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Two new bromoindoles from red alga Laurencia similis
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Chinese Chemical Letters 20 (2009) 456–458 www.elsevier.com/locate/cclet
Two new bromoindoles from red alga Laurencia similis Hua Su a,b, Zhao Hui Yuan a, Jing Li a,b, Shu Ju Guo a,b, Li Ping Deng a,b, Li Jun Han a, Xiao Bin Zhu a,*, Da Yong Shi a,* a
Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China Graduate School of the Chinese Academy of Sciences, Beijing 100049, China
b
Received 2 September 2008
Abstract Two new bromoindole alkaloids have been isolated from the ethanolic extract of the red alga Laurencia similis. On the basis of chemical and spectroscopic methods (including 1D and 2D NMR technique), their structures have been elucidated as 2,20 ,5,50 ,6,60 sixibromo-3, 30 -bi-1H-indole and 3, 5-dibromo-1-methylindole, respectively. # 2008 Xiao Bin Zhu. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. Keywords: Laurencia similis; Bromoindole alkaloid; 2,20 ,5,50 ,6,60 -Sixibromo-3,30 -bi-1H-indole; 3,5-Dibromo-1-methylindole
The genus Laurencia (order Ceramiales, family Rhodomelaceae) has been a favorite for chemical investigation since the 1960s. Numerous metabolites have been reported, the most abundant being sesquiterpenes followed by nonterpenoid C15 acetogenins and diterpenes [1–4]. Many of them are halogenated and are distinctive to the genus. Of the more than thirty species of Laurencia that have been studied so far, Laurencia similes is exceptional in that the usual metabolites are missing and that they contain instead polybromoindoles [5]. The typical example are 1-methyl-2, 3, 5, 6-tetrabromoindole and 2, 3, 5, 6-tetrabromoindole, isolated from Borneo, Malaysia, collection [5]. As part of our search for bioactive substances from marine organisms systematically and assess the chemical and biological diversities of seaweeds distributed along Chinese coast, the red alga Laurencia similes was collected from Sanya Bay, Hainan Province. Chemical investigation of this alga lead to isolation and structure elucidation of two new bromoindole alkaloids: 2, 20 , 5, 50 , 6, 60 -sixibromo-3, 30 -bi-1H-indole 1 and 3, 5-dibromo-1-methylindole 2. The air-dried alga L. similis (1.1 kg) was powdered and extracted with 95% EtOH at room temperature. The resulting extractive solution was filtered and evaporated under reduced pressure (<45 8C) to yield a dark residue (34.2 g), and then partitioned between H2O and EtOAc. The EtOAc phase (28.5 g) was subjected to column chromatography (CC) over silica gel eluting with a gradient of increasing EtOAc in petroleum ether (PE, 0–100%) to give 6 fractions on the basis of TLC analysis. Fraction V (0.6 g) eluted by 25% EtOAc in PE was decolored by column chromatography over Sephadex LH-20 eluting with PE-CHCl3-MeOH (5:5:1) to give the decolored fraction (0.3 g). The subsequent fraction was further separated by CC over silica gel by using PE-acetone (15:1) as eluent to afford Compound 1 (6 mg), and the sub-fraction that eluted with PE-CHCl3-MeOH (5:5:1) was purified by Sephadex LH-20 to yield Compound 2 (3 mg).
* Corresponding authors. E-mail addresses: [email protected] (X.B. Zhu), [email protected] (D.Y. Shi). 1001-8417/$ – see front matter # 2008 Xiao Bin Zhu. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. doi:10.1016/j.cclet.2008.12.016
H. Su et al. / Chinese Chemical Letters 20 (2009) 456–458
457
Table 1 1 H and 13C NMR data of 1 and 2, at 500 and 125 MHz, respectively, in CDCl3. No.
1
2 dC
dH 2 3 3a 4 5 6 7 7a NH MeN
112.1 107.9 128.7 123.6 116.4 118.3 115.4 135.7
7.57 (s)
7.70 (s)
(s) (s) (s) (d) (s) (s) (d) (s)
dH
dC
7.07 (s)
128.8 (d) 88.7 (s) 128.8 (s) 122.0 (d) 113.8 (s) 125.6 (d) 111.0 (d) 135.0 (s)
7.69 (d, J = 1.8) 7.34 (dd, J = 1.8, 8.7) 7.17 (d, J = 8.7)
8.45 (br. s) 3.76 (s) 1
33.2 (q)
1
Assignments were corroborated by H, H-COSY, HMQC, and HMBC experiments.
Fig. 1. The structures and Key HMBC correlations of Compounds 1 and 2.
Compound 1 was obtained as amorphous powder. Low-resolution EI mass spectrum exhibited a molecular ion cluster at m/z 709/707/705/703/701 with an intensity ratio of 28:73:100:77:30, indicating that 1 was polyhalogenated. Furthermore, two fragments quasi-molecular ion peaks were also found in the EIMS at m/z 626 [M-Br]+ and 226 [M-6Br]+. The molecular formula C16H6N279Br381Br3 was deduced from the HREIMS at m/z 705.5561 [M]+ (calcd. for 705.5570). Both the 1H and 13C NMR spectra contained only half the number of signals expected from the molecular formula, which together with the molecular formula suggest that 1 was a symmetrical dimer. The 1H NMR spectrum displayed three signals including one exchangeable broad singlet at d 8.45 (1H, NH-1), two aromatic proton signals at d 7.57 (1H, H-4) and 7.70 (1H, H-7). The 13C NMR and DEPT spectrum showed eight carbon signals including six quaternary carbons, two CH groups (Table 1). Detailed comparison with the reported NMR data of the known compound 2, 3, 5, 6-tetrabromo-1H-indole [6,7] suggested that 1 possessed a tribromoindole skeleton. These data revealed that 1 was a biindole with a symmetrical substitution pattern of six bromine atoms group. After the NMR signals of protons and corresponding carbons were assigned unambiguously from HSQC, the key HMBC correlations (Fig. 1) from H-4 to C-5, C-6 and C-7a, from H-7 to C-5, C-6 and C-3a, respectively, confirmed that Compound 1 corresponds to 2, 20 , 5, 50 , 6, 60 -sixibromo-3, 30 -bi-1H-indole. Compound 2 was obtained as a colorless crystal mixture with 3, 5, 6-tribromo-1-methyl-1H-indole (ratio ca.1:3, based on NMR-signal intensities). They displayed one spot on TLC, and attempts to separate these two compounds by different column-chromatography steps as well as by prep. TLC with different solvent systems failed. Fortunately, 3,5,6-tribromo-1-methyl-1H-indole could be distinguished by the NMR-signal intensities. Aided by 2D NMR (1H-1HCOSY, HMQC and HMBC) and MS analysis, the structure of 2 could be established as 3, 5-dibromo-1methylindole. Structural confirmation of 3, 5, 6-tribromo-1-methyl-1H-indole was readily achieved by the analysis of their NMR and MS data and by comparison with this reported in [7]. The low-resolution EI-MS exhibited a characteristic molecular-ion cluster at m/z 291/289/287 in a ratio of 1:2:1, indicating two Br-atoms. The molecular
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H. Su et al. / Chinese Chemical Letters 20 (2009) 456–458
formula was deduced as C9H7Br2N by positive HRFABMS (m/z 288.8940 [M]+, C9H779Br81BrN; calcd.288.8925). The 13CNMR with DEPT spectrum of 2 (Table 1) showed the presence of nine C-atoms, with one Me and four CH groups, as well as four quaternary C-atoms. The 1H NMR spectrum (Table 1) exhibited four aromatic proton singnals at d: 7.69 (d, 1H, J = 1.8 Hz, H-4), 7.34 (dd, 1H, J = 1.8, 8.7 Hz, H-6), 7.17 (d, 1H, J = 8.7 Hz, H-7), 7.07(1H, s, H-2) and one Me at d: 3.76 (3H, s, H3-8). Detailed comparison of the spectroscopic data of 2 with 1-methyl-2, 3, 5-tribromoindole [7] and 3, 5-dibromoindole [8] suggested that 2 was an N-methylated bibromoindole. The 2D NMR experiments (mainly including HMQC and HMBC) together with the four singnals at d(H) 7.69 (H-C(4)), 7.34 (H-C(6)), 7.17 (H-C(7)) and 7.07 (H-C(2)) confirmed that Br-atoms were attached to C(3) and C(5), respectively. The HMBC plot displayed cross-peaks (Fig. 1), including from H-4 to C-6 and C-7a, from H-6 to C-7a, from H-7 to C-5 and C-3a, and from Me-N(1) to C-2 and C-7a (Fig. 1), respectively. Therefore, the structure of Compound 2 was determined as 3, 5-dibromo-1-methylindole. Acknowledgments This work was financially supported by NSFC (No. 30530080), National 863 project (No. 2007AA09Z410, No. 2006AA06Z362, 2007AA091604), National Science & Technology Pillar Program (No. 2006BAB03A12) and key Innovative Project of the Academy (No. KZCX2-YW-209). References [1] [2] [3] [4] [5] [6] [7] [8]
S.N. Ayyad, J. Jakupovic, M. Abdel-Mogib, Phytochemistry 36 (1994) 1077. M. Suzuki, M. Daitoh, C.S. Vairappan, et al. J. Nat. Prod. 64 (2001) 597. D. Iliopoulou, V. Roussis, C. Pannecouque, et al. Tetrahedron 58 (2002) 6749. C.S. Vairappan, M. Suzuki, T. Ave, et al. Phytochemistry 58 (2001) 517. M. Masuda, S. Kawaguchi, Y. Takahashi, et al. Botanica Marina 42 (1999) 199. G.T. Carter, K.L. Rinehart Jr., L.H. Li, et al. Tetrahedr. Lett. 19 (1978) 4479. N.Y. Ji, X.M. Li, L.P. Ding, Helv. Chim. Acta 90 (2007) 385. B. Hugon, F. Anizon, C. Bailly, et al. Bioorg. Med. Chem. 15 (2007) 5965.
Chinese Chemical Letters 20 (2009) 456–458 www.elsevier.com/locate/cclet
Two new bromoindoles from red alga Laurencia similis Hua Su a,b, Zhao Hui Yuan a, Jing Li a,b, Shu Ju Guo a,b, Li Ping Deng a,b, Li Jun Han a, Xiao Bin Zhu a,*, Da Yong Shi a,* a
Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China Graduate School of the Chinese Academy of Sciences, Beijing 100049, China
b
Received 2 September 2008
Abstract Two new bromoindole alkaloids have been isolated from the ethanolic extract of the red alga Laurencia similis. On the basis of chemical and spectroscopic methods (including 1D and 2D NMR technique), their structures have been elucidated as 2,20 ,5,50 ,6,60 sixibromo-3, 30 -bi-1H-indole and 3, 5-dibromo-1-methylindole, respectively. # 2008 Xiao Bin Zhu. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. Keywords: Laurencia similis; Bromoindole alkaloid; 2,20 ,5,50 ,6,60 -Sixibromo-3,30 -bi-1H-indole; 3,5-Dibromo-1-methylindole
The genus Laurencia (order Ceramiales, family Rhodomelaceae) has been a favorite for chemical investigation since the 1960s. Numerous metabolites have been reported, the most abundant being sesquiterpenes followed by nonterpenoid C15 acetogenins and diterpenes [1–4]. Many of them are halogenated and are distinctive to the genus. Of the more than thirty species of Laurencia that have been studied so far, Laurencia similes is exceptional in that the usual metabolites are missing and that they contain instead polybromoindoles [5]. The typical example are 1-methyl-2, 3, 5, 6-tetrabromoindole and 2, 3, 5, 6-tetrabromoindole, isolated from Borneo, Malaysia, collection [5]. As part of our search for bioactive substances from marine organisms systematically and assess the chemical and biological diversities of seaweeds distributed along Chinese coast, the red alga Laurencia similes was collected from Sanya Bay, Hainan Province. Chemical investigation of this alga lead to isolation and structure elucidation of two new bromoindole alkaloids: 2, 20 , 5, 50 , 6, 60 -sixibromo-3, 30 -bi-1H-indole 1 and 3, 5-dibromo-1-methylindole 2. The air-dried alga L. similis (1.1 kg) was powdered and extracted with 95% EtOH at room temperature. The resulting extractive solution was filtered and evaporated under reduced pressure (<45 8C) to yield a dark residue (34.2 g), and then partitioned between H2O and EtOAc. The EtOAc phase (28.5 g) was subjected to column chromatography (CC) over silica gel eluting with a gradient of increasing EtOAc in petroleum ether (PE, 0–100%) to give 6 fractions on the basis of TLC analysis. Fraction V (0.6 g) eluted by 25% EtOAc in PE was decolored by column chromatography over Sephadex LH-20 eluting with PE-CHCl3-MeOH (5:5:1) to give the decolored fraction (0.3 g). The subsequent fraction was further separated by CC over silica gel by using PE-acetone (15:1) as eluent to afford Compound 1 (6 mg), and the sub-fraction that eluted with PE-CHCl3-MeOH (5:5:1) was purified by Sephadex LH-20 to yield Compound 2 (3 mg).
* Corresponding authors. E-mail addresses: [email protected] (X.B. Zhu), [email protected] (D.Y. Shi). 1001-8417/$ – see front matter # 2008 Xiao Bin Zhu. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. doi:10.1016/j.cclet.2008.12.016
H. Su et al. / Chinese Chemical Letters 20 (2009) 456–458
457
Table 1 1 H and 13C NMR data of 1 and 2, at 500 and 125 MHz, respectively, in CDCl3. No.
1
2 dC
dH 2 3 3a 4 5 6 7 7a NH MeN
112.1 107.9 128.7 123.6 116.4 118.3 115.4 135.7
7.57 (s)
7.70 (s)
(s) (s) (s) (d) (s) (s) (d) (s)
dH
dC
7.07 (s)
128.8 (d) 88.7 (s) 128.8 (s) 122.0 (d) 113.8 (s) 125.6 (d) 111.0 (d) 135.0 (s)
7.69 (d, J = 1.8) 7.34 (dd, J = 1.8, 8.7) 7.17 (d, J = 8.7)
8.45 (br. s) 3.76 (s) 1
33.2 (q)
1
Assignments were corroborated by H, H-COSY, HMQC, and HMBC experiments.
Fig. 1. The structures and Key HMBC correlations of Compounds 1 and 2.
Compound 1 was obtained as amorphous powder. Low-resolution EI mass spectrum exhibited a molecular ion cluster at m/z 709/707/705/703/701 with an intensity ratio of 28:73:100:77:30, indicating that 1 was polyhalogenated. Furthermore, two fragments quasi-molecular ion peaks were also found in the EIMS at m/z 626 [M-Br]+ and 226 [M-6Br]+. The molecular formula C16H6N279Br381Br3 was deduced from the HREIMS at m/z 705.5561 [M]+ (calcd. for 705.5570). Both the 1H and 13C NMR spectra contained only half the number of signals expected from the molecular formula, which together with the molecular formula suggest that 1 was a symmetrical dimer. The 1H NMR spectrum displayed three signals including one exchangeable broad singlet at d 8.45 (1H, NH-1), two aromatic proton signals at d 7.57 (1H, H-4) and 7.70 (1H, H-7). The 13C NMR and DEPT spectrum showed eight carbon signals including six quaternary carbons, two CH groups (Table 1). Detailed comparison with the reported NMR data of the known compound 2, 3, 5, 6-tetrabromo-1H-indole [6,7] suggested that 1 possessed a tribromoindole skeleton. These data revealed that 1 was a biindole with a symmetrical substitution pattern of six bromine atoms group. After the NMR signals of protons and corresponding carbons were assigned unambiguously from HSQC, the key HMBC correlations (Fig. 1) from H-4 to C-5, C-6 and C-7a, from H-7 to C-5, C-6 and C-3a, respectively, confirmed that Compound 1 corresponds to 2, 20 , 5, 50 , 6, 60 -sixibromo-3, 30 -bi-1H-indole. Compound 2 was obtained as a colorless crystal mixture with 3, 5, 6-tribromo-1-methyl-1H-indole (ratio ca.1:3, based on NMR-signal intensities). They displayed one spot on TLC, and attempts to separate these two compounds by different column-chromatography steps as well as by prep. TLC with different solvent systems failed. Fortunately, 3,5,6-tribromo-1-methyl-1H-indole could be distinguished by the NMR-signal intensities. Aided by 2D NMR (1H-1HCOSY, HMQC and HMBC) and MS analysis, the structure of 2 could be established as 3, 5-dibromo-1methylindole. Structural confirmation of 3, 5, 6-tribromo-1-methyl-1H-indole was readily achieved by the analysis of their NMR and MS data and by comparison with this reported in [7]. The low-resolution EI-MS exhibited a characteristic molecular-ion cluster at m/z 291/289/287 in a ratio of 1:2:1, indicating two Br-atoms. The molecular
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H. Su et al. / Chinese Chemical Letters 20 (2009) 456–458
formula was deduced as C9H7Br2N by positive HRFABMS (m/z 288.8940 [M]+, C9H779Br81BrN; calcd.288.8925). The 13CNMR with DEPT spectrum of 2 (Table 1) showed the presence of nine C-atoms, with one Me and four CH groups, as well as four quaternary C-atoms. The 1H NMR spectrum (Table 1) exhibited four aromatic proton singnals at d: 7.69 (d, 1H, J = 1.8 Hz, H-4), 7.34 (dd, 1H, J = 1.8, 8.7 Hz, H-6), 7.17 (d, 1H, J = 8.7 Hz, H-7), 7.07(1H, s, H-2) and one Me at d: 3.76 (3H, s, H3-8). Detailed comparison of the spectroscopic data of 2 with 1-methyl-2, 3, 5-tribromoindole [7] and 3, 5-dibromoindole [8] suggested that 2 was an N-methylated bibromoindole. The 2D NMR experiments (mainly including HMQC and HMBC) together with the four singnals at d(H) 7.69 (H-C(4)), 7.34 (H-C(6)), 7.17 (H-C(7)) and 7.07 (H-C(2)) confirmed that Br-atoms were attached to C(3) and C(5), respectively. The HMBC plot displayed cross-peaks (Fig. 1), including from H-4 to C-6 and C-7a, from H-6 to C-7a, from H-7 to C-5 and C-3a, and from Me-N(1) to C-2 and C-7a (Fig. 1), respectively. Therefore, the structure of Compound 2 was determined as 3, 5-dibromo-1-methylindole. Acknowledgments This work was financially supported by NSFC (No. 30530080), National 863 project (No. 2007AA09Z410, No. 2006AA06Z362, 2007AA091604), National Science & Technology Pillar Program (No. 2006BAB03A12) and key Innovative Project of the Academy (No. KZCX2-YW-209). References [1] [2] [3] [4] [5] [6] [7] [8]
S.N. Ayyad, J. Jakupovic, M. Abdel-Mogib, Phytochemistry 36 (1994) 1077. M. Suzuki, M. Daitoh, C.S. Vairappan, et al. J. Nat. Prod. 64 (2001) 597. D. Iliopoulou, V. Roussis, C. Pannecouque, et al. Tetrahedron 58 (2002) 6749. C.S. Vairappan, M. Suzuki, T. Ave, et al. Phytochemistry 58 (2001) 517. M. Masuda, S. Kawaguchi, Y. Takahashi, et al. Botanica Marina 42 (1999) 199. G.T. Carter, K.L. Rinehart Jr., L.H. Li, et al. Tetrahedr. Lett. 19 (1978) 4479. N.Y. Ji, X.M. Li, L.P. Ding, Helv. Chim. Acta 90 (2007) 385. B. Hugon, F. Anizon, C. Bailly, et al. Bioorg. Med. Chem. 15 (2007) 5965.