Phytochemical investigation And antimicrobial activity of crude extract and essential oils From Ocimum gratissimum

Abstract

Medicinal plants are exploited by human beings as pharmaceuticals, agrochemicals, and poisons since ancient times. Ocimum gratissimum is one of these medicinal plants which belongs to the genus Ocimum and is commonly used in Ethiopia as a traditional medicine to treat infectious diseases of the upper respiratory tract, bowl, skin, and eye. Thus, in this study, phytochemical investigation and antimicrobial activity of evaluation of O. gratissimum were done. The shade dried root of the plant was grinded and extracted by maceration technique using chloroform/methanol 1:1 (v/v) resulted in 7 g (3.5%) of crude extract. The silica gel column chromatography of crude extract led to the isolation of three compounds. The structure of the isolated compounds were elucidated using spectroscopic techniques (1D and 2D NMR). Finally, compound-1 was identified as 7-hydroxy-8-((E)-3-hydroxy-7,8- diisopropyl-2,9,9-trimethyldec-7-en-2-yl)-3-phenyl-4H-chromen-4-one, compound-2 was identified as 17-((E)-5-ethyl-6-methylhept-3-en-2-yl)-2,3,4,7,8,9,10, 11,12,13,14,15,16,17- tetradecahydro-10,13-dimethyl-1H-cyclopenta[α]phenanthren-3-ol ( Stigmasterol), and compound-3 was identified as icosahydro-9-hydroxy-5a, 5b, 8, 8, 11a-pentamethyl-1-(prop- 1-en-2-yl)-1H-cyclopenta[α]chrysene-3a-carboxylic acid ( Betulinic acid) with melting points of 160-162, 166-170, 276-277 °C, respectively. The hydro-distillation of the seed and leaves of the plant were resulted three essential oils (EO-1, EO-2, and EO-3). The oils were characterized by GC-MS and all of them afforded Benzene-1,2,3-trimethoxy-5-(2-propenyl)- (Elemicin) 36.12, 16, and 36.08%, respectively as major component. The antimicrobial activities of the crude extract, isolated compounds, and the essential oils were evaluated against four bacterial strains (B. cereus, E. coli, S. aureus, S. typhi and) and a fungal strains C. albicans using disc diffusion method. Generally, the crude extract showed low activity with inhibition zone 11±0, 11±0, 9.5±3.54, 12±2.5, 10.5±2.12 mm, respectively against all the tested strains when compared with standard drugs Gentamycin (23±1.41, 22.5±3.53, 22.5±2.12, and 23±1.41 mm, respectively) and Clotrimazole (15.5±0.71 mm). The essential oil EO-3 showed the highest zone of inhibition 8.5±0.71, 9.25±0.35, 8.5±.71, 9.25±0.35, and 8±1.41 mm, respectively against all the tested strains than the two essential oils. Therefore, the antimicrobial activity displayed by the plant validates the traditional claims.