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Natural Product Research: Formerly Natural Product Letters Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/gnpl20
A new chromone from Hymenocallis littoralis Salisb. (Amaryllidaceae) a
b
a
Dinh Thi Phuong Anh , Tran Bach Duong & Vu Dinh Hoang a
School of Chemical Engineering, Hanoi University of Science and Technology, 01 Dai Co Viet Street, Hanoi, Vietnam b
Institute of Industrial Chemistry, Dien Bridge Street, Hanoi, Vietnam Published online: 21 Aug 2014.
To cite this article: Dinh Thi Phuong Anh, Tran Bach Duong & Vu Dinh Hoang (2014) A new chromone from Hymenocallis littoralis Salisb. (Amaryllidaceae), Natural Product Research: Formerly Natural Product Letters, 28:21, 1869-1872, DOI: 10.1080/14786419.2014.951931 To link to this article: http://dx.doi.org/10.1080/14786419.2014.951931
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://www.tandfonline.com/page/termsand-conditions
Natural Product Research, 2014 Vol. 28, No. 21, 1869–1872, http://dx.doi.org/10.1080/14786419.2014.951931
A new chromone from Hymenocallis littoralis Salisb. (Amaryllidaceae) Dinh Thi Phuong Anha, Tran Bach Duongb and Vu Dinh Hoanga* a School of Chemical Engineering, Hanoi University of Science and Technology, 01 Dai Co Viet Street, Hanoi, Vietnam; bInstitute of Industrial Chemistry, Dien Bridge Street, Hanoi, Vietnam
Downloaded by [University of Edinburgh] at 15:22 15 October 2014
(Received 6 May 2014; final version received 3 August 2014) A new chromone, 5,7-dihydroxy-6,8-dimethoxy-2-methyl-4H-chromen-4-one (1), together with seven known compounds, 5,7-dihydroxy-6-methoxy-2-methyl-4H-chromen-4-one (pisonin B) (2), 5,7-dihydroxy-2-methyl-4H-chromen-4-one (noreugenin) (3), 5-hydroxy-7-methoxy-2-methyl-4H-chromen-4-one (eugenin) (4), (2S)-7,40 -dihydroxyflavan (5), 30 ,7-dihydroxy-40 -methoxy-8-methylflavan (6), 30 ,7-dihydroxy-40 methoxyflavan (7) and 6,8-dimethyl-5,7,40 -trihydroxyflavanone ((2 )-farrerol) (8), were isolated from Hymenocallis littoralis Salisb. (Amaryllidaceae) growing in Vietnam. Their structures were determined based on spectroscopic and physicochemical analyses. Keywords: Hymenocallis littoralis; Amaryllidaceae; flavonoid; chromone
1. Introduction The Amaryllidaceae family comprises more than 75 genera, of which Hymenocallis genus includes about 70 species (Zhong 2013). They have been attracting considerable attention due to the complex structural types of their alkaloids. However, little attention has been paid to the nonnitrogenous constituents of this family. The Hymenocallis genus was first studied for its phytochemistry in 1920, which resulted in the isolation of lycorine (Nury et al. 2004). Despite a variety of biological activities reported for Hymenocallis alkaloids (Martin 1987), these compounds had received little scientific interest until 1993, when Pancratium littorale Jacq. (Amaryllidaceae), from which the antineoplastic alkaloid pancratistatin had been isolated, was reclassified as Hymenocallis littoralis Salisb. (Amaryllidaceae) (Pettit et al. 1995). In 2008, Amina et al. investigated the bulbs and flowers of H. littoralis Salisb. cultivated in Egypt, which resulted in the isolation of four alkaloids, two flavonoids, identification of twenty-six known compounds in the volatile constituents of the plant flowers and report on antimicrobial activity of their petroleum ether extract (Amina et al. 2008). Until today, there has been no report on nonnitrogenous constituents of Hymenocallis genus in Vietnam. In this study, we identified some non-nitrogenous constituents of H. littoralis. The column chromatography of the nonnitrogenous fraction of the methanol extract of the whole plant (see Section 3) resulted in the isolation and characterisation of a new chromone, 5,7-dihydroxy-6,8-dimethoxy-2-methyl-4Hchromen-4-one (1), and seven known compounds, isolated for the first time from the species, 5,7-dihydroxy-6-methoxy-2-methyl-4H-chromen-4-one (pisonin B) (2), 5,7-dihydroxy-2methyl-4H-chromen-4-one (noreugenin) (3), 5-hydroxy-7-methoxy-2-methyl-4H-chromen-4one (eugenin) (4), (2S)-7,40 -dihydroxyflavan (5), 30 ,7-dihydroxy-40 -methoxy-8-methylflavan (6), 30 ,7-dihydroxy-40 -methoxyflavan (7) and 6,8-dimethyl-5,7,40 -trihydroxyflavanone ((2 )-farrerol) (8).
*Corresponding author. Email: [email protected] q 2014 Taylor & Francis
Downloaded by [University of Edinburgh] at 15:22 15 October 2014
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2. Results and discussion Compound 1 was isolated as colourless needles with m.p. 112 – 113oC. Its molecular formula, C12H12O6, was inferred from the pseudomolecular ion peak at m/z 253.07124 [M þ H]þ and supported by the NMR spectra. Its IR spectrum revealed the presence of a hydroxyl group (3449 cm21), a conjugated carbonyl group (1660 cm21), an olefinic bond (1623 cm21) and an aromatic system (1593 and 1401 cm21). In its 1H NMR spectrum, two singlets at d 3.75 and 3.77 were attributed to two aromatic methoxy groups (OCH3-6 and OCH3-8). Moreover, the 1H NMR spectrum exhibited signals of one chelated hydroxyl group (d 12.85) and one methyl singlet (d 2.40, s, 3H, CH3-2). The 1H NMR spectrum was similar to that of pisonin B (2), except that H-8 in 2 was replaced by a methoxy group in 1. The downfield proton signal at d 12.68 indicated the presence of a hydroxyl group at C-5 and a carbonyl group at C-4. Detailed analysis of 13C NMR data (TMS, DMSO-d6) of similar 5-hydroxy-chromones with two methoxy and one hydroxyl groups substituted at C-6, C-7 and C-8 indicated that the chemical shifts of 1 displayed a very good fit with 5,7-dihydroxy6,8-dimethoxy-2-phenyl-4H-chromen-4-one and clear differences with the other two possible substitution patterns (Horie et al. 1998; Supplementary Table S1), suggesting the structure 5,7dihydroxy-6,8-dimethoxy-2-methyl-4H-chromen-4-one for compound 1. According to the HSQC and HMBC spectra, the structure of 1 (shown in Figure 1) was established and confirmed. The HMBC spectrum (Supplementary Figure S1) revealed long-range correlations of H-3 (d 6.18) with C-2 (d 167.6) and C-10 (d 102.6); of CH3-2 (d 2.40) with C-2 (d 167.6) and C-3 (d 107.5) evidencing the structure of 2-methyl-4-pyron moiety. Cross-peaks of OH-5 (d 12.68) and C-6 (d 131.4), C-5 (d 148.3), C-10 (d 102.6); of OCH3-6 (d 3.77) and C-6 (d 131.4) demonstrated the 5-hydroxy-6-methoxy substitution of the compound. Finally, the correlations of OCH3-8 (d 3.75) with C-8 (d 127.7) confirmed the suggested substitution pattern in the benzene ring, in agreement with the literature data (Horie et al. 1998). Thus, compound 1 was elucidated as 5,7-dihydroxy-6,8-dimethoxy-2-methyl-H-4-chromen4-one. In addition, seven known compounds 2– 8 were identified as 5,7-dihydroxy-6-methoxy-2methyl-4H-chromen-4-one (pisonin B), 5,7-dihydroxy-2-methyl-4H-chromen-4-one (noreuR2
R3 R2
O
3′
CH3
8
HO
R1
9
2
O
6 5
R2
R3
1 OMe
OH
OMe
2 OMe
OH
H
3
H
OH
H
4
H
OMe
H
R2 H
OH
6 CH3
OH
OMe
7
OH
OMe
H 3′ 2′
8
H3C
2 3
5
10
OH
4
O 8
Figure 1. Chemical structures of compounds 1 –8.
OH 4′
1′
O 9
6
3 4
R1
CH3 7
5′ 6′
H
5
HO
10
5′ 6′
R3 4′
1′
O
7
OH R1
2′
R1
R3
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genin), 5-hydroxy-7-methoxy-2-methyl-4H-chromen-4-one (eugenin), (2S)-7,40 -dihydroxyflavan, 30 ,7-dihydroxy-40 -methoxy-8-methylflavan, 30 ,7-dihydroxy-40 -methoxyflavan and 6,8dimethyl-5,7,40 -trihydroxyflavanone ((2 )-farrerol), respectively, by comparing their spectroscopic data with those reported in the literature (Hans et al. 1988; Hough et al. 1995; Masaoud et al. 1995; Tsui & Brown 1996; Diaa et al. 1998; Gonza´lez et al. 2000; Wu et al. 2011).
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3. Experimental 3.1. General procedure NMR experiments were performed on a Bruker AM500 FT-NMR Spectrometer (Bruker Biospin, Zurich, Switzerland) using TMS as internal standard. The positive-ion high-resolution ESI-MS spectrum was recorded on a Fourier transform ion cyclotron resonance mass spectrometer Varian FT-ICR MS 910 (Agilent, California, USA) equipped with a 7 T superconducting magnet. Thin-layer chromatography was conducted on precoated plates DCAlufolien 60 F254 and visualised by UV light (254 nm) and sprayed with Vont’s reagent. Column chromatography was carried out with normal phase (silica gel 90– 240 mesh, 240 –430 mesh, Merck Ltd., Hanoi, Vietnam).
3.2. Plant materials The sample H. littoralis was collected in Hanoi on December 2010 by MSc Dinh Thi Phuong Anh and identified by Dr Vu Van Chuyen at the Institute of Ecology and Biological Resources, Vietnam Academy of Science and Technology. Voucher specimen (Number CPC010) has been deposited at the Centre of Pharmaceutical Chemistry, Vietnam Institute of Industrial Chemistry.
3.3. Extraction and isolation The air-dried and powdered plant materials (18.5 kg) were extracted with methanol by Soxhlet extraction for 10 h. The combined extracts were concentrated under vacuum to yield crude residue (268.36 g) which was then acidified by 2% H2SO4 and ultrasonicated, giving a homogenous mixture. After removing the sediment complex by shaking with light petroleum, the mixture was extracted with chloroform, adjusted with 5% Na2CO3 to pH , 6 and concentrated to afford total flavonoid residue (45.99 g). The residue was chromatographed on a silica gel column using a gradient from light petroleum – acetone (5:1 to 2:1, v/v) providing five fractions (A– E). Fraction E was subjected to silica gel column eluted with a gradient light petroleum –ethyl acetate (49:1 to 1:1, v/v), to yield compounds 2 (10 mg), 5 (11 mg), 1 (25 mg), 8 (35 mg) and 3 (5 mg). Fraction D was purified by silica gel column with a gradient from light petroleum –ethyl acetate– methanol (20:10:0.1 to 3:10:0.1, v/v) to yield compounds 4 (32 mg), 6 (20 mg) and 7 (17 mg).
3.4. 5,7-Dihydroxy-6,8-dimethoxy-2-methyl-4H-chromen-4-one (1) Colourless needles, m.p. 112-1138C; IR (KBr) y max (cm21): 3449, 2924– 2852, 1660, 1623, 1593 –1401, 1117; 1H NMR (500 MHz, DMSO-d6), d 12.68 (s, 5-OH), 6.25 (s, 7-OH), 6.18 (1H, br s, H-3), 3.77 (3H, s, 8-OCH3), 3.75 (3H, s, 6-OCH3), 2.40 (3H, s, 2-CH3); 13C NMR (125 MHz, DMSO-d6), d (ppm): 182.3 (s, C-4), 167.6 (s, C-2), 150.7 (s, C-7), 148.3 (s, C-5), 145.9 (s, C-9), 131.4 (s, C-6), 127.7 (s, C-8), 107.5 (d, C-3), 102.6 (s, C-10), 60.8 (q, 8-OCH3), 60.1 (q, 6-OCH3), 20.0 (q, 2-CH3); HR MS found: m/z 253.07124 [M þ H]þ, Calcd for C12H13O6 253.07067.
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4. Conclusion Phytochemical study on the non-nitrogenous compounds of the methanolic extract of the whole plant of H. littoralis has led to the isolation of 5,7-dihydroxy-6,8-dimethoxy-2-methyl-4H-chromen-4one, 5,7-dihydroxy-6-methoxy-2-methyl-4H-chromen-4-one (pisonin B), 5,7-dihydroxy-2-methyl4H-chromen-4-one (noreugenin), 5-hydroxy-7-methoxy-2-methyl-4H-chromen-4-one (eugenin), (2S)-7,40 -dihydroxyflavan, 30 ,7-dihydroxy-40 -methoxy-8-methylflavan, 30 ,7-dihydroxy-40 -methoxyflavan and 6,8-dimethyl-5,7,40 -trihydroxyflavanone ((2)-farrerol) reported for the first time from the species. Among them, 5,7-dihydroxy-6,8-dimethoxy-2-methyl-4H-chromen-4-one is a new compound and its structure was established by spectral analysis. Supplementary material Experimental details relating to this paper are available online. Acknowledgements This work was supported by the Science and Technology Fund of the Ministry of Education and Training [grant number B2010-01-317].
References Amina HA-D, Soad MT, Hala MH, Eman S, Eri K, Hiromitsu T. 2008. Phytochemical and biological investigation of Hymenocallis littoralis Salisb. Chem Biodivers. 5:332–340. Diaa TAY, Ramadan MA, Khalifa AA. 1998. Acetophenones, a chalcone, a chromone and flavonoids from Pancratium maritimum. Phytochemistry. 49:2579–2583. Gonza´lez AG, Leo´n F, Sa´nchez-Pinto L, Padro´n JI, Bermejo J. 2000. Phenolic compounds of dragon’s blood from Dracaena draco. J Nat Prod. 63:1297–1299. Hans A, Markus S, Manuel AC. 1988. Flavonoid and other constituents of Bauhinia manca. Phytochemistry. 27:1835–1841. Horie T, Ohtsuru Y, Shibata K, Yamashita K, Tsukayama M, Kawamura Y. 1998. 13C NMR spectral assignment of the A-ring of polyoxygenated flavones. Phytochemistry. 47:865–874. Hough PJ, Osibogun IM, Woldemariam TZ, Jones K. 1995. Heteronuclear NMR studies of the chromone alkaloids and the revision of the structure of some piperidino-chromone alkaloids. Plant Med. 61:154–157. Martin SF. 1987. The alkaloids. Vol 30. In: Brossi A, editor. New York: Academic Press; p. 351–376. Masaoud M, Ripperger H, Porzel A, Adam G. 1995. Cinnabarone, a bioflavonoid from dragon’s blood of Dracaena cinnabari. Phytochemistry. 38:751–753. Nury R, Matilde G, Medina JD. 2004. Search for bioactive alkaloids in Hymenocallis species. Pharma Biol. 42:280–285. Pettit GR, Pettit GR, III, Groszek G, Backhaus RA, Donbek DL, Barr RJ. 1995. Antineoplastic agents, 301. An investigation of the Amaryllidaceae genus Hymenocallis. J Nat Prod. 58:756–759. Tsui W-Y, Brown GD. 1996. Chromones and chromanones from Baeckea frutescens. Phytochemistry. 43:871–876. Wu MC, Peng CF, Chen IS, Tsai IL. 2011. Antitubercular chromones and flavonoids from Pisonia aculeate. J Nat Prod. 74:976–982. Zhong J. 2013. Amaryllidaceae and sceletium alkaloids. Nat Prod Rep. 30:849–868.
Natural Product Research: Formerly Natural Product Letters Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/gnpl20
A new chromone from Hymenocallis littoralis Salisb. (Amaryllidaceae) a
b
a
Dinh Thi Phuong Anh , Tran Bach Duong & Vu Dinh Hoang a
School of Chemical Engineering, Hanoi University of Science and Technology, 01 Dai Co Viet Street, Hanoi, Vietnam b
Institute of Industrial Chemistry, Dien Bridge Street, Hanoi, Vietnam Published online: 21 Aug 2014.
To cite this article: Dinh Thi Phuong Anh, Tran Bach Duong & Vu Dinh Hoang (2014) A new chromone from Hymenocallis littoralis Salisb. (Amaryllidaceae), Natural Product Research: Formerly Natural Product Letters, 28:21, 1869-1872, DOI: 10.1080/14786419.2014.951931 To link to this article: http://dx.doi.org/10.1080/14786419.2014.951931
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://www.tandfonline.com/page/termsand-conditions
Natural Product Research, 2014 Vol. 28, No. 21, 1869–1872, http://dx.doi.org/10.1080/14786419.2014.951931
A new chromone from Hymenocallis littoralis Salisb. (Amaryllidaceae) Dinh Thi Phuong Anha, Tran Bach Duongb and Vu Dinh Hoanga* a School of Chemical Engineering, Hanoi University of Science and Technology, 01 Dai Co Viet Street, Hanoi, Vietnam; bInstitute of Industrial Chemistry, Dien Bridge Street, Hanoi, Vietnam
Downloaded by [University of Edinburgh] at 15:22 15 October 2014
(Received 6 May 2014; final version received 3 August 2014) A new chromone, 5,7-dihydroxy-6,8-dimethoxy-2-methyl-4H-chromen-4-one (1), together with seven known compounds, 5,7-dihydroxy-6-methoxy-2-methyl-4H-chromen-4-one (pisonin B) (2), 5,7-dihydroxy-2-methyl-4H-chromen-4-one (noreugenin) (3), 5-hydroxy-7-methoxy-2-methyl-4H-chromen-4-one (eugenin) (4), (2S)-7,40 -dihydroxyflavan (5), 30 ,7-dihydroxy-40 -methoxy-8-methylflavan (6), 30 ,7-dihydroxy-40 methoxyflavan (7) and 6,8-dimethyl-5,7,40 -trihydroxyflavanone ((2 )-farrerol) (8), were isolated from Hymenocallis littoralis Salisb. (Amaryllidaceae) growing in Vietnam. Their structures were determined based on spectroscopic and physicochemical analyses. Keywords: Hymenocallis littoralis; Amaryllidaceae; flavonoid; chromone
1. Introduction The Amaryllidaceae family comprises more than 75 genera, of which Hymenocallis genus includes about 70 species (Zhong 2013). They have been attracting considerable attention due to the complex structural types of their alkaloids. However, little attention has been paid to the nonnitrogenous constituents of this family. The Hymenocallis genus was first studied for its phytochemistry in 1920, which resulted in the isolation of lycorine (Nury et al. 2004). Despite a variety of biological activities reported for Hymenocallis alkaloids (Martin 1987), these compounds had received little scientific interest until 1993, when Pancratium littorale Jacq. (Amaryllidaceae), from which the antineoplastic alkaloid pancratistatin had been isolated, was reclassified as Hymenocallis littoralis Salisb. (Amaryllidaceae) (Pettit et al. 1995). In 2008, Amina et al. investigated the bulbs and flowers of H. littoralis Salisb. cultivated in Egypt, which resulted in the isolation of four alkaloids, two flavonoids, identification of twenty-six known compounds in the volatile constituents of the plant flowers and report on antimicrobial activity of their petroleum ether extract (Amina et al. 2008). Until today, there has been no report on nonnitrogenous constituents of Hymenocallis genus in Vietnam. In this study, we identified some non-nitrogenous constituents of H. littoralis. The column chromatography of the nonnitrogenous fraction of the methanol extract of the whole plant (see Section 3) resulted in the isolation and characterisation of a new chromone, 5,7-dihydroxy-6,8-dimethoxy-2-methyl-4Hchromen-4-one (1), and seven known compounds, isolated for the first time from the species, 5,7-dihydroxy-6-methoxy-2-methyl-4H-chromen-4-one (pisonin B) (2), 5,7-dihydroxy-2methyl-4H-chromen-4-one (noreugenin) (3), 5-hydroxy-7-methoxy-2-methyl-4H-chromen-4one (eugenin) (4), (2S)-7,40 -dihydroxyflavan (5), 30 ,7-dihydroxy-40 -methoxy-8-methylflavan (6), 30 ,7-dihydroxy-40 -methoxyflavan (7) and 6,8-dimethyl-5,7,40 -trihydroxyflavanone ((2 )-farrerol) (8).
*Corresponding author. Email: [email protected] q 2014 Taylor & Francis
Downloaded by [University of Edinburgh] at 15:22 15 October 2014
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2. Results and discussion Compound 1 was isolated as colourless needles with m.p. 112 – 113oC. Its molecular formula, C12H12O6, was inferred from the pseudomolecular ion peak at m/z 253.07124 [M þ H]þ and supported by the NMR spectra. Its IR spectrum revealed the presence of a hydroxyl group (3449 cm21), a conjugated carbonyl group (1660 cm21), an olefinic bond (1623 cm21) and an aromatic system (1593 and 1401 cm21). In its 1H NMR spectrum, two singlets at d 3.75 and 3.77 were attributed to two aromatic methoxy groups (OCH3-6 and OCH3-8). Moreover, the 1H NMR spectrum exhibited signals of one chelated hydroxyl group (d 12.85) and one methyl singlet (d 2.40, s, 3H, CH3-2). The 1H NMR spectrum was similar to that of pisonin B (2), except that H-8 in 2 was replaced by a methoxy group in 1. The downfield proton signal at d 12.68 indicated the presence of a hydroxyl group at C-5 and a carbonyl group at C-4. Detailed analysis of 13C NMR data (TMS, DMSO-d6) of similar 5-hydroxy-chromones with two methoxy and one hydroxyl groups substituted at C-6, C-7 and C-8 indicated that the chemical shifts of 1 displayed a very good fit with 5,7-dihydroxy6,8-dimethoxy-2-phenyl-4H-chromen-4-one and clear differences with the other two possible substitution patterns (Horie et al. 1998; Supplementary Table S1), suggesting the structure 5,7dihydroxy-6,8-dimethoxy-2-methyl-4H-chromen-4-one for compound 1. According to the HSQC and HMBC spectra, the structure of 1 (shown in Figure 1) was established and confirmed. The HMBC spectrum (Supplementary Figure S1) revealed long-range correlations of H-3 (d 6.18) with C-2 (d 167.6) and C-10 (d 102.6); of CH3-2 (d 2.40) with C-2 (d 167.6) and C-3 (d 107.5) evidencing the structure of 2-methyl-4-pyron moiety. Cross-peaks of OH-5 (d 12.68) and C-6 (d 131.4), C-5 (d 148.3), C-10 (d 102.6); of OCH3-6 (d 3.77) and C-6 (d 131.4) demonstrated the 5-hydroxy-6-methoxy substitution of the compound. Finally, the correlations of OCH3-8 (d 3.75) with C-8 (d 127.7) confirmed the suggested substitution pattern in the benzene ring, in agreement with the literature data (Horie et al. 1998). Thus, compound 1 was elucidated as 5,7-dihydroxy-6,8-dimethoxy-2-methyl-H-4-chromen4-one. In addition, seven known compounds 2– 8 were identified as 5,7-dihydroxy-6-methoxy-2methyl-4H-chromen-4-one (pisonin B), 5,7-dihydroxy-2-methyl-4H-chromen-4-one (noreuR2
R3 R2
O
3′
CH3
8
HO
R1
9
2
O
6 5
R2
R3
1 OMe
OH
OMe
2 OMe
OH
H
3
H
OH
H
4
H
OMe
H
R2 H
OH
6 CH3
OH
OMe
7
OH
OMe
H 3′ 2′
8
H3C
2 3
5
10
OH
4
O 8
Figure 1. Chemical structures of compounds 1 –8.
OH 4′
1′
O 9
6
3 4
R1
CH3 7
5′ 6′
H
5
HO
10
5′ 6′
R3 4′
1′
O
7
OH R1
2′
R1
R3
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genin), 5-hydroxy-7-methoxy-2-methyl-4H-chromen-4-one (eugenin), (2S)-7,40 -dihydroxyflavan, 30 ,7-dihydroxy-40 -methoxy-8-methylflavan, 30 ,7-dihydroxy-40 -methoxyflavan and 6,8dimethyl-5,7,40 -trihydroxyflavanone ((2 )-farrerol), respectively, by comparing their spectroscopic data with those reported in the literature (Hans et al. 1988; Hough et al. 1995; Masaoud et al. 1995; Tsui & Brown 1996; Diaa et al. 1998; Gonza´lez et al. 2000; Wu et al. 2011).
Downloaded by [University of Edinburgh] at 15:22 15 October 2014
3. Experimental 3.1. General procedure NMR experiments were performed on a Bruker AM500 FT-NMR Spectrometer (Bruker Biospin, Zurich, Switzerland) using TMS as internal standard. The positive-ion high-resolution ESI-MS spectrum was recorded on a Fourier transform ion cyclotron resonance mass spectrometer Varian FT-ICR MS 910 (Agilent, California, USA) equipped with a 7 T superconducting magnet. Thin-layer chromatography was conducted on precoated plates DCAlufolien 60 F254 and visualised by UV light (254 nm) and sprayed with Vont’s reagent. Column chromatography was carried out with normal phase (silica gel 90– 240 mesh, 240 –430 mesh, Merck Ltd., Hanoi, Vietnam).
3.2. Plant materials The sample H. littoralis was collected in Hanoi on December 2010 by MSc Dinh Thi Phuong Anh and identified by Dr Vu Van Chuyen at the Institute of Ecology and Biological Resources, Vietnam Academy of Science and Technology. Voucher specimen (Number CPC010) has been deposited at the Centre of Pharmaceutical Chemistry, Vietnam Institute of Industrial Chemistry.
3.3. Extraction and isolation The air-dried and powdered plant materials (18.5 kg) were extracted with methanol by Soxhlet extraction for 10 h. The combined extracts were concentrated under vacuum to yield crude residue (268.36 g) which was then acidified by 2% H2SO4 and ultrasonicated, giving a homogenous mixture. After removing the sediment complex by shaking with light petroleum, the mixture was extracted with chloroform, adjusted with 5% Na2CO3 to pH , 6 and concentrated to afford total flavonoid residue (45.99 g). The residue was chromatographed on a silica gel column using a gradient from light petroleum – acetone (5:1 to 2:1, v/v) providing five fractions (A– E). Fraction E was subjected to silica gel column eluted with a gradient light petroleum –ethyl acetate (49:1 to 1:1, v/v), to yield compounds 2 (10 mg), 5 (11 mg), 1 (25 mg), 8 (35 mg) and 3 (5 mg). Fraction D was purified by silica gel column with a gradient from light petroleum –ethyl acetate– methanol (20:10:0.1 to 3:10:0.1, v/v) to yield compounds 4 (32 mg), 6 (20 mg) and 7 (17 mg).
3.4. 5,7-Dihydroxy-6,8-dimethoxy-2-methyl-4H-chromen-4-one (1) Colourless needles, m.p. 112-1138C; IR (KBr) y max (cm21): 3449, 2924– 2852, 1660, 1623, 1593 –1401, 1117; 1H NMR (500 MHz, DMSO-d6), d 12.68 (s, 5-OH), 6.25 (s, 7-OH), 6.18 (1H, br s, H-3), 3.77 (3H, s, 8-OCH3), 3.75 (3H, s, 6-OCH3), 2.40 (3H, s, 2-CH3); 13C NMR (125 MHz, DMSO-d6), d (ppm): 182.3 (s, C-4), 167.6 (s, C-2), 150.7 (s, C-7), 148.3 (s, C-5), 145.9 (s, C-9), 131.4 (s, C-6), 127.7 (s, C-8), 107.5 (d, C-3), 102.6 (s, C-10), 60.8 (q, 8-OCH3), 60.1 (q, 6-OCH3), 20.0 (q, 2-CH3); HR MS found: m/z 253.07124 [M þ H]þ, Calcd for C12H13O6 253.07067.
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4. Conclusion Phytochemical study on the non-nitrogenous compounds of the methanolic extract of the whole plant of H. littoralis has led to the isolation of 5,7-dihydroxy-6,8-dimethoxy-2-methyl-4H-chromen-4one, 5,7-dihydroxy-6-methoxy-2-methyl-4H-chromen-4-one (pisonin B), 5,7-dihydroxy-2-methyl4H-chromen-4-one (noreugenin), 5-hydroxy-7-methoxy-2-methyl-4H-chromen-4-one (eugenin), (2S)-7,40 -dihydroxyflavan, 30 ,7-dihydroxy-40 -methoxy-8-methylflavan, 30 ,7-dihydroxy-40 -methoxyflavan and 6,8-dimethyl-5,7,40 -trihydroxyflavanone ((2)-farrerol) reported for the first time from the species. Among them, 5,7-dihydroxy-6,8-dimethoxy-2-methyl-4H-chromen-4-one is a new compound and its structure was established by spectral analysis. Supplementary material Experimental details relating to this paper are available online. Acknowledgements This work was supported by the Science and Technology Fund of the Ministry of Education and Training [grant number B2010-01-317].
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