Design, synthesis, in vitro – In vivo biological evaluation of novel thiazolopyrimidine compounds as antileishmanial agent with PTR1 inhibition

The leishmaniasis are a group of vector-borne diseases caused by a protozoan parasite from the genus Leishmania. In this study, a series of thiazolopyrimidine derivatives were designed and synthesized as novel antileishmanial agents with LmPTR1 inhibitory activity. The final compounds were evaluated for their in vitro antipromastigote activity, LmPTR1 and hDHFR enzyme inhibitory activities, and cytotoxicity on RAW264.7 and L929 cell lines. Based on the bioactivity results, three compounds, namely L24f, L24h and L25c, were selected for evaluation of their in vivo efficacy on CL and VL models in BALB/c mice. Among them, two promising compounds, L24h and L25c, showed in vitro antipromastigote activity against L. tropica with the IC50 values of 0.04 μg/ml and 6.68 μg/ml; against L. infantum with the IC50 values of 0.042 μg/ml and 6.77 μg/ml, respectively. Moreover, the title compounds were found to have low in vitro cytotoxicity on L929 and RAW264.7 cell lines with the IC50 14.08 μg/ml and 21.03 μg/ml, and IC50 15.02 μg/ml and 8.75 μg/ml, respectively. LmPTR1 enzyme inhibitory activity of these compounds was determined as 257.40 μg/ml and 59.12 μg/ml and their selectivity index (SI) over hDHFR was reported as 42.62 and 7.02, respectively. In vivo studies presented that L24h and L25c have a significant antileishmanial activity against footpad lesion development of CL and at weight measurement of VL group in comparison to the reference compound, Glucantime®. Also, docking studies were carried out with selected compounds and other potential Leishmania targets to detect the putative targets of the title compounds. Taken together, all these findings provide an important novel lead structure for the antileishmanial drug development.