Synthesis and Antileishmanial Activity of Lipophilic Aromatic Aminoalcohols

In this work, we report on the preparation and evaluation of the in vitro antileishmanial activity of a series of lipophilic aromatic aminoalcohols. All compounds were assessed for their in vitro activity against promastigotes of three Leishmania species The most lipophilic aminoalcohols bearing an aliphatic moiety with eight to 12 carbon atoms displayed a good activity against L. amazonensis and L. major, and two of them also showed antiproliferative activity against L. chagasi. The best results were obtained for the N-dodecanoyl ethylenediamine derivative and for N-decyl aminoalcohol (IC50 = 5.2 and 0.7 μM, respectively).


INTRODUCTION
Leishmaniasis is an infective parasitic disease, endemic in the American, African, and Asian tropical countries, with an estimated 1.5-2 million cases per year in 88 countries, and it is classified as one of the "most neglected diseases" [1]. Leishmaniasis is a major vector-borne disease caused by more than 20 species of the protozoan genus Leishmania [2]. Human leishmanial infection can manifest itself in three most common forms: cutaneous leishmaniasis, mucocutaneous leishmaniasis, or visceral leishmaniasis (commonly known as Kala-azar). This last clinical manifestation produces severe weight loss, anemia, and systemic impairment, leading to death when untreated. The fatality rate is almost 100% in children and women from poor families [3,4].
Drugs currently in use, such as the antimony derivative glucantime, bis-amidines, pentamidine, and the glycomacrolide amphotericin B, display high liver and heart toxicities and lead to clinical resistance after a few weeks of treatment [5,6]. Other limitations to the use of these drugs include the cost of the treatment and the need for parenteral administration [5]. All these factors contribute to compliance difficulties and treatment failures, and there is a real need to discover new potent and selective agents, either natural or synthetic, for the treatment of this increasing parasitosis.
Leishmania and other protozoa belonging to the trypanosomatid family have distinct polyamine metabolisms compared to mammalian cells, opening the possibility of identifying new targets for antiparasitic drug development [7,8,9,10,11]. Polyamines such as putrescine and spermidine are aliphatic organic compounds that play vital roles in several eukaryotic cellular processes, such as growth, protein/nucleic acid synthesis, and macromolecular biosynthesis [12,13]. Trypanosomes are unusual organisms in that spermidine is also used in the synthesis of trypanothione, which is both unique and essential to those parasites. The cloning, expression, purification, and crystallization of trypanothione reductase in Leishmania species was recently reported [14,15].
We describe in the present paper the synthesis of lipophilic aromatic aminoalcohols and their in vitro biological activities against Leishmania promastigote forms. These types of compounds, bearing a covalent bonded aliphatic chain attached to an aminoalcohol fragment, could interact with membrane lipids and be transported into the cytoplasm where they can possibly interfere with the lipid or polyamine transport or metabolism of the parasite [16].

RESULTS AND DISCUSSION
Among the evaluated compounds, the less lipophilic N-phenethylethanolamine 3a and its analogues 3b-d were inactive against all Leishmania species promastigotes at tested concentrations (Table 1). In the aminodiol series 5a-d, compounds 5a and 5c showed a good activity against L. major promastigotes (IC 50 values of 13.6 and 4.6 μM, respectively). Lipophilic aminoalcohols 7a-c, bearing an aliphatic amide moiety, were active against both L. amazonensis and L. major promastigote forms. Compound 7b, a decanoylethylenediamine derivative, showed the best activity against L. amazonensis (IC 50 of 18.6 μM) and L. major (IC 50 of 5.2 μM).
The two alkylated aminoalcohols (9a,b) displayed the best inhibitory activity against all Leishmania promastigotes tested, with IC 50 values ranging from 0.7 to 49.0 μM. Compound 9b, bearing an octyl chain, was the most efficient against the three species with IC 50 values of 18.5, 0.7, and 30.0 μM, for L. amazonensis, L. major, and L. chagasi promastigote forms, respectively.
From these results, we can observe a pattern of sensitivity of Leishmania species to the tested compounds. L. major promastigotes were the most sensitive to the tested aminoalcohols, with IC 50 values <20 μM. This strain also showed the smallest IC 50 between the 14 compounds tested (0.7 μM). This pattern of sensitivity of the parasites to different drugs is not surprising as it has been reported in several studies [23,24,25,26]. The results point to the importance of lipophilicity for antileishmanial activity: the two most active compounds are alkylated (9b) or acylated (7b) aminoalcohols, while none of the less lipophilic compounds (3a-d) was active.

CONCLUSION
This work describes the preparation and biological evaluation of several aminoalcohols prepared by the reaction of aromatic halides and aromatic glycidyl ethers with aminoalcohols (3a-d and 5a-d), aliphatic amides (7a-c), and aliphatic amines (9a,b). Five compounds (7a-c and 9a,b) displayed a good activity against L. amazonensis, seven compounds (5a, 5c, 7a-c, and 9a,b) were active against L. major, and only two (9a,b) were active against L. chagasi. These results show that the lipophilicity of the respective aminoalcohols is of great importance for antileishmanial activity, as compounds 7b and 9b, containing aliphatic side chains with 10 or eight carbons, showed the best activity against L. amazonensis and L. major promastigote forms.