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Delamanid, bedaquiline, and pretomanid have been recently added in the anti-tuberculosis (anti-TB) treatment regimens and have emerged as potential solutions for combating drug-resistant TB. These drugs have proven to be effective in treating drug-resistant TB when used in combination. However, concerns have been raised about the eventual loss of these drugs due to evolving resistance mechanisms and certain adverse effects such as prolonged QT period, gastrointestinal problems, hepatotoxicity, and renal disorders. This Perspective emphasizes the properties of these first-in-class drugs, including their mechanism of action, pharmacokinetics/pharmacodynamics profiles, clinical studies, adverse events, and underlying resistance mechanisms. A brief coverage of efforts toward the generation of best-in-class leads in each class is also provided. The ongoing clinical trials of new combinations of these drugs are discussed, thus providing a better insight into the use of these drugs while designing an effective treatment regimen for resistant TB cases.

Visceral leishmaniasis is responsible for up to 30,000 deaths every year. Current treatments have shortcomings that include toxicity and variable efficacy across endemic regions. Previously, we reported the discovery of GNF6702, a selective inhibitor of the kinetoplastid proteasome, which cleared parasites in murine models of leishmaniasis, Chagas disease, and human African trypanosomiasis. Here, we describe the discovery and characterization of LXE408, a structurally related kinetoplastid-selective proteasome inhibitor currently in Phase 1 human clinical trials. Furthermore, we present high-resolution cryo-EM structures of the Leishmania tarentolae proteasome in complex with LXE408, which provides a compelling explanation for the noncompetitive mode of binding of this novel class of inhibitors of the kinetoplastid proteasome.

Although the antimalarial agent artemisinin itself is not active against tuberculosis, conjugation to a mycobacterial-specific siderophore (microbial iron chelator) analogue induces significant and selective antituberculosis activity, including activity against multi- and extensively drug-resistant strains of Mycobacterium tuberculosis. The conjugate also retains potent antimalarial activity. Physicochemical and whole-cell studies indicated that ferric-to-ferrous reduction of the iron complex of the conjugate initiates the expected bactericidal Fenton-type radical chemistry on the artemisinin component. Thus, this "Trojan horse" approach demonstrates that new pathogen-selective therapeutic agents in which the iron component of the delivery vehicle also participates in triggering the antibiotic activity can be generated. The result is that one appropriate conjugate has potent and selective activity against two of the most deadly diseases in the world.

A series of 3,4-diaryloxazolones were prepared and evaluated for their ability to inhibit cyclooxygenase-2 (COX-2). Extensive structure-activity relationship work was carried out within this series, and a number of potent and selective COX-2 inhibitors were identified. The replacement of the methyl sulfone group on the 4-phenyl ring by a sulfonamide moiety resulted in compounds with superior in vivo antiinflammatory properties. In the sulfonamide series, the introduction of a methyl group at the 5-position of the oxazolone ring gave rise to very COX-2-selective compounds but with decreased in vivo activity. Selected 3,4-diaryloxazolones exhibited excellent activities in experimental models of arthritis and hyperalgesia. The in vivo activity of these compounds was confirmed with the evaluation of their antipyretic effectiveness and their ability to inhibit migration of proinflammatory cells. As expected from their COX-2 selectivity, most of the active compounds lacked gastrointestinal toxicity in vivo in rats after a 4-day treatment of 100 mg/kg/day. Within this novel series, sulfonamides 9-11 have been selected for further preclinical evaluation.

The thiazolidinedione moiety of ciglitazone and its analogues can be replaced by an alpha-alkoxy or alpha-thioether carboxylic acid group. The influence of the nature of the R group, the length of the connector to the aromatic backbone of the molecule, and the stereochemistry have been studied. The most potent compounds have glucose-lowering activity at doses as low as 0.01 mg/kg.

A regio and stereospecific synthesis of 2-methyl-(Z)-4-(phenylimino)naphth[2,3-d]oxazol-9-one (1) was achieved by using titanium tetrachloride in methylene chloride in the preparation of the imine. The regiochemistry was assigned by single-crystal X-ray analysis. In vitro tests showed that this diastereomer is selectively active for some solid cancer tumors.

Varieties of thioalkyl-containing quinone and hydroquinone analogues of quinocarcin (1a) were prepared effectively, by addition of mercaptan to 3a-c, which were derived from 1a via DX-52-1 (1b). Antitumor activities of these analogues were preliminarily evaluated by growth inhibition of HeLa S3 cells (in vitro) and increased life span of P388 implanted mice (in vivo). Bis(alkylthio)quinones 4a-d and 5a-d, and corresponding hydroquinones 9b-d exhibited high activities both in vitro and in vivo. They were superior to 1a especially in single administration. Selected compounds 4a, 4d, 5a, 5d, and 9b were subjected to further evaluation, and bis(methylthio)quinone 5a was revealed to possess broad-spectrum activity toward human xenographted carcinomas MX-1, Co-3, St-4, and LC-06.

A series of benzyloxazolidine-2,4-diones, containing oxazole-based side chains, were found to lower blood glucose levels in the genetically obese ob/ob mouse. Incorporation of a benzofuran structural element in these compounds provides greatly enhanced in vivo potency. The syntheses and structure-activity relationships for this series are detailed.

The synthesis of a series of substituted heterocyclic alkoxypropionic acids is described. They were evaluated for antiinflammatory effects in two animal models of chronic inflammation; adjuvant arthritis and type II collagen arthritis in the rat. The desired profile of biological activity was characterized by the reduction of inflammation with the coincident restoration toward normal levels of the biochemical markers (acute phase proteins) associated with the inflammatory response, an effect that was not shared by classical nonsteroidal antiinflammatory agents. Romazarit, (Ro 31-3948, 7), 2-[[2-(4-chlorophenyl)-4-methyl-5-oxazolyl]methoxy]-2-methylpropio nic acid, was selected for further evaluation. In contrast to NSAIDs, romazarit was inactive in animal models of acute inflammation, and furthermore it did not inhibit the cyclooxygenase enzyme in vitro or in vivo. Inhibition of interleukin-1-mediated events in vitro has been observed.

The synthesis and antiinflammatory activity of 5-substituted 2-arylbenzoxazoles are described. Initial screening on carrageenin-induced rat paw edema showed that alpha-methylacetic substitution in the 5 position was preferable to substitutions with the equivalent esters, amides, alcohols, amines or tetrazoles. Halogen substitution in the aryl ring led to the most active compounds which were 2-(4-chlorophenyl)-alpha-methyl-5-benzoxazoleacetic acid (14) and 2-(4-fluorophenyl)-alpha-methyl-5-benzoxazoleacetic acid (29). These compounds were three to five times more active than phenylbutazone as assessed from ED30 values determined on rat paw edema 5 hr after single oral doses.

A series of [[(4,5-dihydro-2-oxazolyl)phenoxy]alkyl]isoxazoles has been synthesized and evaluated as antipicornavirus agents. The effect of alkyl groups in the 4- and 5-position of the oxazoline ring, as well as the alkyl chain length, on antiviral activity was examined. Compound 14 was evaluated in vivo and was found to significantly reduce mortality at an oral dose of 4 mg/kg in mice infected intracerebrally with poliovirus-2. Compound 14 was also effective in preventing paralysis when administered intraperitoneally to mice infected subcutaneously with a lethal dose of ECHO-9 virus. On the basis of the results of these studies, compound 14 is a strong candidate for clinical evaluation as a systemic agent for the treatment of picornavirus infections.

The preparation and activity against Plasmodium berghei of derivatives of 1-(4-methoxycinnamoyl)-4-(5-phenyl-4-oxo-2-oxazolin-2-yl)piperazine are described. Replacement of the cinnamoyl group was accomplished by acylation or alkylation of 1-(5-phenyl-4-oxo-2-oxazolin-2-yl)piperazine. Modifications of the 5-phenyl group were prepared either by a sequence of reactions involving mandelic ester-pemoline-piperazine pemoline or by the reaction of 5-aryl-2-thio-2,4-oxazolidinedione with piperazine or N-substituted piperazines. In a similar manner, pemoline was allowed to react with N-arylpiperazine, hexahydro-1H-1,4-diazepine, and 2,6-dimethylpiperazine to provide N-arylpiperazine pemoline derivatives and variations in the piperazine moiety. Several compounds in which the 2-oxazolin-4-one ring was replaced with other heterocyclic rings were prepared as were several open-chain analogs. Five compounds (three of them substituted in the para position of the 5-phenyl group and two N-arylpiperazine pemoline derivatives) were found to be active against Plasmodium berghei. The remaining active compound possessed changes in the cinnamoyl group and substitution on the 5-phenyl group.