Studies on the antimicrobial constituents from the roots of Oxytropis hirta Bunge

The antifungal and antibacterial chemical constituents in agriculture were identified from the roots of Oxytropis hirta Bunge. The 75% ethanol extract from the roots of O. hirta was further extracted by petroleum ether, ethy acetate and n-butanol, respectively. The most active ethy acetate phase was isolated and identifed for its chemcial constituents by mordern column chromatography and spectroscopy techniques, and the antimicrobial activity of the isolated compounds was evaluted. The results showed that the ethyl acetate phase had the best antimicrobial activity. It showed antifugal activities against Thanatephorus cucumeris and Botrytis cinerea with inhibitory rates of 57.2% and 55.4% at 1 × 10³ mg/L, respectively. It also showed antibacterial activities against Pseudomonas solanacearum and Pseudomonas syringae pv. actinidae with the antibacterial circle diameter of 21.8 mm and 19.0 mm, respectively. Six compounds were isolated and identified from the ethyl acetate phase of O. hirta as β-amyrin ( 1 ), 3-oxo-azukisapogenol ( 2 ), 5α-stigmast-9(11)-en-3β-ol ( 3 ), stigmast-4-ene-3,6-dione ( 4 ), 3β,22β,24-trihydroxy-olean-12-ene ( 5 ) and azukisapogenol ( 6 ). The results of antibacterial activity showed that the minimum inhibitory concentration (MIC) of compound 1 against Staphylococcus aureus was 50 mg/L, and the MIC of compound 1 against P. solanacearum, P. syringae and Bacilus subtilis was 100 mg/L. The EC₅₀ value of compound 6 against T. cucumeris and B. cinerea were 117.4 mg/L and 86.2 mg/L, respectively. The ethyl acetate phase of O. hirta showed better inhibitory activity against pathogenic fungi and bacteria. Triterpenoids are one of the main active constituents and have the potential to be further developed as fungicides.