Francionamento bioguiado e caracterização química de compostos com atividade antimicrobiana de geoprópolis de Uruçu nordestina: abelha indígena sem ferrão Melipona scutellaris

Abstract

Long historical records of reverence by distinct ci vilizations emerge from the last 25 years of scientific studies on stingless bees, native eusocial species inhabiting the tropical and subtropical areas of the world, over extensive documentation devoted to the globally widespread Apis mellifera. Differences from the honeybees include peculiar nest strengthened arquictetures built in beeswax and plant resi ns, amalgamated with pollen, seeds or soil material to produce geopropolis, compositionally dissociated of traditional propolis, even sharing a prevailing activity against gram-positi ve bacteria, attributable to terpenic derivatives. A bioassay-guided fractionation technique was aimed to separate active compounds against Staphylococcus aureus in geopropolis from Melipona scutellaris, concerni ng its potential biological relevance. Among the ethanolic extracts of the six lots of geopropolis ramdomly collected from a meliponary settled in the Bahia State of Brazil, during a year, the “dark-brown” variety was highlighted by the same antistaphylococcal acti vity of ethyl acetate fraction (MIC 62,5-31,25µg/mL), which unveiled at least si x target compounds from bioautography in the purification step, even because their chromatographic profiles by RP-HPLC-PDA remained equivalent to the original extract, motivating its chromatographic fractionation by Low-Pressure Silica Gel Column Chromatography, followed by preparative RP-HPLC-PDA of the poorly resolved fraction F1 (MIC 1,95 – 0,98 μg/mL), yelding sub-fractions SF2 (3,90- 1,95 µg/mL) and SF3 (7,81-3,90 µg/mL). Although escaping from the isolation purpose, the fragmentation profiles of compounds in fractions, sub-fractions and extracts, determined by RP-HPLC-ESI-TQ-MSn, allowed propositions of components closely related to the structure of a diterpenic core bonded to a cinnamic acid group, consistent with the homologous UV spectral scans, associated to the 1H-NMR spectra of fraction F2 (7,81-3,90 µg/mL), relatively the most purified one available. Differing extracts consisted, in contrast, of the variability of mass spectra, suggesting mimics of Apis mellifera heterogeneous collecting behavior in the choice for resin sources by native bees. Antibacterial assays involving bioautography and resazurin microtitre plate-based minimum inhibitory, followed by bactericidal, concentrations (MIC/MBC) methods conducted the fractionation process, whilst the screening by MIC/MBC composed the antimicrobial profile of “dark brown” extract and its most active derivatives against S. aureus, displaying a panel of standardized human pathogenic bacterial strains, recongni zed as highly susceptible gram-positive species, in particular Micrococcus, Bacillus and Staphylococcus, includi ng the selected MRSA isolate, over the gram-negative ones, demonstrating the promising potential of geopropolis as a repository of natural products candidates to the challenges of drugs development in the course of health claims.