The EC50 values of these purified tetrahydro-b-carboline derivatives were 0.625–1.334 lmol/mL and 1.063–2.072 lmol/mL in ABTS assay and DPPH assay, respectively. It is the first time for us to identify (3S)-1,2,3,4-tetrahydro-b-carboline-3-carboxylic acid as an in vitro antioxidant in AGE