3,4-Dihydroxymandelic acid amides of alkylamines as antioxidants for lipids

The antioxidative and radical scavenging activity of the 3,4-dihydroxymandelic acid (DHMA) amides of hexylamine, 2-ethylhexylamine, octylamine, and cyclohexylamine was determined by several physicochemical test systems. The amides were synthesized by protecting group-free coupling of in situ prepared N-hydroxysuccinimidylester of DHMA and the amines. The radical scavenging activity was determined using the DPPH (2,2-diphenyl-1-picrylhydrazyl) method and by quenching superoxide anions generated using a horse radish peroxidase/H 2 O 2 system. In the DPPH assay, all amides show higher radical scavenging activity (EC 50 0.09-0.12 mol/mol DPPH ) compared to the standard antioxidants ascorbic acid (EC 50 0.27 mol/mol DPPH ) and tocopherol (EC 50 0.25 mol/mol DPPH ). The amides are also more potent superoxide radical scavengers (IC 50 0.9, tocopherol 0.08). The DHMA octylamide in combination with ascorbic acid shows a synergistic antioxidative effect in the emulsion model. In conclusion, the new alkylamides of DHMA are easy to synthesize, potent radical scavengers and protect lipids, in particular the highly unsaturated, both in bulk and in emulsions against autoxidation.