Agroindustrial residues, such as leaves of fruit plants, can be sources of bioactive molecules, thus adding value to co-products that are rarely explored in agroindustry. In this context, this study aimed to look into the phytochemical profiles in detail and to explore the antitumor potential of S. tuberosa and S. mombin leaves. We observed that, S. tuberosa leaf extract was cytotoxic in both tumor and healthy cells. S. mombin extracts selectively inhibited cell proliferation in the tumor cell line for prostate cancer (PC3) and did not significantly affect healthy cells. The metabolic profiles of the extracts were evaluated by gas chromatography coupled with mass spectrometry and twenty-three metabolites were identified. The correlation of metabolic profiles with cytotoxic tests indicated possible chemical markers that may be responsible for the inhibition of cell proliferation. This study revealed that the unexplored co-products in agroindustry may have great therapeutic potential, and therefore should be screened for biologically active compounds.

Electrochemical methods are powerful in the characterization and design of redox-modulating agents. We, herein, report the electrochemical investigation, in aprotic medium, of eleven synthetic 3-thio-substituted-nor-beta-lapachones, along with the determination of cytotoxic activity and correspondent selectivity index, against several cancer cell lines and one normal cell. Four of the quinones are novel compounds. The redox behavior is representative of two independent systems: the easy reduction of the quinone moiety and, at far more negative potential, the reductive cleavage of the C-S-C bonding; and the anodic part controlled by the oxidation of the sulfur moiety. The compounds have shown relevant cytotoxic activity, with emphasis on 3-phenyl-thio-2,2-dimethyl-2,3-dihydronaphtho[1,2-b]furan-4,5-dione (compound 2), which mechanism of molecular action was shown to be related to reactive oxygen species (ROS) release. Despite the absence of a linear correlation, there is a trend: the majority of the thionaphthoquinones, with values of first wave reduction potential, less negative than -0.65 V, were active. The less electrophilic compound (3-(cyclohexylthio)-2,2-dimethyl-2,3-dihydronaphtho[1,2-b]furan-4,5-dione, cyclohexyl derivative) is also the less cytotoxic toward cancer cells. Agents containing chalcogens and quinones can be used to attack entities with a disturbed redox balance.