Larvicidal Activity of Cinnamic Acid Derivatives: Investigating Alternative Products for Aedes aegypti L. Control

Abstract

The mosquito Aedes aegypti transmits the virus that causes dengue, yellow fever, Zika and Chikungunya viruses, and in several regions of the planet represents a vector of great clinical importance. In terms of mortality and morbidity, infections caused by Ae. aegypti are among the most serious arthropod transmitted viral diseases. The present study investigated the larvicidal potential of seventeen cinnamic acid derivatives against fourth stage Ae. aegypti larvae. The larvicide assays were performed using larval mortality rates to determine lethal concentration (LC₅₀). Compounds containing the medium alkyl chains butyl cinnamate (7) and pentyl cinnamate (8) presented excellent larvicidal activity with LC₅₀ values of around 0.21-0.17 mM, respectively. While among the derivatives with aryl substituents, the best LC₅₀ result was 0.55 mM for benzyl cinnamate (13). The tested derivatives were natural compounds and in pharmacology and antiparasitic studies, many have been evaluated using biological models for environmental and toxicological safety. Molecular modeling analyses suggest that the larvicidal activity of these compounds might be due to a multi-target mechanism of action involving inhibition of a carbonic anhydrase (CA), a histone deacetylase (HDAC2), and two sodium-dependent cation-chloride co-transporters (CCC2 e CCC3).

Keywords: Chikungunya; Zika; cinnamic ester; dengue; larvicidal activity; medicinal plants; mosquitoes; natural products; yellow fever.

Scheme 1

Synthesis of the cinnamic acid derivatives: (a) ROH, H₂SO₄, reflux, (b) Et₃N, RX, acetone, reflux, (c) ROH, THF, TPP, DIAD, 0 °C at room temperature.

Figure 1

The best larvicidal activity among different cinnamic acid derivative concentrations: (a) ethyl cinnamate, (b) isopropyl cinnamate, (c) methoxyethyl cinnamate, (d) butyl cinnamate, (e) pentyl cinnamate, (f) isopentyl cinnamate, (g) hexyl cinnamate, (h) benzyl cinnamate and (i) 3-metoxybenzyl cinnamate against Ae. aegypti larvae after 24 h (expressed in mg/mL and convert mM). PC = positive control, NC = negative control. (*) Indicates results that are significantly different from the controls.

Figure 1

The best larvicidal activity among different cinnamic acid derivative concentrations: (a) ethyl cinnamate, (b) isopropyl cinnamate, (c) methoxyethyl cinnamate, (d) butyl cinnamate, (e) pentyl cinnamate, (f) isopentyl cinnamate, (g) hexyl cinnamate, (h) benzyl cinnamate and (i) 3-metoxybenzyl cinnamate against Ae. aegypti larvae after 24 h (expressed in mg/mL and convert mM). PC = positive control, NC = negative control. (*) Indicates results that are significantly different from the controls.

Figure 1

The best larvicidal activity among different cinnamic acid derivative concentrations: (a) ethyl cinnamate, (b) isopropyl cinnamate, (c) methoxyethyl cinnamate, (d) butyl cinnamate, (e) pentyl cinnamate, (f) isopentyl cinnamate, (g) hexyl cinnamate, (h) benzyl cinnamate and (i) 3-metoxybenzyl cinnamate against Ae. aegypti larvae after 24 h (expressed in mg/mL and convert mM). PC = positive control, NC = negative control. (*) Indicates results that are significantly different from the controls.

Figure 2

Structure–activity relationship (SAR) of cinnamic acid derivatives for larvicidal activity.

Figure 3

Predicted free energies of binding of compound 8 to its potential targets. The color scale goes from best (green) to worst (red) ΔGs of binding.

Figure 4

Predicted binding modes of compound 8 to CA, HDAC2, CCC2 and CCC3 (left) and the observed network of interactions with each target along the 200 MD snapshots used for Molecular Mechanics-Poisson-Boltzmann Surface Area (MM-PBSA) calculations (right). The receptors are depicted in gray and the ligand in cyan. Atoms are colored following the scheme: red for oxygen, blue for nitrogen and yellow for sulfur. Only residues interacting with the ligand on more than 50% of the analyzed MD snapshots are labelled. The Zn²⁺ ions at the active sites of CA and HDAC2 are represented as purple spheres. In the interaction diagrams, all atoms are represented only for amino acids forming hydrogen bonds with the ligand. In these, hydrogen bonds are represented by dashed lines, carbon atoms are represented in black and the same color scheme as in the left pictures is followed for the rest of the ligand atom types.