Leishmaniases are neglected diseases caused by parasites belonging to the genus Leishmania, which can cause cutaneous leishmaniasis (CL) varying from an single cutaneous lesion that cure spontaneously to mucosal scars causing patient’ morbidity, and visceral leishmaniasis (VL), which can be fatal, if acute and left untreated (Desjeux, 2004; World Health Organization, 2022). Leishmania parasites present two main morphological forms, promastigote and amastigote, which are found in the digestive tract of the vector insect and in the phagocytic cells in mammalian hosts, respectively (Grimaldi and Tesh, 1993). In the Americas, CL can be caused by Leishmania braziliensis, L. amazonensis, L. guyanensis, L. shawi, L. laisoni and L. naiffi species; while VL is usually caused by L. infantum (Kevric et al., 2015).

The treatment against leishmaniasis is carried out to avoid the mortality caused by VL and to reduce the morbidity caused by the mucosal lesions in the CL. Usually, it consists of systemic administration of pentavalent antimonials (Torres-Guerrero et al., 2017; Berbert et al., 2018). However, these drugs interact also with host cell proteins causing loss of function and, consequently, toxicity in organs as kidney, liver and heart (Clementi et al., 2011; Georgiadou et al., 2015). Other products, such as amphotericin B (AmpB) in its free form or in lipid formulations, pentamidine, miltefosine and paramomycin are also used, although they cause toxicity, present high cost and the emergence of resistant strains is also reported (Sundar and Chakravarty, 2015; Ponte-Sucre et al., 2017).

AmpB is an antifungal agent used in the treatment against leishmaniasis (Copeland and Aronson, 2015; Cunha et al., 2015; Frézard and Demicheli, 2010). The mechanism of action of drug is based on its binding to parasite membrane sterols, causing alterations in the cell permeability, leading to the loss of cations and consequent cell death (Sundar and Singh, 2018). As consequence, AmpB has been showed to be effective against distinct Leishmania spp. able to cause CL and VL, such as L. infantum, L. braziliensis and L. amazonensis (Ribeiro et al., 2014; Lage et al., 2015; Freitas et al., 2021). The drug incorporated in lipid formulations presents advantages over the free form, mainly related to the low toxicity; however, these products present high cost, which limit their use in countries where leishmaniasis is a neglected disease (Vyas and Gupta, 2006).

Given the aforementioned limitations, the identification of new antileishmanial agents, effective in combating the parasite in infected hosts but causing minimal toxicity, is highly desirable. Therefore, the search for natural compounds and their synthetic derivatives has become an alternative; since they present lower production cost and can be chemically modified to reach maximal therapeutic efficacy and low toxicity (Cortes et al., 2020; Gervazoni et al., 2020).

Vanillin (C8H8O3) is an organoleptic compound of natural vanilla acquired from the pods of an orchid named Vanilla planifolia. It is an aromatic aldehyde (3-methoxy-4-hydroxybenzaldehyde) belonging to the group of phenolic compounds, with functional groups including aldehyde, ether, and phenol (Walton et al., 2003; Banerjee and Chattopadhyay, 2019). Vanillin and their derivatives have showed distinct biological applications, as anticancer (Rakoczy et al., 2021), antibacterial (Mok et al., 2020), and antidiabetics agents (Salau et al., 2021). In a study, vanillin was evaluated regarding to its in vivo and in vitro toxicity in mammalian cells and by antioxidant and anti-Toxoplasma action in a murine model. The authors observed that vanillin presented an efficient antioxidant action with negligible cytotoxic effect in host cells, which were associated with high anti-Toxoplasmaactivity in the treated mice (Oliveira et al., 2014). The authors concluded their study suggesting that vanillin and its derivatives could has importance as new therapeutic agents to combat parasitic infections.

In this context, in the present study, we have evaluated two synthetic derivatives from vanillin called [4-(2-hydroxy-3-(4-octyl-1H-1,2,3-triazol-1-yl)propoxy)-3-methoxybenzaldehyde] or 3s and [4-(3-(4-decyl-1H-1,2,3-triazol-1-yl)-2-hydroxypropoxy)-3-methoxybenzaldehyde] or 3t, as antileishmanial agents against distinct Leishmania species able to cause CL and VL in the world. The compounds were prepared in three steps using readily available and low-cost reagents; making then them be easy to prepare and with low-cost production. Briefly, vanillin was alkylated with epichlorohydrin, an epoxide ring opening reaction was carried out with sodium azide followed by copper (I)-catalyzed alkyne-azide cycloaddition (CuAAC) reaction with appropriate terminal alkynes, afforded the compounds 3s and 3t.

The two molecules were characterized chemically in a study developed by our group (Santiago et al., 2022), and, in the present work, they were tested against L. infantum, L. braziliensis and L. amazonensis promastigote and amastigote-like stages. In addition, the cytotoxicity in murine and human cells, the treatment of infected macrophages and the inhibition of the infection upon pre-incubation of the parasites were investigated. The mechanism of action of the compounds 3s and 3t was evaluated in L. infantum parasites, as well as cytokine levels were evaluated using the culture supernatant from treated and infected murine cells.