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Promising inhibitory activities of the parasite multiplication were obtained upon evaluation of in vivo anti-malarial activities of new pyrazolylpyrazoline derivatives against Plasmodium berghei infected mice. Further evaluation of 5b and 6a against chloroquine-resistant strain (RKL9) of P. falciparum showed higher potency than chloroquine. In vitro antileishmanial activity testing against Leishmania aethiopica promastigote and amastigote forms indicated that 5b, 6a and 7b possessed promising activity compared to miltefosine and amphotericin B deoxycholate. Moreover, antileishmanial activity reversal of the active compounds via folic and folinic acids showed comparable results to the positive control trimethoprim, indicating an antifolate mechanism via targeting leishmanial DHFR and PTR1. The compounds were nontoxic at 125, 250 and 500mg/kg. In addition, docking of the most active compound against putative malarial target Pf-DHFR-TS and leishmanial PTR1 rationalised the observed activities. Molecular dynamics simulations confirmed a stable and high potential binding of 7a against leishmanial PTR1. [ABSTRACT FROM AUTHOR]

Herein we introduce new compounds as conjugates of arylnicotinic acids with aryl (thio)semicarbazide derivatives. Based on a structure-guided approach, they were designed to possess anti-leishmanial activity through anti-folate mechanism, via targeting Leishmania major pteridine reductase 1 (Lm -PTR1). The in vitro anti-promastigote and anti-amastigote activity were promising for many thiosemicarbazide derivatives and superior to the reference miltefosine. The most active compounds 8i and 8j exhibited their anti-amastigote activity with IC 50 values of 4.2 and 3.3 μM, respectively, compared to reference miltefosine (IC 50 value of 7.3). Their anti-folate mechanism was confirmed via the ability of folic and folinic acids to reverse the anti-leishmanial activity of these compounds, comparably to Lm -PTR1 inhibitor trimethoprim. Interestingly, the in vitro cytotoxicity test of the most active compounds displayed higher selectivity indices than that of miltefosine emphasizing their safety on mammalian cells. Furthermore, the docking experiments on Lm -PTR1 as a putative target rationalized the in vitro anti-leishmanial activity. The in silico predictions exhibited promising pharmacokinetics and drug-likeness profiles of the most active compounds. Generally, this work introduces a fruitful matrix for new anti-leishmanial chemotype which would extend the chemical space for the anti-leishmanial activity. Image 1 • Certain arylnicotinic acids conjugated with aryl (thio)semicarbazides were designed to target folate pathway of L. major , especially Lm -PTR1. • Reversal of anti-leishmanial activity of the most active compounds by folic acid and folinic acid validated the anti-folate mechanism. • The in vitro cytotoxicity test of the most active compounds displayed higher selectivity indices than that of miltefosine. • Docking experiments on Lm-PTR1 as a putative target rationalized the in vitro antileishmanial activity. • In silico predictions exhibited promising pharmacokinetics and drug-likeness profiles of the most active compounds. [ABSTRACT FROM AUTHOR]