Chemical and biological investigations of Albizia chinensis (Osbeck.) Merr

A total of five compounds,namely lupeol (1),α-amyrin (2),stigmasterol (3),β-sitosterol (4) and 7,3 -dimethoxyluteolin (5) were isolated from a methanol extract of Albizia chinensis stem bark. The structures of the isolated compounds were established using nuclear magnetic resonance (NMR) spectroscopic studies,as well as using comparative thin layer chromatography (co-TLC) with standards. The methanol extract of the A. chinensis stem bark and its n-hexane-,carbon tetrachloride-,chloroform- and aqueous-soluble partitionates were evaluated for antioxidant activity with 1,1-diphenyl-2-picrylhydrazyl (DPPH),Folin-Ciocalteu reagent and phosphomolybdenum total antioxidant assays,where butylated hydroxytoluene (BHT) and ascorbic acid were used as standards. The carbon tetrachloride-soluble fraction contained a moderate amount of phenolic compounds (60.76 ± 0.45 mg of GAE/g of extract) and it exhibited significant free radical-scavenging activity (IC50 10.21 ± 0.84 μg ml-1). A positive correlation was observed between the total phenolic content and the total antioxidant capacity of A. chinensis. The general toxicity was determined using a brine shrimp lethality bioassay,where the carbon tetrachloride (LC50 0.608 ± 0.19 μg ml-1) and hexane (LC50 0.785 ± 0.26 μg ml-1) soluble partitionates had considerable bioactive properties. The crude extract and its chloroform- and aqueous-soluble fractions displayed significant antimicrobial activity against eighteen microorganisms with inhibition zones ranging from 7.0 mm to 26.0 mm.