通过对白桦脂醇不同位点的修饰及进一步抗氧化活性分析，探讨白桦脂醇各修饰位点与抗氧化活 性间的关系。方法 以白桦脂醇为起始物，以四氢呋喃（THF）或二甲基甲酰胺（DMF）作溶剂，控制反应温度及 酸酐当量，进行酰化、羟基保护、氯铬酸吡啶鎓盐（PCC）氧化、脱保护基等反应合成7 个目标化合物，即 3，28-二乙酰基白桦脂醇、3，28-二烯丙酰基白桦脂醇、28-乙酰基白桦脂醇、28-烯丙酰基白桦脂醇、3-乙酰 基白桦脂醇、3-烯丙酰基白桦脂醇和3-羰基白桦脂醇。采用1，1-二苯基-2-三硝基苯肼（DPPH）法测定目标化 合物的体外抗氧化活性。结果 白桦脂醇衍生物的结构通过核磁共振（NMR）图谱、高分辨液质联用（HRLC-MS） 综合解释得以验证。DPPH 法测试结果显示，白桦脂醇、3-乙酰基或烯丙酰基白桦脂醇及28-乙酰基或烯丙酰 基白桦脂醇对DPPH 均有一定的清除作用，且呈浓度依赖性，28-乙酰基或烯丙酰基白桦脂醇对DPPH 的清除 效果优于白桦脂醇及3-乙酰基或烯丙酰基白桦脂醇。在相同条件下，3-羰基白桦脂醇与3，28-双酰基（乙酰基 或烯丙酰基）取代白桦脂醇无明显清除DPPH 的作用。此外，烯丙酰基修饰的白桦脂醇体外抗氧化活性优于对 应的乙酰基修饰的白桦脂醇。结论 建立了简单易行的白桦脂醇酰化及羟基官能团保护方法。28-烯丙酰基白 桦脂醇表现出更优良的体外抗氧化活性，提示白桦脂醇28-位引入吸电子作用基团可能提高其抗氧化作用。

To explore the relationship between each modification site of betulin and its antioxidant activity by modifying different sites of betulin and further analyzing its antioxidant activity. Methods Seven target compounds，including 3，28-diacetyl betulin，3，28-diallyacyl betulin，28-acetyl betulin，28-allyacyl betulin，3- acetyl betulin， 3-allyacyl betulin and 3-carbonyl betulin were synthesized via acylation， hydroxyl protection， pyridinium chlorochromate （PCC） oxidation， deprotection， and other reactions using betulin as the starting material，as well as tetrahydrofuran （THF） or dimethylformamide （DMF） as the solvent. The reaction temperature and anhydride equivalent were also controlled. In vitro antioxidant activity of target compounds was determined using DPPH （1，1-diphenyl-2-trinitrophenylhydrazine）. Results The structure of betulin derivatives were verified through comprehensive interpretation of nuclear magnetic resonance （NMR） spectra， and high-resolution liquid chromatography-mass spectrometry （HRLC-MS）. The DPPH trial results showed that betulin，3-acetyl or allyacyl betulin， and 28-acetyl or allyacyl betulin all have a certain scavenging effect on DPPH. The clearance rates of DPPH increased with increasing concentration of these compounds. The clearance effects of 28-acetyl or allyacyl betulin on DPPH is better than that of betulin and 3-acetyl or allyacyl betulin. There is no significant difference between the antioxidant activity of 3-carbonyl betulin and 3， 28-diacetyl or diallyacyl betulin under the same condition. Moreover， in vitro antioxidant activity of allyacyl derivatives is better than that of acetyl derivatives. Conclusion A feasible method for acylation of betulin and protection of hydroxyl functional groups was established. 28-allyacyl betulin exhibits slightly higher in vitro antioxidant activity than betulin and other betulin derivatives. It was suggested that introduction of an eletron-withdrawing group at the 28-position of betulin may enhance its antioxidant effect.

R284.3

广东省科技厅项目（2012A030100015）；广州中医药大学大学生创新创业训练计划项目（202310572306）。