The quinolone decoquinate is coadministered with feed for treatment of parasites which cause coccidiosis in poultry. However, from a drug-development perspective, the biological activity is often not adequately exploited due to poor physicochemical properties. Here we convert decoquinate into N-alkyl quinolone amides that, in contrast to decoquinate, are active against the tuberculosis bacterium with MIC 90 values ranging from 1.4 to 3.64 µM, and quinoline O-carbamates active against apicomplexan parasites that cause malaria, toxoplasmosis, and neosporosis with IC 50 values of 0.32-1.5 nM for the best derivative. Uniquely for the TB-active amides, disruption of cell wall homoeostasis is identified as one target. With IC 50 values against fetal lung fibroblast cells of 40 to >100 μM, the derivatives are selective for the pathogens. Structures of the most active derivatives are determined by NMR spectroscopy and X-ray crystallography. Analogues lacking the decyl side chain of decoquinate are inactive.

Available anti-malarial tools have over the ten-year period prior to 2012 dramatically reduced the number of fatalities due to malaria from one million to less than six-hundred and thirty thousand. Although fewer people now die from malaria, emerging resistance to the first-line anti-malarial drugs, namely artemisinins in combination with quinolines and arylmethanols, necessitates the urgent development of new anti-malarial drugs to curb the disease. The quinolones are a promising class of compounds, with some demonstrating potent in vitro activity against the malaria parasite. This review summarizes the progress made in the development of potential anti-malarial quinolones since 2008. The efficacy of these compounds against both asexual blood stages and other stages of the malaria parasite, the nature of putative targets, and a comparison of these properties with anti-malarial drugs currently in clinical use, are discussed.

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Dihydroartemisinin (DHA), either used in its own right or as the active drug generated in vivo from the other artemisinins in current clinical use-artemether and artesunate-induces quiescence in ring-stage parasites of Plasmodium falciparum (Pf). This induction of quiescence is linked to artemisinin resistance. Thus, we have turned to structurally disparate artemisinins that are incapable of providing DHA on metabolism. Accordingly, 11-azaartemisinin 5 and selected N-sulfonyl derivatives were screened against intraerythrocytic asexual stages of drug-sensitive Pf NF54 and drug-resistant K1 and W2 parasites. Most displayed appreciable activities against all three strains, with IC values <10.5 nm. The p-trifluoromethylbenzenesulfonyl-11-azaartemisinin derivative 11 [(4'-trifluoromethyl)benzenesulfonylazaartemisinin] was the most active, with IC values between 2 and 3 nm. The compounds were screened against Pf NF54 early and transmissible late intraerythrocytic-stage gametocytes using luciferase and parasite lactate dehydrogenase (pLDH) assays. The 2'-thienylsulfonyl derivative 16 (2'-thiophenesulfonylazaartemisinin) was notably active against late-stage (IV-V) gametocytes with an IC value of 8.7 nm. All compounds were relatively nontoxic to human fetal lung WI-38 fibroblasts, showing selectivity indices of >2000 toward asexual parasites. Overall, the readily accessible 11-azaartemisinin 5 and the sulfonyl derivatives 11 and 16 represent potential candidates for further development, in particular for transmission blocking of artemisinin-resistant parasites.

Tuberculosis is the deadliest infectious disease affecting humankind with a death toll of approximately 1.7 million people in 2016. The increasing prevalence of multidrug‐resistant strains of the causative pathogen, Mycobacterium tuberculosis (Mtb) which results in reduced effectiveness of the current therapies, underscores the urgent need for the development of new antitubercular drugs. In the search for such drugs, we investigated two series of ciprofloxacin (CPX) derivatives (analogues and hybrids). We herein report the design, synthesis, and biological activity of these series against the human virulent Mtb H37Rv strain in vitro. The small propionyl analogue 11 (MIC90 1.6 μM; SI > 61) and the large cholesteryl hybrid 32 (MIC90 2.0 μM; SI > 6) were the most active derivatives, comparable to CPX (MIC90 1.8 μM). However, the slightly less active but non‐cytotoxic para‐fluorobenzyl hybrid 28 (MIC90 3.7 μM; SI 27) was more selective toward bacteria than 32. Thus, the CPX derivatives 11 and 28 were identified as preferred antitubercular hits for further investigation including distribution, metabolism and pharmacokinetic parameters determination and in vivo activity assessment in animal models.