The dichloromethane extract of A. glabrata leaves was fractionated by column chromatography affording a pure compound 10-benzoiloxy-6,8,9-trihydroxy-thymol isobutyrate (1). The mass spectrum indicated a molecular ion at m/z 388 in agreement with the molecular formula C21H24O7, m/z 370 (12%) [M-H2O]+, 178 (46%), 165 (43%), 150 (15%), 137 (5 %), 122 (23%), 105 (100%), 91 (5%), 71 (40%). The 1H NMR spectrum (Figure 2) indicates the presence of a benzoate group at 7.98, 7.55 and 7.40 ppm; singlets at 6.65 and 6.58 ppm for 2 and 5 aromatic hydrogens, respectively. The signals for the isopropyl group at 2.52 and 1.09 ppm. A singlet at 4.64 ppm for two hydrogens of methylene group in the 10-position of the molecule and the hydrogens of methylene group in C-9 were observed as a doublet each at 4.56 and 4.49 ppm. The 13C NMR spectrum (Table 1) was in agreement with the proposed structure. Eleven thymol derivatives have been obtained by Bohlmann et al 1977 from A. glabrata, but all of them differ from the new thymol derivative 1.
General
NMR measurements, including DEPT experiments, were performed at 400 MHz for 1H and 100 MHz for 13C on a Varian Mercury Plus 400 spectrometer, using CDCl3 as the solvent and TMS as internal reference. Mass spectra were recorded at 20 eV on a Hewlett-Packard 5989B Series II Plus spectrometer adapted to a HP 5890 gas chromatography. Column chromatography was carried out on Merck silica gel grade 60 (70-230 mesh).
Plant material
Specimens of Ageratina glabrata (Kunth) R.M. King & H. Rob., Asteraceae, were collected on January 4, 2006 near km 191 of México-Morelia state road No.15, in the municipality of San José de la Cumbre, State of Michoacán, México (N 19º40'859'', W 100º50'423'' and 2,234 meters above sea level). A voucher specimen (No. 188319) is deposited at the Herbarium of the Instituto de Ecología, A.C., Centro Regional del Bajío, Pátzcuaro, Michoacán, Mexico, where Prof. Jerzy Rzedowski kindly identified the plant material (Figure 1).
Preparation of plant extract
Air-dried leaves of A. glabrata (200 g) were extracted with CH2Cl2 (1.5 L) at room temperature for three days, three consecutive times. Filtration and evaporation of the extract afforded green viscous oil (19 g).
Isolation of the thymol derivative (1) from dichloromethane extract
The dichloromethane extract (0.5 g) was chromatographed on silica gel column using n-hexane and ethyl acetate mixture of increasing polarity, and finally pure ethyl acetate. Elution with hexane:EtOAc (9:1) afforded a mixture of thymol derivatives. The sub-fraction 30-32 (100 mg) was subjected to rechromatography on silica gel (5 g). Elution with n-hexane-AcOEt (8:2) afforded pure 10-benzoiloxy-6,8,9-trihydroxy-thymol isobutyrate (1) (20 mg). Identification was supported by spectroscopic analyses.
Revista Brasileira de Farmacognosia
Print version ISSN 0102-695X
Rev. bras. farmacogn. vol.21 no.5 Curitiba Sept./Oct. 2011 Epub Sep 02, 2011
http://dx.doi.org/10.1590/S0102-695X2011005000158
Guadalupe García PI; Edgar García SIII; Isabel Martínez GI; Thomas R. F. SciorII; José L Salvador III; Mauro M Martínez PIII; Rosa E. del Río*,III
ILaboratorio de Neuroquímica, Facultad de Ciencias Químicas, Benemérita Universidad Autónoma de Puebla, Puebla, Mexico
IILaboratorio de Farmacomodelaje, Facultad de Ciencias Químicas, Benemérita Universidad Autónoma de Puebla, Puebla, Mexico
IIIInstituto de Investigaciones Químico-Biológicas, Universidad Michoacana de San Nicolás de Hidalgo, Morelia, Mexico
IILaboratorio de Farmacomodelaje, Facultad de Ciencias Químicas, Benemérita Universidad Autónoma de Puebla, Puebla, Mexico
IIIInstituto de Investigaciones Químico-Biológicas, Universidad Michoacana de San Nicolás de Hidalgo, Morelia, Mexico
*Correspondence
Rosa E. del Río
Instituto de Investigaciones Químico-Biológicas, Universidad Michoacana de San Nicolás de Hidalgo.
Ed. B-1, C.U. Morelia, Mich. ,58030, Mexico.
ndelrio@umich.mx
Tel. +52 443 3265790 ext. 102; 3265790 ext. 103.
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