Phytochemical and antimicrobial evaluation of Miconia burchellii Triana (Melastomataceae)

Four novel triterpenoid saponins, 1α,3β,23-trihydroxy-olean-12-en-28-oic acid 28-O-β-glycopyranoside ester (1), 1α,3β,23-trihydroxy-urs-12-en-28-oic acid 28-O-β-glycopyranoside ester (2), 3-O-β-galloyl-1α,23-dihydroxy-olean-12-en-28-oic acid 28-O-β-glycopyranoside ester (3) and 3-O-β-galloyl-1α,23-dihydroxy-urs-12-en-28-oic acid 28-O-β-glycopyranoside ester (4) and two new pentacyclic triterpenoids, 3-O-β-trans-p-coumaroyl-1α-hydroxy-urs-12-en-28-oic acid (5) and 3-O-β-cis-p-coumaroyl-1α-hydroxy-urs-12-en-28-oic acid (6), together with six known compounds were isolated from the ethanolic extracts of Miconia burchellii leaves and stem bark. Their structures were established by HR-MS, 1D and 2D NMR and comparison with literature data. Additionally, the antimicrobial activity of the leaves and stem bark extracts and fractions was evaluated using the micro broth dilution technique. The crude extract, the ethyl acetate and methanol fractions of the stem bark were the most active against the tested bacteria, showing growth inhibition of both Gram-positive (Staphylococcus aureus and Staphylococcus epidermidis) and Gram-negative (Escherichia coli and Pseudomonas aeruginosa). To the best of our knowledge, this is the first study to report on the antimicrobial activity of M. burchellii.