation of the CH2Cl2 and MeOH crude extracts of the roots of Melodorum fruticosum Lour. led to the isolation of 15 known compounds, of which 5, 10, and 12-15 are reported for the first time from this plant. In addition, melodorinol (7) was derivatized to afford six new (7a-7d and 7f-7g) analogues and one known compound (7e). Their structures were identified on the basic of spectroscopic data. Most of them were evaluated for their cytotoxicity against KB, HeLa, MCF-7 and HepG-2 cell lines. Compounds 4 and 7b were the most potent to all cell lines.

Keywords: Melodorum fruticosum, Heptene, Flavonoid, Terpenoid, Melodoinol analogue, Cytotoxicity.

The genus Melodorum, family Annonaceae, contains 55 species distributed throughout tropical Asia [1]. M. fruticosum Lour. (synonym: Sphaerocoryne affinis {Teij sm. & Binn.) Ridl.}, locally H H H H OH HO known as “Lam Duan”, is a shrub distributed in South East Asia. In HO HO Thai traditional medicine, flowers were used as an ingredient of a 1 2 3 medicinal recipe known as “Geasorn Thung Gao”, which was used 7 5 R1 6 4 3 as a tonic stimulant, a mild cardiotonic and to reduce fever. R O HO O 1 2 HO O OR2 O Previous phytochemical studies of this plant revealed terpenoids, 1 R O 2 OH O aromatic compounds, flavonoids and heptenes [2]. In the present OH O study, phytochemical investigation of the CH Cl and MeOH crude 6 2 2 5 R1 = R 2 =H extracts from the roots of M. fruticosum led to the isolation of four HO 4 R1 =BzR2 =Ac O 9 R1 =H R2 =H OH triterpenoids, β-sitosterol (1) [3], stigmasterol (2) [3], polycarpol (3) O O 7 R1 =BzR2 =H 10 R =H R= [2a] and lanosta-7,9(11),24-trien-3β,21-diol (12) [4], four heptenes, 1 2 O HO 13 R1 =H R2 =H acetylmelodorinol (4) [2c], melodorinol (7) [2c], (4Z)-6- 11 R2 = R 2 = 8 HO benzoyloxy-7-hydroxy-2,4-heptadien-4-olide (8) [2c] and (4Z)-6,7- HO dihydroxy-2,4-heptadien-4-olide (13), six flavonoids, chamanetin OH

(5) [5], chrysin (6) [2c], pinocembrin (9) [2a], isochamanetin (10) OH [5], dichamanetin (11) [5] and catechin (14) [6], and one terpenoid HO O OGlu OH glycoside, ampelopsisionoside (15) [7] (Figure 1). HO OH OH H OH O 12 14 15

All isolated compounds were tested for cytotoxicity against KB, Figure 1: The isolated compounds from the roots of M. fruticosum. HeLa, MCF-7 and HepG-2 cell lines. Compound 5 showed selective cytotoxicity against KB cells with an IC50 value of 2.4 µM The significant cytotoxicity against KB and HeLa cells of the and showed moderate cytotoxicity against HeLa, MCF-7 and naturally acetylated compound 4 led us to investigate the structural HepG-2 with IC50 values of 35.0, 37.5 and 21.5 µM, respectively. modification and cytotoxicity of the melodorinol derivatives, 7a-7g. Compound 6 showed moderate cytotoxicity, while compound 9 revealed no cytotoxicity against all four cell lines (Table 1). Among For these studies, compound 7 was selected for further the heptene compounds, compound 4 was the most cytotoxic derivatization. Nucleophilic acylation of the OH group at position 6 against KB, HeLa and MCF-7 cell lines with IC50 values of 2.2, 2.2, of compound 7 with anhydrides having different alkyl (7a-7d and 4.2 and 16.3 µM, respectively, while compound 7, which lacked the 7f) and a phenyl (7e) side chain led to the isolation of six acyl acetyl group at position 6, showed lower activities against all four melodorinol derivatives (7a-7f, Scheme 1). In addition, compound cell lines. Notably, the acetyl group seemed to be involved in the 7g was prepared by methanolysis of compound 7 (Scheme 2). antiproliferative activity of these cell lines. Heptene 13, which lacked the benzoyl moiety at position 7, was inactive against all cell Table 2 shows the in vitro cytotoxicity of the melodorinol lines. It is noteworthy that the benzoyl moiety seemed to play a derivatives (7a-7g) against KB, HeLa, MCF-7 and HepG-2 cells. pivotal role in the antiproliferative activity of these cell lines. 634 Natural Product Communications Vol. 10 (4) 2015 Hongnak et al.

Table 1: In vitro cytotoxicity of isolated compounds. at Walai Rukhavej Botanical Research Institute, Mahasarakham

IC50 (µM) University, where a voucher specimen (khumkratok no. 1-13) is Compound KB HeLa MCF-7 HepG-2 deposited. A mixture of 1 and 2 NTa NTa NTa NTa 3 65.1 NAb 18.9 13.8 4 2.2 2.2 4.2 16.3 Extraction and purification: The air-dried roots of M. fruticosum 5 2.4 35.0 37.5 21.5 (3.3 kg) were successively extracted with CH2Cl2 (3×5 L) and 6 26.9 33.9 32.5 28.9 MeOH (3×5 L) at room temperature. The solvents were evaporated 7 14.3 10.0 7.4 16.2 8 20.8 42.6 14.6 38.2 to afford CH2Cl2 (110 g) and MeOH crude extracts (24.4 g). The 151.8 279.4 254.4 NAb 9 CH2Cl2 crude extract was subject to vacuum liquid chromatography 10 15.6 78.1 19.5 32.6 11 11.1 54.9 43.1 32.9 (VLC) over silica gel (Merck Art 7730), using successively as 12 50.4 132.0 52.6 51.5 eluants n-hexane, CH2Cl2, EtOAc and MeOH with increasing 13 NAb NAb NAb NAb polarity to afford 7 fractions, (F1-F7). Fraction F1 (7.26 g) was 14 NTa NTa NTa NTa 15 NAb NAb NAb NAb fractioned on a silica gel column (using n-hexane-EtOAc, gradient Doxorubicin 0.24 0.09 0.18 0.57 system) to give a mixture of compounds 1 and 2 (15.4 mg) and 3 a Not tested. b No activity at 200 µM (1.32 g). Fraction F2 (52.5 g) was chromatographed on a silica gel column with a gradient system of n-hexane and EtOAc to give 3 sub-fractions (F2.1-F2.3). Sub-fraction F2.1 was further chromatographed on a silica gel column eluted with 30% EtOAc- n-hexane to afford compound 4 (2.72 g). Sub-fraction F2.2 was purified using a chromatotron eluting with 35% EtOAc-n-hexane to

give compounds 5 (57.9 mg) and 6 (30.1 mg). Sub-fraction F2.3 was further separated by chromatotron (using 40% EtOAc- n-hexane, as eluent) to give compounds 7 (42.0 mg) and 8 (11.3

Scheme 1: Nucleophilic acyl substitution reactions of melodorinol (7). mg). Fraction F4 was subject to silica gel CC using a gradient of n-hexane and EtOAc providing compounds 9 (39.7 mg), 10 (44.1 mg) and 11 (74.3 mg). F6 was separated by chromatotron (using 50% EtOAc-n-hexane, as eluent) providing compound 12 (10.4 mg). The MeOH crude extract was dissolved in water and loaded onto a Dianion HP-20 column and eluted with MeOH. The MeOH Scheme 2: Methanolysis of melodorinol (7). eluant was chromatographed by silica gel CC using a gradient

system of CH2Cl2 and MeOH providing 3 fractions (M1-M3). Compounds 7a-7b presented lower IC50 values against KB, HeLa Fraction M1 was purified using a chromatotron eluted with 50% and MCF-7 cells than compound 7. It seems that enhancing the side EtOAc-n-hexane to afford compound 13 (16.3 mg). Fraction M2 chain hydrophobicity (7a-7b) led to an increase in antiproliferative was applied to a C18 reversed-phase silica gel column and eluted activity against the KB, HeLa and MCF-7 cells. On the other hand, with 30% water-MeOH to yield compound 14 (15.0 mg). Fraction longer side chains in the acyl group (7c-7d) did not show a M3 was separated on a chromatotron using CH2Cl2 and MeOH (9:1) significant difference in antiproliferative activity. In contrast, to give compound 15 (7.7 mg). acylation of compound 7 with a hydrophilic moiety (7f) resulted in low to no activities against the four cell lines; compound 7g, which General procedure for modification of melodorinol derivatives no longer has the lactone ring was inactive against all cell lines. (7a-7f): To melodorinol (50 mg, 0.19 mmol) in CH2Cl2 (3.84 mL) was added triethylamine (TEA, 214 µL, 1.54 mmol), 4- Table 2: In vitro cytotoxicity of melodorinol derivatives (7a-7g). (dimethylamino)pyridine (DMAP, trace amount) and propionic IC50 (µM) Compound KB HeLa MCF-7 HepG-2 anhydride (74.2 µL, 0.58 mmol). The solution was stirred at room 7a 2.9 3.2 2.8 13.5 temperature for 1 h. The reaction mixture was diluted with CH2Cl2, 7b 1.9 2.3 2.4 10.8 washed with brine and dried over anhydrous Na SO . After 7c 3.1 5.1 8.2 13.5 2 4 7d 6.4 8.4 10.8 23.5 removing the solvent, the residue was purified on a chromatotron by 7e 4.0 3.6 4.5 13.7 elution with 30% EtOAc/n-hexane to give the melodorinol 7f 51.9 93.0 103.0 108.8 7g 145.4 136.2 92.8 115.9 derivatives. Doxorubicin 0.24 0.09 0.18 0.57 Propanoylmelodorinol (7a): Following the general procedure, Among the isolated and modified compounds, heptenes had the reaction of 7 (50.0 mg, 0.19 mmol), propionic anhydride (74.2 µL, most potent antiproliferative activity against cancer cells. The 0.58 mmol), triethylamine (TEA, 214 µL, 1.54 mmol), and 4- analogue 7b exhibited the best activity against KB, HeLa, MCF-7 (dimethylamino)pyridine (DMAP, trace amount) in CH2Cl2 (3.84 and HepG-2 with IC50 values of 1.9, 2.3, 2.4, and 10.8 µM, mL) after 1 h yielded compound 7a (21.1 mg, 34.7%) as a yellow respectively. Based on preliminary structure activity relationship oil. analysis of the functional groups we found that a benzoyl group, a Rf: 0.45 (50% EtOAc/n-hexane). lactone ring and a hydrophobic ester group seem to play an : -5.4 (c 0.26, CHCl3). 1 important role in inhibition of proliferative activity. The different H NMR (CDCl3, 400 MHz) δH: 7.95 (2H, d, J = 7.1 Hz, H-10, 14), lengths of the side chains of the hydrophobic acyl moiety seem to 7.51 (1H, t, J = 7.4 Hz, H-12), 7.38 (2H, t, J = 7.7 Hz, H-11,13), have only a small effect on cell line activity. 7.30 (1H, d, J = 5.5 Hz, H-3), 6.21 (1H, d, J = 5.5 Hz, H-2), 6.09 (1H, m, H-6), 5.26 (1H, d, J = 8.0 Hz, H-5), 4.48 (2H, m, H-7), Experimental 2.31 (2H, q, J = 7.5 Hz, H-16), 1.07 (3H, t, J = 7.5 Hz, H-17). 13 Plant material: Roots of Melodorum fruticosum were collected C NMR (CDCl3, 100 MHz) δC: 173.2 (C-15), 168.5 (C-1), 166.0 from Mahasarakham province, Thailand in November 2012. The (C-8), 150.7 (C-4), 143.3 (C-3), 133.3 (C-12), 129.7 (C-9, 10, 14), plant material was identified by Dr Suttitra Khumkratok, a botanist Chemical constituents of Melodorum fruticosum Natural Product Communications Vol. 10 (4) 2015 635

+ 128.5 (C-11, 13), 121.6 (C-2), 109.0 (C-5), 67.2 (C-6), 64.6 (C-7), HRMS-ESI m/z: [M+Na ] calcd for C20H22O6Na: 381.1314; found 27.5 (C-16), 9.0 (C-17). 381.1315. + HRMS-ESI m/z: [M+Na ] calcd for C17H16O6Na: 339.0845; found 339.0842. Benzoylmelodorinol (7e): Following the general procedure, reaction of 7 (50.0 mg, 0.19 mmol), benzoic anhydride (128 mg, Butanoylmelodorinol (7b): Following the general procedure, 0.58 mmol), triethylamine (TEA, 214 µL, 1.54 mmol), and 4- reaction of 7 (50.0 mg, 0.19 mmol), butyric anhydride (94.2 µL, (dimethylamino)pyridine (DMAP, trace amount) in CH2Cl2 (3.84 0.58 mmol), triethylamine (TEA, 214 µL, 1.54 mmol), and 4- mL) after 1 h yielded compound 7e (22.8 mg, 32.6%) as a yellow (dimethylamino)pyridine (DMAP, trace amount) in CH2Cl2 (3.84 oil. mL) after 1 h yielded compound 7b (21.3 mg, 33.6%) as a yellow Rf: 0.46 (50% EtOAc/n-hexane). oil. : +23.1 (c 0.34, CHCl3). 1 Rf: 0.47 (50% EtOAc/n-hexane). H NMR (CDCl3, 400 MHz) δH: 8.06 (4H, t, J = 8.1 Hz, H-,10, 14, : -8.1 (c 0.18, CHCl3). 17, 21), 7.59 (2H, m, H-12, 19), 7.46 (4H, m, H-11, 13, 18, 20), 1 H NMR (CDCl3, 400 MHz) δH: 8.05 (2H, d, J = 7.2 Hz, H-10, 14), 7.42 (1H, d, J = 5.5 Hz, H-3), 6.39 (1H, m, H-6), 6.32 (1H, d, J = 7.60 (1H, t, J = 7.4 Hz, H-12), 7.47 (2H, t, J = 7.7 Hz, H-11, 13), 5.5 Hz, H-2), 5.47 (1H, d, J = 8.1 Hz, H-5), 4.73 (2H, m, H-7). 13 7.40 (1H, d, J = 5.5 Hz, H-3), 6.30 (1H, d, J = 5.5 Hz, H-2), 6.18 C NMR (CDCl3, 100 MHz) δC: 168.4 (C-1), 166.0 (C-8), 165.4 (1H, m, H-6), 5.34 (1H, d, J = 8.0 Hz, H-5), 4.57 (2H, m, H-7), (C-15), 150.9 (C-4), 143.3 (C-3), 133.4 (C-12), 133.3 (C-19), 129.8 2.35 (2H, t, J = 7.4 Hz, H-16), 1.67 (2H, m, H-17) 0.95 (3H, t, J = (C-17, 21), 129.7 (C-10, 14), 129.6 (C-16), 129.5 (C-9), 128.5 7.4 Hz, H-18). (C-11, 13, 18, 20), 121.7 (C-2), 108.9 (C-5), 68.0 (C-6), 64.6 (C-7). 13 + C NMR (CDCl3, 100 MHz) δC: 172.4 (C-15), 168.4 (C-1), 166.0 HRMS-ESI m/z [M+Na ] calcd for C21H16O6Na: 387.0845; found (C-8), 150.7 (C-4), 143.3 (C-3), 133.3 (C-12), 129.7 (C-9, 10, 14), 387.0847. 128.5 (C-11, 13), 121.6 (C-2), 109.0 (C-5), 67.1 (C-6), 64.6 (C-7), 36.0 (C-16), 18.2 (C-17), 13.6 (C-18). Succinoylmelodorinol (7f): Following the general procedure, + HRMS-ESI m/z: [M+Na ] calcd for C18H18O6Na: 353.1001; found reaction of 7 (20.0 mg, 0.08 mmol), succinic anhydride (23.1 mg, 353.1000. 0.23 mmol), triethylamine (TEA, 214 µL, 1.54 mmol), and 4- (dimethylamino)pyridine (DMAP, trace amount) in CH2Cl2 (3.84 Pentanoylmelodorinol (7c): Following the general procedure, mL) after 1 h yielded compound 7f (18.2 mg, 65.8%) as a yellow reaction of 7 (50.0 mg, 0.19 mmol), pentanoic anhydride (116 µL, oil. 0.58 mmol), triethylamine (TEA, 214 µL, 1.54 mmol), and 4- Rf: 0.12 (50% EtOAc/n-hexane). (dimethylamino)pyridine (DMAP, trace amount) in CH2Cl2 (3.84 : -1.3 (c 0.37, CHCl3). 1 mL) after 1 h yielded compound 7c (21.9 mg, 33.1%) as a yellow H NMR (CDCl3, 400 MHz) δH: 7.92 (2H, d, J = 7.4 Hz, H-10, 14), oil. 7.48 (1H, t, J = 7.4 Hz, H-12), 7.35 (2H, t, J = 7.8 Hz, H-11, 13), Rf; 0.49 (50% EtOAc/n-hexane). 7.32 (1H, d, J = 5.5 Hz, H-3), 6.19 (d, J = 5.5 Hz, H-2), 6.10 – : -4.5 (c 0.12, CHCl3). 6.03 (1H, m, H-6), 5.26 (1H, d, J = 8.0 Hz, H-5), 4.46 (2H, m, H- 1 H NMR (CDCl3, 400 MHz) δH: 8.02 (2H, d, J = 7.0 Hz, H-10, 14), 7), 2.58 (4H, s, H-16, 17). 13 7.58 (1H, t, J = 7.4 Hz, H-12), 7.45 (2H, t, J = 7.7 Hz, H-11, 13), C NMR (CDCl3, 100 MHz) δC: 177.6 (C-19), 171.1 (C-15), 168.6 7.37 (1H, d, J = 5.5 Hz, H-3), 6.28 (1H, d, J = 5.5 Hz, H-2), 6.15 (C-1), 166.1 (C-8), 150.8 (C-4), 143.5 (C-3), 133.3 (C-12), 129.7 (1H, m, H-6), 5.32 (1H, d, J = 8.0 Hz, H-5), 4.54 (2H, d, J = 5.7 (C-10, 14), 129.4 (C-9), 128.5 (C-11, 13), 121.6 (C-2), 108.6 (C-5), Hz, H-7), 2.35 (2H, t, J = 7.5 Hz, H-16), 1.59 (2H, m, H-17), 1.30 67.8 (C-6), 64.6 (C-7), 28.9 (C-16), 28.8 (C-17). + (2H, m, H-8), 0.86 (3H, t, J = 7.3 Hz, H-19). HRMS-ESI m/z [M+Na ] calcd for C18H16O8Na: 383.0743; found 13 C NMR (CDCl3, 100 MHz) δC: 172.6 (C-15), 168.4 (C-1), 166.0 383.0742. (C-8), 150.7 (C-4), 143.3 (C-3), 133.3 (C-12), 129.7 (C-9, 10, 14), 128.5 (C-11, 13), 121.6 (C-2), 109.0 (C-5), 67.1 (C-6), 64.6 (C-7), 7-Benzoyloxy-1,3,6-trimethoxyhepta-1,4-dione (3,6-Dimethoxy- 33.9 (C-16), 26.9 (C-17), 22.2 (C-18), 13.6 (C-19). 2,5-dihydromelodienone) (7g): A solution of 7 (50 mg, 0.19 mmol) + o HRMS-ESI m/z: [M+Na ] calcd for C19H20O6Na: 367.1158; found in 1M methanolic HCl (3.84 mL) was stirred at 70 C for 24 h. The 367.1159. reaction mixture was evaperated to dryness, quenched with water Hexanoylmelodorinol (7d): Following the general procedure, and extracted with CH2Cl2. The organic layer was washed with reaction of 7 (50.0 mg, 0.19 mmol), hexanoic anhydride (133 µL, brine and dried over anhydrous Na2SO4. After removal of the 0.58 mmol), triethylamine (TEA, 214 µL, 1.54 mmol), and 4- solvent, the crude product was purified by chromatotron eluting (dimethylamino)pyridine (DMAP, trace amount) in CH2Cl2 (3.84 with 30% EtOAc-n-hexane yielding compound 7g (10.1 mg, mL) after 1 h yielded compound 7d (20.5 mg, 29.8%) as a yellow 15.5%) as a yellow oil. oil. Rf: 0.39 (50% EtOAc/n-hexane). Rf: 0.52 (50% EtOAc/n-hexane). : -7.7 (c 0.12, CHCl3). 1 : -3.2 (c 0.45, CHCl3). H NMR (CDCl3, 400 MHz) δH: 7.97 (2H, d, J = 7.0 Hz, H-10, 14), 1 H NMR (CDCl3, 400 MHz) δH: 8.02 (2H, d, J = 7.1 Hz, H-10, 14), 7.51 (1H, t, J = 7.4 Hz, H-12), 7.38 (2H, t, J = 7.7 Hz, H-11, 13), 7.57 (1H, t, J = 7.4 Hz, H-12), 7.44 (1H, t, J = 7.7 Hz, H-11, 13), 4.37 (1H, dd, J = 11.7, 4.2 Hz, H-7), 4.25 (1H, m, H-7), 4.18 (1H, 7.37 (1H, d, J = 5.5 Hz, H-3), 6.28 (1H, d, J = 5.5 Hz, H-2), 6.15 m, H-3), 3.99 (1H, m, H-6), 3.69 (3H, s, 1-OCH3), 3.38 (3H, s, 6- (1H, m, H-6), 5.32 (1H, d, J = 8.0 Hz, H-5), 4.54 (2H, d, J = 5.7 OCH3), 3.36 (3H, s, 3-OCH3), 2.81 (2H, m, H2), 2.74 (1H, ddd, J = Hz, H-7), 2.33 (2H, t, J = 7.5 Hz, H-16), 1.61 (2H, m, H-17), 1.26 17.4, 8.5, 4.4 Hz, H-5), 2.62 (1H, ddd, J = 17.0, 8.1, 4.9 Hz, H-5). 13 (4H, m, H-18, 19), 0.84 (2H, t, J = 6.9 Hz, H-20). C NMR (CDCl3, 100 MHz) δC: 204.3 (C-4), 172.3 (C-1), 166.3 13 C NMR (CDCl3, 100 MHz) δC: 172.6 (C-15), 168.4 (C-1), 166.0 (C-8), 113.1 (C-12), 129.7 (C-9, 10, 14), 128.4 (C-11, 13), 76.0 (C- (C-8), 150.7 (C-4), 143.3 (C-3), 133.4 (C-12), 129.7 (C-9, 10, 14), 3), 74.8 (C-6), 65.0 (C-7), 58.8 (3-OCH3), 58.0 (6-OCH3), 52.1 (1- 128.5 (C-11, 13), 121.6 (C-2), 109.0 (C-5), 67.1 (C-6), 64.6 (C-7), OCH3), 46.1 (C-2), 45.7 (C-5). + 34.2 (C-16), 31.2 (C-17), 24.5 (C-18), 22.2 (C-19), 13.8 (C-20). HRMS-ESI m/z [M+Na ] calcd for C17H22O7Na: 361.1263; found 361.1265. 636 Natural Product Communications Vol. 10 (4) 2015 Hongnak et al.

Cytotoxicity assay: All tested compounds were subjected to under the above conditions. At the end of incubation, 10 µL of cytotoxic evaluation against KB (human epidermoid carcinoma), tetrazolium reagent was added to each well, followed by further HeLa (human cervix adenocarcinoma), MCF-7 (human breast incubation at 37ºC for 4 h. The supernatant was decanted, and adenocarcinoma) and HepG-2 (human hepatocellular carcinoma) DMSO (100 µL/well) was added to allowed formosan cell lines employing the colorimetric method [8]. Doxorubicin, used solubilization. The optical density (OD) of each well was detected as the reference substance, exhibits activity against KB, HeLa, using a Microplate reader at 550 nm and for correction at 595 nm. MCF-7 and HepG-2 cell lines. 3-(4,5-Dimethylthiazol-yl)-2,5- Each determination represented the average mean of 6 replicates. diphenyl-tetrazolium bromide (Sigma Chemical Co., USA) was The 50% inhibition concentration (IC50 value) was determined by dissolved in saline to make a 5 mg/mL stock solution. Cancer cells curve fitting. (3×10³ cells) suspended in 100 µg/wells of MEM medium containing 10% fetal calf serum (FCS, Gibco BRL, Life Acknowledgments – The authers are grateful to the Technology, NY USA) were seeded onto a 96 wells culture plate Ratchadaphiseksomphot Endowment Fund of Chulalongkorn (Costar, Corning Incorporated, NY 14831, USA). After 24 h pre- University (RE 556053018-FW) for partially supporting this incubation at 37ºC in a humidified atmosphere of 5% CO2/95% air project. We also thank Dr. Wisuttaya Worawalai for her technical to allow cellular attachment, various concentrations of test solution assistance. (10 µL/wells) were added and these were then incubated for 48 h

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