Isolation and structural elucidation of antibacterial triterpenoids compounds from stem bark of Psorospermum Febrifugum (spach var. febrifugum)

Abstract

In this study, Psorospermum febrifugum stem bark was investigated for the antibacterial compounds present in its stem bark. The stem bark of Psorospermum febrifugum was collected in Mpigi District, Misindye hill in Buwungu village- Buwama sub country in Uganda. Extraction of the plant material was done using ethyl acetate and methanol in a ratio of 1:1. The crude extract was separated using a separating funnel into hexane extract, ethyl acetate extract and methanol extract. The crude extracts (hexane, ethyl acetate and methanol) were screened for antibacterial activity against P. aeruginosa, E. coli, S. aureus and S. pyogenes using the modified agar diffusion method. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were done on the most active antibacterial crude extract using broth diffusion method. Phytochemical screening was done on the active antibacteraial (ethyl acetate) extract. Isolation and purification of the compounds on the most active antibacterial (ethyl acetate) extract was done using a combination of column chromatography and thin layer chromatography. The pure compounds were identified using 1D and 2D 1H and 13C NMR techniques as well as Mass spectrometry (MS). The results of the bioactivity tests carried out in this study indicate that Psorospermum febrifugum has potential antibacterial activity. The ethyl acetate extract showed the highest zone of inhibition of (19.1± 0.14) mm and (18.3±0.07) mm against S. aureus and S. pyogenes respectively. The hexane extract showed no zone of inhibition against any tested bacterial strain and the methanol extract had moderate antibacterial activity. Phytochemical screening of ethyl acetate extract confirmed the presence of terpeniods, phenols, reducing sugar, carbohydrates and tannins. Three compounds, Betulinic acid (1), Oleanolic acid (2) and Oleanolic acetate acid (3) were identified and characterized from the ethyl acetate extract. A promising antibacterial activity was exhibited by all the three compounds. Compound 2 exhibited the highest zone of inhibition of (14.2± 0.07) mm against both bacterial strains. Compound 3 exhibited the lowest zone of inhibition of (6.5± 0.2) mm against S.aureus and (8.1±0.14) mm against P.aeruginosa and compound 1 showed a moderate zone of inihibition. This justifies the use of this plant in traditional medicine and indicates a promising potential for the development of medicinal agents from Psorospermum febrifugum stem bark.