Synthesis and Evaluation of Methyl 4-(7-Hydroxy-4,4,8-Trimethyl-3-Oxabicyclo[3.3.1]Nonan-2-yl)Benzoate as an Antileishmanial Agent and Its Synergistic Effect with Miltefosine

Abstract

In our interest in oxabicyclic compounds as potent antileishmanial agents, the present work deals with the chemical synthesis of a new oxabicyclic derivative, methyl 4-(7-hydroxy-4,4,8-trimethyl-3-oxabicyclo[3.3.1]nonan-2-yl)benzoate (PS-207). This oxabicyclic derivative showed a good antileishmanial effect on the parasite, on both the promastigote and the amastigote. The mode of parasitic death from PS-207 seemed to be apoptosis-like. Interestingly, the combination of PS-207 with a low dose of miltefosine showed a synergistic effect against the parasite.

Keywords: Leishmania donovani; drug development; miltefosine.

FIG 1

(A) Chemical synthesis of PS-207 from starting material 4-(4,4,8-trimethyl-7-oxo-3-oxabicyclo[3.3.1]non-2-yl)-benzoic acid methyl ester (PS-203) (16). (B) The effect of oxabicyclic derivative on L. donovani promastigote cells. The IC₅₀ of PS-207 against L. donovani promastigote cells was 18.39 ± 0.72 μM. (C) The antileishmanial effect on the amastigote stage of the parasite was observed after counting the number of amastigote cells in treated human monocyte-derived macrophages. L. donovani amastigote cells were treated with an IC₅₀ dose of PS-207 for 24 h. A total of 100 Giemsa-stained macrophages were counted manually for amastigotes in each cell. In comparison to the control, which was considered 100%, the percentage decrease in the number of amastigote cells in treated macrophages is shown. Flow cytometric analyses for mode of death in L. donovani promastigote cells treated with 0.2% DMSO for 24 h (control) (D), an IC₅₀ dose of miltefosine for 24 h (positive control) (E), or an IC₅₀ dose of PS-207 for 24 h (F) that were double stained with PI and annexin V-FITC.

FIG 2

Effect of combination of PS-207 with 5 μM miltefosine on L. donovani promastigote cells. L. donovani promastigote cells were treated with different concentrations of PS-207 in combination with 5 μM miltefosine for 24 h. The untreated promastigote cells were used as the control. The IC₅₀ of PS-207 against promastigote cells was 1.50 ± 0.25 μM in combination with 5 μM miltefosine.