Design and synthesis of benzylidene derivatives of curcumin, and evaluation of its antioxidant and chelating activities

Abstract

A number of curcumin derivatives, including 4-arylidene curcumin derivatives (4-arylidene-1,7-bisaryl-hepta-1,6-diene-3,5-diones), have been synthesised, purified and characterized. 4-(4-Hydroxy-3-methoxybenzylidene) curcumin (3; IC₅₀; 35 ± 2.02), 4-(4-Hydroxy-benzylidene) curcumin (9; IC₅₀; 42 ± 0.9), and 4-(3, 4, 5-trimethoxybenzylidene) curcumin (10; IC₅₀; 58 ± 2.0), were found to have more antioxidant property than ascorbic acid (IC₅₀; 111 ± 1.20), in the DPPH. Additionally, it was shown that 4-(4-Hydroxy-3-methoxybenzylidene) curcumin (3; IC₅₀; 1.42 ± 0.11), 4-(4-Hydroxy-benzylidene) curcumin (9; IC₅₀; 1.73 ± 0.026), and 4-(3, 4, 5-trimethoxybenzylidene) curcumin (10; IC₅₀; 2.53 ± 0.145) exhibited higher antioxidant activity in ABTS assays than ascorbic acid (IC₅₀; 2.53 ± 0.01). However, Fe²⁺ chelating activity of 4-(4-Hydroxy-3-methoxybenzylidene) curcumin (3; 54 ± 3.5), 4-pyridilidene curcumin (4; 42 ± 1.8), 4-(4-Hydroxy-benzylidene) curcumin (9; 56 ± 0.1) and 4-(3, 4, 5-trimethoxybenzylidene) curcumin (10; 57 ± 2.4) exhibited better chelating activity than EDTA (35 ± 2.1). The structural activity relationship (SAR) has been used in this study to investigate the free radical scavenging and Fe²⁺ chelating activity of curcumin and its derivatives. Studies on chelating and antioxidant activity has shown that this class of 4-arylidene curcumin derivatives has much better chelating and antioxidant activity than curcumin, the parent molecule.