Synthesis and In Vitro Antioxidant Activity Evaluation of Ester Derivatives of Betulin
Objective 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.
betulinester derivativessynthesisantioxidant activitymodification site
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