Two new flavonoids from Adenium obesum grown in Oman

Abstract

In this study, two new antimicrobial flavonoid compounds were isolated and characterized, and their biological activities were assayed. The pure antimicrobial compounds were isolated and characterized from the ethyl acetate extract using different chromatographic techniques. The antimicrobial activity of the isolated pure compounds was assessed using disk diffusion method. Phytochemical investigation on the ethyl acetate crude extract of stem of Adenium obesum (A. obesum) resulted in the isolation of two pure new flavonoids 5,7,3′,4′-tetrahydroxy flavone 1 and 3,5,7,3′,4′,5′-hexahydroxyflavone 2 with several other minor compounds. Their structures were deduced on the basis of 1H NMR, 13C NMR, DEPT 90 and 135, COXY, HMBC, and MS. The pure antimicrobial flavonoid compounds showed significant antibacterial activities against Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, and Proteus vulgaris in the disk diffusion assay. Inhibition zones were 9–14 mm. The maximum inhibition was shown by compound 2 at concentration 200 μg/ml against P. vulgaris (IZ = 14 mm) when compared with the standard amoxicillin. The results showed that the isolated pure antimicrobial flavonoid compounds have significant antimicrobial activity, which can be used as antibiotics. This is the first report on isolation of these secondary metabolites from A. obesum.

Keywords

• Adenium obesum
• Apocynaceae
• Flavonoids
• Antimicrobial activity
• Oman