The extract from stem bark of Stryphnodendron obovatum Benth. was chromatographed on a Sephadex ® LH-20 column, and yielded nine compounds: gallic acid (GA), p-hydroxybenzoic acid (PHB), gallocatechin (GC), epigallocatechin (EPG), 4'-O-methylgallocatechin (MGC), epigallocatechin-(4b→8)-epigallocatechin (EPEP), epigallocatechin-(4b→8)-gallocatechin (EPGC), robinetinidol-(4a→8)-gallocatechin (ROGC) and robinetinidol-(4b→8)-epigallocatechin (ROEP). Evaluation of the antioxidant capacity in vitro by the methods of DPPH free radical (IC 50 ; mg/mL) and reduction of the phosphomolybdenum complex (RAC) gave the following results, respectively: crude extract 4.52 and 0.8242; ethyl-acetate fraction 4.04 and 0.9537; aqueous fraction 5.58 and 0.9275. The crude extract and ethyl-acetate fraction were shown to possess an antioxidant capacity comparable to that of vitamin C (4.93 and 1.0). The values obtained by the DPPH free-radical method for the isolated compounds were IC 50 (μM): GA=8.89; PHB=10.12; GC=16.46; EPG=13.20; MGC=21.00; EPEP=6.89; EPGC=4.91; ROGC=7.78 and ROEP=6.20. Vitamin C and trolox showed 30.11 and 30.10, respectively. Dimers showed greater activity in scavenging free radicals, possibly related to the number of hydroxyls. However, compounds without a hydroxyl at position 5 of the A-ring (5-deoxy-proanthocyanidins) did not change the antioxidant activity of the DPPH free radical, as evaluated here for the first time. Among the monomers, there appeared to be a direct relationship in scavenging of free radicals because of the stereochemistry of the compounds. The presence of a methyl radical on the B-ring significantly reduced the scavenging of free radicals of gallocatechin. All compounds showed greater scavenging of radicals than vitamin C and trolox, and these two compounds showed no significant difference from each other.Uniterms: Stryphnodendron obovatum. Antioxidant capacity. Condensed tannins. DPPH free radical. Phosphomolybdenum complex.O extrato das cascas de Stryphnodendron obovatum submetido à cromatografia em coluna, Sephadex ® LH-20, forneceu nove substâncias: ácido gálico (GA), ácido p-hidróxibenzóico (PHB), galocatequina (GC), epigalocatequina (EPG), 4'-O-metilgalocatequina (MGC), epigalocatequina-(4b→8)-epigalocatequina (EPEP), epigalocatequina-(4b→8)-galocatequina (EPGC), robinetinidol-(4a→8)-galocatequina (ROGC) e robinetinidol-(4b→8)-epigalocatequina (ROEP). A capacidade antioxidante in vitro pelos métodos do radical livre DPPH (IC 50 ; mg/mL) e do complexo fosfomolibdênio (CAR) apresentou os seguintes resultados, respectivamente: extrato bruto 4,52 e 0,8242; fração acetato de etila 4,04 e 0,9537 e fração aquosa 5,58 e 0,9275 demonstrando possuírem capacidade antioxidante quando comparados com vitamina C 4,93 e 1,0. Os valores obtidos pelo método do radical livre DPPH com as substâncias isoladas foram: IC 50 (μM): GA=8,89; PHB=10,12; GC=16,46; EPG=13,20; MGC=21,00; EPEP=6,89; EPGC=4,91; ROGC=7,78 e ROEP=6,20 tendo sido avaliadas aqui pela primeira vez. Entre os monômeros, parece haver uma ...