1,2,4-Oxadiazole and 1,2,3-triazole containing heterocyclic compounds continue to gain interest in synthesis of chemical entities and exhibit various biological activities as anti-protozoal and anti-cancer agents. By using the principle of bioisosterism, a series of novel oxadiazolyl pyrrolo triazole diones; namely, (3aS,6aR)-1-((3-(4-substituted phenyl)-1,2,4-oxadiazol-5-yl)methyl)-5-phenyl-1,6a-dihydropyrrolo[3,4-d][1,2,3] triazole-4,6(3aH,5H)-diones (5a–k) was designed and synthesized by the 1,3-dipolar cycloaddition reaction of novel 5-azidomethyl 3-aryl substituted 1,2,4-oxadiazoles (4a–k) with N-phenyl maleimide. The structures of all the cycloadducts were elucidated by means of spectroscopic methods and physical characteristics. The in vitro anti-protozoal and cytotoxic activities of these novel heterocyclic compounds were investigated.A series of novel dihydropyrrolo[3,4-d][1,2,3]triazoles (5a–k) were designed and synthesized. The title compounds were assayed for their anti-protozoal activity against Trypanosoma brucei rhodesiense, Trypanosoma cruzi, Leishmania donovani, Plasmodium falciparum and cytotoxicity against L6 cells.Highlights► A series of novel dihydropyrrolo[3,4-d][1,2,3]triazole derivatives were synthesized. ► They were evaluated for anti-protozoal and cytotoxic activities. ► Hammett correlations were established for chloromethyl and azidomethyl oxadiazoles.

Acetylenic fatty acids are known to display several biological activities, but their antimalarial activity has remained unexplored. In this study, we synthesized the 2-, 5-, 6-, and 9-hexadecynoic acids (HDAs) and evaluated their in vitro activity against erythrocytic (blood) stages of Plasmodiumfalciparum and liver stages of Plasmodiumyoelii infections. Since the type II fatty acid biosynthesis pathway (PfFAS-II) has recently been shown to be indispensable for liver stage malaria parasites, the inhibitory potential of the HDAs against multiple P. falciparum FAS-II (PfFAS-II) elongation enzymes was also evaluated. The highest antiplasmodial activity against blood stages of P. falciparum was displayed by 5-HDA (IC50 value 6.6 μg/ml), whereas the 2-HDA was the only acid arresting the growth of liver stage P. yoelii infection, in both flow cytometric assay (IC50 value 2-HDA 15.3 μg/ml, control drug atovaquone 2.5 ng/ml) and immunofluorescence analysis (IC50 2-HDA 4.88 μg/ml, control drug atovaquone 0.37 ng/ml). 2-HDA showed the best inhibitory activity against the PfFAS-II enzymes PfFabI and PfFabZ with IC50 values of 0.38 and 0.58 μg/ml (IC50 control drugs 14 and 30 ng/ml), respectively. Enzyme kinetics and molecular modeling studies revealed valuable insights into the binding mechanism of 2-HDA on the target enzymes. All HDAs showed in vitro activity against Trypanosomabruceirhodesiense (IC50 values 3.7–31.7 μg/ml), Trypanosomacruzi (only 2-HDA, IC50 20.2 μg/ml), and Leishmaniadonovani (IC50 values 4.1–13.4 μg/ml) with generally low or no significant toxicity on mammalian cells. This is the first study to indicate therapeutic potential of HDAs against various parasitic protozoa. It also points out that the malarial liver stage growth inhibitory effect of the 2-HDA may be promoted via PfFAS-II enzymes. The lack of cytotoxicity, lipophilic nature, and calculated pharmacokinetic properties suggests that 2-HDA could be a useful compound to study the interaction of fatty acids with these key P. falciparum enzymes.2-, 5-, 6-, and 9-hexadecynoic acids (HDAs) were synthesized and evaluated in vitro against various parasitic protozoa. 2-HDA inhibited both liver and blood stage Plasmodium infections and multiple plasmodial FAS-II target enzymes. 2-HDA was further studied through enzyme kinetics, docking studies and for pharmacokinetic properties.

The type II fatty acid pathway (FAS-II) is a validated target for antimicrobial drug discovery. An activity-guided isolation procedure based on Plasmodium falciparum enoyl-ACP reductase (PfFabI) enzyme inhibition assay on the n  -hexane-, the CHCl3-CHCl3- and the aq MeOH extracts of the Turkish marine sponge Agelas oroides yielded six pure metabolites [24-ethyl-cholest-5α-7-en-3-β-ol (1), 4,5-dibromopyrrole-2-carboxylic acid methyl ester (2), 4,5-dibromopyrrole-2-carboxylic acid (3), (E)-oroidin (4), 3-amino-1-(2-aminoimidazoyl)-prop-1-ene (5), taurine (6)] and some minor, complex fatty acid mixtures (FAMA–FAMG). FAMA, consisting of a 1:2 mixture of (5Z,9Z)-5,9-tricosadienoic (7) and (5Z,9Z)-5,9-tetracosadienoic (8) acids, and FAMB composed of 8, (5Z,9Z)-5,9-pentacosadienoic (9) and (5Z,9Z)-5,9-hexacosadienoic (10) acids in ≈3:3:2 ratio were the most active PfFabI inhibitory principles of the hexane extract (IC50 values 0.35 μg/ml). (E)-Oroidin isolated as free base (4a) was identified as the active component of the CHCl3 extract. Compound 4a was a more potent PfFabI inhibitor (IC50 0.30 μg/ml = 0.77 μM) than the (E)-oroidin TFA salt (4b), the active and major component of the aq MeOH extract (IC50 5.0 μg/ml). Enzyme kinetic studies showed 4a to be an uncompetitive PfFabI inhibitor (Ki: 0.4 ± 0.2 and 0.8 ± 0.2 μM with respect to substrate and cofactor). In addition, FAMA and FAMD (mainly consisting of methyl-branched fatty acids) inhibited FabI of Mycobacterium tuberculosis (MtFabI, IC50s 9.4 and 8.2 μg/ml, respectively) and Escherichia coli (EcFabI, IC50s 0.5 and 0.07 μg/ml, respectively). The majority of the compounds exhibited in vitro antiplasmodial, as well as trypanocidal and leishmanicidal activities without cytotoxicity towards mammalian cells. This study represents the first marine metabolites that inhibit FabI, a clinically relevant enzyme target from the FAS-II pathway of several pathogenic microorganisms.