Antibacterial activity of extract, fractions and some compounds from the médicinal plant Psychotria succculenta Hiern.(Rubiaceae)

Abstract
Infectious diseases remain one of the main causes of mortality and morbidity worldwide. In spite of the World Health Organization efforts, the number of new chemical entities to combat these threats is still low due to antibiotic resistance. As an alternative approach, plants have been adopted as a source to provide such drugs. Psychotria succulenta Hiern. (Rubiaceae) is a scrub commonly found in Tropical regions and used in folk medicine for the treatment of diseases such as abdominal pain and intestinal infections. The aim of this study was to isolate secondary metabolites and evaluate the antibacterial activity of extract, fractions and some compounds in order to further confirm the use of P. succulent in traditional medicine. The Minimum Inhibitory Concentrations (MICs) were determined by the liquid microdilution method in vitro on four bacterial strains including Pseudomonas aeruginosa, Escherichia coli, Staphylococcus aureus and Klebsiella pneumoniae. The n-BuOH and the EtOAc fractions were the most active with MIC values ranging from 16 to 64 µg/mL against the above microbial strains. These fractions were then subjected to column chromatography on silica gel and sephadex LH-20 to afford 15 compounds including alkaloids, triterpenes, phenolic compounds, iridoid and ethyl glucose. Their structures were elucidated by spectroscopic analysis including 1D-NMR, 2D-NMR and by comparison with literature data. Some of the isolated compounds showed moderate activity against the tested strains. Although only a moderate activity was observed for the isolated compounds, the EtOAc and n-BuOH fractions of P. succulenta which exhibited a significant antibacterial activity could further be submitted to more investigation for the discovery of new phytodrugs against infectious diseases.
Keywords : Psychotria succulenta, Rubiaceae, antibiotic resistance, antimicrobial activities, isolation and structure elucidation.