Chemical composition and antioxidant and antibacterial activity of Platymiscium gracile Benth.: A species threatened by extinction

Sawdust of Platymiscium gracile Benth. (Fabaceae) was extracted by percolation using n-hexane, dichloromethane, ethyl acetate, and methanol sequentially. Then, fractions were screened for their phenolic contents and antioxidant and antibacterial properties. The phenolic contents ranged from 13,667 ± 773 (ethyl acetate fraction) to 36,350 ± 3049 mg GAE/100 g extract (hexane fraction). In general, all fractions displayed a significant antioxidant activity with values ranging from 20,055 ± 1341 and 194,919 ± 7163 μmol TE/100 g extract, 1785 ± 225 and 32,264 ± 326 mg AAE/100 g extract, 30,081 ± 1618 and 901,706 ± 20,393 μmol TE/100 g extract for the DPPH, FRAP, and ABTS assays, respectively. Eleven compounds were isolated and identified, corresponding to homopterocarpin, scoparone, 8-hydroxyhomopterocarpin, calycosin, 3,4-dimethoxycinnamaldehyde, medicarpin, liquiritigenin, isoliquiritigenin, 3,4,5-trimethoxycinnamaldehyde, 8-methoxyhomopterocarpin, and oleanolic aldehyde acetate. Radical scavenging and antioxidant properties of isolated compounds showed that isoliquiritigenin exhibited the highest activity with values of 1173 ± 61 and 8104 ± 38 μmol TE/g for DPPH radical and ABTS radical cation assays, respectively, and presented 23.6 ± 0.7 mg AAE/g for reducing power assay. In addition, MIC values of isoliquiritigenin for S. aureus, B. cereus, and E. faecalis were 62.5 µg/mL (MIC value for Ampicillin® was 250 µg/mL against B. cereus). The results suggested that P. gracile might be an important source of metabolites with antibacterial and antioxidant activity; therefore, greater efforts should be made for the conservation of this species. Keywords: Platymiscium gracile Benth., Total phenolics, DPPH assay, FRAP assay, B. cereus, Isoliquiritigenin