Synthesis of Chalcone Derivatives from Halogenated Vanillin and their Activity Test as Antioxidant

Abstract

Synthesis of 3-chloro-4-hydroxy-5-methoxybenzaldehyde, 3-bromo-4-hydroxy-5-methoxybenzaldehyde and 2',4'-dihydroxy-3-bromo-4-hydroxy-5-methoxyhalcone and evaluation of their antioxidant activity have been carried out. 3-Chloro-4-hydroxy-5-methoxybenzaldehyde was obtained through chlorination of vanillin using Ca(ClO)2, while 3-bromo-4-hydroxy-5-methoxybenzaldehyde was obtained via bromination of vanillin using KBrO3 in glacial acetic acid solvent and 47% HBr catalyst. Then, 2',4'-dihydroxy-3-bromo-4-hydroxy-5-methoxychalcone was prepared from 3-bromo-4-hydroxy-5-methoxybenzaldehyde and 2-4-dihydroxyacetophenone through Claisen-Schmidt condensation in the presence of KOH (40%) base and KSF montmorillonite in methanol. Elucidation of the structure of these compounds was performed using FTIR, GC-MS, TLC-Scanner, MS-Direct, 1H-NMR, and 13C-NMR. The synthesized benzaldehydes and chalcone were tested for their antioxidant activities using DPPH method, where 2,6-di-tert-butyl-4-methylphenol (BHT) was used as positive control. The results showed that 3-chloro-4-hydroxy-5-methoxybenzaldehyde, 3-bromo-4-hydroxy-5-methoxybenzaldehyde and 2',4'-dihydroxy-3-bromo-4-hydroxy-5-methoxyhalcone were obtained in 53%, 97%, and 1%, respectively. The antioxidant activity assay showed that BHT, 3-chloro-4-hydroxy-5-methoxybenzaldehyde, 3-bromo-4-hydroxy-5-methoxybenzaldehyde and 2',4'-dihydroxy-3-bromo-4-hydroxy-5-methoxyhalcone displayed the IC50 of 27.94, 244.11, 269.44 and 162.10 µg/mL, respectively.