This work describes a green synthesis, the characterization, and biological evaluation of silver nanoparticles (AgNPs). The AgNPs suspension was synthesized using aqueous leaf extract of Eucalyptus grandis, which presented a characteristic band at 407 nm in the UV-Vis spectrum. The AgNPs presented a spherical shape and size of 9.7 ± 0.3 nm. The nanoparticles were stable over a month, indicating that E. grandis’ extract is suitable for their preparation and stabilization. The X-ray analysis showed that the crystallinity of AgNPs corresponded to the centered face phase of silver. The antibacterial and leishmanicidal activities of AgNPs were evaluated. The AgNPs presented antibacterial activity on the Gram-negative bacteria Escherichia coli at 53.9 µg mL-1. The leishmanicidal activity evaluation against promastigote forms of Leishmania infantum, Leishmania amazonensis, and Leishmania braziliensis showed that the biological response is dependent on the volume of AgNP suspension. It was demonstrated that L. infantum was more sensitive to the nanoparticle’s treatment than L. amazonensis and L. braziliensis. The treatment of L infantum promastigotes with 150 µL of AgNP suspension reduced parasite growth by 67.9%, a result which was similar to the treatment with 1 (66.7%) or 2 µL (70.6%) of amphotericin B used as a positive control.

The fungal Hemileia vastatrix is the causal agent of coffee leaf rust, one of the worst and devastating disease in coffee cultures worldwide. As a result of our research on natural products for the development of novel agrochemicals, we found that the hexane extract from leaves of the Brazilian medicinal plant Garcinia gardneriana, at 500 μg mL-1, inhibited in 98% the germination of H. vastatrix urediniospores. This extract showed no phytotoxicity when tested for seed germination and seedling growth inhibitory activity using sensible plant species. Also, the hexane extract from leaves was tested for anti-acetylcholinesterase activity, which constitutes a mechanism of action of major commercial insecticides used in agriculture, and showed low activity even at concentrations about two times higher than the half maximal inhibitory concentration (IC50) found in the antifungal assays. Gas chromatography-mass spectrometry (GC-MS) analysis showed that the hexane extract is constituted mainly by the pentacyclic triterpene lupeol, together with a series of sesquiterpenes as minor components. This is the first report on the investigation of antifungal, phytotoxic and acetylcholinesterase activities of extracts from leaves of G. gardneriana. These findings indicate that G. gardneriana may constitute a promising source of natural products for controlling the coffee leaf rust fungus.