The structural characterization of a new flavonoid from bergamot fruit (Citrus bergamia Risso) carrying the 3-hydroxy-3-methyl glutaryl (HMG) ester moiety has been accomplished, and its antioxidant ability was tested from a chemical point of view. The peculiarity of the new molecule, named peripolin, relies on the presence of the HMG chemical group linked to the sugar portion of neoeriocitrin; the structure was elucidated using both high-resolution mass spectrometry and nuclear magnetic resonance experiments performed on the purified molecule extracted from the fruit. The antioxidant ability of the new molecule was tested by classical chemical approaches, such as DPPH, ABTS and FRAP assays, and from a theoretical point of view. ¹H and ¹³C NMR experiments and HR-ESI-MS/MS experiments show unequivocally that the HMG moiety is linked to the primary position of the glucose unit of neohesperidose, while the chemical tests and the computational results show that peripolin possesses strong antioxidant behavior, similar to that of neoeriocitrin and remarkably higher respect to the other flavonoids present in the fruit. Furthermore, the quantitative assays carried out by UPLC-MS/MS showed that its amount in the fruit is similar to that of the other main flavonoids. Furthermore, molecular dynamics simulations allowed us to investigate the possible conformations adopted by the antioxidants in the presence of water molecules. In particular, the switch of open-closed conformations of HMG-containing species was evidenced. As far as the reaction with DPPH, the calculation of ΔG_rea supported the experimental outcomes regarding the peripolin and neoeriocitrin activity. In conclusion, bergamot fruit, already known for its potential to lower the level of blood cholesterol, has been proven to contain molecules such as neoeriocitrin and the newly characterized peripolin, which could have important in-vivo antioxidant characteristics.

中文翻译：

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Peripolin的结构表征及佛手柑中HMG黄酮类化合物的抗氧化活性研究

已经完成了来自佛手柑果实 (Citrus bergamia Risso) 的带有 3-羟基-3-甲基戊二酰 (HMG) 酯部分的新类黄酮的结构表征，并从化学角度测试了其抗氧化能力。这种名为 peripolin 的新分子的特性依赖于与新圣草素的糖部分相连的 HMG 化学基团的存在。通过对从水果中提取的纯化分子进行的高分辨率质谱和核磁共振实验，阐明了该结构。新分子的抗氧化能力通过经典的化学方法（例如 DPPH、ABTS 和 FRAP 测定）以及从理论角度进行测试。¹小时和¹³C NMR 实验和 HR-ESI-MS/MS 实验明确表明，HMG 部分与新橙皮苷葡萄糖单元的主要位置有关，而化学测试和计算结果表明 peripolin 具有很强的抗氧化行为，类似于新圣草素的含量和对水果中存在的其他类黄酮的显着更高的尊重。此外，通过 UPLC-MS/MS 进行的定量分析表明，其在水果中的含量与其他主要黄酮类化合物的含量相似。此外，分子动力学模拟使我们能够研究抗氧化剂在水分子存在下采用的可能构象。特别是，证明了含 HMG 物种的开闭构象的转换。至于与 DPPH 的反应，ΔG 的计算_rea支持关于 peripolin 和 neoeriocitrin 活性的实验结果。总之，佛手柑果实以其降低血液胆固醇水平的潜力而闻名，已被证明含有新圣草素和新发现的 peripolin 等分子，这些分子可能具有重要的体内抗氧化特性。