Flos Sophorae Immaturus (FSI) possessed potential xanthine oxidase (XO) inhibitory activity as a uric acid-lowing natural product. The present work identified and quantified the free and bound polyphenols of FSI by UPLC-QTOF-MS. Then determined the primary polyphenols with XO inhibitory effect and clarified their potential mechanisms by omission experiment, interaction assay, inhibition type, and fluorescence measurements. The results revealed that nine polyphenols were detected in the free polyphenol extract and ten polyphenols were detected in the bound polyphenol extract. Meanwhile, seven polyphenols were identified as XO inhibitors, including quercetin, kaempferol, isorhamnetin, rutin, hyperoside, protocatechuic acid, and quercitrin with the IC₅₀ values of 0.03, 0.11, 0.07, 5.62, 11.48, 22.13, and 367.82 mg/mL, but their inhibition stability was lower than 24 h. Although the content of quercetin (18.87 mg/g) was not the highest, it played a crucial role to the XO inhibitory effect of FSI. Furthermore, kaempferol and isorhamnetin alone revealed the sub-additive effect with quercetin, while the combination of other polyphenols with quercetin generated the interference or antagonism effects. Quercetin, isorhamnetin, and kaempferol were mixed-type and competitive inhibitors, which significantly quenched the fluorescence intensity of XO. Moreover, the binding processes of quercetin-XO, kaempferol-XO, and isorhamnetin-XO were spontaneous and endothermic, and the hydrophobic interaction was the key driving force. In general, quercetin, kaempferol, and isorhamnetin in FSI can be used as potential XO inhibitors.

Flos Sophorae Immaturus (FSI) 作为一种降低尿酸的天然产物，具有潜在的黄嘌呤氧化酶 (XO) 抑制活性。目前的工作通过 UPLC-QTOF-MS 鉴定和量化了 FSI 的游离和结合多酚。然后通过遗漏实验、相互作用测定、抑制类型和荧光测量确定了具有XO抑制作用的初级多酚，并阐明了它们的潜在作用机制。结果表明，在游离多酚提取物中检测到九种多酚，在结合多酚提取物中检测到十种多酚。同时，7种多酚被鉴定为XO抑制剂，包括槲皮素、山奈酚、异鼠李素、芦丁、金丝桃苷、原儿茶酸和槲皮苷，IC ₅₀分别为 0.03、0.11、0.07、5.62、11.48、22.13 和 367.82 mg/mL，但其抑制稳定性低于 24 h。槲皮素的含量（18.87 mg/g）虽然不是最高的，但对FSI的XO抑制作用起着至关重要的作用。此外，单独的山柰酚和异鼠李素显示出与槲皮素的亚加成作用，而其他多酚与槲皮素的组合产生干扰或拮抗作用。槲皮素、异鼠李素和山柰酚是混合型竞争性抑制剂，可显着猝灭XO的荧光强度。此外，槲皮素-XO、山柰酚-XO和异鼠李素-XO的结合过程是自发的和吸热的，疏水相互作用是关键驱动力。一般来说，槲皮素、山柰酚、