Gallocatechin analogues from <i>Olax subscorpioidea</i> Oliv. against multiresistant clinical bacterial isolates

The recurrence of bacterial infections is commonly associated with the multiple interactions between humans and their environment. These interactions have progressively contributed to the development of antimicrobial resistance among numerous clinically important pathogenic bacteria. The present study targeted the antibacterial activity of natural products derived from the stem bark of O. subscorpioidea against clinical isolates of bacteria. This included the Gram-positive bacterium Staphylococcus aureus and three Gram-negative bacteria, Pseudomonas aeruginosa, Providencia stuartii, and Escherichia coli. The plant material was extracted by maceration, and chromatography was performed to isolate the chemical constituents from plant extracts as well as from the reaction medium. The resulting compounds were characterized using spectroscopic and spectrometric techniques. The antibacterial activity was assessed by the microdilution method. Five compounds were isolated, including olasubscorpioside A (1), 4′-O-methylgallocatechin (2), olasubscorpioside C (3), olasubscorpioside B (5a), isoolasubcorpioside B (5b), and glyceryl-1-eicosanoate (6). The semisynthetic derivatives 4′-O-methylgallocatechin (2) (also isolated from the plant extract) and tetra-O-allyl olasubscorpioside A (4) were prepared and characterized. Interestingly, olasubscorpioside A (1) and 4′-O-methylgallocatechin (2) displayed a significant antibacterial effect (MIC = 8 µg/mL) against the pathogenic isolate Staphylococcus aureus resistant to methicillin, ofloxacin, kanamycin, tetracycline, and erythromycin. Compound 2 had a better activity relative to 1 against Pseudomonas aeruginosa (from MIC > 256 to 128 µg/mL) and Escherichia coli (from MIC = 128 to 64 µg/mL). Gallocatechins from the stem bark of Olax subscorpioidea are promising bioactive molecules to fight against multiresistant bacteria.