The research has established a method to directly extract and determine free quercetin (aglycone form) from Flos Sophorae Immaturus methanol extract by using a simple HPLC method. Conducting experiment with system HPLC Agilent 1260 Infinity, reverse column ZORBAX SB-C18 (temperature 25oC), flow rate 0.5 ml/min, average pressure 30 and 35 bar, and diode array detector (DAD), we found that these parameters is suitbale: λmax = 370 nm, injection volume is 20 µl, analysis time 16 minutes, mobile phase (% volume) consists of methanol (15%), acetonitril (20%) and solvent C (65%, contains 1% acetic acid, methanol, acetonitril and H2O, 40%, 15% and 45% respectively. After using a combination of irocratic elution and standard addition, retention time of free quercetin in Flos Sophorae Immaturus methanol extract has found to be 8.84 ± 0,05 (min). Relative standard deviation (RSD) of retetion time, peak area and peak height have been less than 1%, this results have indicated that the proposed method has fullfilled the validation parameters such as selectivity/specitifity, precision/repeatability. This study provided useful information for screening activity of quercetin by using different methods.

Two compounds (C2 and C6) were isolated and purified from Sophora japonica L. extract. Using nuclear magnetic resonance (NMR) spectroscopy, mass spectroscopy and thin layer chromatography, C2 and C6 were identified as quercetin and neohesperidin. The antioxidant activity of C2 and C6 (at concentration of 200 µM) is equivalent to vitamin C (at concentration of 0.57-1.14 µM/ml). Both compounds C2 and C6 have inhibitory activity on β-amyloid aggregation. At concentration of 1 mM of each compound, aggregation rate of β-amyloid (Amyloid form deposited in Alzheime's brain) are 51.14 and 80.57%, respectively, compar to control sample (89.64%).