This study evaluated the chemical composition, antioxidant and anticholinesterase activities, and the toxicity of hydroethanolic extracts of the Parkia platycephala Benth. Hot extraction with 70% hydroethanolic solution was used to obtain crude extracts of the leaf (LE), bark (BE), flower (FE), and seed (SE). Separation and identification of the compounds were performed by liquid chromatography with diode array detection and gas chromatography coupled with mass spectrometry. Antioxidant and anticholinesterase activities were performed by the 2,2-diphenyl-1-picrylhydrazyl (DPPH•) and Ellman methods, respectively, and the preliminary toxicity by the method with Artemia salina. Chromatography analysis indicated naringin, kaempferol, stigmasterol, and β-sitosterol in all extracts. Gallic acid is prominent in the LE and FE, while ferulic acid is abundant in the BE and lupeol and lupeol acetate are prominent in the SE. The BE antioxidant activity (lethal concentration of 50% (IC50) = 14.72 ± 0.13 µg mL-1) is equivalent to the standard rutin (IC50 = 15.85 ± 0.08 µg mL-1). The SE had the best acetylcholinesterase inhibition potential (IC50 = 5.73 ± 0.68 µg mL-1). Aside from the SE, which is not toxic, the other extracts had low (LE, FE) and moderate (BE) toxicity. The extracts of P. platycephala have potential antioxidant and therapeutic uses, especially against Alzheimer’s disease.

Ouratea fieldingiana is a native medicinal plant from Northeastern Brazil and many biological properties are due to the phenolic constituents. The objective of this work was performing the characterization of O. fieldingiana leaf constituents to correlate with antioxidant and anticholinesterase activities by in vitro and in silico studies and thus contribute to find new agents against Alzheimer’s disease. The high-performance liquid chromatography revealed the presence of the flavonoids rutin, isoquercitrin, kaempferol-3-O-rutinoside, quercetin, apigenin and amentoflavone. The antioxidant activities by the (2,2-diphenyl-1-picrylhydrazyl) (DPPH) and 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) methodologies, showed good results with half maximal inhibitory concentration (IC50) values ranging from 5.63 to 11.47 µg mL-1 and 2.72 to 23.71 µg mL-1, respectively. Acetylcholinesterase inhibition assay pointed out the flavone apigenin with best activity. Computational studies evaluated the interaction of flavonoids with the enzyme acetylcholinesterase co-crystallized with the galantamine, used as standard. All flavonoids exhibited binding energy greater than that of galantamine, but only apigenin showed strong interaction with the active site of the enzyme and other bind probably to different allosteric centers. Then, O. fieldingiana extract and flavonoids with good anti-radical activity and presenting a broad-spectrum action against acetylcholinesterase (AChE) enzyme ought to be tested in clinical studies to discover new neuro-therapeutic candidates.