Helicteres velutina K. Schum (Sterculiaceae), a member of Malvaceae sensu lato, is a Brazilian endemic plant that has been used by the indigenous tribe Pankarare as an insect repellent. A previous study has reported the isolation of terpenoids, flavonoids and pheophytins, in addition to the larvicidal activity of crude H. velutina extracts derived from the aerial components (leaves, branches/twigs, and flowers). The present study reports the biomonitoring of the effects of fractions and isolated compounds derived from H. velutina against A. aegypti fourth instar larvae. A crude ethanol extract was submitted to liquid–liquid extraction with hexane, dichloromethane, ethyl acetate and n-butanol to obtain their respective fractions. Larvicidal evaluations of the fractions were performed, and the hexane and dichloromethane fractions exhibited greater activities than the other fractions, with LC50 (50% lethal concentration) values of 3.88 and 5.80 mg/mL, respectively. The phytochemical study of these fractions resulted in the isolation and identification of 17 compounds. The molecules were subjected to a virtual screening protocol, and five molecules presented potential larvicidal activity after analyses of their applicability domains. When molecular docking was analysed, only three of these compounds showed an ability to bind with sterol carrier protein-2 (1PZ4), a protein found in the larval intestine. The compounds tiliroside and 7,4′-di-O-methyl-8-O-sulphate flavone showed in vitro larvicidal activity, with LC50 values of 0.275 mg/mL after 72 h and 0.182 mg/mL after 24 h of exposure, respectively. This is the first study to demonstrate the larvicidal activity of sulphated flavonoids against A. aegypti. Our results showed that the presence of the OSO3H group attached to C-8 of the flavonoid was crucial to the larvicidal activity. This research supports the traditional use of H. velutina as an alternative insecticide for the control of A. aegypti, which is a vector for severe arboviruses, such as dengue and chikungunya.

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.

Abstract:Malvoideae is the largest subfamily of Malvaceae, including 110 genera and 1,730 species distributed predominantly in tropical regions, with a few representatives in temperate regions. In Brazil, the subfamily occurs throughout the country and all phytogeographic domains.

This work presents a floristic survey of the subfamilies Bombacoideae, Byttnerioideae, Grewioideae and Helicterioideae (Malvaceae s.l.) in the Raso da Catarina Ecoregion (RCE), Bahia, Brazil. The samples analyzed were collected from September 2013 to May 2015. The analyses were supplemented with dried collections kept in the herbaria: ALCB, HRB, HUEFS, HUNEB, HST, IPA, PEUFR, R and RB. The identifications were based mainly on specialized bibliographies, protologues, types and herbaria collections. Ten genera and 22 species of the subfamilies were recorded, nine endemic to Brazil. Waltheria L. was the most representative genus with five species, followed by Ceiba Mill. and Melochia L. with three species each, Helicteres L., Luehea Willd., Pachira Aubl. and Pseudobombax Dugand presented two species each and other genera were represented by one species each. Among the species recorded, Luehea candicans Mart. represents a new record for the Caatinga biome. The species most commonly found in the study area were Helicteres velutina K.Schum., Melochia tomentosa L., Waltheria brachypetala Turcz., W. indica L. and W. rotundifolia Schrank. The taxonomic treatment includes identification key, descriptions, illustrations, photos, geographical distribution, reproductive phenology and comments about all studied species. Keywords: biodiversity, Caatinga, morphology, semiarid, taxonomy.