Fitoterapia 70 Ž1999. 575]578
A new chlorosesquiterpene lactone from Ambrosia maritima Ahmed A. MahmoudU , Ahmed A. Ahmed, Ashraf A. El. Bassuony Department of Chemistry, Faculty of Science, El-Minia Uni¨ ersity, El-Mina 61519, Egypt Received 11 January 1999; accepted 6 March 1999
Abstract A new chloro-pseudoguaianolide-type sesquiterpene lactone, 11b-hydroxy-13-chloro11,13-dihydrohymenin Ž1., was isolated from the Egyptian medicinal plant Ambrosia maritima. The structure was determined by spectroscopic methods, particularly high-resolution 1 H, 13 C-NMR and 2D 1 H] 1 H and 1 H] 13 C COSY NMR analysis. Q 1999 Elsevier Science B.V. All rights reserved. Keywords: Ambrosia maritima; Sesquiterpene lactones; 11b-Hydroxy-13-chloro-11,13-dihydrohymenin
1. Introduction Ambrosia maritima L. ŽAsteraceae . is one of the few increasingly used Egyptian medicinal plants. It is a common folk medicine used in the treatment of renal colic and calculi w1x, and showed molluscicidal and ovicidal activity w2x. It has been studied for control of bilharziosis and was proved to have lethal effect on snails, miracidiae and cercaria w3x. Previous phytochemical studies of this species showed that pseudoguaianolide-type sesquiterpene lactones are the main secondary metabolites w1,4]8x. Recently, some of these compounds showed cytotoxic activity against V-79, KB, P-388 and L1210 cells w8x. Their biological importance prompted U
Corresponding author. Tel.: q20-86-3291-49; fax: q20-86-3426-01. E-mail address: [email protected]
0367-326Xr99r$ - see front matter Q 1999 Elsevier Science B.V. All rights reserved. PII: S 0 3 6 7 - 3 2 6 X Ž 9 9 . 0 0 0 9 1 - X
A.A. Mahmoud et al. r Fitoterapia 70 (1999) 575]578
us to reinvestigate this plant in the search for new constituents. In the present work, we report the isolation and structural elucidation of the new chloro-pseudoguaianolide, 11b-hydroxy-13-chloro-11,13-dihydrohymenin Ž1. from the aerial parts.
2. Results and discussion The positive ion CI-mass spectrum of 1 showed a molecular peak at mrz 315 consistent with the molecular formula C 15 H 19 ClO5 . The presence of a chlorine atom was supported by an isotopic peak at mrz 317 corresponding to C 15 H 19 Cl 37 O5 , while the nature of this chlorine containing group could be deduced from the fragments mrz 269 wMq]CH 2 Cl q 1x, 253 wMq] ŽCH 2 Cl q Me. q 1x and 235 wMq] ŽCH 2 Cl q Me q H 2 O. q 1x. In agreement with the molecular formula, the 13 C-NMR spectrum displayed 15 carbon signals, whereas the DEPT experiments indicated these signals corresponding to two CH 3 , three CH 2 , five CH and five quaternary carbons. It further showed the presence of two carbonyl groups at d 208.4 and 175.7, one disubstituted double bond at d 163.6 and 130.9, one secondary and two tertiary oxygenated carbons at d 80.9, 83.2 and 75.0, respectively. The structure of 1 was deduced from the 1 H and 13 C-NMR spectra ŽTable 1. which were in part similar to those exhibited by hymenin, previously isolated w8,9x. However, the signals of the exomethylene protons H-13a and H-13b were missing, instead a pair of doublets AB system Ž J s 11.2 Hz. were observed at d 3.69 and 3.60. Also, the 13 C-NMR spectrum showed replacement of these exomethylene signals by two carbons resonating at d 75.0 Ž s . and 46.80 Ž t .. The results of the 1 H] 1 H and 1 H] 13 C COSY experiments allowed the assignments of the two sequences ]CHŽ2. s CHŽ3. ] and ]OCHŽ6. ]CHŽ7. ]CH 2 Ž8. ]CH 2 Ž9. ]CHŽ10. ] CH 3 Ž14. ] of the pseudoguaianolide framework. The only remaining signals were the methyl singlet at d 1.24, which was assigned to Me-15 and those at d 3.69 and 3.60, which correlated in the 1 H] 13 C COSY spectrum with a methylene carbon at
A.A. Mahmoud et al. r Fitoterapia 70 (1999) 575]578 Table 1 1 H- and
C-NMR data of compound 1 Ž500 MHz, CDCl 3 , d ppm. dC a
1 2 3 4 5 6 7 8
83.2 Ž s . 163.6 Ž d . 130.9 Ž d . 208.4 Ž s . 56.9 Ž s . 80.9 Ž d . 42.4 Ž d . 20.4 Ž t .
31.4 Ž t .
10 11 12 13
37.8 Ž d . 175.7 Ž s . 75.0 Ž s . 46.8 Ž t .
17.6 Ž q . 15.0 Ž q .
] 7.40 6.20 ] ] 4.82 2.92 2.10 1.71 1.59 1.65 1.70 ] ] 3.60 3.69 1.10 1.24
H] 1 H COSY
d, J s 6.0 Hz d, J s 6.0 Hz
d, J s 9.2 Hz ddd, J s 9.2, 10.0, 2.5 Hz m m m m m
H-7 H-6, H-7a, H-7b H-7, H-8b, H-9a,b H-7, H-8a, H-9a,b H-8a,b, H-9b, H-10 H-8a,b, H-9a, H-10 H-9a,b, H-14
d, J s 11.2 Hz d, J s 11.2 Hz d, J s 7.0 Hz s
H-13a H-13b H-10
Multiplicities were deduced from DEPT experiments.
d 46.8. This indicated, together with some fragments in the CIMS resulting from loss of CH 2 Cl, that the chlorine atom was present at C-13. Moreover, replacement of the olefinic signal C-11 in hymenin by a tertiary oxygenated carbon at d 75.0 in 1 established a hydroxyl group at C-11. The relative configuration at C-11 could be determined by the NOE difference spectroscopy with inspection of the molecular model. Irradiation of H-6a gave NOEs with H-7 and H-13b which determined the a-orientation of these protons.
3. Experimental 3.1. Plant material Ambrosia maritima was collected in North Sinai, Egypt in July 1996. A voucher specimen has been deposited in the Department of Botany, Faculty of Science, El-Minia University. 3.2. Extraction and isolation Air-dried aerial parts Ž1 kg. were powdered and extracted with petrol Ž60]808C. ]Et 2 O]MeOH 1:1:1 at room temperature. The resulting extract Ž20 g. was fractionated by Si-gel CC eluting with petrol, followed by gradient of petrol]Et 2 O up to 100% Et 2 O and Et 2 O]MeOH. Repetitive separation and
A.A. Mahmoud et al. r Fitoterapia 70 (1999) 575]578
purification on Sephadex LH-20 column eluting with hexane]CH 2 Cl 2 ]MeOH 4:7:0.5 and PTLC eluting with petrol]Et 2 O afforded 13 mg of 1. 3.3. 11b-Hydroxy-13-chloro-11,13-dihdrohymenin Ž1.. Colourless oil, IR bands ŽCHCl 3 .: 3600, 3500 ŽOH., 1760 ŽCsO g-lactone., 1710 Ž a ,b-unsaturated CsO. cmy1 ; positive ion CIrMS mrz Ž%.: 315 wC 15 H 19 ClO5 ŽMqq 1, 80.x, 317 wC 15 H 19 Cl 37 O5 ŽMqq 1, 19.x, 269 ŽMq]CH 2 Cl q 1, 58., 253 ŽMq]CH 2 Cl, Me q 1, 30., 235 ŽMq]CH 2 Cl, Me, H 2 O q 1, 40., 219 Ž35., 207 Ž72., 154 Ž100., 130 Ž75., 129 Ž84., 114 Ž75.; 1 H- and 13 C-NMR spectral data Žsee Table 1..
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