本研究以糙米为材料，通过碱解得到结合态酚粗提物，采用多种色谱手段分离纯化得到4种单体物质，通过高效液相色谱-质谱（LC-MS）、核磁共振（NMR）等波谱学方法鉴定其化学结构。4个单体化合物分别为6-羟基-2-氧代-1,2,3,4-四氢喹啉-4-羧酸甲酯（1）、4-羧甲氧基-6-羟基-2-喹诺酮（2）、4-羧基-6-羟基-2-喹诺酮（3）和2-(5-羟基-2-氧代吲哚-3-基)乙酸甲酯（4）。其中化合物1为新天然产物，化合物2为首次从糙米中分离报道的。采用高效液相色谱（HPLC）对糙米结合酚提取物中4个单体成分的含量进行了测定，其中化合物1含量最高，为0.90 mg/g DW。同时以1,1-二苯基-2-三硝基苯肼（1,1-diphenyl-2-picrylhydrazy，DPPH）、铁离子还原能力（ferric reducing ability of plasma，FRAP）和氧自由基吸收能力（oxygen radical absorbance capacity，ORAC）为指标评价4个单体的抗氧化活性。DPPH自由基清除能力最好的是化合物4，其IC50值为72.19 μM；FRAP法还原能力最强的是化合物2，FRAP值为249.60 mmol FeE/mol；ORAC法显示化合物3和4抗氧化能力最强，分别为2.87和2.69 μmol TE/μmol。研究结果有助于推进对糙米结合酚的认知，为糙米功效物质开发利用提供科学依据。

Brown rice bound phenolics were extracted by alkaline hydrolysis and separated by multiple chromatographic methods. Four monomers were obtained and their structures were identified by high performance liquid chromatography-tandem mass spectrometry (LC-MS) and nuclear magnetic resonance (NMR). The isolated compounds were elucidated as 6-hydroxy-2-oxo-1,2,3,4-tetrahydroquinoline-4-carboxylic acid methyl ester (1), 4-carboxymethoxy-6-hydroxy-2-quinolone (2), 4-carboxyl-6-hydroxy-2-quinolone(3) and 2 - (5-hydroxy-2-oxoindole-3-yl) acetate methyl ester (4). Compound 1 was a new natural product and compound 2 was reported from brown rice for the first time. The contents of four monomers were determined by high performance liquid chromatography (HPLC) and the content of compound 1 was the highest (0.9 mg/g DW). Antioxidant activity of four compounds was evaluated using the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging, ferric ion reducing antioxidant power (FRAP) assays and oxygen radical absorbance capacity (ORAC) methods, respectively. The strongest DPPH radical scavenging activity was compound 4, with the IC50 value being 72.19 μM. Compound 2 exhibited the highest FRAP reducing activity, which was 249.60 mmol FeE/mol. ORAC method showed that compounds 3 and 4 had the best antioxidant capacity, which were 2.87 and 2.69 μmol TE/μmol, respectively. These results will promote the cognition of brown rice bound phenolics. It can also provide scientific basis for the development and utilization of functional substances in brown rice.

广东省重点研发计划项目（2020B020225004）；国家自然科学基金项目（31871798；31972082）；广东特支计划本土创新创业团队项目（2019BT02N112）；广东省自然科学基金（2016A030312001）；科技创新战略专项资金-高水平农科院建设（R2017YJ-YB2006；R2018QD-081；R2018PY-JC002）；广东省农业科学院创新基金项目（202112）