Synthesis and biological evaluation of fluorescent leishmanicidal analogues of hexadecylphosphocholine (miltefosine) as probes of antiparasite mechanisms

The leishmanicidal mechanism of miltefosine (hexadecylphosphocholine, MT) is not clearly understood. Valuable insights into its mode of action could be obtained by fluorescence techniques, given suitably emitting analogues. In this regard, the synthesis and biological characterization of two fully competent NIT fluorescent analogues is reported here: all-(E)-13-phenyltrideca-6,8,10,12-tetraenylphosphocholine (PTE-MT) and all(E)-13-phenyltrideca-8,10,12-trien-6-ynylphosphocholine (PTRI-MT). Both compounds show large absorption coefficients and a,modest, but usable, fluorescence yield. Their activities were very similar to that of NIT and were recognized by the NIT uptake system of Leishmania. Their localization in living L. donovani promastigotes by confocal microscopy show a homogeneous intracellular distribution of the fluorescence. The concentration of PTRI-MT within the parasites (ca. 1.7 mM) showed a 100-fold enrichment relative to its external concentration. These results are consistent with a multiple target leishmanicidal mechanism for NIT and validate the application of these analogues for pharmacokinetic and diagnostic studies concerning the chemotherapy of leishmaniasis.