Anti-Zika Virus Activity and Isolation of Flavonoids from Ethanol Extracts of Curatella americana L. Leaves.

The ethnomedicinal plant Curatella americana L. (Dilleniaceae) is a common shrub in the Brazilian Cerrado, whose ethanolic extract showed significant in vitro anti-Zika virus activity by the MTT colorimetric method. Currently, there is no drug in clinical use specifically for the treatment of this virus; therefore, in this work, the antiviral and cytotoxic properties of the ethanolic extract, fractions, and compounds were evaluated. The ethanolic extract of the leaves showed no cytotoxicity for the human MRC-5 cell and was moderately cytotoxic for the Vero cell (CC50 161.5 ± 2.01 µg/mL). This extract inhibited the Zika virus multiplication cycle with an EC50 of 85.2 ± 1.65 µg/mL. This extract was fractionated using the liquid-liquid partition technique, and the ethyl acetate fraction showed significant activity against the Zika virus with an EC50 of 40.7 ± 2.33 µg/mL. From the ethyl acetate fraction, the flavonoids quercetin-3-O-hexosylgallate (1), quercetin-3-O-glucoside (2), and quercetin (5) were isolated, and in addition to these compounds, a mixture of quercetin-3-O-rhamnoside (3) and quercetin-3-O-arabinoside (4) was also obtained. The isolated compounds quercetin and quercetin-3-O-hexosylgallate inhibited the viral cytopathic effect at an EC50 of 18.6 ± 2.8 and 152.8 ± 2.0, respectively. Additionally, analyses by liquid chromatography coupled to a mass spectrometer allowed the identification of another 24 minor phenolic constituents present in the ethanolic extract and in the ethyl acetate fraction of this species.

Anti-arboviral activity and chemical characterization of hispidulin and ethanolic extracts from Millingtonia hortensis L.f. and Oroxylum indicum (L.) Kurz (Bignoniaceae).

Millingtonia hortensis L.f. and Oroxylum indicum (L.) Kurz (Bignoniaceae) are native species from the Asian continent. They are popularly used in traditional medicine and their extracts are rich in flavonoids. In this work, ethanolic extracts of stems and leaves of these species were evaluated against the Chikungunya, Zika and Mayaro virus. The extracts were subjected to analysis by ultra-efficient liquid chromatography coupled to mass spectrometry. Additionally, M. hortensis leaves extract was fractionated, leading to the isolation of hispidulin. Anti-arboviral activity against the three viruses was detected for M. hortensis leaves extract with EC50 ranging from 37.8 to 134.1 µg/mL and for O. indicum stems extract with EC50 ranging from 18.6 to 55.9 µg/mL. Hispidulin inhibited viral cytopathic effect of MAYV (EC50 value 32.2 µM) and CHIKV (EC50 value 78.8 µM). In LC-DAD-ESI-MS/MS analysis we characterized 25 flavonoids confirming once again the presence of these substances in extracts of these species.