Estudo fitoquímico e avaliação biológica dos extratos, fases e compostos isolados de três espécies do gênero Pavonia (Malvaceae) frente ao Aedes aegypti (L.)

Abstract

Medicinal plants represent alternatives to allopathic therapies, and the Malvaceae family stands out for the presence of bioactive compounds with anticancer, anti-inflammatory, antimicrobial, and antiviral properties. The species Pavonia malacophylla, Pavonia cancellata, and Pavonia blanchetiana are popularly known as ‘malva-rosa’, ‘malva- rasteira’ and ‘algodão-bravo’, respectively, and are distributed throughout much of Brazil. This research aimed to isolate and structurally characterize the chemical constituents of the three species and evaluate the larvicidal potential of their extracts, phases, and isolated substances against L4 larvae of the Aedes aegypti mosquito. Initially, the aerial parts of the species were dehydrated, crushed, and macerated with 95% EtOH. Their crude ethanolic extracts (CEE) were separately subjected to liquid-liquid chromatography with hexane, chloroform, ethyl acetate, and n-butanol, obtaining their respective phases, in addition to the hydroalcoholic phases. A biological screening of these extracts and phases against the L4 larval stage of the A. aegypti mosquito was performed, using different concentrations of the test samples, and mortality was evaluated over 24 hours. The phytochemical study of the three species used classical chromatographic techniques, HPLC, GC/MS, HPLC/MS, in addition to one- and two- dimensional 1H and 13C NMR spectroscopic methods, resulting in the isolation and identification of eighteen compounds described in a published article (Appendix 2), plus four substances derived from caffeoylquinic acid in P. malacophylla; steroids, triterpenes, pheophytins, methoxylated and glycosylated flavonoids, hydrocarbons, fatty acids, phenolic acids, and phenylpropanoids were found in P. cancellata; in addition to five glycosylated flavonoids in P. blanchetiana, supplemented by twelve more compounds that were recorded by mass spectrometry. The larvicidal activity of the extracts from the three plant species was evaluated against L4 larvae of A. aegypti. The extracts from P. malacophylla and P. cancellata stood out in this activity, presenting LC50 values of 3.0 mg/mL and 2.8 mg/mL, respectively. Analysis of the hexane, chloroform, ethyl acetate, n-butanolic, and hydroalcoholic phases showed that the hexane phase presented the best larvicidal results, with LC50 values of 0.46 mg/mL for P. malacophylla and 0.79 mg/mL for P. cancellata. The hexane phase of the P. blanchetiana EEB showed the highest larvicidal activity among all samples evaluated, with an LC50 of 0.043 mg/mL. Compared to the CEE, the chloroform phases of the three species showed similar LC50 values, followed by moderate activity in the ethyl acetate, hydroalcoholic, and n-butanolic phases. Overall, among all samples evaluated, P. malacophylla stood out most significantly in terms of larvicidal activity, indicating greater biological potential against A. aegypti larvae. Analysis of flavonoid activity against L4 A. aegypti larvae showed that kaempferol exhibited the highest larvicidal activity at 1.0 mg/mL, attributed to the absence of glycosylation and greater lipophilicity, which facilitates permeation through the larval cuticle and cell membranes. Thus, these results contributed to the chemical and biological knowledge of the Malvaceae family, in addition to highlighting the larvicidal potential of species of the genus Pavonia against Aedes aegypti, providing data that indicate the possibility of developing a more effective natural product for vector control.