Hardwickiic acid and Lupeol from Leaves of Croton macrostachyus and their Antibacterial Activity

Croton macrostachyus, one of the Croton species found in Ethiopia, is used traditionally for the treatment of various health ailments, including diabetes, malaria, stomachache, ascariasis, abdominal pain, gonorrhea, wounds, ringworm infestation, and hemorrhoids. The main objective of this study was to isolate and characterize compounds from the C. macrostachyus leaves and determine their antibacterial activities. Maceration was used to extract the plant material for isolating compounds, and the column chromatography technique was applied. The antibacterial activities of the crude leaf extracts, obtained using petroleum ether, chloroform, and methanol, were determined by measuring the diameters of the zone of inhibition. Phytochemical screening of methanol, chloroform, and petroleum ether extract from leaves revealed the presence of terpenes, flavonoids, alkaloids, and saponins. Furthermore, the in vitro antibacterial activity of leaf extracts against Escherichia coli, Staphylococcus aureus, Klebsiella pneumoniae, and Listeria monocytogenes will be investigated using the agar plate disc diffusion technique. The maximum inhibition zone (15.83 ± 0.22 mm) was recorded in methanol extracts against E. coli at a 150 mg/mL concentration. All concentrations of the crude extract, except for petroleum ether extract at a concentration of 50 mg/mL against S. aureus (8.69 ± 0.25 mm), showed higher inhibition than positive control against tested pathogens. Antibacterial-guided fractionation of the methanol extract of the leaves was subjected to column chromatography on silica gel, and preparative TLC subsequently isolated selected fractions to give the two compounds: lupeol and hardwickiic acid. Their structures were elucidated based on spectral studies and compared with published data. Lupeol and Hardwickiic acid were evaluated for their antibacterial activities. The isolated compounds displayed significant antibacterial activity but less than crude extracts.