Antimalarial activity of 1,2,3,4-tetrahydroacridin-9(10H)-ones (THAs) has been known since the 1940s and has garnered more attention with the development of the acridinedione floxacrine (1) in the 1970s and analogues thereof such as WR 243251 (2a) in the 1990s. These compounds failed just prior to clinical development because of suboptimal activity, poor solubility, and rapid induction of parasite resistance. Moreover, detailed structure-activity relationship (SAR) studies of the THA core scaffold were lacking and SPR studies were nonexistent. To improve upon initial findings, several series of 1,2,3,4-tetrahydroacridin-9(10H)-ones were synthesized and tested in a systematic fashion, examining each compound for antimalarial activity, solubility, and permeability. Furthermore, a select set of compounds was chosen for microsomal stability testing to identify physicochemical liabilities of the THA scaffold. Several potent compounds (EC(50) < 100 nM) were identified to be active against the clinically relevant isolates W2 and TM90-C2B while possessing good physicochemical properties and little to no cross-resistance.

The continued proliferation of malaria throughout temperate and tropical regions of the world has promoted a push for more efficacious treatments to combat the disease. Unfortunately, more recent remedies such as artemisinin combination therapies have been rendered less effective due to developing parasite resistance, and new drugs are required that target the parasite in the liver to support the disease elimination efforts. Research was initiated to revisit antimalarials developed in the 1940s and 1960s that were deemed unsuitable for use as therapeutic agents as a result of poor understanding of both physicochemical properties and parasitology. Structure–activity and structure–property relationship studies were conducted to generate a set of compounds with the general 6-chloro-7-methoxy-2-methyl-4(1H)-quinolone scaffold which were substituted at the 3-position with a variety of phenyl moieties possessing various properties. Extensive physicochemical evaluation of the quinolone series was carried out to downselect the most promising 4(1H)-quinolones, 7, 62, 66, and 67, which possessed low-nanomolar EC50 values against W2 and TM90-C2B as well as improved microsomal stability. Additionally, in vivo Thompson test results using Plasmodium berghei in mice showed that these 4(1H)-quinolones were efficacious for the reduction of parasitemia at >99% after 6 days.

Though malaria mortality rates are down 48% globally since 2000, reported occurrences of resistance against current therapeutics threaten to reverse that progress. Recently, antimalarials that were once considered unsuitable therapeutic agents have been revisited to improve physicochemical properties and efficacy required for selection as a drug candidate. One such compound is 4(1H)-quinolone ICI 56,780, which is known to be a causal prophylactic that also displays blood schizonticidal activity against P. berghei. Rapid induction of parasite resistance, however, stalled its further development. We have completed a full structure-activity relationship study on 4(1H)-quinolones, focusing on the reduction of cross-resistance with atovaquone for activity against the clinical isolates W2 and TM90-C2B, as well as the improvement of microsomal stability. These studies revealed several frontrunner compounds with superb in vivo antimalarial activity. The best compounds were found to be curative with all mice surviving a Plasmodium berghei infection after 30 days.

Preclinical and clinical development of numerous small molecules is prevented by their poor aqueous solubility, limited absorption, and oral bioavailability. Herein, we disclose a general prodrug approach that converts promising lead compounds into aminoalkoxycarbonyloxymethyl (amino AOCOM) ethersubstituted analogues that display significantly improved aqueous solubility and enhanced oral bioavailability, restoring key requirements typical for drug candidate profiles. The prodrug is completely independent of biotransformations and animalindependent because it becomes an active compound via a pHtriggered intramolecular cyclization−elimination reaction. As a proof-of-concept, the utility of this novel amino AOCOM ether prodrug approach was demonstrated on an antimalarial compound series representing a variety of antimalarial 4(1H)-quinolones, which entered and failed preclinical development over the last decade. With the amino AOCOM ether prodrug moiety, the 3-aryl-4(1H)-quinolone preclinical candidate was shown to provide single-dose cures in a rodent malaria model at an oral dose of 3 mg/kg, without the use of an advanced formulation technique.

Malaria deaths have been decreasing over the last 10-15 years, with global mortality rates having fallen by 47% since 2000. While the World Health Organization (WHO) recommends the use of artemisinin-based combination therapies (ACTs) to combat malaria, the emergence of artemisinin resistant strains underscores the need to develop new antimalarial drugs. Recent in vivo efficacy improvements of the historical antimalarial ICI 56,780 have been reported, however, with the poor solubility and rapid development of resistance, this compound requires further optimization. A series of piperazine-containing 4(1H)-quinolones with greatly enhanced solubility were developed utilizing structure-activity relationship (SAR) and structure-property relationship (SPR) studies. Furthermore, promising compounds were chosen for an in vivo scouting assay to narrow selection for testing in an in vivo Thompson test. Finally, two piperazine-containing 4(1H)-quinolones were curative in the conventional Thompson test and also displayed in vivo activity against the liver stages of the parasite.

bMalaria kills approximately 1 million people a year, mainly in sub-Saharan Africa. Essential steps in the life cycle of the parasite are the development of gametocytes, as well as the formation of oocysts and sporozoites, in the Anopheles mosquito vector. Preventing transmission of malaria through the mosquito is necessary for the control of the disease; nevertheless, the vast majority of drugs in use act primarily against the blood stages. The study described herein focuses on the assessment of the transmissionblocking activities of potent antierythrocytic stage agents derived from the 4(1H)-quinolone scaffold. In particular, three 3-alkylor 3-phenyl-4(1H)-quinolones (P4Qs), one 7-(2-phenoxyethoxy)-4(1H)-quinolone (PEQ), and one 1,2,3,4-tetrahydroacridin-9(10H)-one (THA) were assessed for their transmission-blocking activity against the mosquito stages of the human malaria parasite (Plasmodium falciparum) and the rodent parasite (P. berghei). Results showed that all of the experimental compounds reduced or prevented the exflagellation of male gametocytes and, more importantly, prevented parasite transmission to the mosquito vector. Additionally, treatment with ICI 56,780 reduced the number of sporozoites that reached the Anopheles salivary glands. These findings suggest that 4(1H)-quinolones, which have activity against the blood stages, can also prevent the transmission of Plasmodium to the mosquito and, hence, are potentially important drug candidates to eradicate malaria. There were an estimated 154 million to 289 million cases and 610,000 to 971,000 deaths from malaria in 2010 (1). Plasmodium falciparum, the deadliest of the five malaria species that infect humans, mainly affects children under the age of 5 years in Africa (2-6). In areas where malaria is endemic, such as Africa, Southeast Asia, and South America, P. falciparum has developed resistance to many commercially available antimalarials, such as chloroquine (CQ), mefloquine (MFQ), and sulfadoxine-pyrimethamine (SP) (7). Currently, artemisinin derivatives, which have potent activity against blood stages and early-stage gametocytes, are the only drugs that are effective for treating drug-resistant P. falciparum (8,9). However, recent evidence suggests that parasite resistance to artemisinin and its derivatives is emerging in Southeast Asia (4, 10), thus indicating the need for new drugs to combat this disease.Development of new antimalarials has traditionally been focused on the asexual blood stages, which are responsible for the proliferation of the parasite in the human host and for the clinical symptoms of the disease (11). However, gametocytes (i.e., the sexual stages), as well as the mosquito stages (i.e., ookinetes, oocysts, and salivary gland sporozoites), are important drug targets, because they are necessary for disease transmission (12). Currently, there are a limited number of antimalarials that are effective against the sexual and the vector stages of malaria parasites. Therefore, we investigated the transmission-blocking activity of 4(...

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SUMMARYA four step synthesis of [5,8, from [14Cl-labelled acetylene is described. [ I k2l-acetylene was converted to 5-chloro-[l,2-14Cl-pentyne via reaction of its monolithium salt with 3-bromo-1 -chloropropane. The doubly labelled 5-chloropentyne thus obtained was transformed to [5,6-14Cl-hex-5-ynoic acid which was then coupled with 1 -chloro-tetradeca-2.5-diyne to give the title compound. Using 242-aminoethoxy)ethanol and 1 -(2-hydroxyethyl)piperazine, amides and (31, which had previously been found to be potent inhibitors of the 5-lipoxygenase enzyme, were prepared from [ 14Cl-labelled eicosatriynoic acid by way of acylimidazole chemistry.