New Sulphated Flavonoids and Larvicidal Activity of Helicteres velutina K. Schum (Sterculiaceae)

Abstract

Helicteres velutina K. Schum (Sterculiaceae), commonly known in Brazil as ‘pitó’, is traditionally used by indigenous peoples as insecticides and repellents. The present work reports on the the phytoconstituents from aerial parts of H. velutina and evaluation of the larvicidal potential of its extract. The compounds were isolated using chromatographic techniques and identified by NMR, IR and LC-HRMS. This study led to the isolation of a fatty acid, one aliphatic alcohol, four chlorophyll derivatives, one steroid, triterpenes, a lignan, and flavonoids, highlighting the new compounds in the literature, 5,4′-di-hydroxy-7-methoxy-8-O-sulphate flavone (mariahine) (15a) and 5,3′-di-hydroxy-7,4′-dimethoxy-8-O-sulphate flavone (condadine) (15b). The work presented here contributes to the chemotaxonomic knowledge of the Sterculiaceae family by describing the occurrence of sulphated flavonoids in this family for the first time. The crude ethanolic extract of H. velutina featured robust larvicidal activity against Aedes aegypti larvae, showing that the extract can be useful as a domestic larvicide, just as indicated by traditional use, to combat A. aegypti, a vector insect of severe viral diseases, such as dengue and Zika.

Insights on the Larvicidal Mechanism of Action of Fractions and Compounds from Aerial Parts of Helicteres velutina K. Schum against Aedes aegypti L.

“…In Brazil and in other parts of the world, plant extracts (medicinal, native, and adapted) and their derivatives have been tested against different disease vectors, including A. aegypti and A. albopictus [17]. The species H. velutina stands out for its popular use as repellent [11] and for its proven larvicidal activity of the extract, fractions, and isolated substances against A. aegypti [12,13].…”

“…Both flavonoids tested here were isolated from the dichloromethane fraction [12], according to the results obtained. The 7,4 -di-O-methyl-8-O-sulphate flavone has the most promising activity of the fraction, different from tiliroside, which triggered later activity and resembled the results found in the negative control.…”

“…The material was identified by Prof. Adilva de Souza Conceição, and a specimen voucher was kept in the Herbarium of the State University of Bahia. The plant material was oven dried at 40 • C, and 1976.0 g of the powder was macerated with 95% ethanol for 72 h. The extract solution was dried under reduced pressure at 40 • C and provided 39.7 g of crude ethanolic extract (CEE) that was submitted to liquid-liquid chromatography using hexane, dichloromethane, ethyl acetate, and n-butanol, resulting in their respective fractions and a hydroalcoholic fraction [12].…”

“…In this context, Helicteres velutina K. Schum (Sterculiaceae) species, popularly known as "pitó" and traditionally used as insect repellent, can be highlighted [11]. Scientific studies have shown its larvicidal activity against A. aegypti [11][12][13]. Regarding the phytochemicals from the genus Helicteres, previous studies have reported the occurrence of steroids, saponins, and phenolic compounds, such as flavonoids and tannins [13,14].…”

“…In order to continue the ongoing work with H. velutina against A. aegypti larvae, this study investigates the possible mechanisms of action involved in the larvicidal activity of fractions and isolated substances [12,13] by analyzing in vitro cytotoxicity and NO production.…”