METABÓLITOS SECUNDÁRIOS DAS FOLHAS DE Galianthe thalictroides (RUBIACEAE)

Abstract

Galianthe thalictroides (K.Schum.) E. L. Cabral is a shrub species found in few regions of the world, with reports of its occurrence in Argentina, Paraguay and, in Brazil, in the states of Minas Gerais, São Paulo, Paraná, Santa Catarina, Rio Grande do Sul and Mato Grosso do Sul. In the previous study of this species (data not yet published) the ethanolic extract of the leaves was analyzed by HPLC-DAD-MS, resulting in the annotation of 21 peaks compatible with alkaloids. β-Carboline alkaloids have also been isolated from the roots of the plant, which is popularly used in Mato Grosso do Sul for the treatment and prevention of cancer. In addition to alkaloids, the study of roots resulted in the isolation of Rubiaceae-type cyclopeptides, and both alkaloids and isolated cyclopeptides were reported as potential antitumor agents. In view of the above, the present work aims to carry out the chemical study of the leaves of the plant G. thalictroides, mainly aiming at the isolation and identification of alkaloids, as well as testing the antimicrobial activity of its compounds, phases and extract individually and associated with antibiotics. commercials. For the chemical study, the ethanolic extract of the leaves (EFGT) was prepared by maceration. The 9:1 methanol-water solution of EFGT was partitioned with hexane and, later, with chloroform, and the latter fraction concentrated the alkaloids, which was confirmed by analysis by analytical thin layer chromatography using Dragendorff's solution as developer. Aliquots of the chloroform fraction were subjected to separation methodologies by liquid column chromatography techniques and also by semi-preparative high performance liquid chromatography. The antimicrobial activity test was performed through assays using the Broth Microdilution Method and Checkboard Assay against strains of Staphylococcus aureus (SA), Escherichia coli (EC) and Enterococcus faecalis (EF), in addition to clinical strains of S. aureus resistant to clarithromycin, erythromycin and penicillin G (SAC), S. aureus resistant to penicillin G (19S) and vancomycin resistant Enterococcus faecium (EFC). As a result of the chemical study, eight β-carboline alkaloids were isolated: (3,3-dimethyl-7-(9H-pyrido[3,4-b]indol-1-yl)-2-oxabicyclo[2.2.1]heptan-1-yl)methanol (1) (7-(5-methoxy-9H-pyrido[3,4-b]indol-1-yl)-3,3-dimethyl-2-oxabicyclo[2.2.1]heptan-1-yl)methanol (2), rel-(2R,3R,6R,8R)-8-((9H-pyrido[3,4-b]indol-1-yl)methyl)-2-(3,4- dihydroxyphenyl)-8-methyl-6-(2-methylprop-1-en-1-yl)-2,3,4,6,7,8-hexahydropyrano[3,2-g]chromene-3,5-diol (3), rel-(2R,3R,6S,8R)-8-((9H-pyrido[3,4-b]indol-1-yl)methyl)-2-(3,4-dihydroxyphenyl)-8-methyl-6-(2-methylprop-1-en-1-yl)-2,3,4,6,7,8-hexahydropyran[3,2-g]chromene-3,5-diol (4), 3-(2-hydroxypropan-2-yl)-1-methyl-2-(9H-pyrido[3,4-b]indol-1-yl)cyclopentanol (5), 5-methoxy-1-(1,3 ,3-Trimethyl-2-oxabicyclo[2.2.1]heptan-7-yl)-9Hpyrido[3,4-b]indole (6), (E)-2,6-dimethyl-7-(9H- pyrido[3,4-b]indol-1-yl)hept-6-ene-2,3-diol (7) and 2,6-dimethyl-1-(9H-pyrido[3,4-b]indol- 1-yl)heptane-1,2,6 triol (8), which were identified by one- and two-dimensional nuclear magnetic resonance experiments. Six of the isolated alkaloids are unprecedented in the literature, highlighting a new category of β-carboline alkaloids, of indolemonoterpene origin and which has a flavonol bound to the structure. Alkaloid 6 showed significant activity against 19S and SA strains, moderate activity for SAC and EFC, in addition to acting as a synergist together with ampicillin against SAC and 19S strains and additive against EFC. Alkaloids 1, 2 and 4 showed moderate activity against SA, SAC, EF, EFC and 19S strains when tested individually and alkaloid 1 in combination with ampicillin showed additive activity against SAC, EFC and 19S.