Compounds Isolated from <i>Paepalanthus</i> spp. (Eriocaulaceae) and Their Evaluation in Antimicrobial, Cytotoxic, and Antiviral Assays

<i>Paepalanthus acanthophyllus</i> and <i>P. bromelioides</i> belong to the Eriocaulaceae family. According to the literature, secondary metabolites isolated in <i>Paepalanthus</i> have interesting biological activities. This research aimed to isolate constituents from the capitula of the mentioned species and to evaluate their cytotoxic, antimicrobial, and antiviral activities. Through maceration and several types of separation procedures, the crude extracts were produced, and the structures of constituents were identified mostly by nuclear magnetic resonance. Cytotoxic and antimicrobial activities were evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide and 2,3,5-triphenyl-2<i>H</i>-tetrazolium chloride methods, respectively, while antiviral activity was evaluated by enzymatic and phenotypic assays. Two flavonoids were isolated in the dichloromethane fraction, and four flavonoids and one benzoic acid derivative were isolated in the ethyl acetate fraction of <i>P. acanthophyllus</i>. Paepalantine was isolated from <i>P. bromelioides</i>. The isolated compounds did not show significant cytotoxicity, and the highest values of growth-inhibitory activity observed reached 29.17% (colon cancer) and 19.24% (breast cancer). Antimicrobial evaluation showed the best result to 6-methoxykaempferol against <i>S. aureus</i> (MIC = 250 μg mL^-1). Antiviral evaluation showed that 6-methoxykaempferol-3-<i>O</i>-β-D-6″-(<i>p</i>-coumaroyl)-glucopyranoside inhibited the ZIKV enzyme NS2B-NS3pro in the lowest micromolar range (IC₅₀ = 1.95 μM); however, it did not show inhibition when evaluated in phenotypic assays with the ZIKV replicon.