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Two new secoiridoid glucosides from Syringa velutina Kom.
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Chinese Chemical Letters 20 (2009) 702–705 www.elsevier.com/locate/cclet
Two new secoiridoid glucosides from Syringa velutina Kom. Xue Song Feng a,b,**, Yang Qu a, Zhao Hua Wu c, Lei Xu a, Dong Song Zhang a, Hui Yuan Gao a, Li Jun Wu a,* a
School of Traditional Chinese Medicines, Shenyang Pharmaceutical University, Shenyang 110016, China b School of Pharmaceutical Sciences, China Medical University, Shenyang 110001, China c Pharmacy Department, Mudanjiang Medical University, Mudanjiang 157011, China Received 10 November 2008
Abstract Chemical investigation of Syringa velutina Kom. led to the isolation of two new secoiridoid glucosides. Their structures were identified as 60 -O-(6, 7-dihyrofoliamenthoyl)-8-epi-kingisidic acid (syrveoside A, 1) and 60 -O-menthiafoloyl-8-epi-kingisidic acid (syrveoside B, 2) on the basis of chemical and physicochemical evidence. # 2009 Published by Elsevier B.V. on behalf of Chinese Chemical Society. Keywords: Syringa velutina Kom.; Secoiridoid glucosides; Syrveoside A; Syrveoside B
Syringa (S.) velutina Kom. has been widely cultivated in the northern parts of China and Korea. The leaf, flower bud, and bark of this plant have been used in traditional Chinese medicine to treat infectious fevers, counteract inflammations, dampness and acute icteric hepatitis for many centuries [1]. Previous phytochemistry study on the S. velutina led to the isolation of lignans, iridoid glucosides, phenyl propanoids, and so on [2,3]. For the purpose to find much more bioactive agents, the study on chemical constituents of S. velutina was carried out, and two new seoiridoid glucosides esterified with a liner monoterpenoid acid (compounds 1 and 2) along with four known lignans were obtained. In this paper, the isolation and structural elucidation of two new compounds were reported. The leaves of S. velutina Kom. were collected in Xinmin, Liaoning Province, China in May 2005 and identified by Prof. Qi Shi Sun (School of Traditional Chinese Medicine, Shenyang Pharmaceutical University). A voucher specimen (No. 20050517) was deposited in the Herbarium of Section of medicinal plants of Shenyang Pharmaceutical University. The air-dried material (5 kg) was extracted with 70% ethanol (20 L) at room temperature for 2 weeks. The extract was concentrated under reduced pressure to afford an extraction (1560 g, 31.2%), which was suspended in water and subjected to D101 macroporous resins with ethanol–water to elute. A part of the 30% ethanol–water soluble fraction (300 g) was subjected to silica gel column chromatography and semi-prep. HPLC to furnish compounds 1 (11.7 mg, 0.0002%) and 2 (10.5 mg, 0.0002%), respectively.
* Corresponding author at: School of Traditional Chinese Medicines, Shenyang Pharmaceutical University, Shenyang 110016, China. ** Corresponding author at: School of Pharmaceutical Sciences, China Medical University, Shenyang 110001, China. E-mail addresses: [email protected] (X.S. Feng), [email protected] (L.J. Wu). 1001-8417/$ – see front matter # 2009 Published by Elsevier B.V. on behalf of Chinese Chemical Society. doi:10.1016/j.cclet.2009.02.012
X.S. Feng et al. / Chinese Chemical Letters 20 (2009) 702–705
703
Table 1 13 C NMR (150 MHz), 1H NMR (600 MHz) and DEPT (150 MHz) spectral data of compound 1 and 2 (in DMSO-d6, d ppm, J Hz). Position
1
2
dC
DEPT
dH
dC
DEPT
dH
95.4 152.1 108.6 27.1 33.6
CH CH C CH CH2
5.17 (d, 1H, J = 7.8 Hz) 7.45 (s, 1H)
95.5 152.4 108.3 27.1 33.6
CH CH C CH CH2
5.21 (d, 1H, J = 7.8 Hz) 7.48 (s, 1H)
7 8 9 10 11
171.5 73.6 40.6 21.0 167.4
C CH CH CH3 C
171.5 73.6 40.1 21.0 167.3
C CH CH CH3 C
Glucose 10 20 30 40 50 60
99.9 74.0 76.3 70.0 73.1 62.9
CH CH CH CH CH CH2
99.9 74.0 76.2 70.0 73.1 62.9
CH CH CH CH CH CH2
167.1 126.9 142.9 23.2 40.6 71.3 145.8 111.4
C C CH CH2 CH2 C CH CH2
12.1 27.8
CH3 CH3
Iridoid group 1 3 4 5 6
Monoterpene terpene 167.0 100 127.0 200 300 142.6 400 25.7 500 35.4 29.0 600 700 40.0 800 58.8 900 1000
12.1 19.4
2.85 (m, 1H) 2.67 (dd, 1H, J = 15.9, 3.9 Hz) 2.28 (dd, 1H, J = 15.9, 11.9 Hz) 4.16 (m, 1H) 2.02 (m, 1H) 1.34 (d, 3H, J = 6.3 Hz)
4.55 (d, 1H, J = 7.8 Hz) 3.38 (m, 1H) 3.15 (m, 1H) 3.14 (m, 1H) 2.99 (m, 1H) 4.41 (d, 1H, J = 11.0 Hz) 4.13 (dd, 1H, J = 11.0, 6.1 Hz)
C C CH CH2 CH2 CH CH2 CH2
6.64 2.11 1.19 1.52 1.24 3.33
CH3 CH3
1.74 (s, 3H) 0.84 (d, 3H, J = 6.5 Hz)
(t, 1H, J = 7.0 Hz) (m, 2H) (m, 1H) 1.35 (m, 1H) (m, 1H) (m, 1H) 1.41 (m, 1H) (m, 2H)
2.86 (m, 1H) 2.67 (dd, 1H, J = 16.0, 4.0 Hz) 2.29 (dd, 1H, J = 16.0, 11.8 Hz) 4.19 (m, 1H) 2.03 (m, 1H) 1.34 (d, 3H, J = 6.2 Hz)
4.56 (d, 1H, J = 7.9 Hz) 3.42 (t, 1H, J = 7.0 Hz) 3.19 (t, 1H, J = 8.8 Hz) 3.14 (m, 1H) 3.00 (m, 1H) 4.41 (d, 1H, J = 11.0 Hz) 4.13 (dd, 1H, J = 11.0, 6.0 Hz)
6.66 (t, 1H, J = 7.6 Hz) 2.14 (m, 1H) 2.07 (m, 1H) 1.46 (m, 2H) 5.84 5.14 4.95 1.71 1.14
(dd, 1H, J = 17.0, 10.6 Hz) (dd, 1H, J = 17.0, 0.6 Hz) (br.d, 1H, J = 10.6 Hz) (s, 3H) (s, 3H)
Compound 1 was obtained as white amorphous powder (MeOH) with a negative optical rotation (½a23 D 35.9 (c 0.08, MeOH)). Its molecular formula was established as C26H38O13 by HR-ESI-MS m/z 581.2204 [M+Na]+ (calcd. for C26H38O13Na, 581.2205). The IR spectrum showed absorption bands at 3377, 1707 (broad band), 1641 cm1 due to hydroxyl, unsaturated carbonyl, a, b-unsaturated ester, and lactone functions. Its 1H NMR spectrum (Table 1) showed signals assignable to three methyls [dH 0.84 (d, 3H, J = 6.5 Hz), 1.34 (d, 3H, J = 6.3 Hz), 1.74 (s, 3H)], two olefinic protons [dH 7.45 (s, 1H), 6.44 (t, 1H, J = 7.0 Hz)], two acetal protons [dH 5.17 (d, 1H, J = 7.8 Hz), 4.55 (d, 1H, J = 7.8 Hz)], one of which should be assigned to the anomeric proton of a sugar unit, along with other alkyl groups signals. Its 13C NMR spectrum exhibited 26 carbon signals, including three carboxyl carbons [dC 171.5, 167.4, 167.0], four olenfic carbons [dC 108.6, 127.0, 142.6, 152.1], a glucose unit [dC 99.9, 74.0, 76.3, 70.0, 73.1, 62.9], one acetal carbon [dC 95.4] belonging to the aglycone, and 14 other alkyl carbon signals. The direct correlations between the proton and carbon were assigned by its HSQC spectrum (Table 1). According to the spectra data above, the structure of 1 was supposed to contain one 8-epi-kingisidic acid unit [4–6] and one 6,7-dihyrofoliamenthoyl moiety [7,8]. In its HMBC spectrum, the correlations between 10-CH3 and C-8, 9; H2-6 and C-4, 5, 7, 9; H-8 and C-1, 7; H-10 and C-1, H-1 and C-3, 5, 8, 10 ; H-3 and C-11 assigned the 8-epi-kingisidic acid unit (Fig. 1). The anomeric configuration of glucose was assigned to be b based on the J-value of the anomeric proton. More over, the HMBC correlations between H2-60 (dC 4.13, 4.41) and C-100 (dC 167.0) connected the 6, 7-dihyrofoliamenthoyl to C-60 . The stereochemistry of the double bond at C-200 , 300
704
X.S. Feng et al. / Chinese Chemical Letters 20 (2009) 702–705
Fig. 1. Structures of compounds 1, 2 and key HMBC and NOESY correlations of 1.
was supposed to be E on the basis of chemical shift of C-900 at dC 12.1, while the methyl carbon of a Z-type configuration usually could be observed at about dC 19–25 [9]. Thus, the planar structure of compound 1 was identified as shown (Fig. 1). The relative stereostructure of 1 was determined by consideration of NOESY experiments on 1 (Fig. 1). NOESY correlations between H-400 /CH3-900 confirmed the double bond of C-200 , 300 to be E-form, between CH3-10/H-5, H-9; H-1/H-8 confirmed the stereostructure of 1 to be the same as 8-epikingisidic acid. The results above identified the structure of 1 as 60 -O-(6, 7-dihyrofoliamenthoyl)- 8-epi-kingisidic acid, namely, syrveoside A. Compound 2 was obtained as white amorphous powder (MeOH), with a negative optical rotation (½a23 D 25.7 (c 0.07, MeOH)). Its molecular formula was established as C26H36O13 on the basis of the HR-ESI-MS m/z 579.2053 [M+Na]+ (calcd. for C26H36O13Na, 579.2048). The IR spectrum also showed absorption bands at 3378, 1704 (broad band), 1640 cm1 due to hydroxyl, unsaturated carbonyl, a, b-unsaturated ester, and lactone functions. The 1H and 13C NMR spectral data of compound 2 were similar to those of 1 except for the signals of monoterpenic acid fragment. The differences at C-600 , 700 , 800 were found for the presence of one terminal olefin group [dC 111.4, 145.8] and one quaternary carbon bearing an oxygen [dC 71.3] in compound 2. This evidence suggested that 2 possessed a dehydrated and hydroxylated structure of 1. Thus the monoterpenic acid unit was identified as menthiafoloyl [10]. The structure of compound 2 was determined as 60 -O-menthiafoloyl-8-epi-kingisidic acid, namely, syrveoside B, which showed similar NOESY correlations to those of 1. Acknowledgments This research was supported by the National Key Project of Scientific and Technical Supporting Programs funded by Ministry of Science & Technology of China (No. 2006BAD31B05). References [1] [2] [3] [4]
D. Lu, P.Y. Li, Acad. Periodical Changchun Coll. Tradit. Chin. Med. 4 (17) (2001) 58. H.J. Park, M.S. Lee, K.T. Lee, I.C. Sohn, Y.N. Han, K.I. Miyamoto, Chem. Pharm. Bull. 47 (7) (1999) 1029. L.G. Zhou, X.S. Feng, K.Y. Huang, L. He, X.M. Deng, D.C. Wang, J. Chin. Med. Mater. 31 (5) (2008) 976. W. Damtoft, W.R. Jensen, J. Thorsen, Phytochemistry 32 (4) (1993) 1071.
X.S. Feng et al. / Chinese Chemical Letters 20 (2009) 702–705 [5] [6] [7] [8] [9] [10]
Y.Y. Chan, L.L. Yann, F.W. Lin, C.Y. Li, Y.C. Wu, L.S. Shi, M.J. Liou, T.S. Wu, Phytochemistry 47 (6) (1998) 1073. T. Tanahashi, Y. Takenaka, N. Nagakura, J. Nat. Prod. 60 (1997) 514. K.U. Ayse, S. Karsten, D. Omu¨r, Z. Axel, Phytochemistry 63 (2003) 959. M. Kikuchi, Y. Yamauchi, Y. Takahashi, M. Sugiyama, Yakugaku Zasshi 109 (7) (1989) 460. C.H. Brieskorn, P. Noble, Phytochemistry 22 (5) (1983) 1207. R. Taskova, N. Handjieva, D. Peev, S. Popov, Phytochemistry 49 (5) (1998) 1323.
705
Chinese Chemical Letters 20 (2009) 702–705 www.elsevier.com/locate/cclet
Two new secoiridoid glucosides from Syringa velutina Kom. Xue Song Feng a,b,**, Yang Qu a, Zhao Hua Wu c, Lei Xu a, Dong Song Zhang a, Hui Yuan Gao a, Li Jun Wu a,* a
School of Traditional Chinese Medicines, Shenyang Pharmaceutical University, Shenyang 110016, China b School of Pharmaceutical Sciences, China Medical University, Shenyang 110001, China c Pharmacy Department, Mudanjiang Medical University, Mudanjiang 157011, China Received 10 November 2008
Abstract Chemical investigation of Syringa velutina Kom. led to the isolation of two new secoiridoid glucosides. Their structures were identified as 60 -O-(6, 7-dihyrofoliamenthoyl)-8-epi-kingisidic acid (syrveoside A, 1) and 60 -O-menthiafoloyl-8-epi-kingisidic acid (syrveoside B, 2) on the basis of chemical and physicochemical evidence. # 2009 Published by Elsevier B.V. on behalf of Chinese Chemical Society. Keywords: Syringa velutina Kom.; Secoiridoid glucosides; Syrveoside A; Syrveoside B
Syringa (S.) velutina Kom. has been widely cultivated in the northern parts of China and Korea. The leaf, flower bud, and bark of this plant have been used in traditional Chinese medicine to treat infectious fevers, counteract inflammations, dampness and acute icteric hepatitis for many centuries [1]. Previous phytochemistry study on the S. velutina led to the isolation of lignans, iridoid glucosides, phenyl propanoids, and so on [2,3]. For the purpose to find much more bioactive agents, the study on chemical constituents of S. velutina was carried out, and two new seoiridoid glucosides esterified with a liner monoterpenoid acid (compounds 1 and 2) along with four known lignans were obtained. In this paper, the isolation and structural elucidation of two new compounds were reported. The leaves of S. velutina Kom. were collected in Xinmin, Liaoning Province, China in May 2005 and identified by Prof. Qi Shi Sun (School of Traditional Chinese Medicine, Shenyang Pharmaceutical University). A voucher specimen (No. 20050517) was deposited in the Herbarium of Section of medicinal plants of Shenyang Pharmaceutical University. The air-dried material (5 kg) was extracted with 70% ethanol (20 L) at room temperature for 2 weeks. The extract was concentrated under reduced pressure to afford an extraction (1560 g, 31.2%), which was suspended in water and subjected to D101 macroporous resins with ethanol–water to elute. A part of the 30% ethanol–water soluble fraction (300 g) was subjected to silica gel column chromatography and semi-prep. HPLC to furnish compounds 1 (11.7 mg, 0.0002%) and 2 (10.5 mg, 0.0002%), respectively.
* Corresponding author at: School of Traditional Chinese Medicines, Shenyang Pharmaceutical University, Shenyang 110016, China. ** Corresponding author at: School of Pharmaceutical Sciences, China Medical University, Shenyang 110001, China. E-mail addresses: [email protected] (X.S. Feng), [email protected] (L.J. Wu). 1001-8417/$ – see front matter # 2009 Published by Elsevier B.V. on behalf of Chinese Chemical Society. doi:10.1016/j.cclet.2009.02.012
X.S. Feng et al. / Chinese Chemical Letters 20 (2009) 702–705
703
Table 1 13 C NMR (150 MHz), 1H NMR (600 MHz) and DEPT (150 MHz) spectral data of compound 1 and 2 (in DMSO-d6, d ppm, J Hz). Position
1
2
dC
DEPT
dH
dC
DEPT
dH
95.4 152.1 108.6 27.1 33.6
CH CH C CH CH2
5.17 (d, 1H, J = 7.8 Hz) 7.45 (s, 1H)
95.5 152.4 108.3 27.1 33.6
CH CH C CH CH2
5.21 (d, 1H, J = 7.8 Hz) 7.48 (s, 1H)
7 8 9 10 11
171.5 73.6 40.6 21.0 167.4
C CH CH CH3 C
171.5 73.6 40.1 21.0 167.3
C CH CH CH3 C
Glucose 10 20 30 40 50 60
99.9 74.0 76.3 70.0 73.1 62.9
CH CH CH CH CH CH2
99.9 74.0 76.2 70.0 73.1 62.9
CH CH CH CH CH CH2
167.1 126.9 142.9 23.2 40.6 71.3 145.8 111.4
C C CH CH2 CH2 C CH CH2
12.1 27.8
CH3 CH3
Iridoid group 1 3 4 5 6
Monoterpene terpene 167.0 100 127.0 200 300 142.6 400 25.7 500 35.4 29.0 600 700 40.0 800 58.8 900 1000
12.1 19.4
2.85 (m, 1H) 2.67 (dd, 1H, J = 15.9, 3.9 Hz) 2.28 (dd, 1H, J = 15.9, 11.9 Hz) 4.16 (m, 1H) 2.02 (m, 1H) 1.34 (d, 3H, J = 6.3 Hz)
4.55 (d, 1H, J = 7.8 Hz) 3.38 (m, 1H) 3.15 (m, 1H) 3.14 (m, 1H) 2.99 (m, 1H) 4.41 (d, 1H, J = 11.0 Hz) 4.13 (dd, 1H, J = 11.0, 6.1 Hz)
C C CH CH2 CH2 CH CH2 CH2
6.64 2.11 1.19 1.52 1.24 3.33
CH3 CH3
1.74 (s, 3H) 0.84 (d, 3H, J = 6.5 Hz)
(t, 1H, J = 7.0 Hz) (m, 2H) (m, 1H) 1.35 (m, 1H) (m, 1H) (m, 1H) 1.41 (m, 1H) (m, 2H)
2.86 (m, 1H) 2.67 (dd, 1H, J = 16.0, 4.0 Hz) 2.29 (dd, 1H, J = 16.0, 11.8 Hz) 4.19 (m, 1H) 2.03 (m, 1H) 1.34 (d, 3H, J = 6.2 Hz)
4.56 (d, 1H, J = 7.9 Hz) 3.42 (t, 1H, J = 7.0 Hz) 3.19 (t, 1H, J = 8.8 Hz) 3.14 (m, 1H) 3.00 (m, 1H) 4.41 (d, 1H, J = 11.0 Hz) 4.13 (dd, 1H, J = 11.0, 6.0 Hz)
6.66 (t, 1H, J = 7.6 Hz) 2.14 (m, 1H) 2.07 (m, 1H) 1.46 (m, 2H) 5.84 5.14 4.95 1.71 1.14
(dd, 1H, J = 17.0, 10.6 Hz) (dd, 1H, J = 17.0, 0.6 Hz) (br.d, 1H, J = 10.6 Hz) (s, 3H) (s, 3H)
Compound 1 was obtained as white amorphous powder (MeOH) with a negative optical rotation (½a23 D 35.9 (c 0.08, MeOH)). Its molecular formula was established as C26H38O13 by HR-ESI-MS m/z 581.2204 [M+Na]+ (calcd. for C26H38O13Na, 581.2205). The IR spectrum showed absorption bands at 3377, 1707 (broad band), 1641 cm1 due to hydroxyl, unsaturated carbonyl, a, b-unsaturated ester, and lactone functions. Its 1H NMR spectrum (Table 1) showed signals assignable to three methyls [dH 0.84 (d, 3H, J = 6.5 Hz), 1.34 (d, 3H, J = 6.3 Hz), 1.74 (s, 3H)], two olefinic protons [dH 7.45 (s, 1H), 6.44 (t, 1H, J = 7.0 Hz)], two acetal protons [dH 5.17 (d, 1H, J = 7.8 Hz), 4.55 (d, 1H, J = 7.8 Hz)], one of which should be assigned to the anomeric proton of a sugar unit, along with other alkyl groups signals. Its 13C NMR spectrum exhibited 26 carbon signals, including three carboxyl carbons [dC 171.5, 167.4, 167.0], four olenfic carbons [dC 108.6, 127.0, 142.6, 152.1], a glucose unit [dC 99.9, 74.0, 76.3, 70.0, 73.1, 62.9], one acetal carbon [dC 95.4] belonging to the aglycone, and 14 other alkyl carbon signals. The direct correlations between the proton and carbon were assigned by its HSQC spectrum (Table 1). According to the spectra data above, the structure of 1 was supposed to contain one 8-epi-kingisidic acid unit [4–6] and one 6,7-dihyrofoliamenthoyl moiety [7,8]. In its HMBC spectrum, the correlations between 10-CH3 and C-8, 9; H2-6 and C-4, 5, 7, 9; H-8 and C-1, 7; H-10 and C-1, H-1 and C-3, 5, 8, 10 ; H-3 and C-11 assigned the 8-epi-kingisidic acid unit (Fig. 1). The anomeric configuration of glucose was assigned to be b based on the J-value of the anomeric proton. More over, the HMBC correlations between H2-60 (dC 4.13, 4.41) and C-100 (dC 167.0) connected the 6, 7-dihyrofoliamenthoyl to C-60 . The stereochemistry of the double bond at C-200 , 300
704
X.S. Feng et al. / Chinese Chemical Letters 20 (2009) 702–705
Fig. 1. Structures of compounds 1, 2 and key HMBC and NOESY correlations of 1.
was supposed to be E on the basis of chemical shift of C-900 at dC 12.1, while the methyl carbon of a Z-type configuration usually could be observed at about dC 19–25 [9]. Thus, the planar structure of compound 1 was identified as shown (Fig. 1). The relative stereostructure of 1 was determined by consideration of NOESY experiments on 1 (Fig. 1). NOESY correlations between H-400 /CH3-900 confirmed the double bond of C-200 , 300 to be E-form, between CH3-10/H-5, H-9; H-1/H-8 confirmed the stereostructure of 1 to be the same as 8-epikingisidic acid. The results above identified the structure of 1 as 60 -O-(6, 7-dihyrofoliamenthoyl)- 8-epi-kingisidic acid, namely, syrveoside A. Compound 2 was obtained as white amorphous powder (MeOH), with a negative optical rotation (½a23 D 25.7 (c 0.07, MeOH)). Its molecular formula was established as C26H36O13 on the basis of the HR-ESI-MS m/z 579.2053 [M+Na]+ (calcd. for C26H36O13Na, 579.2048). The IR spectrum also showed absorption bands at 3378, 1704 (broad band), 1640 cm1 due to hydroxyl, unsaturated carbonyl, a, b-unsaturated ester, and lactone functions. The 1H and 13C NMR spectral data of compound 2 were similar to those of 1 except for the signals of monoterpenic acid fragment. The differences at C-600 , 700 , 800 were found for the presence of one terminal olefin group [dC 111.4, 145.8] and one quaternary carbon bearing an oxygen [dC 71.3] in compound 2. This evidence suggested that 2 possessed a dehydrated and hydroxylated structure of 1. Thus the monoterpenic acid unit was identified as menthiafoloyl [10]. The structure of compound 2 was determined as 60 -O-menthiafoloyl-8-epi-kingisidic acid, namely, syrveoside B, which showed similar NOESY correlations to those of 1. Acknowledgments This research was supported by the National Key Project of Scientific and Technical Supporting Programs funded by Ministry of Science & Technology of China (No. 2006BAD31B05). References [1] [2] [3] [4]
D. Lu, P.Y. Li, Acad. Periodical Changchun Coll. Tradit. Chin. Med. 4 (17) (2001) 58. H.J. Park, M.S. Lee, K.T. Lee, I.C. Sohn, Y.N. Han, K.I. Miyamoto, Chem. Pharm. Bull. 47 (7) (1999) 1029. L.G. Zhou, X.S. Feng, K.Y. Huang, L. He, X.M. Deng, D.C. Wang, J. Chin. Med. Mater. 31 (5) (2008) 976. W. Damtoft, W.R. Jensen, J. Thorsen, Phytochemistry 32 (4) (1993) 1071.
X.S. Feng et al. / Chinese Chemical Letters 20 (2009) 702–705 [5] [6] [7] [8] [9] [10]
Y.Y. Chan, L.L. Yann, F.W. Lin, C.Y. Li, Y.C. Wu, L.S. Shi, M.J. Liou, T.S. Wu, Phytochemistry 47 (6) (1998) 1073. T. Tanahashi, Y. Takenaka, N. Nagakura, J. Nat. Prod. 60 (1997) 514. K.U. Ayse, S. Karsten, D. Omu¨r, Z. Axel, Phytochemistry 63 (2003) 959. M. Kikuchi, Y. Yamauchi, Y. Takahashi, M. Sugiyama, Yakugaku Zasshi 109 (7) (1989) 460. C.H. Brieskorn, P. Noble, Phytochemistry 22 (5) (1983) 1207. R. Taskova, N. Handjieva, D. Peev, S. Popov, Phytochemistry 49 (5) (1998) 1323.
705