Open Access 
Abstract
Introduction: Melodorum fruticosum is distributed widely in ASEAN countries. Although this species has been used in folk medicine to cure some diseases, its chemical constituents and biological activity have not been systematically studied. This paper reports the isolation and structural elucidation of seven compounds from the n-hexane extract as well as their cytotoxicity against Jurkat and MCF-7-cell lines.
Method: Dried powder of Melodorum fruticosum stem was macerated in ethanol at room temperature to prepare the crude extract. This crude was separated into n-hexane, ethyl acetate, and the remaining aqueous extracts by the liquid‒liquid partition method. Then, the organic compounds were isolated by chromatographic methods and chemically structurally elucidated by modern spectroscopic techniques. Cytotoxicity assays were performed using the sulforhodamine B method (SBR assay).
Results: The n-hexane extract showed potential activity against the MCF-7-cell line with an IC50 value of 14.37 ± 3.18 µg/mL. From this extract, seven compounds consisting of techtochrysin (1), pinostrobin (2), flavokawin B (3), 2ʹ-hydroxy-3ʹ,4ʹ,6ʹ-trimethoxychalcone (4), 2ʹ-hydroxy-4ʹ,5ʹ,6ʹ-trimethoxychalcone (5), stigmast-4-ene-3-one (6), and lupeol (7) were isolated and chemically elucidated.
Conclusion: It is necessary to continue to isolate and perform a bioassay of organic compounds from this extract to determine the bioactive components.
INTRODUCTION
Melodorum fruticosum Lour. Merr. (a synonym name, Rauwenhoffia siamensis Scheff) belongs to the Annonaceae family. It is distributed in Vietnam, Laos, Cambodia, Thailand, Malaysia, and Indonesia. In Vietnamese folk medicine, leaves of M. fruticosum were used to treat digestive ailments and breast swelling, and roots were used to treat abdominal distension and blood tonic for postpartum women 1 . Flowers and bark of M. fruticosum possess antiviral, antioxidant, and cytotoxic activities 2 . Some extracts and compounds isolated from M. fruticosum revealed significant cytotoxicity against some cancer cell lines, such as A-549, MCF-7, HT-29, SK-MEL-5, Malme-3 M, 9-PS, and KBMRI 3 , 4 . Previously, phytochemical studies reported the presence of flavonoids, alkaloids, steroids, heptenoids, and tannins from leaves, stem bark, and flowers of M. fruticosum 3 , 4 , 5 , 6 . This paper showed the cytotoxicity against the Jurkat and MCF-7 cancer cell lines of the n -hexane extract of the M. fruticosum stem and the chemical elucidation of some compounds isolated from this one.
MATERIALS AND METHODS
General experimental procedures
The NMR spectra were registered on Bruker Avance at 500 MHz for 1 H-NMR and 125 MHz for 13 C-NMR. HR-ESI-MS spectra were recorded on a Bruker MicrOTOF-QII. The optical specific rotation was measured on a Kruss (Germany) polarimeter with a tube length of 0.5 decimetres.
Plant material
The stem of Melodorum fruticosum L. was collected at Di Linh Ward, Lam Dong Province, Vietnam, in July 2017. The scientific name of this species was authenticated by Dr. Dang Van Son, Institute of Tropical Biology, Vietnam Academy of Science and Technology. A voucher specimen (N o US-A012) was deposited in the herbarium of the Department of Organic Chemistry, University of Science, Vietnam National University - Ho Chi Minh City.
Extraction and isolation
The dried powder of M. fruticosum stem (90 kg) was macerated in ethanol at room temperature, and then the filtrated solution was evaporated at reduced pressure to give a crude extract (6 kg). The liquid‒liquid partition method with n -hexane and ethyl acetate, in turn, was used to separate the crude extract into different fractions.
The n -hexane extract (250 g) was subjected to normal-phase silica gel column chromatography. The eluent solvent systems n -hexane:ethyl acetate (stepwise, 99:1, 98:2, 95:5, 90:10, 80:20, 50:50, 0:100) were used to afford 11 fractions (H1‒H11). Fraction H3 (20.0 g) was further separated into 6 subfractions (H3.1‒H3.6) by normal-phase silica gel column chromatography eluted with n -hexane:ethyl acetate (stepwise, 95:5, 90:10, 80:20). Subfraction H3.2 (4.48 g) was subjected to silica gel column chromatography and eluted with solvent systems of n -hexane:ethyl acetate (95:5, 90:10, in turn) to give compound 1 (10.0 mg). The same method was applied to subfraction H3.3 (2.58 g) to afford 3 (8.9 mg) and 5 (7.0 mg). A silica gel column chromatography eluted with n -hexane:ethyl acetate (95:5, 90:10, in turn) was applied to subfraction H3.5 (4.36 g) to afford four subfractions (H3.5.1‒H3.5.4). Compounds 6 (7.0 mg) and 7 (9.6 mg) were isolated from subfraction H3.5.1 (0.20 g), while compound 2 (12.0 mg) was obtained from subfraction H3.5.3 (1.02 g) via silica gel column chromatography eluted with n -hexane:ethyl acetate (stepwise, 95:5, 90:10). Finally, compound 4 (7.4 mg) was isolated from fraction H3.6 (4.05 g) through silica gel column chromatography, eluted with n -hexane:ethyl acetate (95:5, 90:10, in turn), further purified by Sephadex LH-20, and eluted with methanol.
Cytotoxic assay
The cytotoxicity activities against Jurkat and MCF-7 cancer cell lines of the n -hexane extract and compounds 1 and 2 , using the sulforhodamine B method (SBR assay) and camptothecin as a positive control, were determined as described in a previous report 7 . This assay was performed at the Molecular Biology Laboratory, Faculty of Biology, University of Science. Vietnam National University-Ho Chi Minh City.
RESULTS
From the n -hexane extract of Melodorum fruticosum collected in Di Linh Ward, Lam Dong Province, seven compounds, 1 (10.0 mg), 2 (12.0 mg), 3 (8.9 mg), 4 (7.4 mg), 5 (7.0 mg), 6 (7.0 mg), and 7 (9.6 mg), were isolated. Their physical properties and spectroscopic data were obtained as follows.
Techtochrysin (1): Yellow powder. HR-ESI-MS: m/z 291.0628 [M+Na] + (calcd. for C 1 6 H 12 O 4 Na, 291.0633). 1 H-NMR data (DMSO- d 6 ) ( J in Hertz): δ H 7.03 ( s , H-3), 6.40 ( d , 2.0, H-6), 6.82 ( d , 2.0, H-8), 8.11 ( dd , 8.0, 1.5, H-2ʹ/H-6ʹ), 7.59 ( m , H-3ʹ/H-5ʹ), 7.62 ( m , H-4ʹ), 3.88 ( s , 7-OCH 3 ), and 12.81 ( s , 5-OH). 13 C-NMR (DMSO- d 6 ): δ C 163.5 (C-2), 105.3 (C-3), 182.0 (C-4), 161.1 (C-5), 98.1 (C-6), 156.1 (C-7), 92.8 (C-8), 157.4 (C-9), 104.9 (C-10), 130.6 (C-1ʹ), 126.4 (C-2ʹ/C-6ʹ), 129.1 (C-3ʹ/C-5ʹ), 132.1 (C-4ʹ) and 56.1 (7-OCH 3 ). Selected HMBC correlations: see Figure 1 .
Pinostrobin (2): Yellow powder. 0 ( c 0.10, acetone) (Pinostrobin, not mentioned) [9] . HR-ESI-MS: m/z 293.0784 [M+Na] + (calcd. for C 16 H 14 O 4 Na, 293.0790). 1 H-NMR data (DMSO- d 6 ) ( δ H , J in Hertz): 5.63 ( dd , 13.0, 3.0, H-2), 2.83 ( dd , 17.0, 3.0, H-3a), 3.31 ( dd , 17.0, 13.0, H-3b), 6.10 ( d , 2.5, H-6), 6.15 ( d , 2.5, H-8), 7.52 ( dd , 8.5, 1.0, H-2ʹ/H-6ʹ), 7.43 ( m , H-3ʹ/H-5ʹ), 7.39 ( m , H-4ʹ), 3.80 ( s , 7-OCH 3 ), and 12.10 ( s , 5-OH). 13 C-NMR data (DMSO- d 6 ): δ C 78.5 (C-2), 42.1 (C-3), 196.4 (C-4), 163.2 (C-5), 94.7 (C-6), 167.4 (C-7), 93.8 (C-8), 162.6 (C-9), 102.6 (C-10), 138.5 (C-1ʹ), 126.6 (C-2ʹ/C-6ʹ), 128.5 (C-3ʹ/C-5ʹ), 128.5 (C-4ʹ) and 55.8 (7-OCH 3 ). Selected HMBC correlations: see Figure 1 .
Flavokawin B (3): Yellow powder. HR-ESI-MS: m/z 285.1180 [M+H] + (calcd. for C 1 7 H 16 O 4 +H, 285.1127). 1 H-NMR data (CDCl 3 ) ( δ H , J in Hertz): 7.61 ( dd , 8.0, 1.5, H-2/H-6), 7.41 ( m , H-3/H-5), 7.40 ( m , H-4), 7.74 ( d , 16.0, H-7), 7.90 ( d , 16.0, H-8), 6.11 ( d , 2.5, H-3ʹ), 5.97 ( d , 2.5, H-5ʹ), 3.92 ( s , 4ʹ-OCH 3 ), and 3.84 ( s , 6ʹ-OCH 3 ). 13 C-NMR data (CDCl 3 ): δ C 135.6 (C-1), 128.4 (C-2/C-6), 128.9 (C-3/C-5), 130.1 (C-4), 142.3 (C-7), 127.6 (C-8), 192.7 (C-9), 106.4 (C-1ʹ), 166.3 (C-2ʹ), 93.9 (C-3ʹ), 168.4 (C-4ʹ), 91.3 (C-5ʹ), 162.6 (C-6ʹ), 55.9 (4ʹ-OCH 3 ) and 55.6 (6ʹ-OCH 3 ). Selected HMBC correlations: see Figure 1 .
2 ʹ -Hydroxy-3 ʹ ,4 ʹ ,6 ʹ -trimethoxychalcone (4): Yellow powder. HR-ESI-MS: m/z 337.1054 [M+Na] + (calcd. for C 18 H 18 O 5 Na, 337.1052). 1 H-NMR data (DMSO- d 6 ) ( δ H , J in Hertz): 7.72 ( dd , 80, 1.5, H-2/H-6), 7.45 ( m , H-3/H-5), 7.44 ( m , H-4), 7.63 ( d , 16.0, H-7), 7.66 ( d , 16.0, H-8), 12.63 ( s , 2ʹ-OH), 6.31 ( s , H-5ʹ), 3.65 ( s , 3ʹ-OCH 3 ), and 3.92 ( s , 4ʹ-OCH 3 /6ʹ-OCH 3 ). 13 C-NMR data (DMSO- d 6 ): δ C 134.7 (C-1), 128.4 (C-2/C-6), 128.9 (C-3/C-5), 134.7 (C-4), 142.4 (C-7), 127.6 (C-8), 192.7 (C-9), 107.1 (C-1ʹ), 157.7 (C-2ʹ), 130.0 (C-3ʹ), 157.6 (C-4ʹ), 88.5 (C-5ʹ), 157.2 (C-6ʹ), 60.0 (3ʹ-OCH 3 ), 56.3 (4ʹ-OCH 3 ) and 56.0 (6ʹ-OCH 3 ). Selected HMBC correlations: see Figure 1 .
2 ʹ -Hydroxy-4 ʹ ,5 ʹ ,6 ʹ -trimethoxychalcone (5): Yellow powder. HR-ESI-MS: m/z 337.1048 [M+Na] + (calcd. for C 18 H 18 O 5 Na, 337.1052). 1 H-NMR data (CDCl 3 ) ( δ H , J in Hertz): 7.64 ( dd , 8.0, 1.5, H-2/H-6), 7.43 ( m , H-3/H-5), 7.39 ( m , H-4), 7.84 ( d , 15.5, H-7), 7.93 ( d , 15.5, H-8), 13.64 ( s , 2ʹ-OH), 6.29 ( s , H-3ʹ), 3.84 ( s , 4ʹ-OCH 3 ), 3.90 ( s , 4ʹ-OCH 3 ), and 3.94 ( s , 6ʹ-OCH 3 ). 13 C-NMR data (CDCl 3 ): δ C 135.3 (C-1), 128.4 (C-2/C-6), 129.0 (C-3/C-5), 130.3 (C-4), 143.2 (C-7), 126.6 (C-8), 193.0 (C-9), 108.8 (C-1ʹ), 162.7 (C-2ʹ), 96.6 (C-3ʹ), 155.0 (C-4ʹ), 135.4 (C-5ʹ), 160.2 (C-6ʹ), 61.9 (4ʹ-OCH 3 ), 61.3 (5ʹ-OCH 3 ), and 56.1 (6ʹ-OCH 3 ). Selected HMBC correlations: see Figure 1 .
Stigmast-4-ene-3-one (6): White powder. HR-ESI-MS: m/z 435.3555 [M+Na] + (calcd. for C 29 H 48 ONa, 435.3603). 1 H-NMR data (CDCl 3 ) ( δ H , J in Hertz): 5.72 ( s , H-4), 0.71 ( s , H-18), 1.18 ( s , H-19), 0.92 ( d , 6.5, H-21), 0.84 ( d , 7.5, H-26), 0.81 ( d , 7.5, H-27), and 0.85 ( t , 7.5, H-29). 13 C-NMR data (CDCl 3 ): δ C 35.7 (C-1), 34.0 (C-2), 199.6 (C-3), 123.7 (C-4), 171.8 (C-5), 33.0 (C-6), 32.1 (C-7), 35.7 (C-8), 53.9 (C-9), 38.6 (C-10), 21.0 (C-11), 39.7 (C-12), 42.4 (C-13), 56.0 (C-14), 24.2 (C-15), 28.2 (C-16), 56.0 (C-17), 12.0 (C-18), 17.4 (C-19), 36.1 (C-20), 18.7 (C-21), 34.0 (C-22), 26.1 (C-23), 45.9 (C-24), 29.2 (C-25), 20.0 (C-26), 19.0 (C-27), 23.1 (C-28), and 11.9 (C-29). Selected HMBC correlations: see Figure 1 .
Lupeol (7) : White powder. 1 H-NMR data (CDCl 3 ) ( δ H , J in Hertz): δ H 3.19 ( dd , 11.5, 5.0, H-3), 2.39 ( ddd , 11.5, 11.5, 6.9, H-19), 0.97 ( s , H-23), 0.76 ( s , H-24), 0.83 ( s , H-25), 1.03 ( s , H-26), 0.94 ( s , H-27), 0.79 ( s , H-28), 4.68 ( d , 2.5, H-29a), 4.56 ( m , H-29b), and 1.68 ( brs , H-30). 13 C-NMR data (CDCl 3 ): δ C 38.8 (C-1), 27.5 (C-2), 79.0 (C-3), 38.9 (C-4), 55.4 (C-5), 18.4 (C-6), 34.3 (C-7), 41.0 (C-8), 50.5 (C-9), 37.2 (C-10), 21.0 (C-11), 25.2 (C-12), 38.1 (C-13), 42.8 (C-14), 27.5 (C-15), 35.6 (C-16), 43.2 (C-17), 48.3 (C-18), 48.2 (C-19), 151.0 (C-20), 29.9 (C-21), 40.0 (C-22), 28.0 (C-23), 15.4 (C-24), 16.1 (C-25), 16.0 (C-26), 14.6 (C-27), 18.0 (C-28), 109.3 (C-29), and 19.3 (C-30). Selected HMBC correlations: see Figure 1 .
DISCUSSION
Compound 1 was isolated as a yellow powder. The high-resolution mass spectrum of 1 showed a sodiated molecular ion peak at m/z 291.0628 [M+Na] + (calcd. for C 1 6 H 12 O 4 Na, 291.0633). The proton spectrum of 1 displayed a singlet signal at δ H 12.81 of the hydroxy group at C-5 possessing an intramolecular hydrogen bond with the carbonyl group at C-4 in the flavonoid skeleton, as usual. Two doublet signals at δ H 6.40 and 6.82 with the small coupling constant of 2.0 Hz were assigned to H-6 and H-8, respectively, of ring A. One singlet aromatic proton signal at δ H 7.03 ( s , H-3) was H-3 of ring C. Five aromatic protons at δ H 8.11 ( dd , 8.0, 1.5 Hz, H-2ʹ/H-6ʹ), 7.59 ( m , H-3ʹ/H-5ʹ), and 7.62 ( m , H-4ʹ) belonged to a phenyl group (ring C). In addition, at a high magnetic field, there was a singlet methoxy proton signal at δ H 3.88 ( s , 7-OCH 3 ). This information suggested that 1 was a flavone possessing a hydroxy group at C-5 and a methoxy group at C-7. This corresponded to the presence of fourteen carbon signals, including one methoxy carbon, two aromatic carbons at δ C 126.4 (C-2ʹ/C-6ʹ) and 129.1 (C-3ʹ/C-5ʹ), appearing in double intensity and possessing both HSQC and HMBC experiments with protons H-2ʹ/H-6ʹ and H-3ʹ/H-5ʹ, respectively, of a symmetrical benzene B ring. This phenyl group, attached to C-2, was determined by the HMBC cross-peaks of the proton H-3 to carbon C-1ʹ ( δ C 130.6) and of protons H-2ʹ/H-6ʹ to carbons C-2 and C-1ʹ ( Figure 1 ). The HMBC spectrum also revealed the cross-peaks of the hydroxy proton with carbons C-5, C-6, and C-10 and of the methoxy proton with carbon at δ C 156.1 (C-7). Based on the compatibility of the NMR data of 1 with those in the literature 8 , 1 was assigned to be techtochrysin.
Compound 2 was isolated as a yellow powder. The HR-ESI-MS spectrum of 2 displayed a quasi-molecular ion peak at m/z 293.0784 [M+Na] + (calcd. for C 16 H 14 O 4 Na, 293.0790). The comparison of the NMR data of 1 and 2 showed that carbons C-2 and C-3 of 2 were saturated, which was confirmed by the presence of two methylene proton signals at δ H 2.83 ( dd , 17.0, 3.0 Hz, H-3a) and 3.31 ( dd , 17.0, 13.0 Hz, H-3b) and one oxygenated methine proton at δ H 5.63 ( dd , 13.0, 3.0 Hz, H-2), instead of the singlet olefinic proton H-3 as in 1 . This corresponded to the observation of one methylene carbon signal at δ C 42.1 (C-3) and one oxygenated methine at δ C 78.5 (C-2), where its HSQC spectrum showed correlations to protons H-3 and H-2, respectively. This feature was further confirmed by the HMBC cross-peaks of both protons H-2 and H-3 to a carbonyl carbon at δ C 196.4 (C-4) and of proton H-2 to carbons C-1ʹ and C-2ʹ/C-6ʹ. The positions of the two substituents (-OH and -OCH 3 ) were confirmed by the HMBC correlations, as shown in Figure 1 . Due to the null specific optical rotation and the good compatibility of NMR data of 2 with published data 9 , 2 was thus determined to be a racemic mixture of pinostrobin.
Compound 3 was isolated as a yellow powder. Its molecular formula was determined to be C 1 7 H 16 O 4 based on the protonated molecular ion peak at m/z 285.1180 [M+H] + (calcd. for C 1 7 H 16 O 4 +H, 285.1127). Similar to 1 , the proton spectrum of 3 revealed two doublet signals with small coupling constants at δ H 6.11 ( d , 2.5 Hz, H-3ʹ) and 5.97 ( d , 2.5 Hz, H-5ʹ) of ring A, signals at δ H 7.61 ( dd , 8.0, 1.5 Hz, H-2/H-6), 7.41 ( m , H-3/H-5), and 7.40 ( m , H-4) of ring B. However, in comparison to the NMR data of 1, instead of an olefinic methine as in 1 ( δ H 7.03, δ C 105.3, C-3), the NMR spectra of 3 showed one more methoxy signal and two olefinic carbons in the E -configuration [( δ H 7.74, d , 16.0 Hz, δ C 142.3, C-7) and 7.90 ( d , 16.0 Hz, δ C 127.6, C-8)]. These features showed that 3 would be a chalcone. This was in accordance with the unsaturated degree value of 10 in 3 calculated from the molecular formula of C 1 7 H 16 O 4 as well as the HMBC cross-peaks of protons of the trans -double bond with the carbonyl carbon C-9 ( δ C 192.7) and the quaternary carbon C-1 ( δ C 135.6) of the B ring. Finally, 3 was elucidated as flavokawin B by the good compatibility of its NMR data with those of flavokawin B 10 .
Compound 4 was isolated as a yellow powder. The molecular formula of 4 was identified to be C 18 H 18 O 5 based on the pseudomolecular ion peak at m/z 337.1054 [M+Na] + (calcd. for C 18 H 18 O 5 Na, 337.1052) in the HR-ESI-MS. The similarity in the NMR data of 4 and 3 with just one difference of the replacement of the aromatic methine proton in 3 by a methoxy group in 4 . The comparison of NMR data of 4 with the 2ʹ-hydroxy-3ʹ,4ʹ,6ʹ-trimethoxychalcone in the literature was compatible 11 . The positions of the hydroxy and three methoxy groups were supported by HMBC experiments, as presented in Figure 1 . Therefore, the chemical structure of 4 was as shown.
Compound 5 was isolated as a yellow powder. The HR-ESI-MS spectrum of 5 showed a pseudomolecular ion peak at m/z 337.1048 [M+Na] + (calcd. for C 18 H 18 O 5 Na, 337.1052); therefore, the molecular formula of 5 was determined to be C 18 H 18 O 5 . Although two compounds 4 and 5 were isolated from two different fractions, they possessed the same molecular formula of C 18 H 18 O 5 and similar chemical shift values therefore, 5 should be a positional isomer of 4 . The comparison of NMR data of 5 with 2ʹ-hydroxy-4ʹ,5ʹ,6ʹ-trimethoxychalcone 12 showed good compatibility. Its HMBC experiment well supported the proposed structure with cross-peaks of the hydroxy proton at δ H 13.64 ( s , 2ʹ-OH) to carbons at δ C 108.8 (C-1ʹ), 162.7 (C-2ʹ), and 96.6 (C-3ʹ), of the methine proton at δ H 6.29 ( s , H-3ʹ) to carbons at δ C 108.8 (C-1ʹ), 155.0 (C-4ʹ), and 135.4 (C-5ʹ), and of three methoxy protons with carbons C-4ʹ, C-5ʹ and C-6ʹ. Therefore, 5 was determined to be 2ʹ-hydroxy-4ʹ,5ʹ,6ʹ-trimethoxychalcone.
Compound 6 was isolated as a white powder. The molecular formula of 6 was determined to be C 29 H 48 O via the sodiated molecular ion peak at m/z 435.3555 [M+Na] + (calcd. for C 29 H 48 ONa, 435.3603). The 13 C-NMR spectrum of 6 showed signals of 29 carbons, consisting of one carbonyl carbon at δ C 199.6 (C-3) and two olefinic carbons at δ C 123.7 (C-4) and 171.8 (C-5) of a conjugated ketone system. The remaining 26 carbons resonated at a high magnetic field from 11 to 56 ppm. These results suggested that 6 could be a sterol possessing a conjugated ketone group (>C=CH‒CO‒). Its 1 H-NMR spectrum with two singlets, three doublets, and a triplet signal from 0.7 to 1.2 ppm was characterized for a stigmastane skeleton. In addition, the sole signal that resonated at the low magnetic field at δ H 5.72 ( s ) belonged to the olefinic proton. The positions of two olefinic carbons, C-4 and C-5, were determined by the HMBC cross-peaks of the olefinic proton to carbons at δ C 34.0 (C-2), 171.8 (C-5), 33.0 (C-6), and 38.6 (C-10). This meant that the position of the conjugated carbonyl carbon was suggested to be at C-3. In the comparison of the NMR data of 6 with published data 13 , 6 was thus determined to be stigmast-4-ene-3-one.
Compound 7 was isolated as a white powder. The 1 H and 13 C-NMR data analysis of 7 suggested that it possessed a lupane skeleton characterized by signals of an isopropenyl unit at δ H 4.68 (1H, d , 2.5 Hz, H-29a), 4.56 (1H, m , H-29b), and 1.68 (3H, brs , H-30) in the proton spectrum and two olefinic carbon signals at δ C 151.0 (C-20) and 109.3 (C-29) in the 13 C-NMR spectrum. In addition, 7 had a hydroxy group at C-3 as usual, which was confirmed by the HMBC cross-peaks of two singlet methyl proton signals at δ H 0.97 (s, H-23) and 0.76 (s, H-24) to carbon C-3. Compound 7 was determined to be lupeol via the good compatibility of its NMR data with those published in the literature 14 .
The n -hexane extract and compounds 1 and 2 were evaluated for their cytotoxicity against Jurkat and MCF-7 cancer cell lines. The results showed that the n -hexane extract possessed significant cytotoxicity against the MCF-7 cancer cell line with an IC 50 value of 14.37 ± 3.18 µg/mL. However, compounds 1 and 2 revealed weak activities against the two surveyed cancer cell lines. Therefore, the components that induced the toxicity of the n -hexane extract could be from other compounds in this extract. The isolation and bioassay of organic compounds from this extract should be continued.
CONCLUSION
From the n -hexane extract of Melodorum fruticosum stem, seven compounds were isolated consisting of two flavonoids (techtochrysin and pinostrobin), three chalcones (flavokawin B, 2ʹ-hydroxy-3ʹ,4ʹ,6ʹ-trimethoxychalcone, and 2ʹ-hydroxy-4ʹ,5ʹ,6ʹ-trimethoxychalcone), a steroid (stigmast-4-ene-3-one), and a triterpenoid (lupeol). Their chemical structures were elucidated based on NMR and HR-MS data analysis as well as comparison to published data. The n -hexane extract showed significant cytotoxicity against the MCF-7-cell line with an IC 50 value of 14.37 ± 3.18 µg/mL, whereas compounds 1 and 2 isolated from this extract were inactive. To the best of our knowledge, except for 1 , six remaining compounds were isolated from Melodorum fruticosum for the first time.
ABREVIATIONS
HR-ESI-MS: High resolution electrospray ionization-Mass spectrometry
1 H-NMR: Proton nuclear magnetic resonance
13 C-NMR: Carbon-13 nuclear magnetic resonance
HSQC: Heteronuclear single quantum coherence
HMBC: Heteronuclear multiple bond correlation
s : singlet
brs : broad singlet
d : doublet
dd : doublet of doublets
ddd : doublet of doublet of doublets
t : triplet
m : multiplet
calcd.: calculated
IC 50 : Half-maximal inhibitory concentration
Jurkat cell: immortalized T-lymphocyte cell line
MCF - 7 cell: breast cancer cell line
COMPETING INTEREST
The authors declare no competing financial interest.
AUTHORS’ CONTRIBUTION
Du T.T.X. and Nguyen T.M.H. contributed to conducting experiments and acquiring data. Nguyen N.K.V. and Nguyen K.P.P. interpreted NMR and MS data. Nguyen T.H.T. provided final approval of the manuscript to be submitted.
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