Phytochemical Investigation, Antibacterial And Antioxidant Activities Of The Roots Extracts Of Laggera Tomentosa

Abstract

Laggera tomentosa (Asteraceae/compositae) is an endemic Ethiopian medicinal plant traditionally used for the treatment of various ailments including toothache, stomachache, swelling, ringworm, skin infections, external parasites, common cold and headache. In view of its traditional uses and the absence of scientific reports so far, an attempt was made to explore the chemical, antibacterial and antioxidant studies of the solvent extracts of the roots of L. tomentosa. In this regard, the roots (300 g) were successively extracted with n-hexane, EtOAc and MeOH to afford 2.85 g (oil), 4.06 g and 5.94 g, respectively. The phytochemical screening results of EtOAc and MeOH extracts revealed the presence of alkaloids, anthraquinone, flavonoids, steroids, cardiac glycoside, terpenoids and phenols, whereas saponins and anthraquinone glycosides are absent. The n-hexane extract (oil) was analyzed for the first time by GC-MS which showed the presence of eleven components with 2,5-dimethoxy-p-cymene identified as the major constituent (59.39%). The EtOAc extract was subjected to silica gel column chromatography and gave four compounds identified as lauric acid,  stigmasterol, chrysophanol and emodin. Structure elucidation of these compounds was done by employing various spectroscopic techniques including UV-Vis, IR and NMR and comparing with literature data. The radical scavenging activities of the n-hexane, EtOAc and MeOH extracts were assessed using DPPH and found to inhibit the radical by 55.8, 84.3 and 72.5%, respectively. The result was found close to ascorbic acid indicating strong ability of the extracts to act as radical scavenger. The extracts and isolated compounds were also evaluated for their antibacterial activities by disc diffusion method against four bacterial strains such as S. aureus, K. pneumonia, P. mirabilis and E. coli. The EtOAc extract (19 mm) and emodin (18 mm) exhibited promising antibacterial activities compared to the standard drug (21 mm) at 1 mg/mL concentration. Therefore, the results obtained support the traditional uses of this plant against bacteria.