A Novel Mannich Derivative of Protocatechuic Acid: Synthesis, Crystal Structure and Antioxidant Activity

A novel Mannich derivative of protocatechuic acid, 3-diethylaminomethyl-4,5-dihydroxy-benzoic acid (PADE), was synthesized for the first time. The structure of PADE was confirmed by infrared spectrum, mass spectrum, and X-ray crystallography. The derivative PADE crystallizes in the monoclinic space group P2(1)/c with cell parameters of a = 8.820(2) Ǻ, b = 11.469(3) Ǻ, c = 14.227(4) Ǻ, β = 107.128(3)°, V = 1375.3(6) Ǻ3 and Z = 4. The average H···A distance is 1.980 Ǻ, which indicates the existence of strong hydrogen bond. The intermolecular and intramolecular hydrogen bonds generate the Mannich derivative PADE into a three-dimensional architecture. The antioxidant activity of PADE was evaluated by scavenging 1,1-diphenyl-2-picrylhydrazyl (DPPH) and reducing power determination. The results showed that PADE displayed dose-dependency in DPPH radical scavenging and reducing power assays. DPPH radical scavenging activity of PADE (IC50, 1.2 × 10−5 mol/l) was higher than that of protocatechuic acid (5.2 × 10−5 mol/l) and ascorbic acid (2.5 × 10−5 mol/l). The reducing power of PADE was higher than that of ascorbic acid but weaker than that of the raw material protocatechuic acid. The 3D structure of PADE is stabilized by intermolecular and intramolecular hydrogen bonds, which may raise its antioxidant activity.