10-benzoiloxy-6,8,9-trihydroxy-thymol isobutyrate

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 

Analgesic effect of leaf extract from Ageratina glabrata in the hot plate test

Guadalupe García P^I; Edgar García S^III; Isabel Martínez G^I; Thomas R. F. Scior^II; José L Salvador ^III; Mauro M Martínez P^III; 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

*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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