Chemical constituents of Palisota ambigua (Commelinaceae) with their antibacterial activities

Abstract

Background: The development and spread of resistance by bacteria to existing antibiotics are becoming more common nowadays. Considering the ethnopharmacological relevance of Palisota ambigua (Commelinaceae), this study was designed to investigate the antibacterial activities of chemical constituents of P. ambigua against two Gram-positive (Staphylococcus aureus ATCC 25923 and Streptococcus pneumoniae ATCC 49619) and two Gram-negative (Escherichia coli ATCC 8739 and Klebsiella pneumoniae 109 (isolate)) bacteria. Methods: The plant extracts were prepared by maceration in organic solvents. Chromatography techniques were used for isolation and purification of compounds. Their structures were determined through spectroscopic and spectrometric data, as well as by comparison with literature data. The broth microdilution method was used for antibacterial assays through the determination of minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). Results: The methanolic extract, the ethyl acetate (EtOAc), and (n-butanol) n-BuOH fractions from the aerial parts of P. ambigua exhibited significant to moderate antibacterial activity (MIC = 32 – 512 µg/ml). The chemical investigation of fractions led to the isolation of twelve known compounds namely, N-benzoyl-L-phenylalanyl-L-phenylalaninol acetate (aurantiamide acetate) (1), 20-hydroxyecdysone (2), rubrosterone (3), β-sitosterol 3-O-β-D-glucopyranoside (4), 3β-hydroxystigmast-5-en-7-one (5), lupeol (6), betulinic acid (7), bis(2-ethylhexyl) terephthalate (8), 2,3-di-O-dodecanoyl-sn-glycerol 1-O-(6-O-α-D-galactopyranosyl)-β-D-galactopyranoside (9), docosanoic acid (10), pallidol (11), and apigenin (12). All isolates displayed antibacterial activity varying from weak to moderate against the tested pathogenic bacteria. Among the tested compounds, 20-hydroxyecdysone-2,3,22-triacetate (2a) was the most active with a MIC value of 32 µg/mL against Klebsiella pneumoniae and Staphylococcus aureus. Conclusion: The results of the present study indicate that P. ambigua contains antibacterial isolates, therefore confirming some of its uses in traditional medicine.