Estudo fitoquímico de Paepalanthus acanthophyllus e Paepalanthus bromelioides (Eriocaulaceae) e avaliação citotóxica e antimicrobiana de compostos isolados

Abstract

Paepalanthus acanthophyllus and P. bromeliodes species belong to one of the largest genera of the Eriocaulaceae family, a pantropical family that may be found in the Brazilian Cerrado. According to the literature, isolated compounds derived from the secondary metabolism of Paepalanthus have interesting biological activities. Thus, the objective of this work was to isolate the chemical constituents of the floral capitula of the species P. acanthophyllus and P. bromelioides, and to evaluate the antimicrobial and cytotoxic activities of the isolated compounds. The floral capitula of P. acanthophyllus were macerated in MeOH and the resulting crude extract was partitioned with solvents hexane, CH2Cl2 and EtOAc. The floral capitula of the species P. bromelioides were macerated and the crude extracts were prepared in CH2Cl2 and MeOH. In the fractionation process, liquid chromatography on silica gel column and Sephadex LH-20, and medium and high-performance liquid chromatography were used. The structural elucidation of the isolated compounds was performed by analyzing the spectra obtained by one- and two-dimensional NMR spectroscopy and high-resolution mass spectrometry. The cytotoxicity test was evaluated against human breast (MCF-7) and colon (HCT 116) cancer cells using the MTT method. Antimicrobial evaluation was performed against Staphylococcus aureus (NEWP0023) and Escherichia coli (NEWP0022), using the TTC method and with gentamicin as a positive control. In P. acanthophyllus, the flavonoids 6-methoxykaempferol (PaD-01) and 3',4'-dimethoxyfisetin (PaD-02) were isolated in the CH2Cl2 fraction. 6-methoxykaempferol (PaAc-01) was also isolated in the AcOEt fraction, as well as p-hydroxybenzoic acid (PaAc-02 and PaAc-03), 6-methoxykaempferol-3-O-β-D-6''-(p-coumaroyl)-glucopyranoside (PaAc-04, PaAc-06 and PaAc-07), 6-methoxykaempferol-3-O-β-Dglucopyranoside (PaAc-08) and 6-methoxykaempferol-7-O-β-D-glucopyranoside (PaAc-09). In P. bromelioides, naphthopyranone paepalantine (PbD-01) was isolated in the crude dichloromethane extract. Biological tests showed a low activity. Among the isolated compounds, the flavonoid 6-methoxykaempferol showed the best activity against both tumor cells, with percentage inhibition values equivalent to 29.17  6.09 (colon cancer) and 19.24  2.78 (breast cancer) at a concentration of 50 µM. The antimicrobial evaluation showed a more effective result of 6- methoxykaempferol against S. Aureus (250 µg.mL-1 ). The chemical investigation resulted in the isolation of seven compounds, with the compound PaAc-09 being isolated for the first time in the literature, PaD-02 and PaAc-02 reported for the first time in the family and PaAc-01 and PaAc-06 reported for the first time in the species. Compounds PaAc-08 and PbD-01 were previously isolated from P. acanthophyllus and P. bromelioides species, respectively.