This study extends earlier reports regarding the in vitro and in vivo efficacies of the nitroimidazopyran PA-824 against Mycobacterium tuberculosis. PA-824 was tested in vitro against a broad panel of multidrugresistant clinical isolates and was found to be highly active against all isolates (MIC < 1 g/ml). The activity of PA-824 against M. tuberculosis was also assessed grown under conditions of oxygen depletion. PA-824 showed significant activity at 2, 10, and 50 g/ml, similar to that of metronidazole, in a dose-dependent manner. In a short-course mouse infection model, the efficacy of PA-824 at 50, 100, and 300 mg/kg of body weight formulated in methylcellulose or cyclodextrin/lecithin after nine oral treatments was compared with those of isoniazid, rifampin, and moxifloxacin. PA-824 at 100 mg/kg in cyclodextrin/lecithin was as active as moxifloxacin at 100 mg/kg and isoniazid at 25 mg/kg and was slightly more active than rifampin at 20 mg/kg. Long-term treatment with PA-824 at 100 mg/kg in cyclodextrin/lecithin reduced the bacterial load below 500 CFU in the lungs and spleen. No significant differences in activity between PA-824 and the other single drug treatments tested (isoniazid at 25 mg/kg, rifampin at 10 mg/kg, gatifloxacin at 100 mg/kg, and moxifloxacin at 100 mg/kg) could be observed. In summary, its good activity in in vivo models, as well as its activity against multidrug-resistant M. tuberculosis and against M. tuberculosis isolates in a potentially latent state, makes PA-824 an attractive drug candidate for the therapy of tuberculosis. These data indicate that there is significant potential for effective oral delivery of PA-824 for the treatment of tuberculosis.Therapy for tuberculosis (TB) is arduous due to its long duration and the need to use multidrug regimens. The current standard regimen of isoniazid (INH), rifampin (RIF), and pyrazinamide (PZA) requires 6 to 8 months of daily treatment. In part due to noncompliance with treatment, therapy is now further complicated by the emergence of drug-resistant strains, with the global prevalence of drug resistance being from 1 to 3% (27). A further, equally important issue with tuberculosis therapy is the treatment of patients in which the infection may be in a latent state. Supposedly, 1:3 people throughout the world harbor latent bacilli, which have the potential to reactivate and cause active disease (21, 23). Current anti-TB drugs are mainly effective against replicating and metabolically active bacteria, and therefore, there is an urgent need for novel drugs that are also effective against persisting or latent bacterial infections, as well as those that can overcome the increasing problem of drug resistance.A series of bicyclic nitroimidazofurans, originally investigated as radiosensitizers for use in cancer chemotherapy (1), were found to possess activity against cultured replicating Mycobacterium tuberculosis and had significant in vivo activity in a murine infection model (3,17,25). A subsequent series of 3-substituted nitroimidazopyrans (NAP...

Purine nucleoside phosphorylase (PNP, EC 2.4.2.1) is a salvage enzyme important to the T-cell-mediated part of the immune system and as such is an important therapeutic target. This paper describes the design, synthesis, and enzymatic evaluation of potent, competitive inhibitors of PNP. Potential inhibitors were designed using the three-dimensional structure of the enzyme in an iterative process that involved interactive computer graphics to model the native enzyme and complexes of it with the inhibitors, Monte Carlo-based conformational searching, and energy minimization. Studies of the enzyme/inhibitor complexes were used to determine priorities of the synthetic efforts. The resulting compounds were then evaluated by determination of their IC50 values and by X-ray diffraction analysis using difference Fourier maps. In this manner, we have developed a series of 9-(arylmethyl)-9-deazapurines (2-amino-7-(arylmethyl)-4H-pyrrolo[3,2-d]-pyrimidin-4-ones) that are potent, membrane-permeable inhibitors of the enzyme. The IC50 values of these compounds range from 17 to 270 nM (in 1 mM phosphate), with 9-(3,4-dichlorobenzyl)-9-deazaguanine being the most potent inhibitor. X-ray analysis explained the role of the aryl groups and revealed the rearrangement of hydrogen bonds in the binding of the 9-deazaguanines in the active site of PNP relative to the binding of the 8-aminoguanines that results in more potent inhibition of the enzyme.

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Alicyclic and heteroalicyclic derivatives of 9-deazaguanine (2-amino-1,5-dihydro-4H-pyrrolo[3,2-d] [pyrimidin-4-one) are, with one exception, potent inhibitors of purine nucleoside phosphorylase (PNP) equaling the corresponding 9-arylmethyl derivatives previously investigated. The mode of binding of these compounds to PNP was determined by X-ray crystallography.

X-ray crystallography and computer-assisted molecular modeling (CAMM) studies aided in the design of a potent series of mammalian purine nucleoside phosphorylase (PNP) inhibitors. Enhanced potency was achieved by designing substituted 9-(arylmethyl)-9-deazaguanine analogs that interact favorably with all three of the binding subsites of the PNP active site, namely the purine binding site, the hydrophobic pocket, and the phosphate binding site. The most potent PNP inhibitor prepared during our investigation, (S)-9-[1-(3-chlorophenyl)-2-carboxyethyl]-9-deazaguanine (18b), was shown to have an IC50 of 6 nM, whereas the corresponding (R)-isomer was 30-fold less potent.

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The 1,2-dihydropyrido[3,4-b]pyrazines (1) are mitotic inhibitors with significant antitumor activity in mice. Also, the active imidazo[4,5-b]pyridine 3 was shown to cause the accumulation of cells at mitosis. Routes were developed for the synthesis of congeners of 3 by cyclization of 4-(substituted amino)-5,6-diaminopyridines with ethyl orthoformate. Oxidative cyclization of either 4,5- or 5,6-diaminopyridines with aryl aldehydes produced the [4,5-c] and [4,5-b] imidazopyridine ring systems, respectively. The latter reaction with 6-(substituted amino)-4,5-diaminopyridines gave imidazo[4,5-c]pyridine ring analogues of 1. Biological studies indicated that the target compounds were less active than 1 and 3.

Reaction of alpha-aminoacetophenone oximes (2) with ethyl 6-amino-4-chloro-5-nitropyridine-2-carbamate (1) gave ethyl 6-amino-5-nitro-4-[(2-oxo-2-phenylethyl)amino]pyridine-2-carbamate oximes (3), which were hydrolyzed under acidic conditions to give the corresponding ketones (4). Related pyridines substituted with a keto side chain were prepared from 1 and 1,3-diaminopropanone oximes and by oxidation of the side-chain hydroxy group of ethyl 6-amino-4- [[3-(N-methyl-N-phenylamino)-2-hydroxypropyl]amino]-5-nitropyridine-7- carbamates (6). Catalytic hydrogenation of the nitro group of 4 over Raney nickel in a large volume of ethanol gave the 1-deaza-7,8-dihydropteridines (7). Several of the oximes 3 were successfully hydrogenated to give 7 directly. The resulting 1-deaza-7,8-dihydropteridines showed potent cytotoxicity against cultured L1210 cells and significant anticancer activity against lymphocytic leukemia P-388 in mice. These biological activities are attributed to the accumulation of cells at mitosis.