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The emerging antibiotic resistance of Gram-positive pathogens represents a significant challenge to the management of human infections. The novel oxazolidinone tedizolid demonstrates antimicrobial activity across a broad range of Gram-positive pathogens and greater potency than linezolid against wild-type and drug-resistant pathogens, including linezolid-resistant Staphylococcus aureus strains possessing mutations in chromosomal genes encoding 23S rRNA or ribosomal proteins L3 or L4. Strains harboring such mutations are also selected for much less frequently with tedizolid than with linezolid. In addition, tedizolid has a significant potency advantage over linezolid-resistant strains carrying the horizontally transferable cfr gene. Methylation of A2503 of 23S rRNA by the Cfr methyltransferase confers resistance to linezolid (and a variety of other 50S ribosomal subunit-targeted antibiotics) but not to tedizolid because of structural differences in A-ring C5 substituents between the 2 drugs. The greater potency and improved resistance profile of tedizolid provides the microbiologic basis for considering this molecule as an alternative to linezolid for the treatment of serious infections caused by Gram-positive pathogens.

TR-701 is the prodrug of the microbiologically active molecule TR-700, a novel orally and intravenously administered oxazolidinone antibacterial agent. The in vitro activity of TR-700 was evaluated against 1,063 bacterial clinical isolates including staphylococci, enterococci, streptococci, Moraxella catarrhalis , Haemophilus influenzae , and a variety of anaerobic bacterial species. The test strains were recent (2005 to 2008) clinical isolates from diverse U.S. (80%) and non-U.S. (20%) sites. MIC assays were conducted using reference broth microdilution and agar dilution methods with the principal comparators linezolid and vancomycin. TR-700 was four- to eightfold more potent than linezolid against staphylococci and generally fourfold more potent against enterococci and streptococci. TR-700 was less active against M. catarrhalis and H. influenzae but was twofold more active than linezolid. Against anaerobic species, the activity of TR-700 was equivalent to or up to fourfold higher than that of linezolid. These results indicate that TR-700 is a promising new oxazolidinone antibacterial agent with greater in vitro potency than linezolid against clinically important gram-positive bacteria.

TR-701 is the orally active prodrug of TR-700, a novel oxazolidinone that demonstrates four- to eightfold-greater activity than linezolid (LZD) against Staphylococcus and Enterococcus spp. In this study evaluating the in vitro sensitivity of LZD-resistant isolates, TR-700 demonstrated 8- to 16-fold-greater potency than LZD against all strains tested, including methicillin-resistant Staphylococcus aureus (MRSA), strains of MRSA carrying the mobile cfr methyltransferase gene, and vancomycin-resistant enterococci. The MIC 90 for TR-700 against LZD-resistant S. aureus was 2 μg/ml, demonstrating the utility of TR-700 against LZD-resistant strains. A model of TR-700 binding to 23S rRNA suggests that the increased potency of TR-700 is due to additional target site interactions and that TR-700 binding is less reliant on target residues associated with resistance to LZD.

Oxazolidinones possessing a C-5 carboxamide functionality (reverse amides) represent a new series of compounds that block bacterial protein synthesis. These reverse amides also exhibited less potency against monoamine oxidase (MAO) enzymes and thus possess less potential for the side effects associated with MAO inhibition. The title compound (14) showed reduced in vivo myelotoxicity compared to linezolid in a 14-day safety study in rats, potent in vivo efficacy in murine systemic infection models, and excellent pharmacokinetic properties.

The discovery and initial optimization of a novel anthranilic acid derived class of antibacterial agents which suffered from extensive protein binding has been previously reported. The structure-activity relationships around the carboxylic acid substituent are described herein. This acid was replaced by several alternative functional groups in attempts to retain bioactivity while reducing protein binding. Only groups with an acidic proton retained activity, and analogs containing those groups maintained the protein binding inherent to this class of antibacterial agents.

In the past few years a significant effort has been devoted by Pharmacia toward the discovery of novel antibiotics. We have recently described the identification of an anthranilic acid lead 1 and the optimization resulting in the advanced lead 2. In this report, we describe the preparation of several selected analogs to probe the dependency of this template for antibacterial activity and the affinity these compounds have for human serum albumin (HSA). These analogs illustrate that decreased affinity for HSA can be achieved while retaining relevant antibacterial activity. The most important factor for reduced HSA affinity is decrease in logP rather than a structural change.

In the past few years, a significant effort has been devoted by Pharmacia toward the discovery of novel antibiotics. We have recently described the identification of an anthranilic acid lead 1 and the optimization resulting in the advanced lead 2. In this report, we describe the preparation of several selected amide bioisosteres connecting the A- and the B-rings. The E-alkene provided a rigid analog with equal potency to the corresponding amide. This indicates that the amide is not a recognition element rather acts as an appropriate spatial linker of the two important aryl A and B rings. The work here clearly demonstrates that the amide linker can be replaced with several functionalities without significant deterioration in the MIC activity.

Discovery of novel antibacterial agents is a significant challenge. We have recently reported on our discovery of novel antibacterial agents in which we have rapidly optimized potency utilizing a parallel chemistry approach. These advanced leads suffer from high affinity for human serum albumin (HSA). In an effort to decrease the affinity for HSA we have prepared a series of heterocyclic analogs, which retained antibacterial activity and demonstrated reduced affinity for HSA.

Screening of our compound collection identified PNU-92560, a 2-[1,3,4]thiadiazolo[3,2-a]pyrimidine-6-carboxamide, as a novel antibacterial agent. Extensive analogue development identified that the 2-position of the thiadiazole could be functionalized with a linker that would allow the compound to be attached to a solid support. The extreme insolubility of the analogues prevented the mechanism of action for these compounds to be determined utilizing traditional methodology. The solid-supported compounds were utilized as affinity columns to identify elongation factor Tu (EF-Tu) as a putative target for this class of compounds. The activity of the compounds in a metabolic labeling experiments and in translation assay supports the identity of the target for these compounds to be EF-Tu.

Combinatorial libraries of N-acylated 5-(S)-aminomethyloxazolidinone derivatives of S-oxide and S,S-dioxide tetrahydro-4(2H)-thiopyranyl and thiomorpholine phenyloxazolidinone series have been synthesized on a solid phase and evaluated for antimicrobial activity. Several novel potent leads have been identified, including orally active oxazolidinones with enhanced activity against respiratory tract infection pathogens Haemophilus influenzae and Moraxella catarrhalis.

Antimicrobial compounds incorporating oxazolidinone and quinolone pharmacophore substructures have been synthesized and evaluated. Representative analogues 2, 5, and 6 display an improved potency versus linezolid against gram-positive and fastidious gram-negative pathogens. The compounds are also active against linezolid- and ciprofloxacin-resistant Staphylococcus aureus and Enterococcus faecium strains. The MOA for these new antimicrobials is consistent with a combination of protein synthesis and gyrase A/topoisomerase IV inhibition, with a structure-dependent degree of the contribution from each inhibitory mechanism.

Novel benzazepine oxazolidinone antibacterials were synthesized and evaluated against clinically relevant susceptible and resistant organisms. The effect of ring nitrogen position and N-substitution on antibacterial activity is examined.

A new and promising group of antibacterial agents, collectively known as the oxazolidinones and exemplified by linezolid (PNU-100766, marketed as Zyvox), have recently emerged as important new therapeutic agents for the treatment of infections caused by Gram-positive bacteria. Because of their significance, extensive synthetic investigations into the structure-activity relationships of the oxazolidinones have been conducted at Pharmacia. One facet of this research effort has focused on the identification of bioisosteric replacements for the usual oxazolidinone A-ring. In this paper we describe studies leading to the identification of antibacterial agents incorporating a novel isoxazoline A-ring surrogate. In a gratifying result, the initial isoxazoline analogue prepared was found to exhibit in vitro antibacterial activity approaching that of the corresponding oxazolidinone progenitor. The synthesis and antibacterial activity profile of a preliminary series of isoxazoline analogues incorporating either a C-C or N-C linkage between their B- and C-rings will be presented. Many of the analogues exhibited interesting levels of antibacterial activity. The piperazine derivative 54 displayed especially promising in vitro activity and in vivo efficacy comparable to the activity and efficacy of linezolid.

The emergence of new antibiotic-resistance in the significant Gram-positive pathogens in the last decade created a substantial medical need for new classes of antibacterial agents. Pharmacia Corporation scientists initiated a discovery research program in oxazolidinone chemistry and biology. Indanone-, tetralone-, and indoline-subunit oxazolidinones provided proof-of-concept interim improvements in antibacterial activity and safety SAR for the program. A method for enantiomeric enrichment of analogs was developed and intensive synthesis and evaluation efforts were undertaken with three oxazolidinone subclasses; the piperazine, indoline, and tropones. Members of the piperazinyl-phenyloxazolidinones possessed the most suitable chemical characteristics and biologic activity of the three subclasses. The monofluorophenyl congener eperezolid and the morpholino analog linezolid emerged as the first clinical candidates from the piperazine oxazolidinones. Linezolid was selected for continued human clinical evaluation based upon its' superior pharmacokinetic profile. Microbiologic testing revealed that linezolid compared very favorably against comparator antibiotics in vitro and in animal infection models. Linezolid possessed a unique mechanism of action in that it inhibited functional 70S initiation complex formation and did not cross-react with existing bacterial resistance. Oral bioavailability in humans was determined to be 100% and twice daily dosing in humans resulted in blood levels which even at trough values were in excess of the MIC90 for significant Gram-positive pathogens. The preclinical promise of linezolid was realized in human clinical trials where linezolid was highly efficacious in the treatment of medically significant Gram-positive infections.

Important resistance patterns in Gram-negative pathogens include active efflux of antibiotics out of the cell via a cellular pump and decreased membrane permeability. A 3-arylpiperidine derivative (1) has been identified by high-throughput assay as a potentiator with an IC(50) approximately 90 microM. This report details the evaluation of the tether length, aryl substitution and the importance of the fluorine on antibiotic accumulation. Evaluation of various tether lengths demonstrated that the two-carbon tethered analogues are optimal. Removal of the fluorine has a modest effect on antibiotic accumulation and the defluorinated analogue 17 is equally potent to the original lead 1.

Peptidyl deformylase (PDF) is a metallo protease that catalyzes the removal of a formyl group from the N-termini of prokaryotic prepared polypeptides, an essential step in bacterial protein synthesis. Screening of our compound collection using Staphylococcus aureus PDF afforded a very potent inhibitor with an IC 50 in the low nanomolar range. Unfortunately, the compound that contains a hydroxamic acid did not exhibit antibacterial activity (MIC). In order to address the lack of activity in the MIC assay and to determine what portion of the molecule was responsible for binding to PDF, we prepared several analogues. This paper describes our findings that the hydroxamic acid functionality found in 1 is mainly responsible for the high affinity to PDF. In addition, we identified an alternative class of PDF inhibitors, the N- hydroxy urea 18 , which has both PDF and antibacterial activity.

A series of new nitrogen-carbon-linked (azolylphenyl)oxazolidinone antibacterial agents has been prepared in an effort to expand the spectrum of activity of this class of antibiotics to include Gram-negative organisms. Pyrrole, pyrazole, imidazole, triazole, and tetrazole moieties have been used to replace the morpholine ring of linezolid (2). These changes resulted in the preparation of compounds with good activity against the fastidious Gram-negative organisms Haemophilus influenzae and Moraxella catarrhalis. The unsubstituted pyrrolyl analogue 3 and the 1H-1,2,3-triazolyl analogue 6 have MICs against H. influenzae = 4 microgram/mL and M. catarrhalis = 2 microgram/mL. Various substituents were also placed on the azole moieties in order to study their effects on antibacterial activity in vitro and in vivo. Interesting differences in activity were observed for many analogues that cannot be rationalized solely on the basis of sterics and position/number of nitrogen atoms in the azole ring. Differences in activity rely strongly on subtle changes in the electronic character of the overall azole systems. Aldehyde, aldoxime, and cyano azoles generally led to dramatic improvements in activity against both Gram-positive and Gram-negative bacteria relative to unsubstituted counterparts. However, amide, ester, amino, hydroxy, alkoxy, and alkyl substituents resulted in no improvement or a loss in antibacterial activity. The placement of a cyano moiety on the azole often generates analogues with interesting antibacterial activity in vitro and in vivo. In particular, the 3-cyanopyrrole, 4-cyanopyrazole, and 4-cyano-1H-1,2,3-triazole congeners 28, 50, and 90 had S. aureus MICs

Oxazolidinones are a novel class of synthetic antibacterial agents active against gram-positive organisms including methicillin-resistant Staphylococcus aureus as well as selected anaerobic organisms. Important representatives of this class include the morpholine derivative linezolid 2, which is currently in phase III clinical trials, and the piperazine derivative eperezolid 3. As part of an investigation of the structure-activity relationships of structurally related oxazolidinones, we have prepared and evaluated the antibacterial properties of a series of piperazinyl oxazolidinones in which the distal nitrogen of the piperazinyl ring is substituted with a six-membered heteroaromatic ring. Compounds having MIC values/= 2 microg/mL vs selected gram-positive pathogens were discovered among each of the pyridine, pyridazine, and pyrimidine structural classes. Among these the cyanopyridine 17, the pyridazines 25 and 26, and the pyrimidine 31 exhibited in vivo potency vs S. aureus comparable to that of linezolid.

Oxazolidinone-resistant mutants of Staphylococcus aureus , isolated with a spiral plating technique, had a 16-fold higher MIC (2 versus 32 μg/ml) of eperezolid when compared to the parental sensitive strain. Eperezolid inhibited in vitro protein translation with 50% inhibitory concentrations of 30 μM for the oxazolidinone-sensitive S30 extract and 75 μM for the resistant extract. Experiments mixing various combinations of S100 and crude ribosome preparations from oxazolidinone-sensitive and -resistant S. aureus strains in a transcription-translation assay demonstrated that the resistant determinant resided within the ribosomal fraction. Ribosomes from the oxazolidinone-resistant strain bound less drug than ribosomes from the sensitive strain, indicating that the ribosome is the site of action for the oxazolidinones. These experiments demonstrate that an alteration of the ribosome is responsible for some or all of the oxazolidinone resistance observed in the S. aureus mutant.

Linezolid (formerly U-100766) and eperezolid (formerly U-100592) are novel oxazolidinone antimicrobial agents that are active against multi-drug-resistant staphylococci, streptococci, enterococci, corynebacteria, and mycobacteria. Preliminary studies also demonstrated that the compounds inhibited some test strains of anaerobic bacteria. Therefore, we extended the in vitro evaluation of these agents to include a total of 54 different anaerobic species. Minimal inhibitory concentration (MIC) values were determined using a standard agar dilution method for 143 anaerobic bacterial isolates. Eperezolid and linezolid demonstrated potent activity against the anaerobic Gram-positive organisms with most MIC values in the range of 0.25-4 microg/mL. Viridans streptococci demonstrated MICs of 1-2 microg/mL; Peptostreptococcus species and Propionibacterium species were inhibited by

The oxazolidinones are a new chemical class of synthetic antibacterial agents that are active orally or intravenously against multidrug-resistant Gram-positive bacteria. Their unique mechanism of action and activity against bacteria that pose therapeutic problems in hospital and community treatments make them promising candidates for antimicrobial agents.

Various electron-withdrawing groups were incorporated into the meta position of tropone-substituted 3-phenyl-2-oxazolidinones and their influence on antibacterial activity examined. Consideration of in vitro and in vivo test results indicated that one or two fluorine atoms flanking the para tropone appendage is the optimum arrangement for these compounds. Synthetic routes to enantiomerically enriched analogues are reported.

During the course of our investigations in the oxazolidinone antibacterial agent area, we have identified a subclass with especially potent in vitro activity against mycobacteria. The salient structural feature of these oxazolidinone analogues, 6 (U-100480), 7 (U-101603), and 8 (U-101244), is their appended thiomorpholine moiety. The rational design, synthesis, and evaluation of the in vitro antimycobacterial activity of these analogues is described. Potent activity against a screening strain of Mycobacterium tuberculosis was demonstrated by 6 and 7 (minimum inhibitory concentrations or MIC's < or = 0.125 micrograms/mL). Oxazolidinones 6 and 8 exhibit MIC90 values of 0.50 micrograms/mL or less against a panel of organisms consisting of five drug-sensitive and five multidrug-resistant strains of M. tuberculosis, with 6 being the most active congener. Potent in vitro activity against other mycobacterial species was also demonstrated by 6. For example, 6 exhibited excellent in vitro activity against multiple clinical isolates of Mycobacterium avium complex (MIC's = 0.5-4 micrograms/mL). Orally administered 6 displays in vivo efficacy against M. tuberculosis and M. avium similar to that of clinical comparators isoniazid and azithromycin, respectively. Consideration of these factors, along with a favorable pharmaco-kinetic and chronic toxicity profile in rats, suggests that 6 (U-100480) is a promising antimycobacterial agent.

Bacterial resistance development has become a very serious clinical problem for many classes of antibiotics. The 3-aryl-2-oxazolidinones are a relatively new class of synthetic antibacterial agents, having a new mechanism of action which involves very early inhibition of bacterial protein synthesis. We have prepared two potent, synthetic oxazolidinones, U-100592 and U-100766, which are currently in clinical development for the treatment of serious multidrug-resistant Gram-positive bacterial infections caused by strains of staphylococci, streptococci, and enterococci. The in vitro and in vivo (po and iv) activities of U-100592 and U-100766 against representative strains are similar to those of vancomycin. U-100592 and U-100766 demonstrate potent in vitro activity against Mycobacterium tuberculosis. A novel and practical asymmetric synthesis of (5S)-(acetamidomethyl)-2-oxazolidinones has been developed and is employed for the synthesis of U-100592 and U-100766. This involves the reaction of N-lithioarylcarbamates with (R)-glycidyl butyrate, resulting in excellent yields and high enantiomeric purity of the intermediate (R)-5-(hydroxymethyl)-2-oxazolidinones.

O-, N-, or F-substituted 3-isopropylidene- and 3-isopropyl N-acyl azetidin-2-ones, lacking an ionizable moiety attached to the lactam nitrogen, have in vitro antibacterial activity, being particularly potent vs anaerobes.

The cross-resistance or cross-susceptibility of cefpodoxime and ceftriaxone for 3700 strains of Enterobacteriaceae, oxacillin-susceptible staphylococci, Streptococcus spp., Haemophilus influenzae, Moraxella catarrhalis, and Neisseria gonorrhoeae was evaluated. With the exception of tests with Enterobacter spp. and Morganella morganii, the ceftriaxone minimum inhibitory concentration (MIC) result interpretive criteria predicted bacterial susceptibility (or resistance) to cefpodoxime with an acceptable rate of serious interpretive errors (1.5%) and an absolute categorical agreement > 92%. By using cefpodoxime interpretive criteria for ceftriaxone MICs, the interpretive errors for testing enteric bacilli were reduced from 2.1% to 1.5%.

Four hybrid antibiotics combining structural features of chloramphenicol (1a), sparsomycin (2b), lincomycin (5c), and puromycin (6d)--lincophenicol (1c), chloramlincomycin (5a), sparsolincomycin (5b), and sparsopuromycin (6b)--were synthesized. They were investigated as inhibitors of several partial reactions of procaryotic and eucaryotic protein synthesis as well as potential antimicrobial agents. Lincophenicol (1c) was active as inhibitor of Escherichia coli ribosomal peptidyltransferase-catalyzed puromycin reaction. Both lincophenicol (1c) and sparsophenicol (1b) inhibited the binding of the iodophenol analogue of sparsomycin to E. coli ribosomes. The results are discussed in terms of a retro-inverso hypothesis advanced earlier for interpretation of biological activity of chloramphenicol (1a) and sparsophenicol (1b). Chloramlincomycin (5a) suppressed the growth of Streptococcus pyogenes with MIC 6.25 micrograms/mL.

Incorporation of a bicyclo[1.1.1]pent-1-yl group at the N-1 position of quinolone antibacterial agents affords compounds with potent activity. One of these analogs, U-87947E, exhibits enhanced activity relative to that of ciprofloxacin against gram-positive aerobic bacteria and anaerobic organisms. Time-kill kinetic studies reveal that U-87947E is exquisitely bactericidal against ciprofloxacin-resistant Staphylococcus aureus.

Bacterial resistance development has become a very serious clinical problem for many classes of antibiotics. The 3-aryl-2-oxazolidinones are a relatively new class of synthetic antibacterial agents, having a new mechanism of action which involves very early inhibition of bacterial protein synthesis. We have prepared two potent, synthetic oxazolidinones, U-100592 and U-100766, which are currently in clinical development for the treatment of serious multidrug-resistant Gram-positive bacterial infections caused by strains of staphylococci, streptococci, and enterococci. The in vitro and in vivo (po and iv) activities of U-100592 and U-100766 against representative strains are similar to those of vancomycin. U-100592 and U-100766 demonstrate potent in vitro activity against Mycobacterium tuberculosis. A novel and practical asymmetric synthesis of (5S)-(acetamidomethyl)-2-oxazolidinones has been developed and is employed for the synthesis of U-100592 and U-100766. This involves the reaction of N-lithioarylcarb...

During the course of our investigations in the oxazolidinone antibacterial agent area, we have identified a subclass with especially potent in vitro activity against mycobacteria. The salient structural feature of these oxazolidinone analogues, 6 (U-100480), 7 (U-101603), and 8 (U-101244), is their appended thiomorpholine moiety. The rational design, synthesis, and evaluation of the in vitro antimycobacterial activity of these analogues is described. Potent activity against a screening strain of Mycobacterium tuberculosis was demonstrated by 6 and 7 (minimum inhibitory concentrations or MIC's < or = 0.125 micrograms/mL). Oxazolidinones 6 and 8 exhibit MIC90 values of 0.50 micrograms/mL or less against a panel of organisms consisting of five drug-sensitive and five multidrug-resistant strains of M. tuberculosis, with 6 being the most active congener. Potent in vitro activity against other mycobacterial species was also demonstrated by 6. For example, 6 exhibited excellent in vitro activity against multiple clinical isolates of Mycobacterium avium complex (MIC's = 0.5-4 micrograms/mL). Orally administered 6 displays in vivo efficacy against M. tuberculosis and M. avium similar to that of clinical comparators isoniazid and azithromycin, respectively. Consideration of these factors, along with a favorable pharmaco-kinetic and chronic toxicity profile in rats, suggests that 6 (U-100480) is a promising antimycobacterial agent.

Important resistance patterns in Gram-negative pathogens include active efflux of antibiotics out of the cell via a cellular pump and decreased membrane permeability. A 3-arylpiperidine derivative (1) has been identified by high-throughput assay as a potentiator with an IC50 ∼90 μM. This report details the evaluation of the tether length, aryl substitution and the importance of the fluorine on antibiotic accumulation. Evaluation of various tether lengths demonstrated that the two-carbon tethered analogues are optimal. Removal of the fluorine has a modest effect on antibiotic accumulation and the defluorinated analogue 17 is equally potent to the original lead 1.

This paper describes the discovery of α-trifluoroketoacetamides as potent antibacterial agents against Gram-positive organisms. The initial SAR indicates that the aryl ethyl side chain is essential in maintaining antibacterial activity. The SAR observations have been utilized to design a bioisostere for the α-trifluoroketoacetamide with good activity against Gram-positive organisms.

Trospectomycin sulfate (trospectomycin, TRS) is a novel, broad-spectrum, aminocyclitol antibiotic that is being developed clinically for the treatment of upper respiratory tract infections, bacterial vaginosis, pelvic inflammatory disease, and gonorrhea. This study investigated the bactericidal activity (by time-kill kinetics) and the postantibiotic effect (PAE) of TRS. Species-dependent bacteriostatic/bactericidal activity was observed for TRS; the antibiotic was bacteriostatic for Staphylococcus epidermidis, Enterococcus faecalis , and Escherichia coli , and bactericidal for Haemophilus influenzae, Neisseria gonorrhoeae, Moraxella catarrhalis , and Bacteroides fragilis (one of two test strains). When TRS was tested at four times its minimum inhibitory concentration or at a maximum test concentration of 32 μg/ml, with a 1-hr exposure period, the following PAE values were recorded: S. epidermidis 30032, 1.8 hr, En. faecalis ATCC 29212, 1.6 hr, E. coli UC 311, 1.5 hr, E. coli UC 9451, 1.5 hr, H. influenzae 30063, >4.0 hr, B. fragilis ATCC 25285, 5.2 hr, and B. fragilis UC 12199, 6.7 hr. The broad-spectrum PAE that was observed for TRS is somewhat unique compared with other antibiotics.

In antimicrobic susceptibility testing, minimum inhibitory concentration (MIC) susceptibility break points are defined by correlation of bacteriologic-clinical outcome data with MIC data for the infecting organisms. Disk diffusion [that is, zone-diameter (Z)] correlates are then established that provide for the prediction of organism susceptibility, while misclassification errors are kept to a minimum. The determination of Z break points through an error-rate-bounded classification scheme was first proposed by Metzler and DeHaan (1972). This method involves one MIC break point that separates susceptible and resistant strains. More recently, researchers have preferred to use two MIC break points (susceptible and resistant) that separate susceptible, moderately susceptible, and resistant strains. There is no known methodology for determining the Z break points for this latter situation, other than enumerating solutions for all feasible Z break-point pairs and choosing among the results. Our interest lay in presenting a methodology for determining the Z break points once the MIC break points are established. By deriving an index as a function of Z break points, a search method for finding the optimal Z break points is given. For the data set examined, our index interval solution required only a small percentage of solutions to be examined.

The synthesis and antibacterial activity of a series of N-acyl 3-isopropylidenyl- and 3-isopropyl 2-azetidinones having potent in vitro antibacterial activity, particularly against anaerobic organisms, is described. A distinguishing structural feature of these compounds is the lack of any ionizable moiety appendant to the lactam nitrogen.

QPT-1 was discovered in a compound library by high-throughput screening and triage for substances with whole-cell antibacterial activity. This totally synthetic compound is an unusual barbituric acid derivative whose activity resides in the (−)-enantiomer. QPT-1 had activity against a broad spectrum of pathogenic, antibiotic-resistant bacteria, was nontoxic to eukaryotic cells, and showed oral efficacy in a murine infection model, all before any medicinal chemistry optimization. Biochemical and genetic characterization showed that the QPT-1 targets the β subunit of bacterial type II topoisomerases via a mechanism of inhibition distinct from the mechanisms of fluoroquinolones and novobiocin. Given these attributes, this compound represents a promising new class of antibacterial agents. The success of this reverse genomics effort demonstrates the utility of exploring strategies that are alternatives to target-based screens in antibacterial drug discovery.

The discovery and initial optimization of a novel anthranilic acid derived class of antibacterial agents has been described in a recent series of papers. This paper describes the discovery of 1-acylindazol-3-ols as a novel bioisostere of an anthranilic acid. The synthesis and structure-activity relationships of the indazol bioisosteres are described herein.

Previously we reported the discovery and initial optimization of a novel anthranilic acid derived class of antibacterial agents which suffered from extensive protein binding. This report describes efforts directed toward understanding the relationship of the acidity of the carboxylic acid with the extent of protein binding. The pKa of the acid was modified via the synthesis of a number of anthranilic acid analogs which vary the aromatic ring substituent at the 4-position. The pKa and HSA binding constants have been determined for each of the analogs. Our results indicate a correlation between pKa and HSA Kd. The physical properties and antibacterial activities will be discussed as well as how these results help address the protein binding issue with this series of compounds.

The oxazolidinones are promising agents for the treatment of infections caused by gram-positive bacteria, including multidrug-resistant strains. In ongoing studies we have discovered that a strategically placed chiral center of appropriate absolute configuration improves the antibacterial activity of indolinyl oxazolidinone analogues (gram-positive MIC's0.5 microg/mL for the most potent congeners). The design, synthesis, antibacterial activity and pharmacokinetic profile of a selected series of alpha-methylated indoline derivatives and a related set of tetrahydroquinolyl and dihydrobenzoxazinyl analogues are discussed.

Replacement of the morpholine C-ring of linezolid 1 with a 1,3,4-thiadiazolyl ring leads to oxazolidinone analogues 5 having potent antibacterial activity against both gram-positive and gram-negative organisms. Conversion of the C5 acetamide group to a thioacetamide further increases the potency of these compounds.

The activities of linezolid, an oxazolidinone antibacterial agent active against gram-positive organisms, alone and in combination with 35 antimicrobial agents were tested in vitro against methicillin-sensitive ( n = 1 to 2 strains) and methicillin-resistant ( n = 8 to 10) Staphylococcus aureus strains; vancomycin-sensitive ( n = 6) and vancomycin-resistant ( n = 6 to 8) Enterococcus faecalis strains; vancomycin-sensitive ( n = 5) and vancomycin-resistant ( n = 6) Enterococcus faecium strains; penicillin-sensitive ( n = 2 to 5), penicillin-intermediate ( n = 5 to 6), and penicillin-resistant ( n = 5 to 6) Streptococcus pneumoniae strains; Escherichia coli ( n = 6); and Klebsiella pneumoniae ( n = 6). The fractional inhibitory concentration indices of linezolid in combination with other antimicrobial agents for the organisms tested were generated on checkerboard broth microdilution plates prepared by a semiautomated method. Of 1,380 organism-drug combinations, 1,369 (99.2%) combinations of linezolid with 28 antimicrobial drugs were indifferent, 9 combinations (0.65%) of linezolid with 6 drugs (amoxicillin, erythromycin, imipenem, sparfloxacin, teicoplanin, and tetracycline) were synergistic, and 2 combinations (0.15%) of linezolid with 2 drugs (ofloxacin and sparfloxacin) were antagonistic. Overall, the in vitro data demonstrated that linezolid combined with other antimicrobial agents primarily produces an indifferent response, with infrequent occurrences of synergism and antagonism.

The oxazolidinone linezolid represents a new antibacterial class of potential benefit in managing multidrug-resistant gram-positive infections, including those caused by Streptococcus pneumoniae . In a gerbil model of acute otitis media (AOM) induced by either penicillin-resistant S. pneumoniae (PRSP; amoxicillin MIC = 8 μg/ml, linezolid MIC = 1 μg/ml) or penicillin-susceptible S. pneumoniae (PSSP; amoxicillin MIC = 0.015 μg/ml, linezolid MIC = 1 μg/ml), we explored the plasma and ear fluid levels of linezolid required to demonstrate efficacy. Threshold pathogen doses required to induce bilateral AOM (1,500 CFU/ear with PRSP; 30 CFU/ear with PSSP) were administered to gerbils by intrabullar injection on day 0. At peak infection (∼10 6 to 10 7 CFU/ear flush; day 2 for PRSP-AOM and day 3 for PSSP-AOM), twice-a-day oral doses of linezolid, amoxicillin, or vehicle were administered over 4.5 days prior to collection and assay of middle ear effluents for S. pneumoniae content. Linezolid doses of ≥10 mg/kg of body weight induced significant cure rates of ≥72% versus both PRSP and PSSP infections, whereas amoxicillin at ≤100 mg/kg was consistently effective only versus PSSP-AOM. Plasma and ear fluid levels of linezolid necessary to elicit pneumococcal eradication from the middle ear were measured by high-performance liquid chromatography-tandem mass spectrometry and found to be similar both within and between each infection protocol. The plasma-ear fluid pharmacodynamic profile associated with linezolid efficacy was a T >MIC of ≥42%, a C max /MIC ratio of ≥3.1, and a (24-h area under the curve)/MIC ratio of ≥30 h. Application of this model will be useful in defining preclinical pharmacodynamic relationships of novel antibiotics necessary to cure S. pneumoniae -induced AOM.

Linezolid is a novel oxazolidinone antibacterial agent active against staphylococci (including methicillin-resistant strains), enterococci (including vancomycin-resistant strains), streptococci (including penicillin-intermediate and -resistant Streptococcus pneumoniae), and other aerobic and facultative bacteria. The agent has also demonstrated activity against a broad spectrum of Gram-positive and Gram-negative anaerobic bacteria. Previous time-kill assessments have shown linezolid to be generally bacteriostatic against staphylococci and enterococci, and bactericidal against streptococci. In this study, an anaerobic glovebox technique was employed to conduct time-kill assessments for four strains of anaerobic Gram-positive, and seven strains of anaerobic Gram-negative bacteria. The time-kill experiment was performed using Anaerobe Broth medium. The drugs were tested at four-fold the minimum inhibitory concentration (MIC), or at the higher concentration of 8mg/L for linezolid, 2mg/L for clindamycin, and 8mg/L for metronidazole. Samples for viable count were taken at 0, 6, and 24h, and plated using the Bioscience International Autospiral DW. Exposure of samples to the aerobic environment during plating was held to less than 30min. Plates were counted after a 48h anaerobic incubation (37 degrees C). The species tested included Bacteroides fragilis (2), B. distasonis, B. thetaiotaomicron, Fusobacterium nucleatum, F. varium, Prevotella melaninogenica, Clostridium perfringens, Eubacterium lentum and Peptostreptococcus anaerobius (2). The activity of linezolid was compared to that of metronidazole and clindamycin, two standard anti-anaerobe agents. As expected, the control agents were very active in these assays. Metronidazole yielded log(10)CFU/mL reductions of 3.0 or greater for nine of ten strains; clindamycin yielded log(10)CFU/mL reductions of 2.0 or greater for six of 11 strains, and 3.0 or greater for three strains. Linezolid also produced significant in vitro killing in this model achieving log(10)CFU/mL reductions of 2.0 or greater for six of 11 strains, and 3.0 or greater for four strains. The profile of activity was similar to that of clindamycin indicating that additional developmental studies of linezolid with anaerobic bacteria are warranted.

This paper describes the discovery of α-trifluoroketoacetamides as potent antibacterial agents against Gram-positive organisms. The initial SAR indicates that the aryl ethyl side chain is essential in maintaining antibacterial activity. The SAR observations have been utilized to design a bioisostere for the α-trifluoroketoacetamide with good activity against Gram-positive organisms.

A series of conformationally restricted, [6,5,5] and [6,6,5] tricyclic fused oxazolidinones were synthesized and tested for antibacterial activity. Several compounds in the trans-[6,5,5] series demonstrated potent in vitro and in vivo activity. This work provides valuable information regarding the preferred conformational orientation of the oxazolidinones at the binding site.

Throughout the human experience, diseases caused by pathogenic bacteria have exerted an enormous negative impact on society. Today, for example, approximately one third of the world’s population is infected with Mycobacterium tuberculosis and tuberculosis remains the leading cause of death in the world from infectious disease (Bloom, 1994). The emergence of effective antibacterial agents, from penicillin to more contemporary drugs, was initially thought to mark an end to the burden of microbial disease. However, subsequent events have illustrated the resiliency of bacteria to environmental pressures, including the threat of antibacterial agents.

In Phase I trials subjects received multiple doses of eperezolid (PNU-100592; formerly U-100592) and linezolid (PNU-100766; formerly U-100766), and steady-state samples were drawn at the projected peak and trough timepoints. Serum inhibitory titer and serum bactericidal titer values were determined using single strains of Staphylococcus aureus, Enterococcus faecalis, and Streptococcus pneumoniae. Serum inhibitory titer values generally correlated with drug concentration in serum and inherent organism susceptibility. Against S. aureus and E. faecalis sera from patients dosed with either drug were generally inhibitory at the peak timepoint, but at trough only linezolid exhibited a persistent effect. No bactericidal activity was seen for either drug against S. aureus or E. faecalis. The sera from patients dosed with either drug exhibited inhibition of S. pneumoniae at peak and trough. Bactericidal activity was seen against S. pneumoniae for both drugs at peak time and at trough for many of the sera for patients on the higher dose regimens. The results demonstrated that the sera from most human subjects dosed with eperezolid or linezolid were inhibitory to S. aureus and E. faecalis and S. pneumoniae and that many of the samples exhibited bactericidal activity for S. pneumoniae.