ESTUDO QUÍMICO E BIOLÓGICO DE MICONIA ALBICANS (MELASTOMATACEAE), UMA PLANTA MEDICINAL COMERCIALIZADA NA MEDICINA POPULAR SUL-MATO-GROSSENSE COMO CANELA-DE-VELHO

Abstract

The species Miconia albicans (Melastomataceae), popularly known as “canela-de-velho”, is used in traditional medicine in the form of leaf teas for the treatment of intestinal and infectious diseases and pain. For this reason, it is essential to develop methods to verify the identity and quality of plant material sold as “canela-de-velho”, in addition to evaluating the biological activities of M. albicans. In this context, the present work aims to expand knowledge about the chemical composition of Miconia albicans, by using HPLC-MS data and chemometric analysis to compare plant material sold as a sample of M. albicans, and to evaluate its antimicrobial properties. For this purpose, leaves and stems of M. albicans were collected and identified by botanists, dried, crushed and extracted separately with ethanol to obtain crude extracts. Then, the extracts were successively partitioned with hexane, chloroform and ethyl acetate, resulting in the corresponding phases. The extracts and phases were submitted to chemical profile analysis using GC-MS and HPLC-UV-MS techniques, and the isolation of secondary metabolites from leaves and stems was carried out using a combination of different chromatographic processes. The identification of isolated compounds was performed by NMR and MS. For the comparative analysis of commercialized plant material, a multivariate treatment (Principal Component Analysis – PCA, and Hierarchical Clustering Analysis – HCA) was applied to data obtained by HPLC-UV-EM of ethanolic extracts from 4 commercial samples, 1 reference sample of M. albicans, and two potentially contaminating plant species. The antimicrobial potential of the extracts and phases were evaluated individually and in combination with antibiotics, using the broth microdilution and checkerboard microtiter assay methods. The chromatographic fractionation resulted in the isolation and structural determination of 10 substances, 6 of which are triterpenes (squalene, lupeol, β-amyrin, α-amyrin, betulinic acid and corosolic acid), 1 steroid (stigmasterol), 1 tocopherol (α-tocopherol) and 2 pheophorbids (13²-hydroxy-17³-ethoxypheophorbid A and pheophorbid B), being the first report of pheophorbids in M. albicans. Through the analysis of chemical profiles by HPLC-MS and GC-MS, 32 substances were annotated and/or identified, belonging to the classes of derivatives of gallic and ellagic acids, glycosylated flavonoids, triterpenes, pheophorbides, steroids, fatty alcohol, and tocopherol. In the comparative analysis of the HPLC-UV-MS data, in general, the commercial samples of “canela-de-velho” and M. albicans reference material showed similarity between the chemical profiles, with small variations being observed only in the relative amount between the compounds. We observed the separation of samples into two clusters mainly through PCA analysis, explaining 73.6% of the total variance [PC1(52.5%) and PC2(21.1%)]. However, in the PCA, loading graphs and HCA it was possible to verify that the candidates that developed for this separation were corosolic acid (35.1 min RT retention time and m/z 471.3453[M–H]–) and isorhamnetin-O-hexoside (RT 28.5 min and m/z 477.1047 [M–H]–). The extracts and phases showed promising results against clinical strains of resistant bacteria Staphylococcus aureus and Acinetobacter baumannii in combination with the antibiotics ampicillin and ciprofloxacin.