Contribuição ao conhecimento químico de três quimiotipos de Lippia alba (Mill.) N. E. Brown cultivados no Horto de Plantas Medicinais da UFC

Abstract

Lippia alba (Mill.) N. E. Brown (Verbenaceae), designated in the Brazilian pharmacopeia as "erva-cidreira", is widely used for household preparation of a tea with soothing properties. The existence of chemotypes is common for this species, and in the Northeastern Brazil at least three chemotypes are known, based on the volatile chemical composition. This work reports an evaluating study of the volatile and non-volatile chemical constitution of three chemotypes cultivated at the Horto de Plantas Medicinais/UFC (medicinal plants garden). GLC/MS analysis of the leaf oil, obtained by hydrodistillation, on a seasonal study allowed the validation of the existence of three chemotypes: chemotype I, rich in the monoterpenes myrcene and citral; and chemotype II, rich in limonene and citral, and chemotype III, rich in limonene and carvone. A circadian study of the chemical composition revealed that chemotype I presented a relative decreasing of mircene yielding and an increase of the sesqueterpenes E-caryophyllene and elemol. The non-volatile chemical composition study, by TLC and 'H NMR analysis revealed a great similarity for all chemotypes. Analysis by chromatography of different leaf extract of all chemotypes leads to the isolation of 14 metabolites belonging to important natural product classes. Two iridoid glycosides: mussaenoside and the methyl ester of shanzhiside; three phenylpropanoid glycosides: (3-(3,4- dihydroxyphenyl )ethyl-O-a-L-rhamnopyranosyl (1-->3)13-D-(6'-O-caffeoyl)-glucopyranoside (isoverbascoside), 0-(3,4-dihydroxyphenyl)ethyl-O-D-apio-(3-D-furanosyl (1—*3)-J3-)-(6'-Ocaffeoyl)-glucopyranoside e i3-(3,4-dihydroxyphenyl)ethyl-O-a-Lrhamnopyranosyl (1--+3)- 13-Dglucopyranoside; two biflavones linked through C-O-C bonds; a mixture of J3-sitosterol plus stigmasterol glucosides; a sesquiterpene: 1(3, 6a-dihydroxy-4(15)-eudesmene; the salicilic acid salt; a monoterpene; two y-lactones and an aromatic derivative of salicilic acid. Three reaction derivatives were obtained: peracetyl isoverbascoside and the acid hydrolyze product: methyl ester of (E)-caffeic acid and (3,4-dihydroxyphenyl)ethanol. Biological assays showed that the essential oils of all chemotypes presented phytonematicide activity (Meloidogyne incognita) while the oils of chemotypes I e II showed larvicidal activity (Aedes aegypti larvae) at LD50 = 35,96 and 36,83 ppm, respectively. Evaluation of the antinociceptive activity of the leaf extracts (chemotype II) reveled that the ethyl acetate fraction obtained by liquid partitioning of the aqueous extract was the most active. The major compound of that fraction was isoverbascoside. The latter also showed antimicrobial activity against Staphylococcus aureus, Micrococcus luteus e Candida albicans. The chemical constituents isolation was performed by different chromatographic methods. The identification of the volatile compounds was done by GLOMS. Structure characterization of the isolated substances was made by spectroscopic methods such as: IR, UV, one and two dimensional 1H and 13C NMR (COSY, HMQC, HMBC e NOESY).