ANTIBACTERIAL TRITERPENOID FROM THE LEAVES EXTRACT OF EHRETIA CYMOSA
Ehretia cymosa (Boraginaceae) is an indigenous plant in Ethiopia traditionally used against various diseases including toothache, tetanus, dysentery, gastric ulcers and skin diseases. In view of its traditional use, the leaves were successively extracted on maceration with n-hexane, EtOAc and MeOH to furnish 15 g (3%), 2.63 g (0.5%) and 8.13 g (1.6), respectively. The extracts were subjected to qualitative phytochemical screening and the results of the screening test revealed the presence of phytosterols, flavonoids, terpenoids, phenols, glycosides, and alkaloids. The n-haxane extract after silica gel column chromatography yielded four compounds identified with IR and NMR as compound 1, α-amyrin (2), β-amyrin (3) and bauerenol (4). Similar attempt made to isolate compounds from the EtOAc extract has led to the isolation of same compounds. Compound 1 has not been reported from this genus. The extracts and compound 1 were tested for their antibacterial activity using paper disc diffusion method against two bacterial pathogens such as Pseudomonas aeruginosa and Staphylococcus aureus. The methanol extract displayed remarkable activity against P. aeruginosa with inhibition zone of 30 mm at 25 mg/mL. The result is significant compared with gentamicin (22 mm at 25 mg/mL) as positive control. The antibacterial activity presented herein has demonstrated that all the extracts and compound 1 were active against all the tested bacterial species with the methanol extract exhibited the best activity comparable with the standard drug. Thus the present study supported the traditional use of the leaves of E. cymosa against bacteria.
Key words: Boraginaceae, Ehretia cymosa, Antibacterial activity, NMR, α-amyrin, β-amyrin, bauerenol