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Journal of Asian Natural Products Research Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/ganp20
Venuloxanthone, a new pyranoxanthone from the stem bark of Calophyllum venulosum a
a
Ahmad Azri Fitri bin Ismail , Gwendoline Cheng Lian Ee , Shaari ab
a
c
bin Daud , Soek Sin Teh , Najihah Mohd Hashim & Khalijah Awang
d
a
Chemistry Department, Faculty of Science, Universiti Putra Malaysia, Serdang 43400, Selangor, Malaysia b
Click for updates
Chemistry Department, Faculty of Applied Science, Universiti Teknologi MARA, Jengka 26400, Pahang, Malaysia c
Department of Pharmacy, Faculty of Medicine, University of Malaya, Kuala Lumpur, Malaysia d
Department of Chemistry, Faculty of Science, University of Malaya, Kuala Lumpur, Malaysia Published online: 29 May 2015.
To cite this article: Ahmad Azri Fitri bin Ismail, Gwendoline Cheng Lian Ee, Shaari bin Daud, Soek Sin Teh, Najihah Mohd Hashim & Khalijah Awang (2015): Venuloxanthone, a new pyranoxanthone from the stem bark of Calophyllum venulosum, Journal of Asian Natural Products Research, DOI: 10.1080/10286020.2015.1047353 To link to this article: http://dx.doi.org/10.1080/10286020.2015.1047353
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
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Journal of Asian Natural Products Research, 2015 http://dx.doi.org/10.1080/10286020.2015.1047353
Venuloxanthone, a new pyranoxanthone from the stem bark of Calophyllum venulosum Ahmad Azri Fitri bin Ismaila, Gwendoline Cheng Lian Eea*, Shaari bin Daudab, Soek Sin Teha, Najihah Mohd Hashimc and Khalijah Awangd a
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Chemistry Department, Faculty of Science, Universiti Putra Malaysia, Serdang 43400, Selangor, Malaysia; bChemistry Department, Faculty of Applied Science, Universiti Teknologi MARA, Jengka 26400, Pahang, Malaysia; cDepartment of Pharmacy, Faculty of Medicine, University of Malaya, Kuala Lumpur, Malaysia; dDepartment of Chemistry, Faculty of Science, University of Malaya, Kuala Lumpur, Malaysia (Received 19 October 2014; final version received 28 April 2015) A new pyranoxanthone, venuloxanthone (1), was isolated from the stem bark of Calophyllum venulosum, together with three other xanthones, tovopyrifolin C (2), ananixanthone (3) and caloxanthone I (4), along with two common triterpenes, friedelin (5) and lupeol (6). The structures of these compounds were identified using several spectroscopic analyses which are NMR, GCMS and FTIR experiments. Keywords: Clusiaceae; Calophyllum venulosum; pyranoxanthone; venuloxanthone
1.
Introduction
The Clusiaceae family which consists of about 40 genera [1] is easily found in tropical Asia and Africa [2]. The genus Calophyllum belonging to the Clusiaceae family is widely distributed in Southeast Asia [3]. Calophyllum is known as “bintangor” locally [4,5]. Some Calophyllum plants are used in traditional medicine. The biological activities of Calophyllum are due to the secondary metabolites such as xanthones [6,7], coumarins [8,9] and flavonoids [10]. Among the many biological activities possessed by the Calophyllum plants, anti-HIV [11] and anti-cancer [12] properties have attracted the most attention. Some of these compounds have been shown to have other important biological effects as well, such as antifungal [13], antimicrobial [14] and anti-inflammatory [15] activities. Due to the many therapeutic properties of the Calophyllum plants, we decided to look at the phytochemistry of
Calophyllum venulosum, a species which has never been reported before. We report here the isolation of a new pyranoxanthone, venuloxanthone, from the stem bark of C. venulosum.
2.
Results and discussions
Venuloxanthone (1) (Figure 1) was isolated as yellow crystals with a melting point of 220.5 –222.38C and a molecular mass of 376. The high resolution ESI mass spectrum (HR-ESI-MS) gave a positive molecular ion peak at m/z 377.1391 [M þ H]þ, corresponding to the molecular formula C23H20O5. The FTIR spectrum showed a broad peak at 3444 cm21 for a hydroxyl group, a conjugated carbonyl sharp peak at 1716 cm21, aromatic carbons at 1622 cm21 and an ether group at 1269 cm21. The UV absorption maxima at 398, 284, 223 and 215 implied that compound 1 comprised a xanthone skeleton (Figure 2).
*Corresponding author. Emails: [email protected], [email protected] q 2015 Taylor & Francis
2
A.A.F. bin Ismail et al. O
OH
8 7
9a
9
O
16
1 8a
2
OH
17
OCH3
19 6
11
5
3
4a 4
O
20 O
OH
O
13
12
18
10a 10 O
(1)
(2)
OH
15
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14
O
OH
O
O OH
O
OH
O
O
(3)
O
OH (4)
Figure 1. Structures of compounds 1 –4 isolated from C. venulosum.
A sharp singlet signal at d 13.4 in the H NMR spectrum indicated a chelated hydroxyl (OH-1) in compound 1. The HMBC spectrum gave correlations between this signal and the carbons at d 104.4 (C-9a, 3J) and d 157.9 (C-1, 2J), suggesting this chelated hydroxyl to be attached to C-1 (d 157.9). Two sets of twomethyl singlets were observed at d 1.46
(6H, H-19 & H-20) and d 1.45 (6H, H-15 & H-14). Another two sets of endocyclic olefinic doublets at d 6.72 and d 5.57 (each 1H, d, J ¼ 10.3 Hz) and at d 8.01 and d 5.79 (each 1H, d, J ¼ 10.3 Hz) were attributable to the methyls of the two dimethylpyrone rings fused to the xanthone skeleton. This was supported by the 13C NMR spectrum which revealed
1
O
OH
8
16
1 8a
7
9
2
9a
17 19
6
18 10a
11
5
12 13
O
3
4a
O 15
14
Figure 2. Key HMBC correlations of compound 1.
4
O
20
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Journal of Asian Natural Products Research two methyl signals at d 28.4 (C-19 & C20) and d 27.3 (C-15 & C-14) and four olefinic methine carbons at d 115.6 (C16), 127.3 (C-17) and 120.8 (C-11), 132.7 (C-12). The presence of two quaternary carbon signals at d 78.2 (C-18) and 75.5 (C-13) was also seen. The pyrane ring was assigned to C-2 and C-3 based on the correlation of the signal at d 6.26 (H-4) to the oxygenated carbon at d 160.57 (C-3). 3 J correlations were also observed between H-17 at d 5.57 and C-2 at d 104.37 and also between H-16 at d 6.72 and C-3 at d 160.5. The two remaining doublet signals at d 7.14 (H-7) and d 7.19 (H-8) in the 1H NMR spectrum were assigned to the isolated aromatic protons at C-7 and C-8 in the compound. The positions of these signals were assigned based on their HMBC correlations. H-7 was positioned at C-7 as indicated by HMBC cross peaks with C-6 at d 119.9 via a 2J correlation, and with C-5 at d 151.7 via a 3J correlation. Meanwhile, the H-8 signal was observed to give a 2J correlation with C-8a at d 115.1 and a 3J correlation with C-10a at d 149.3. The remaining free positions on the left xanthone ring at C-5 and C-6 were assigned to the second pyrane ring as a 3 J HMBC correlation was seen between the proton at d 5.79 (H-12) and C-6 (d 119.9). The 3J HMBC correlation between the doublet signal at d 8.01 (H11) and d 75.5 (C-13) further justified the attachment of the second pyrane ring at C-5 and C-6. The COSY spectrum indicated clearly couplings between H-17 at d 5.57 and H-16 at d 6.72, and between H-12 at d 5.79 and H-11 at d 8.01 with coupling constant values typical of orthocoupled protons. The DEPT spectrum gave information for 12 quaternary carbons (C), 7 methine carbons (CH), and 4 methyl carbons (CH3) implying the proposed structure. Hence, compound 1 was elucidated to be 1-hydroxy-60 60 dimethylpyrano[20 ,30 :3,2]-600 ,600 -dimethyl-
3
pyrano[200 ,300 :5,6]xanthone and given the trivial name venuloxanthone. 3. Experimental 3.1 General experimental procedures Melting points were obtained on a Leica Galen III instrument (Leica Micro-systems, Redwoodcity, CA, USA). Ultraviolet spectra were recorded in ethanol (EtOH) on a Shimadzu UV-160A UVVisible Recording Spectrophotometer (Shimadzu Scientific Instruments, Kyoto, Japan). A Perkin-Elmer 100 Series FT-IR spectrometer (Perkin Elmer, Waltham, MA, USA) was used for IR analysis. 1D and 2D NMR spectra were recorded on a JEOL JNM-ECX500 (500 MHz) or JEOL ECA400 (400 MHz) (Jeol, Tachikawa, Japan) spectrometer operating at 125 and 100 MHz, respectively. Mass spectroscopic data were recorded using a Shimadzu GC-MS model QP2010 Plus spectrophotometer (Shimadzu Scientific Instruments, Kyoto, Japan). 3.2 Plant material The stem bark sample of C. venulosum (Voucher specimen no. RG5023) was collected from Sarawak in May 2013. The plant was identified by Associate Professor Dr Rusea Go from the Biology Department, Faculty of Science, Universiti Putra Malaysia where a voucher specimen was deposited. 3.3 Extraction and isolation The stem bark of C. venulosum (2.2 kg) was dried and ground into powder before extraction with solvents of different polarities, starting with nonpolar to polar solvents. The sample was extracted by conventional soaking method starting with hexane, followed by chloroform and methanol for 72 h. The extracts were then concentrated by using a rotary evaporator to give 18.5 g of hexane extract, 23.3 g of
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A.A.F. bin Ismail et al.
chloroform extract and 132.8 g of methanol extract. The crude extracts were then separated using column chromatography. Columns were packed with silica gel, Merck Kieselgel PF254 (Art No. 1.007749.1000; 5– 40 mm) for vacuum column chromatography and Merck Kieselgel 60 (Art. No. 1.09385.1000; 40 – 63 mm) for gravity column chromatography. About 12 g of hexane extract was purified through vacuum column chromatography using solvents of increasing polarity (hexane – chloroform and chloroform – ethyl acetate) to give 23 fractions. Fractions 5– 9 from this vacuum column chromatography were then combined and subjected to a gravity column chromatographic separation, giving yellow crystals of ananixanthone (3). Fractions 12– 15 gave friedelin (5) while fraction 22 gave lupeol (6). Approximately 18 g of chloroform extract was separated via vacuum column chromatography using hexane – ethyl acetate in increasing polarity and ethyl acetate –methanol also in increasing polarity as the mobile phase. From this, 26 fractions were collected and fractions 3– 6 were re-chromatographed in a gravity column chromatography using hexane – ethyl acetate in increasing polarity as the mobile phase to give five fractions. Fraction 4 was found to be tovopyrifolin C (2). Further purification of fractions 11 – 14 from the chloroform extract gave another three fractions. Fraction 3 was then further purified by Sephadex Lipophilic LH-20 with methanol as the eluting solvent. This resulted in the isolation of another xanthone, caloxanthone I (4). Yellowish crystals of a new pyranoxanthone venuloxanthone (1) was obtained from purification of fraction 20 using the solvent system ethyl acetate– hexane in the ratio of 4:6. 3.3.1 Venuloxanthone (1) Yellow needle crystals; m.p. 220.5 – 222.38C; UV lEtOH max (log 1): 398 (0.287),
Table 1. 1H and 13C NMR spectral data of compound 1 (CDCl3). 1
No 1 2 3 4 4a 5 6 7 8 8a 9 9a 10a 11 12 13 14 15 16 17 18 19 20
H (d)
13.49 (s, OH-1) 6.26 (s, 1H)
7.14 (d, J ¼ 9.4 Hz, 1H) 7.19 (d, J ¼ 9.4 Hz, 1H)
8.01 (d, J ¼ 10.3 Hz, 1H) 5.79 (d, J ¼ 10.3 Hz, 1H) 1.45 1.45 6.72 5.57
(s, 3H) (s, 3H) (d, J ¼ 10.3 Hz, 1H) (d, J ¼ 10.3 Hz, 1H)
1.46 (s, 3H) 1.46 (s, 3H)
13
C(d)
157.9 104.3 160.5 94.3 156.7 151.7 119.9 117.8 124.3 115.1 183.4 104.4 149.3 120.8 132.7 75.5 27.3 27.3 115.6 127.3 78.2 28.4 28.4
284 (0.711), 223 (1.035), 215 (1.109) nm; IR vmax cm21: 3444, 1716, 1622, 1269; 1H NMR (500 MHz, CDCl3) and 13C NMR (125 MHz, CDCl3) data refer to Table 1. EI-MS: m/z (ret. int.): 376 (28), 361 (100), 343 (10), 173 (54). HR-ESI-MS: m/z 377.1391 [M þ H]þ (calcd for C23H21O5, 377.1389). Acknowledgment The Sarawak acknowledged.
Biodiversity
Centre
is
Disclosure statement No potential conflict of interest was reported by the authors.
Funding The authors express their gratitude for the financial support from UPM under the RUGS Research Fund.
Journal of Asian Natural Products Research
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References [1] S.H. Goh, I. Jantan, and P.G. Waterman, J. Nat. Prod. 55, 1415 (1992). doi:10. 1021/np50088a005. [2] N.M. Nasir, M. Rahmani, K. Shaari, N.K. Kassim, R. Go, J. Stanslas, and E.J. Jeyaraj, Sains Malaysiana 42, 1261 (2013). [3] C. Morel, D. Se´raphin, J.M. Oger, M. Litaudon, T. Se´venet, P. Richomme, and J. Bruneton, J. Nat. Prod. 63, 1471 (2000). doi:10.1021/np000215m. [4] E.J.H. Corner, Wayside Trees of Malaya (The Malayan Nature Society, Malaysia, 1998). [5] T.C. Whitmore, Palms of Malaya (Oxford University Press, Malaysia, 1973), p. 162. [6] H.R. Dharmaratne, M.T. Napagoda, and S.B. Tennakoon, Nat. Prod. Res. 23, 539 (2009). doi:10.1080/14786410600899 118. [7] G.C.L. Ee, S.H. Mah, M. Rahmani, Y.H. Taufiq-Yap, S.S. Teh, and Y.M. Lim, J. Asian Nat. Prod. Res. 13, 956 (2011). doi:10.1080/10286020.2011. 600248. [8] G.C.L. Ee, S.H. Mah, S.S. Teh, M. Rahmani, R. Go, and Y.H. Taufiq-Yap, Molecules 16, 9721 (2011b). doi:10.3390/ molecules16119721.
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[9] D. Guilet, D. Se´raphin, D. Rondeau, P. Richomme, and J. Bruneton, Phytochemistry 58, 571 (2001). doi:10.1016/ S0031-9422(01)00285-0. [10] B. Ravelonjato, F. Libot, F. Ramiandrasoa, N. Kunesch, P. Gayral, and J. Poisson, Planta Med. 58, 51 (1992). doi:10.1055/s-2006-961389. [11] C. Spino, M. Dodier, and S. Sotheeswaran, Bioorgan. Med. Chem. Lett. 8, 3475 (1998). doi:10.1016/S0960-894X(98) 00628-3. [12] M. Itoigawa, C. Ito, H.T. Tan, M. Kuchide, H. Tokuda, H. Nishino, and H. Furukawa, Cancer Lett. 169, 15 (2001). doi:10.1016/ S0304-3835(01)00521-3. [13] I. Sordat-Diserens, C. Rogers, B. Sordat, and K. Hostettmann, Phytochemistry 31, 313 (1992). doi:10.1016/0031-9422(91) 83061-O. [14] M.C. Yimdjo, A.G. Azebaze, A.E. Nkengfack, A.M. Meyer, B. Bodo, and Z.T. Fomum, Phytochemistry 65, 2789 (2004). doi:10.1016/j.phytochem. 2004.08.024. [15] K. Hostettmann, M. Hostettmann, Methods in Plant Biochemistry, edited by J.B. Harbone (Academic Press, London, 1989), Vol. 1, p. 493.
Journal of Asian Natural Products Research Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/ganp20
Venuloxanthone, a new pyranoxanthone from the stem bark of Calophyllum venulosum a
a
Ahmad Azri Fitri bin Ismail , Gwendoline Cheng Lian Ee , Shaari ab
a
c
bin Daud , Soek Sin Teh , Najihah Mohd Hashim & Khalijah Awang
d
a
Chemistry Department, Faculty of Science, Universiti Putra Malaysia, Serdang 43400, Selangor, Malaysia b
Click for updates
Chemistry Department, Faculty of Applied Science, Universiti Teknologi MARA, Jengka 26400, Pahang, Malaysia c
Department of Pharmacy, Faculty of Medicine, University of Malaya, Kuala Lumpur, Malaysia d
Department of Chemistry, Faculty of Science, University of Malaya, Kuala Lumpur, Malaysia Published online: 29 May 2015.
To cite this article: Ahmad Azri Fitri bin Ismail, Gwendoline Cheng Lian Ee, Shaari bin Daud, Soek Sin Teh, Najihah Mohd Hashim & Khalijah Awang (2015): Venuloxanthone, a new pyranoxanthone from the stem bark of Calophyllum venulosum, Journal of Asian Natural Products Research, DOI: 10.1080/10286020.2015.1047353 To link to this article: http://dx.doi.org/10.1080/10286020.2015.1047353
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.
Downloaded by [New York University] at 05:21 04 August 2015
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
Journal of Asian Natural Products Research, 2015 http://dx.doi.org/10.1080/10286020.2015.1047353
Venuloxanthone, a new pyranoxanthone from the stem bark of Calophyllum venulosum Ahmad Azri Fitri bin Ismaila, Gwendoline Cheng Lian Eea*, Shaari bin Daudab, Soek Sin Teha, Najihah Mohd Hashimc and Khalijah Awangd a
Downloaded by [New York University] at 05:21 04 August 2015
Chemistry Department, Faculty of Science, Universiti Putra Malaysia, Serdang 43400, Selangor, Malaysia; bChemistry Department, Faculty of Applied Science, Universiti Teknologi MARA, Jengka 26400, Pahang, Malaysia; cDepartment of Pharmacy, Faculty of Medicine, University of Malaya, Kuala Lumpur, Malaysia; dDepartment of Chemistry, Faculty of Science, University of Malaya, Kuala Lumpur, Malaysia (Received 19 October 2014; final version received 28 April 2015) A new pyranoxanthone, venuloxanthone (1), was isolated from the stem bark of Calophyllum venulosum, together with three other xanthones, tovopyrifolin C (2), ananixanthone (3) and caloxanthone I (4), along with two common triterpenes, friedelin (5) and lupeol (6). The structures of these compounds were identified using several spectroscopic analyses which are NMR, GCMS and FTIR experiments. Keywords: Clusiaceae; Calophyllum venulosum; pyranoxanthone; venuloxanthone
1.
Introduction
The Clusiaceae family which consists of about 40 genera [1] is easily found in tropical Asia and Africa [2]. The genus Calophyllum belonging to the Clusiaceae family is widely distributed in Southeast Asia [3]. Calophyllum is known as “bintangor” locally [4,5]. Some Calophyllum plants are used in traditional medicine. The biological activities of Calophyllum are due to the secondary metabolites such as xanthones [6,7], coumarins [8,9] and flavonoids [10]. Among the many biological activities possessed by the Calophyllum plants, anti-HIV [11] and anti-cancer [12] properties have attracted the most attention. Some of these compounds have been shown to have other important biological effects as well, such as antifungal [13], antimicrobial [14] and anti-inflammatory [15] activities. Due to the many therapeutic properties of the Calophyllum plants, we decided to look at the phytochemistry of
Calophyllum venulosum, a species which has never been reported before. We report here the isolation of a new pyranoxanthone, venuloxanthone, from the stem bark of C. venulosum.
2.
Results and discussions
Venuloxanthone (1) (Figure 1) was isolated as yellow crystals with a melting point of 220.5 –222.38C and a molecular mass of 376. The high resolution ESI mass spectrum (HR-ESI-MS) gave a positive molecular ion peak at m/z 377.1391 [M þ H]þ, corresponding to the molecular formula C23H20O5. The FTIR spectrum showed a broad peak at 3444 cm21 for a hydroxyl group, a conjugated carbonyl sharp peak at 1716 cm21, aromatic carbons at 1622 cm21 and an ether group at 1269 cm21. The UV absorption maxima at 398, 284, 223 and 215 implied that compound 1 comprised a xanthone skeleton (Figure 2).
*Corresponding author. Emails: [email protected], [email protected] q 2015 Taylor & Francis
2
A.A.F. bin Ismail et al. O
OH
8 7
9a
9
O
16
1 8a
2
OH
17
OCH3
19 6
11
5
3
4a 4
O
20 O
OH
O
13
12
18
10a 10 O
(1)
(2)
OH
15
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14
O
OH
O
O OH
O
OH
O
O
(3)
O
OH (4)
Figure 1. Structures of compounds 1 –4 isolated from C. venulosum.
A sharp singlet signal at d 13.4 in the H NMR spectrum indicated a chelated hydroxyl (OH-1) in compound 1. The HMBC spectrum gave correlations between this signal and the carbons at d 104.4 (C-9a, 3J) and d 157.9 (C-1, 2J), suggesting this chelated hydroxyl to be attached to C-1 (d 157.9). Two sets of twomethyl singlets were observed at d 1.46
(6H, H-19 & H-20) and d 1.45 (6H, H-15 & H-14). Another two sets of endocyclic olefinic doublets at d 6.72 and d 5.57 (each 1H, d, J ¼ 10.3 Hz) and at d 8.01 and d 5.79 (each 1H, d, J ¼ 10.3 Hz) were attributable to the methyls of the two dimethylpyrone rings fused to the xanthone skeleton. This was supported by the 13C NMR spectrum which revealed
1
O
OH
8
16
1 8a
7
9
2
9a
17 19
6
18 10a
11
5
12 13
O
3
4a
O 15
14
Figure 2. Key HMBC correlations of compound 1.
4
O
20
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Journal of Asian Natural Products Research two methyl signals at d 28.4 (C-19 & C20) and d 27.3 (C-15 & C-14) and four olefinic methine carbons at d 115.6 (C16), 127.3 (C-17) and 120.8 (C-11), 132.7 (C-12). The presence of two quaternary carbon signals at d 78.2 (C-18) and 75.5 (C-13) was also seen. The pyrane ring was assigned to C-2 and C-3 based on the correlation of the signal at d 6.26 (H-4) to the oxygenated carbon at d 160.57 (C-3). 3 J correlations were also observed between H-17 at d 5.57 and C-2 at d 104.37 and also between H-16 at d 6.72 and C-3 at d 160.5. The two remaining doublet signals at d 7.14 (H-7) and d 7.19 (H-8) in the 1H NMR spectrum were assigned to the isolated aromatic protons at C-7 and C-8 in the compound. The positions of these signals were assigned based on their HMBC correlations. H-7 was positioned at C-7 as indicated by HMBC cross peaks with C-6 at d 119.9 via a 2J correlation, and with C-5 at d 151.7 via a 3J correlation. Meanwhile, the H-8 signal was observed to give a 2J correlation with C-8a at d 115.1 and a 3J correlation with C-10a at d 149.3. The remaining free positions on the left xanthone ring at C-5 and C-6 were assigned to the second pyrane ring as a 3 J HMBC correlation was seen between the proton at d 5.79 (H-12) and C-6 (d 119.9). The 3J HMBC correlation between the doublet signal at d 8.01 (H11) and d 75.5 (C-13) further justified the attachment of the second pyrane ring at C-5 and C-6. The COSY spectrum indicated clearly couplings between H-17 at d 5.57 and H-16 at d 6.72, and between H-12 at d 5.79 and H-11 at d 8.01 with coupling constant values typical of orthocoupled protons. The DEPT spectrum gave information for 12 quaternary carbons (C), 7 methine carbons (CH), and 4 methyl carbons (CH3) implying the proposed structure. Hence, compound 1 was elucidated to be 1-hydroxy-60 60 dimethylpyrano[20 ,30 :3,2]-600 ,600 -dimethyl-
3
pyrano[200 ,300 :5,6]xanthone and given the trivial name venuloxanthone. 3. Experimental 3.1 General experimental procedures Melting points were obtained on a Leica Galen III instrument (Leica Micro-systems, Redwoodcity, CA, USA). Ultraviolet spectra were recorded in ethanol (EtOH) on a Shimadzu UV-160A UVVisible Recording Spectrophotometer (Shimadzu Scientific Instruments, Kyoto, Japan). A Perkin-Elmer 100 Series FT-IR spectrometer (Perkin Elmer, Waltham, MA, USA) was used for IR analysis. 1D and 2D NMR spectra were recorded on a JEOL JNM-ECX500 (500 MHz) or JEOL ECA400 (400 MHz) (Jeol, Tachikawa, Japan) spectrometer operating at 125 and 100 MHz, respectively. Mass spectroscopic data were recorded using a Shimadzu GC-MS model QP2010 Plus spectrophotometer (Shimadzu Scientific Instruments, Kyoto, Japan). 3.2 Plant material The stem bark sample of C. venulosum (Voucher specimen no. RG5023) was collected from Sarawak in May 2013. The plant was identified by Associate Professor Dr Rusea Go from the Biology Department, Faculty of Science, Universiti Putra Malaysia where a voucher specimen was deposited. 3.3 Extraction and isolation The stem bark of C. venulosum (2.2 kg) was dried and ground into powder before extraction with solvents of different polarities, starting with nonpolar to polar solvents. The sample was extracted by conventional soaking method starting with hexane, followed by chloroform and methanol for 72 h. The extracts were then concentrated by using a rotary evaporator to give 18.5 g of hexane extract, 23.3 g of
Downloaded by [New York University] at 05:21 04 August 2015
4
A.A.F. bin Ismail et al.
chloroform extract and 132.8 g of methanol extract. The crude extracts were then separated using column chromatography. Columns were packed with silica gel, Merck Kieselgel PF254 (Art No. 1.007749.1000; 5– 40 mm) for vacuum column chromatography and Merck Kieselgel 60 (Art. No. 1.09385.1000; 40 – 63 mm) for gravity column chromatography. About 12 g of hexane extract was purified through vacuum column chromatography using solvents of increasing polarity (hexane – chloroform and chloroform – ethyl acetate) to give 23 fractions. Fractions 5– 9 from this vacuum column chromatography were then combined and subjected to a gravity column chromatographic separation, giving yellow crystals of ananixanthone (3). Fractions 12– 15 gave friedelin (5) while fraction 22 gave lupeol (6). Approximately 18 g of chloroform extract was separated via vacuum column chromatography using hexane – ethyl acetate in increasing polarity and ethyl acetate –methanol also in increasing polarity as the mobile phase. From this, 26 fractions were collected and fractions 3– 6 were re-chromatographed in a gravity column chromatography using hexane – ethyl acetate in increasing polarity as the mobile phase to give five fractions. Fraction 4 was found to be tovopyrifolin C (2). Further purification of fractions 11 – 14 from the chloroform extract gave another three fractions. Fraction 3 was then further purified by Sephadex Lipophilic LH-20 with methanol as the eluting solvent. This resulted in the isolation of another xanthone, caloxanthone I (4). Yellowish crystals of a new pyranoxanthone venuloxanthone (1) was obtained from purification of fraction 20 using the solvent system ethyl acetate– hexane in the ratio of 4:6. 3.3.1 Venuloxanthone (1) Yellow needle crystals; m.p. 220.5 – 222.38C; UV lEtOH max (log 1): 398 (0.287),
Table 1. 1H and 13C NMR spectral data of compound 1 (CDCl3). 1
No 1 2 3 4 4a 5 6 7 8 8a 9 9a 10a 11 12 13 14 15 16 17 18 19 20
H (d)
13.49 (s, OH-1) 6.26 (s, 1H)
7.14 (d, J ¼ 9.4 Hz, 1H) 7.19 (d, J ¼ 9.4 Hz, 1H)
8.01 (d, J ¼ 10.3 Hz, 1H) 5.79 (d, J ¼ 10.3 Hz, 1H) 1.45 1.45 6.72 5.57
(s, 3H) (s, 3H) (d, J ¼ 10.3 Hz, 1H) (d, J ¼ 10.3 Hz, 1H)
1.46 (s, 3H) 1.46 (s, 3H)
13
C(d)
157.9 104.3 160.5 94.3 156.7 151.7 119.9 117.8 124.3 115.1 183.4 104.4 149.3 120.8 132.7 75.5 27.3 27.3 115.6 127.3 78.2 28.4 28.4
284 (0.711), 223 (1.035), 215 (1.109) nm; IR vmax cm21: 3444, 1716, 1622, 1269; 1H NMR (500 MHz, CDCl3) and 13C NMR (125 MHz, CDCl3) data refer to Table 1. EI-MS: m/z (ret. int.): 376 (28), 361 (100), 343 (10), 173 (54). HR-ESI-MS: m/z 377.1391 [M þ H]þ (calcd for C23H21O5, 377.1389). Acknowledgment The Sarawak acknowledged.
Biodiversity
Centre
is
Disclosure statement No potential conflict of interest was reported by the authors.
Funding The authors express their gratitude for the financial support from UPM under the RUGS Research Fund.
Journal of Asian Natural Products Research
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