Brazilian Journal of Pharmaceutical Sciences (Sep 2009)
Antioxidant capacity of extracts and isolated compounds from Stryphnodendron obovatum Benth
Abstract
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-(4β→8)-epigallocatechin (EPEP), epigallocatechin-(4β→8)-gallocatechin (EPGC), robinetinidol-(4α→8)-gallocatechin (ROGC) and robinetinidol-(4β→8)-epigallocatechin (ROEP). Evaluation of the antioxidant capacity in vitro by the methods of DPPH free radical (IC50; μg/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 IC50 (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.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-(4β→8)-epigalocatequina (EPEP), epigalocatequina-(4β→8)-galocatequina (EPGC), robinetinidol-(4α→8)-galocatequina (ROGC) e robinetinidol-(4β→8)-epigalocatequina (ROEP). A capacidade antioxidante in vitro pelos métodos do radical livre DPPH (IC50; μg/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: IC50 (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. Vitamina C e trolox mostraram valores de 30,11 e 30,10, respectivamente. Os dímeros mostraram maior atividade no sequestro de radicais livres, possivelmente relacionada com o número de hidroxilas. No entanto, substâncias com ausência de hidroxila na posição 5 do anel A (5-desoxi-proantocianidinas) não alteraram o poder antioxidante frente ao radical livre DPPH, tendo sido avaliadas aqui pela primeira vez. Entre os monômeros, parece haver uma relação direta com a estereoquímica. A presença de um radical metila no anel B reduziu significativamente a atividade da galocatequina. Todas as substâncias isoladas mostraram maior atividade do que a vitamina C e trolox, e estes não mostraram diferença significativa entre si.
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