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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
Two new degradative cassane-type diterpenes isolated from Caesalpinia minax a
a
b
c
Zhao-Cui Sun , Guo-Xu Ma , Jing-Quan Yuan , Hua Wei , Hai-Feng a
a
d
a
Wu , Zhong-Hao Sun , Guo-Hong Wang , Jun-Shan Yang & XuDong Xu
a
a
Key Laboratory of Bioactive Substances and Resources Utilization of Chinese Herbal Medicine, Ministry of Education, Institute of Medicinal Plant Development, Peking Union Medical College and Chinese Academy of Medical Sciences, Beijing, 100193, China b
National Engineering Laboratory of Southwest Endangered Medicinal Resources Development, National Development and Reform Commission, Guangxi Botanical Garden of Medicinal Plant, Nanning, 530023, China c
Institute of Chinese Materia Medica, China Academy of Chinese Medical Sciences, Beijing, 100700, China d
Department of Pharmacy, Shanxi Provincial Hospital of Traditional Chinese Medicine, Taiyuan, 030012, China Published online: 11 Dec 2013.
To cite this article: Zhao-Cui Sun, Guo-Xu Ma, Jing-Quan Yuan, Hua Wei, Hai-Feng Wu, ZhongHao Sun, Guo-Hong Wang, Jun-Shan Yang & Xu-Dong Xu (2014) Two new degradative cassane-type diterpenes isolated from Caesalpinia minax, Journal of Asian Natural Products Research, 16:2, 187-191, DOI: 10.1080/10286020.2013.864282 To link to this article: http://dx.doi.org/10.1080/10286020.2013.864282
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Journal of Asian Natural Products Research, 2014 Vol. 16, No. 2, 187–191, http://dx.doi.org/10.1080/10286020.2013.864282
Two new degradative cassane-type diterpenes isolated from Caesalpinia minax Zhao-Cui Suna1, Guo-Xu Maa1, Jing-Quan Yuanb, Hua Weic, Hai-Feng Wua, Zhong-Hao Suna, Guo-Hong Wangd, Jun-Shan Yanga and Xu-Dong Xua*
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a
Key Laboratory of Bioactive Substances and Resources Utilization of Chinese Herbal Medicine, Ministry of Education, Institute of Medicinal Plant Development, Peking Union Medical College and Chinese Academy of Medical Sciences, Beijing 100193, China; bNational Engineering Laboratory of Southwest Endangered Medicinal Resources Development, National Development and Reform Commission, Guangxi Botanical Garden of Medicinal Plant, Nanning 530023, China; c Institute of Chinese Materia Medica, China Academy of Chinese Medical Sciences, Beijing 100700, China; dDepartment of Pharmacy, Shanxi Provincial Hospital of Traditional Chinese Medicine, Taiyuan 030012, China (Received 26 August 2013; final version received 6 November 2013) Cassane-type diterpenes are main bioactive constituents of Caesalpinia minax HANCE. As a part of our ongoing chemical investigation of C. minax, two new degradative cassane-type diterpenes, named caesalpins I (1) and J (2), were isolated from the EtOAc extract of the seeds of C. minax. The structures were elucidated by means of spectroscopic analysis. Keywords: Fabaceae; cassane-type diterpenes; caesalpin I; caesalpin J
1.
Introduction
The genus Caesalpinia (Fabaceae) contains about 100 species in the world. Many species of this genus are traditional medicinal plants with a wide distribution in the tropical and subtropical regions of southeast Asia [1]. Previous investigations on the genus have shown interesting biological activities such as anti-inflammatory [2], antiviral [3], antibacterial [4], antitumor [5], and antiproliferative [6] effects. The seeds of Caesalpinia minax HANCE, well known as “kushilian” in China, have been used as a traditional folk medicine for the treatment of influenza, fever, and dysentery [7]. Recently, a large number of chemical constituent reports about C. minax showed that cassane-type diterpenes are the main bioactive components [8 –13]. For the presence of such an interesting variety of significant bioactive compounds, we further studied on *Corresponding author. Email: [email protected] q 2013 Taylor & Francis
the EtOAc extract of the seeds of C. minax and isolated two new rare degradative tricylic cassane-type diterpenes, named caesalpins I (1) and J (2) (Figure 1). In this paper, we report the isolation and structural elucidation of the new compounds.
2.
Results and discussion
Compound 1 was obtained as a white amorphous powder with ½a20 D þ 36.3 (c 0.01, MeOH), and its molecular formula C24H34O8 was determined from the quasimolecular ion peak at m/z 473.2166 [M þ Na]þ, deduced by HR-ESI-MS. The IR spectrum showed hydroxyl absorption at 3441 cm21 and a,b-unsaturated carbonyl absorption at 1746 and 1652 cm21 [14]. The 1H NMR spectrum of 1 exhibited four methyl proton signals at dH 1.11 (s, H3-18), 1.12 (s, H3-19), 1.28 (s, H3-20), and 1.96 (s, H3-17). Three acetoxy
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OH 19
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Figure 1. Structures of compounds 1 and 2.
methyl proton signals at dH 2.01 (s), 2.04 (s), and 2.05 (s) indicated the presence of three acetoxy substituents. An olefinic proton signal evident at dH 5.85 (1H, s, H13) revealed the presence of a double bond. The 13C APT spectrum of compound 1 showed the presence of 24 carbons, including four methyl carbon signals at dC 18.0, 23.1, 30.6, and 24.9; three acetyl methyl carbon signals at dC 22.0, 21.2, and 21.8; three methylene carbon signals at dC 23.4 (C-2), 33.6 (C-3), and 37.4 (C-11); five methine carbon signals at dC 75.1 (C1), 75.4 (C-6), 75.9 (C-7), 43.9 (C-8), and 40.5 (C-9); three quaternary carbon signals at dC 38.9 (C-4), 79.3 (C-5), and 44.0 (C10); two olefinic carbon signals at dC 128.9 (C-13) and 166.1 (C-14) and four carbonyl signals at dC 169.1, 171.7, 172.5, and 201.5. The above-mentioned data indicated that compound 1 was a rare tricyclic cassane-type diterpene with a conjugated unsaturated carbonyl moiety, that, together with the molecular formula, suggested that C-15 and C-16 were degraded in the structure [15,16]. All the carbon-bonded
protons were assigned from the HSQC spectrum. In the HMBC spectrum (Figure 2), the correlations of H3-OAc ( dH 2.04) with C-1 ( dC 75.1) and ZOCOCH3 ( dC 169.1), H3-OAc (dH 2.01) with C-6 (dC 75.4) and ZOCOCH3 (dC 171.7), and H3-OAc (dH 2.05) with C-7 (dC 75.9) and ZOCOCH3 (dC 172.5) suggested that the acetoxy groups were located at C-1, C-6, and C-7. Similarly, the HMBC correlations between H3-17 (dH 1.96, s) and C-8 (dC 43.9), C-13 (dC 128.9), and C-14 (dC 166.1); H-13 (dH 5.85, s) and C-12 (dC 201.5) and C-14 (dC 166.1) confirmed the a,b-unsaturated carbonyl moiety at C-12, C-13, and C-14. The relative configuration of compound 1 was determined by the analysis of coupling constants and NOESY spectrum. The oxymethine proton signal at dH 4.78 (H-1) had a triplet with a small coupling constant (J ¼ 2.4 Hz) to both protons on C-2 and the cross-peaks with H3-20 (dH 1.28) indicated that the acetoxy substituent at C-1 to be a-oriented. The NOEs from H6 (dH 5.58) to H3-20 (dH 1.28) and H-7 (dH
O
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O
H3COCO
OH
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OCOCH3 OCOCH3
Figure 2. Key HMBC correlations of compounds 1 and 2.
OCOCH3 OH OCOCH3
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Journal of Asian Natural Products Research
189
5.35) to H-9 (dH 2.81) suggested that H-6 was b-oriented and H-7 was a-oriented. The 3J coupling constant (8.4 Hz) also supported the antiperiplanar relationship between H-6 and H-7. There, the structure of compound 1 was assigned as 1a,6a,7btriacetoxy-5a-hydroxy-12-oxocassa-13 (14)-diene and named caesalpin I. This degradative cassane-type diterpene was isolated for the first time in the genus Caesalpinia. Compound 2 was also obtained as a white amorphous white powder with ½a20 D þ 24.8 (c 0.03, MeOH) and its molecular formula C 26H 36O 10 was assigned from the quasi-molecular ion peak at m/z 531.2198 [M þ Na]þ in the positive-ion mode deduced by HR-ESIMS. The IR spectrum showed hydroxyl absorption at 3418 cm21 and a,b-unsaturated carbonyl absorption at 1738 and 1652 cm21. The NMR data for this compound were similar to those of 1, except for the absence of one olefinic proton signal and the presence of an additional methoxycarbonyl group. In the HMBC spectrum (Figure 2), the correlations of ZOCH3 (dH 3.78) with quaternary carbon C-13 (dC 135.5) and ZOCOCH3 (dC 170.3); H3-17 (dH 1.91) with C-13 (dC 135.5) and C-14 (dC 162.2) suggested that the carboxymethyl group was attached to C-13. The similar NOE spectra of 1 and 2 indicated that their relative configurations were identical. Thus, the structure of compound 2 was established as 1a,6a,7b-triacetoxy-5ahydro-xy-12-oxocassa-13-carboxymethyl13(14)-diene and named caesalpin J.
NMR spectra were obtained with a Bruker AV III 600 NMR spectrometer (chemical shift values are presented as d values with TMS as the internal standard) (Bruker, Billerica, German). HR-ESI-MS were performed on a LTQ-Obitrap XL spectrometer (Thermo Fisher Scientific, Boston, MA, USA). HPLC was carried out on a Lumian K-1001 liquid chromatography (Knauer Ltd, Germany) equipped with a UV/vis K-2501 detector, at a rate of 2 ml/ min and monitored at 210 nm for the semipreparation. C18 reversed-phase silica gel (40 – 63 mm, Merck, Darmstadt, Germany), Sephadex LH-20 (Pharmacia, Uppsala, Sweden), MCI gel (CHP 20P, 75 –150 mm, Mitsubishi Chemical Corporation, Tokyo, Japan), and silica gel (100 – 200 and 300– 400 mesh, Qingdao Marine Chemical plant, Qingdao, China) were used for column chromatography. And precoated silica gel GF254 plates (Zhi Fu Huang Wu Pilot Plant of Silica Gel Development, Yantai, China) were used for TLC. All solvents used were of analytical grade (Beijing Chemical Works, Beijing, China).
3. Experimental 3.1 General experimental procedures
3.3
Optical rotations were obtained on a PerkinElmer 341 digital polarimeter (PerkinElmer, Norwalk, CT, USA). UV and IR spectra were recorded on Shimadzu UV2550 and FTIR-8400S spectrometer (Shimadzu, Kyoto, Japan), respectively.
3.2 Plant material The seeds of C. minax were collected in September 2008 from Nanning, Guangxi Province, China, and identified by Prof. Jing-Quan Yuan, Department of Pharmaceutical Chemistry, Guangxi Botanical Garden of Medicinal Plant. A voucher specimen (No. 21648) was deposited at the Guangxi Botanical Garden of Medicinal Plant. Extraction and isolation
The air-dried and powdered seeds of C. minax (8.0 kg), collected from Nanning district in Guangxi province of China, were extracted three times with methanol. Removal of the methanol under reduced pressure yielded a methanol extract (2020 g). The residue was subjected to
190 Table 1.
Z.-C. Sun et al. 1
H (600 MHz) and 13C (150 MHz) NMR spectral data for compounds 1 and 2. 1a
Position 1 2
dC, type
dH (J in Hz)
dC, type
dH (J in Hz)
75.1, CH 23.4, CH2
4.78, t (2.4) 1.73 – 1.76, m 1.85 – 1.90, m 1.14 – 1.15, m 1.71 – 1.76, m
75.1, CH
4.78, t (2.4) 1.77 – 1.79, m 1.82 – 1.84, m 1.05 – 1.08, m 1.71 – 1.76, m
33.6, CH2
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3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 1-OCOCH3 1-OCOC H3 6-OCOCH3 6-OCOC H3 7-OCOCH3 7-OCOC H3 16-OCOCH3 16-OCOCH3 a
2a
38.9, C 79.3, C 75.4, CH 75.9, CH 43.9, CH 40.5, CH 44.0, C 37.4, CH2 201.5, C 128.9, CH 166.1, C 23.1, CH3 30.6, CH3 24.9, CH3 18.0, CH3 169.1, C 22.0, CH3 171.7, C 21.2, CH3 172.5, C 21.8, CH3
5.58, d (8.4) 5.35, t (8.4) 2.88, m 2.81, m 2.12 – 2.18, m 5.85, s
1.96, 1.11, 1.12, 1.28,
s s s s
2.04, s 2.01, s 2.05, s
23.4, CH2 31.6, CH2 39.5, C 80.2, C 75.8, CH 76.0, CH 44.0, CH 39.8, CH 43.9, C 38.9, CH2 197.0, C 135.5, C 162.2, C 170.3, C 20.0, CH3 31.1, CH3 24.9, CH3 18.0, CH3 169.1, C 22.0, CH3 171.4, C 21.2, CH3 172.8, C 21.8, CH3 172.5, C 52.9, CH3
5.56, d (8.4) 5.53, t (8.4) 2.89, m 2.83, m 2.14 – 2.20, m
1.91, 1.11, 1.12, 1.28,
s s s s
2.04, s 2.01, s 2.06, s 3.78, s
Spectra were recorded in CD3OD.
column chromatography on silica gel eluted with hexane, chloroform, ethyl acetate, and methanol, respectively. The EtOAc fraction (82.5 g) was subjected to silica gel column chromatography using a petroleum ether – CHCl3 – MeOH gradient (from 80:1 to 10:1) as eluent, to yield four fractions (Frs A –D). Fr. A (9.3 g) was separated over Sephadex LH-20 column to get rid of pigmentum, then the fractions were subjected to octadecylsilyl middlepressure liquid chromatography to yield six fractions (Frs A1 – A6). Fraction A3 (0.5 g) was chromatographed on semipreparative high-performance liquid chro-
matography using MeOH – H2O (62:38) to yield caesalpin I (1) in Rt 18.5 min. Fraction A6 (0.8 g) was chromatographed on semi-preparative HPLC using MeOH – H2O (65:35) to yield caesalpin J (2) in Rt 24.0 min. 3.3.1
Caesalpin I (1)
White amorphous powder; ½a20 D þ 36.3 (c 0.01, MeOH); UV lmax (MeOH) nm (log 1): 205 (3.35) and 288 (2.48); IR (KBr) nmax cm21: 3441, 1746, and 1652; For 1H NMR and 13C APT spectral data (MeOH), see Table 1; HR-ESI-MS m/z:
Journal of Asian Natural Products Research
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473.2166 [M þ Na] þ C24H34O8Na, 473.2151).
(calcd
for
3.3.2 Caesalpin J (2) White amorphous powder; ½a20 D þ 24.8 (c 0.03, MeOH); UV lmax (MeOH) nm (log 1): 210 (3.18) and 285 (2.07); IR (KBr) nmax cm21: 3418, 1738, and 1652; For 1H NMR and 13C APT spectral data (MeOH), see Table 1; HR-ESI-MS m/z: 531.2198 [M þ Na] þ (calcd for C26H36O10Na, 531.2206). Acknowledgments The work was financially supported by the technological large platform for comprehensive research and development of new drugs in the Eleventh Five-Year “Significant New Drugs Created” Science and Technology Major Projects (No. 2009ZX09301-003), the National Natural Science Foundation of China (No. 30973626), Innovation Capacitybuilding in Guangxi Science and Technology Agency (No. 10100027-3), the National Science and Technology Support Program (No. 2012BA127B06), the Guangxi Science and Technology Achievements Transformation Project (No. 1298009-22), and the Scientific and Technological Project in Nanning City (No. 201102088C).
Note 1.
These authors contributed equally to this work.
References [1] S.Z. He, Chin. Tradit. Herb. Drugs 31, 225 (2000). [2] H. Hikino, T. Taguchi, H. Fujimura, and Y. Hiramatsu, Planta Med. 31, 214 (1977).
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[3] R.W. Jiang, P.P.H. But, S.C. Ma, W.C. Ye, S.P. Chan, and T.C.W. Mark, Tetrahedron Lett. 43, 2415 (2002). [4] R.A. Dickson, P.J. Houghton, and P.J. Hylands, Phytochemistry 68, 1436 (2007). [5] D.P. Ashok, J.F. Alan, W. Lee, Z. Gray, R. Rex, and F.B. Mark, Tetrahedron 53, 1583 (1997). [6] Y. Hou, S. Cao, P. Brodie, J.S. Miller, C. Birkinshaw, F. Ratovoson, R. Rakotondrajaona, R. Andriantsiferana, V.E. Rasamison, and D.G.I. Kingston, J. Nat. Prod. 71, 150 (2008). [7] Jiangsu New Medical College, Dictionary of Chinese Traditional Medicine (Shanghai Scientific and Technical Publishing House, Shanghai, 1977), p. 1289. [8] Z.H. Wu, J. Huang, W.D. Li, L.J. Wu, and Y. Gao, J. Asian. Nat. Prod. Res. 12, 781 (2010). [9] G.X. Ma, N. Xu, J.Q. Yuan, H. Wei, Q.X. Zheng, Z.C. Zhao, J.S. Yang, and X.D. Xu, J. Asian. Nat. Prod. Res. 14, 1156 (2012). [10] Z. Peng, H.Q. Chen, H. Wang, J. Xu, M.C. Wang, Y.L. Wang, D.Q. Jin, and Y.Q. Guo, Phytochem Lett. (2013). Available from: www.dx.doi.org/10. 1016/j.phytol.2013.07.013 [11] Y. Matsuno, J. Deguchi, T. Hosoya, Y. Hirasawa, C. Hirobe, M. Shiro, and H. Morita, J. Nat. Prod. 72, 976 (2009). [12] G.X. Ma, X.D. Xu, L. Cao, J.Q. Yuan, J.S. Yang, and L.Y. Ma, Planta Med. 78, 1363 (2012). [13] T. Kinoshita, Y. Haga, S. Narimatsu, M. Shimada, and Y. Goda, Chem. Pharm. Bull. 53, 717 (2005). [14] G.X. Ma, J.Q. Yuan, H.F. Wu, L. Cao, X.P. Zhang, L.J. Xu, H. Wei, L.Z. Wu, Q.X. Zheng, L.Y. Li, L.J. Zhang, J.S. Yang, and X.D. Xu, J. Nat. Prod. 76, 1025 (2013). [15] Z.Y. Yang, Y.H. Yin, and L.H. Hu, Helv. Chim. Acta. 92, 121 (2009). [16] Y. Orapun, K. Chatchanok, P. Chanita, and T. Supinya, Tetrahedron 67, 6838 (2011).
Journal of Asian Natural Products Research Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/ganp20
Two new degradative cassane-type diterpenes isolated from Caesalpinia minax a
a
b
c
Zhao-Cui Sun , Guo-Xu Ma , Jing-Quan Yuan , Hua Wei , Hai-Feng a
a
d
a
Wu , Zhong-Hao Sun , Guo-Hong Wang , Jun-Shan Yang & XuDong Xu
a
a
Key Laboratory of Bioactive Substances and Resources Utilization of Chinese Herbal Medicine, Ministry of Education, Institute of Medicinal Plant Development, Peking Union Medical College and Chinese Academy of Medical Sciences, Beijing, 100193, China b
National Engineering Laboratory of Southwest Endangered Medicinal Resources Development, National Development and Reform Commission, Guangxi Botanical Garden of Medicinal Plant, Nanning, 530023, China c
Institute of Chinese Materia Medica, China Academy of Chinese Medical Sciences, Beijing, 100700, China d
Department of Pharmacy, Shanxi Provincial Hospital of Traditional Chinese Medicine, Taiyuan, 030012, China Published online: 11 Dec 2013.
To cite this article: Zhao-Cui Sun, Guo-Xu Ma, Jing-Quan Yuan, Hua Wei, Hai-Feng Wu, ZhongHao Sun, Guo-Hong Wang, Jun-Shan Yang & Xu-Dong Xu (2014) Two new degradative cassane-type diterpenes isolated from Caesalpinia minax, Journal of Asian Natural Products Research, 16:2, 187-191, DOI: 10.1080/10286020.2013.864282 To link to this article: http://dx.doi.org/10.1080/10286020.2013.864282
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 [Monash University Library] at 16:06 04 December 2014
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, 2014 Vol. 16, No. 2, 187–191, http://dx.doi.org/10.1080/10286020.2013.864282
Two new degradative cassane-type diterpenes isolated from Caesalpinia minax Zhao-Cui Suna1, Guo-Xu Maa1, Jing-Quan Yuanb, Hua Weic, Hai-Feng Wua, Zhong-Hao Suna, Guo-Hong Wangd, Jun-Shan Yanga and Xu-Dong Xua*
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a
Key Laboratory of Bioactive Substances and Resources Utilization of Chinese Herbal Medicine, Ministry of Education, Institute of Medicinal Plant Development, Peking Union Medical College and Chinese Academy of Medical Sciences, Beijing 100193, China; bNational Engineering Laboratory of Southwest Endangered Medicinal Resources Development, National Development and Reform Commission, Guangxi Botanical Garden of Medicinal Plant, Nanning 530023, China; c Institute of Chinese Materia Medica, China Academy of Chinese Medical Sciences, Beijing 100700, China; dDepartment of Pharmacy, Shanxi Provincial Hospital of Traditional Chinese Medicine, Taiyuan 030012, China (Received 26 August 2013; final version received 6 November 2013) Cassane-type diterpenes are main bioactive constituents of Caesalpinia minax HANCE. As a part of our ongoing chemical investigation of C. minax, two new degradative cassane-type diterpenes, named caesalpins I (1) and J (2), were isolated from the EtOAc extract of the seeds of C. minax. The structures were elucidated by means of spectroscopic analysis. Keywords: Fabaceae; cassane-type diterpenes; caesalpin I; caesalpin J
1.
Introduction
The genus Caesalpinia (Fabaceae) contains about 100 species in the world. Many species of this genus are traditional medicinal plants with a wide distribution in the tropical and subtropical regions of southeast Asia [1]. Previous investigations on the genus have shown interesting biological activities such as anti-inflammatory [2], antiviral [3], antibacterial [4], antitumor [5], and antiproliferative [6] effects. The seeds of Caesalpinia minax HANCE, well known as “kushilian” in China, have been used as a traditional folk medicine for the treatment of influenza, fever, and dysentery [7]. Recently, a large number of chemical constituent reports about C. minax showed that cassane-type diterpenes are the main bioactive components [8 –13]. For the presence of such an interesting variety of significant bioactive compounds, we further studied on *Corresponding author. Email: [email protected] q 2013 Taylor & Francis
the EtOAc extract of the seeds of C. minax and isolated two new rare degradative tricylic cassane-type diterpenes, named caesalpins I (1) and J (2) (Figure 1). In this paper, we report the isolation and structural elucidation of the new compounds.
2.
Results and discussion
Compound 1 was obtained as a white amorphous powder with ½a20 D þ 36.3 (c 0.01, MeOH), and its molecular formula C24H34O8 was determined from the quasimolecular ion peak at m/z 473.2166 [M þ Na]þ, deduced by HR-ESI-MS. The IR spectrum showed hydroxyl absorption at 3441 cm21 and a,b-unsaturated carbonyl absorption at 1746 and 1652 cm21 [14]. The 1H NMR spectrum of 1 exhibited four methyl proton signals at dH 1.11 (s, H3-18), 1.12 (s, H3-19), 1.28 (s, H3-20), and 1.96 (s, H3-17). Three acetoxy
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OH 19
OCH3
14
10 5
3
OH 19
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1 17
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1
2
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Figure 1. Structures of compounds 1 and 2.
methyl proton signals at dH 2.01 (s), 2.04 (s), and 2.05 (s) indicated the presence of three acetoxy substituents. An olefinic proton signal evident at dH 5.85 (1H, s, H13) revealed the presence of a double bond. The 13C APT spectrum of compound 1 showed the presence of 24 carbons, including four methyl carbon signals at dC 18.0, 23.1, 30.6, and 24.9; three acetyl methyl carbon signals at dC 22.0, 21.2, and 21.8; three methylene carbon signals at dC 23.4 (C-2), 33.6 (C-3), and 37.4 (C-11); five methine carbon signals at dC 75.1 (C1), 75.4 (C-6), 75.9 (C-7), 43.9 (C-8), and 40.5 (C-9); three quaternary carbon signals at dC 38.9 (C-4), 79.3 (C-5), and 44.0 (C10); two olefinic carbon signals at dC 128.9 (C-13) and 166.1 (C-14) and four carbonyl signals at dC 169.1, 171.7, 172.5, and 201.5. The above-mentioned data indicated that compound 1 was a rare tricyclic cassane-type diterpene with a conjugated unsaturated carbonyl moiety, that, together with the molecular formula, suggested that C-15 and C-16 were degraded in the structure [15,16]. All the carbon-bonded
protons were assigned from the HSQC spectrum. In the HMBC spectrum (Figure 2), the correlations of H3-OAc ( dH 2.04) with C-1 ( dC 75.1) and ZOCOCH3 ( dC 169.1), H3-OAc (dH 2.01) with C-6 (dC 75.4) and ZOCOCH3 (dC 171.7), and H3-OAc (dH 2.05) with C-7 (dC 75.9) and ZOCOCH3 (dC 172.5) suggested that the acetoxy groups were located at C-1, C-6, and C-7. Similarly, the HMBC correlations between H3-17 (dH 1.96, s) and C-8 (dC 43.9), C-13 (dC 128.9), and C-14 (dC 166.1); H-13 (dH 5.85, s) and C-12 (dC 201.5) and C-14 (dC 166.1) confirmed the a,b-unsaturated carbonyl moiety at C-12, C-13, and C-14. The relative configuration of compound 1 was determined by the analysis of coupling constants and NOESY spectrum. The oxymethine proton signal at dH 4.78 (H-1) had a triplet with a small coupling constant (J ¼ 2.4 Hz) to both protons on C-2 and the cross-peaks with H3-20 (dH 1.28) indicated that the acetoxy substituent at C-1 to be a-oriented. The NOEs from H6 (dH 5.58) to H3-20 (dH 1.28) and H-7 (dH
O
O
H3COCO
O
H3COCO
OH
OCH3
OCOCH3 OCOCH3
Figure 2. Key HMBC correlations of compounds 1 and 2.
OCOCH3 OH OCOCH3
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5.35) to H-9 (dH 2.81) suggested that H-6 was b-oriented and H-7 was a-oriented. The 3J coupling constant (8.4 Hz) also supported the antiperiplanar relationship between H-6 and H-7. There, the structure of compound 1 was assigned as 1a,6a,7btriacetoxy-5a-hydroxy-12-oxocassa-13 (14)-diene and named caesalpin I. This degradative cassane-type diterpene was isolated for the first time in the genus Caesalpinia. Compound 2 was also obtained as a white amorphous white powder with ½a20 D þ 24.8 (c 0.03, MeOH) and its molecular formula C 26H 36O 10 was assigned from the quasi-molecular ion peak at m/z 531.2198 [M þ Na]þ in the positive-ion mode deduced by HR-ESIMS. The IR spectrum showed hydroxyl absorption at 3418 cm21 and a,b-unsaturated carbonyl absorption at 1738 and 1652 cm21. The NMR data for this compound were similar to those of 1, except for the absence of one olefinic proton signal and the presence of an additional methoxycarbonyl group. In the HMBC spectrum (Figure 2), the correlations of ZOCH3 (dH 3.78) with quaternary carbon C-13 (dC 135.5) and ZOCOCH3 (dC 170.3); H3-17 (dH 1.91) with C-13 (dC 135.5) and C-14 (dC 162.2) suggested that the carboxymethyl group was attached to C-13. The similar NOE spectra of 1 and 2 indicated that their relative configurations were identical. Thus, the structure of compound 2 was established as 1a,6a,7b-triacetoxy-5ahydro-xy-12-oxocassa-13-carboxymethyl13(14)-diene and named caesalpin J.
NMR spectra were obtained with a Bruker AV III 600 NMR spectrometer (chemical shift values are presented as d values with TMS as the internal standard) (Bruker, Billerica, German). HR-ESI-MS were performed on a LTQ-Obitrap XL spectrometer (Thermo Fisher Scientific, Boston, MA, USA). HPLC was carried out on a Lumian K-1001 liquid chromatography (Knauer Ltd, Germany) equipped with a UV/vis K-2501 detector, at a rate of 2 ml/ min and monitored at 210 nm for the semipreparation. C18 reversed-phase silica gel (40 – 63 mm, Merck, Darmstadt, Germany), Sephadex LH-20 (Pharmacia, Uppsala, Sweden), MCI gel (CHP 20P, 75 –150 mm, Mitsubishi Chemical Corporation, Tokyo, Japan), and silica gel (100 – 200 and 300– 400 mesh, Qingdao Marine Chemical plant, Qingdao, China) were used for column chromatography. And precoated silica gel GF254 plates (Zhi Fu Huang Wu Pilot Plant of Silica Gel Development, Yantai, China) were used for TLC. All solvents used were of analytical grade (Beijing Chemical Works, Beijing, China).
3. Experimental 3.1 General experimental procedures
3.3
Optical rotations were obtained on a PerkinElmer 341 digital polarimeter (PerkinElmer, Norwalk, CT, USA). UV and IR spectra were recorded on Shimadzu UV2550 and FTIR-8400S spectrometer (Shimadzu, Kyoto, Japan), respectively.
3.2 Plant material The seeds of C. minax were collected in September 2008 from Nanning, Guangxi Province, China, and identified by Prof. Jing-Quan Yuan, Department of Pharmaceutical Chemistry, Guangxi Botanical Garden of Medicinal Plant. A voucher specimen (No. 21648) was deposited at the Guangxi Botanical Garden of Medicinal Plant. Extraction and isolation
The air-dried and powdered seeds of C. minax (8.0 kg), collected from Nanning district in Guangxi province of China, were extracted three times with methanol. Removal of the methanol under reduced pressure yielded a methanol extract (2020 g). The residue was subjected to
190 Table 1.
Z.-C. Sun et al. 1
H (600 MHz) and 13C (150 MHz) NMR spectral data for compounds 1 and 2. 1a
Position 1 2
dC, type
dH (J in Hz)
dC, type
dH (J in Hz)
75.1, CH 23.4, CH2
4.78, t (2.4) 1.73 – 1.76, m 1.85 – 1.90, m 1.14 – 1.15, m 1.71 – 1.76, m
75.1, CH
4.78, t (2.4) 1.77 – 1.79, m 1.82 – 1.84, m 1.05 – 1.08, m 1.71 – 1.76, m
33.6, CH2
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3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 1-OCOCH3 1-OCOC H3 6-OCOCH3 6-OCOC H3 7-OCOCH3 7-OCOC H3 16-OCOCH3 16-OCOCH3 a
2a
38.9, C 79.3, C 75.4, CH 75.9, CH 43.9, CH 40.5, CH 44.0, C 37.4, CH2 201.5, C 128.9, CH 166.1, C 23.1, CH3 30.6, CH3 24.9, CH3 18.0, CH3 169.1, C 22.0, CH3 171.7, C 21.2, CH3 172.5, C 21.8, CH3
5.58, d (8.4) 5.35, t (8.4) 2.88, m 2.81, m 2.12 – 2.18, m 5.85, s
1.96, 1.11, 1.12, 1.28,
s s s s
2.04, s 2.01, s 2.05, s
23.4, CH2 31.6, CH2 39.5, C 80.2, C 75.8, CH 76.0, CH 44.0, CH 39.8, CH 43.9, C 38.9, CH2 197.0, C 135.5, C 162.2, C 170.3, C 20.0, CH3 31.1, CH3 24.9, CH3 18.0, CH3 169.1, C 22.0, CH3 171.4, C 21.2, CH3 172.8, C 21.8, CH3 172.5, C 52.9, CH3
5.56, d (8.4) 5.53, t (8.4) 2.89, m 2.83, m 2.14 – 2.20, m
1.91, 1.11, 1.12, 1.28,
s s s s
2.04, s 2.01, s 2.06, s 3.78, s
Spectra were recorded in CD3OD.
column chromatography on silica gel eluted with hexane, chloroform, ethyl acetate, and methanol, respectively. The EtOAc fraction (82.5 g) was subjected to silica gel column chromatography using a petroleum ether – CHCl3 – MeOH gradient (from 80:1 to 10:1) as eluent, to yield four fractions (Frs A –D). Fr. A (9.3 g) was separated over Sephadex LH-20 column to get rid of pigmentum, then the fractions were subjected to octadecylsilyl middlepressure liquid chromatography to yield six fractions (Frs A1 – A6). Fraction A3 (0.5 g) was chromatographed on semipreparative high-performance liquid chro-
matography using MeOH – H2O (62:38) to yield caesalpin I (1) in Rt 18.5 min. Fraction A6 (0.8 g) was chromatographed on semi-preparative HPLC using MeOH – H2O (65:35) to yield caesalpin J (2) in Rt 24.0 min. 3.3.1
Caesalpin I (1)
White amorphous powder; ½a20 D þ 36.3 (c 0.01, MeOH); UV lmax (MeOH) nm (log 1): 205 (3.35) and 288 (2.48); IR (KBr) nmax cm21: 3441, 1746, and 1652; For 1H NMR and 13C APT spectral data (MeOH), see Table 1; HR-ESI-MS m/z:
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473.2166 [M þ Na] þ C24H34O8Na, 473.2151).
(calcd
for
3.3.2 Caesalpin J (2) White amorphous powder; ½a20 D þ 24.8 (c 0.03, MeOH); UV lmax (MeOH) nm (log 1): 210 (3.18) and 285 (2.07); IR (KBr) nmax cm21: 3418, 1738, and 1652; For 1H NMR and 13C APT spectral data (MeOH), see Table 1; HR-ESI-MS m/z: 531.2198 [M þ Na] þ (calcd for C26H36O10Na, 531.2206). Acknowledgments The work was financially supported by the technological large platform for comprehensive research and development of new drugs in the Eleventh Five-Year “Significant New Drugs Created” Science and Technology Major Projects (No. 2009ZX09301-003), the National Natural Science Foundation of China (No. 30973626), Innovation Capacitybuilding in Guangxi Science and Technology Agency (No. 10100027-3), the National Science and Technology Support Program (No. 2012BA127B06), the Guangxi Science and Technology Achievements Transformation Project (No. 1298009-22), and the Scientific and Technological Project in Nanning City (No. 201102088C).
Note 1.
These authors contributed equally to this work.
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