The Synthesis of Functionalized 3-Aryl- and 3-Heteroaryloxazolidin-2-ones and Tetrahydro-3-aryl-1,3-oxazin-2-ones via the Iodocyclocarbamation Reaction: Access to Privileged Chemical Structures and Scope and Limitations of the Method.

3-Aryl- and 3-heteroaryloxazolidin-2-ones, by virtue of the diverse pharmacologic activities exhibited by them after subtle changes to their appended substituents, are becoming increasingly important and should be considered privileged chemical structures. The iodocyclocarbamation reaction has been extensively used to make many 3-alkyl-5-(halomethyl)oxazolidin-2-ones, but the corresponding aromatic congeners have been relatively underexplored. We suggest that racemic 3-aryl- and 3-heteroaryl-5-(iodomethyl)oxazolidin-2-ones, readily prepared by the iodocyclocarbamation reaction of N-allylated N-aryl or N-heteroaryl carbamates, may be useful intermediates for the rapid preparation of potential lead compounds with biological activity. We exemplify this point by using this approach to prepare racemic linezolid, an antibacterial agent. Herein, we report the results of our systematic investigation into the scope and limitations of this process and have identified some distinguishing characteristics within the aryl/heteroaryl series. We also describe the first preparation of 3-aryloxazolidin-2-ones bearing new functionalized C-5 substituents derived from conjugated 1,3-dienyl and cumulated 1,2-dienyl carbamate precursors. Finally, we describe the utility of the iodocyclocarbamation reaction for making six-membered tetrahydro-3-aryl-1,3-oxazin-2-ones.

Novel 3-fluoro-6-methoxyquinoline derivatives as inhibitors of bacterial DNA gyrase and topoisomerase IV.

Novel (non-fluoroquinolone) inhibitors of bacterial type II topoisomerases (NBTIs) are an emerging class of antibacterial agents. We report an optimized series of cyclobutylaryl-substituted NBTIs. Compound 14 demonstrated excellent activity both in vitro (S. aureus MIC90=0.125µg/mL) and in vivo (systemic and tissue infections). Enhanced inhibition of Topoisomerase IV correlated with improved activity in S. aureus strains with mutations conferring resistance to NBTIs. Compound 14 also displayed an improved hERG IC50 of 85.9µM and a favorable profile in the anesthetized guinea pig model.

Synthetic calanolides with bactericidal activity against replicating and nonreplicating Mycobacterium tuberculosis.

It is urgent to introduce new drugs for tuberculosis to shorten the prolonged course of treatment and control drug-resistant Mycobacterium tuberculosis (Mtb). One strategy toward this goal is to develop antibiotics that eradicate both replicating (R) and nonreplicating (NR) Mtb. Naturally occurring (+)-calanolide A was active against R-Mtb. The present report details the design, synthesis, antimycobacterial activities, and structure-activity relationships of synthetic calanolides. We identified potent dual-active nitro-containing calanolides with minimal in vitro toxicity that were cidal to axenic Mtb and Mtb in human macrophages, while sparing Gram-positive and -negative bacteria and yeast. Two of the nitrobenzofuran-containing lead compounds were found to be genotoxic to mammalian cells. Although genotoxicity precluded clinical progression, the profound, selective mycobactericidal activity of these calanolides will be useful in identifying pathways for killing both R- and NR-Mtb, as well as in further structure-based design of more effective and drug-like antimycobacterial agents.

Whole cell screen for inhibitors of pH homeostasis in Mycobacterium tuberculosis.

Bacterial pathogens like Mycobacterium tuberculosis (Mtb) encounter acidic microenvironments in the host and must maintain their acid-base homeostasis to survive. A genetic screen identified two Mtb strains that cannot control intrabacterial pH (pHIB) in an acidic environment; infection with either strain led to severe attenuation in mice. To search for additional proteins that Mtb requires to survive at low pH, we introduced a whole-cell screen for compounds that disrupt pHIB, along with counter-screens that identify ionophores and membrane perturbors. Application of these methods to a natural product library identified four compounds of interest, one of which may inhibit novel pathway(s). This approach yields compounds that may lead to the identification of pathways that allow Mtb to survive in acidic environments, a setting in which Mtb is resistant to most of the drugs currently used to treat tuberculosis.

Novel quinoline derivatives as inhibitors of bacterial DNA gyrase and topoisomerase IV.

A structurally novel set of inhibitors of bacterial type II topoisomerases with potent in vitro and in vivo antibacterial activity was developed. Dual-targeting ability, hERG inhibition, and pharmacokinetic properties were also assessed.

Nonsteroidal anti-inflammatory drug sensitizes Mycobacterium tuberculosis to endogenous and exogenous antimicrobials.

Existing drugs are slow to eradicate Mycobacterium tuberculosis (Mtb) in patients and have failed to control tuberculosis globally. One reason may be that host conditions impair Mtb's replication, reducing its sensitivity to most antiinfectives. We devised a high-throughput screen for compounds that kill Mtb when its replication has been halted by reactive nitrogen intermediates (RNIs), acid, hypoxia, and a fatty acid carbon source. At concentrations routinely achieved in human blood, oxyphenbutazone (OPB), an inexpensive anti-inflammatory drug, was selectively mycobactericidal to nonreplicating (NR) Mtb. Its cidal activity depended on mild acid and was augmented by RNIs and fatty acid. Acid and RNIs fostered OPB's 4-hydroxylation. The resultant 4-butyl-4-hydroxy-1-(4-hydroxyphenyl)-2-phenylpyrazolidine-3,5-dione (4-OH-OPB) killed both replicating and NR Mtb, including Mtb resistant to standard drugs. 4-OH-OPB depleted flavins and formed covalent adducts with N-acetyl-cysteine and mycothiol. 4-OH-OPB killed Mtb synergistically with oxidants and several antituberculosis drugs. Thus, conditions that block Mtb's replication modify OPB and enhance its cidal action. Modified OPB kills both replicating and NR Mtb and sensitizes both to host-derived and medicinal antimycobacterial agents.

Linezolid, the first oxazolidinone antibacterial agent.

Linezolid (Zyvox) is the first member of an entirely new class of antibiotics to reach the market in over 35 years; it was approved for use in 2000. A member of the oxazolidinone class of antibiotics, linezolid is highly effective for the treatment of serious Gram-positive infections and has activity that compares favorably with vancomycin for most clinically relevant pathogens. Zyvox is approved for use against serious Gram-positive infections, including those caused by Streptococcus pneumoniae, and the very challenging methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus faecium organisms. Zyvox inhibits bacterial protein synthesis by binding to 23S rRNA in the catalytic site of the 50S ribosome. It can be administered both orally and intravenously and has good tissue distribution. Recent results have demonstrated that oxazolidinone analogs related to linezolid are effective in treating pulmonary tuberculosis caused by resistant Mycobacterium tuberculosis in animal infection models and suggest additional new therapeutic applications for these antibiotics.

The discovery and structure-activity relationships leading to CE-156811, a difluorophenyl cyclopropyl fluoroether: a novel potent antibacterial analog derived from hygromycin A.

SAR studies and optimization of various modified Hygromycin A fluoroalkyl ethers, which led to the discovery of the highly potent 4'-(2-cyclopropyl-2-fluoroethyl ether) antibacterial CE-156811 (1) derived from truncation of the ribose ring and difluorination of the phenyl found in Hygromycin A, are discussed.

Preparation, gram-negative antibacterial activity, and hydrolytic stability of novel siderophore-conjugated monocarbam diols.

A novel series of monocarbam compounds exhibiting promising antibacterial activity against multidrug resistant Gram-negative microorganisms is reported, along with the synthesis of one such molecule MC-1 (1). Also reported are structure-activity relationships associated with the in vitro and in vivo efficacy of 1 and related analogues in addition to the hydrolytic stability of such compounds and possible implications thereof.

Synthesis and biological evaluation of novel hygromycin A antibacterial agents.

Novel hygromycin A derivatives bearing a variety of functionalized aminocyclitol moieties have been synthesized in an effort to increase the antibacterial activity and drug-like properties of this class of agents. A systematic study of the effect of alkylation and removal of the hydroxyls of the aminocyclitol directed us to a series of alkylated aminocyclitol derivatives with improved gram-positive activity.

Addition of PNU-100480 to first-line drugs shortens the time needed to cure murine tuberculosis.

RATIONALE: We recently reported strong bactericidal activity of the oxazolidinone PNU-100480 and its ability to increase the initial bactericidal effect of various combinations of first-line tuberculosis drugs and moxifloxacin in a murine model. OBJECTIVES: To investigate whether the addition of PNU-100480 to the standard first-line regimen of rifampin, isoniazid, and pyrazinamide could shorten the duration of treatment necessary to prevent relapse after treatment discontinuation. METHODS: Following aerosol infection with Mycobacterium tuberculosis H37Rv and a 13-day incubation period, control mice were treated with the first-line regimen while test mice received the same regimen with PNU-100480 or linezolid added for the first 2 or 4 months. Efficacy was assessed on the basis of quantitative cultures of lung homogenates performed monthly during treatment and 3 months after completion of 3, 4, 5, or 6 months of treatment to determine the relapse rate. MEASUREMENTS AND MAIN RESULTS: After 2 months of treatment, mice receiving PNU-100480 in addition to the first-line regimen had lung CFU counts two orders of magnitude lower than control mice receiving the first-line regimen alone. Relapse rates after 4 months of treatment were 90, 35, and 5% when PNU-100480 was added to the first-line regimen for 0, 2, and 4 months, respectively. When the total treatment duration was 3 months, relapse rates were 85 and 35 to 45% when mice received PNU-100480 for 2 and 3 months, respectively; all control mice remained culture positive at the time of treatment completion with 17 to 72 CFU per lung. Addition of linezolid to the first-line regimen had an antagonistic effect resulting in higher CFU counts and failure to render mice culture-negative in 4 months of treatment. CONCLUSIONS: Together with previous findings, these results confirm that PNU-100480, which is now in Phase I clinical testing, has sterilizing activity in the murine model and suggest that it may be capable of shortening treatment duration for drug-susceptible as well as drug-resistant tuberculosis in humans.

In vitro antibacterial activity of CE-156811, a novel analog derived from hygromycin A.

We evaluated a novel truncated hygromycin A analog in which the furanose ring was replaced with a 2-fluoro-2-cyclopropylethyl substituent for its activity against multidrug resistant gram-positive bacteria and compared its activity to the activities of linezolid, quinupristin-dalfopristin, and vancomycin. CE-156811 demonstrated robust in vitro activity against gram-positive bacteria that was comparable to that of linezolid.