POLAR ESTER PRODRUGS OF HETEROCYCLIC HYBRID ANTIBACTERIAL COMPOUNDS AND SALTS THEREOF Cross-Reference to Related Applications

This application claims priority to U.S. Provisional Application No. 60/835,198, filed August 3, 2006.

Statement Regarding Federally Sponsored Research

The invention described herein was supported in whole or in part by SBIR grants number GM060828 and AI068349 from the National Institutes of Health. The United States Government has certain rights in the invention. Field of the Invention

This invention is generally in the field of prodrugs of antibacterial organic compounds. In particular, the invention provides polar ester prodrugs of hybrid antibacterial organic compounds and salts thereof for use in treating bacterial infections and diseases. Background of the Invention Bacterial pathogens continue to pose a serious threat to public health as indicated by a worldwide resurgence of bacterial diseases. One aspect of this resurgence appears to be the result of prior widespread, and largely effective, therapeutic and prophylactic use of antibiotics, which, unfortunately, over time has also selected for resistant strains of various bacterial pathogens. Of particular concern to public health has been the emergence and proliferation of bacterial strains that are resistant to multiple antibiotics in the current arsenal of antimicrobial agents. Such multi-antibiotic resistant ("MAR") bacterial strains include species of Gram positive bacteria, such as, antibiotic resistant strains of Staphylococcus aureus, Enter ococcus fecalis, and Enter ococcus fecium, which, along with antibiotic resistant Gram negative strains of Escherichia coli, constitute the most frequent etiological agents of nosocomial (hospital-acquired) diseases, such as septicemia, endocarditis, and infections of wounds and the urinary tract. S. aureus is currently the most frequent cause of nosocomial bacteremia and skin or wound infection. Streptococcus pneumoniae causes several serious and life-threatening diseases, including a contagious meningitis, bacteremia, and otitis media. Annual mortality from S. pneumoniae infection alone is estimated at between 3-5 million persons globally. More recently, clinical accounts of highly aggressive skin and tissue infections by "flesh-eating" strains of Group A streptococcus bacteria, such as Streptococcus pyogenes, have heightened the concern and

need for new or improved antibacterial agents. Clearly, there is an ongoing need to continue to develop antibacterial compounds that can be used as effective antibiotics to treat and prevent infection by an ever-evolving population of bacterial pathogens.

In recent times, a group of organic compounds has been described which are structural analogs of deoxynucleotides as exemplified by N ³ -substituted uracil and isocytosine and 7-substituted guanine and adenine compounds. Such compounds have been classified as members of "AU" (6-anilinouracil) and "PG" (2-phenylguanine) families of compounds, which are non-traditional antibiotics in that they specifically bind and inhibit the bacterial DNA polymerase IHC ("Pol HIC") that is required for DNA replication in the "low G-C" eubacteria, which include mycoplasmas and the low G-C Gram positive bacteria such as Streptococcus, Enterococcus, Staphylococcus, Bacillus, Clostridium, and Listeria (see, e.g., Wright et al., Curr. Opin. Anti-Infective Investig. Drugs, 1: 45-48 (1999); Tarantino et al., J. Med. Chem., 42: 2035-2040 (1999; Zhi et al., J. Med. Chem., 48: 7063- 7074 (2005); US 5,516,905). Another approach to developing improved antibiotics has been the synthesis of hybrid molecules, such as the family of hybrid molecules consisting of a fluoroquinolone (FQ) antibiotic molecule (see, e.g., Domagala et al., J. Med. Chem., 29: 394-404 (1986)) linked to a β-lactam antibiotic molecule (see, e.g., Hamilton-Miller, J. Antimicr. Chemother., 33: 197-202 (1994)). Such hybrid molecules are "dual-action" antibiotics in that they offer the benefit of a FQ component, which inhibits bacterial type II topoisomerase (Topo II), and a β-lactam component, such as cephalosporins and penicillins, which inhibits bacterial cell wall synthesis (see, e.g, Hamilton-Miller, J. Antimicr. Chemother., 33: 197- 202 (1994)). The FQ and β-lactam components may be linked to one another via an ester linkage in a "prodrug" form, which can undergo hydrolysis after administration to an individual (often catalyzed by an esterase) to provide the two active component antibiotics. Alternatively, linkages less susceptible to spontaneous hydrolysis may be used to enhance the half-life of the hybrid molecule after administration. In this latter case, the FQ active segment may be released in the presence of a β-lactamase, such as produced by β-lactam resistant bacteria, or when the β-lactam antibiotic is acylated during its mode of action (Hamilton-Miller, 1994).

More recently, a new family of stable, dual-action heterocyclic hybrid antibacterial compounds has been described (see, U.S. Patent No. 6,777,420). These compounds contain

a first moiety that is a DNA polymerase III inhibitor of the AU or PG classes, as mentioned above, that is covalently linked to a second moiety that is a pyridone, preferably, a fluoroquinolone (FQ) moiety, which inhibits bacterial type II topoisomerase, such that the "AU-FQ" or "PG-FQ" hybrid compounds inhibit both targets of the respective AU/PG and FQ moieties (see, e.g., Zhi et al., J. Med. Chem., 49: 1455-1465 (2006)). These heterocyclic hybrid antibacterial compounds are of particular interest because they provide a new dual- action class of antibiotics for treating infections by various bacterial strains including those that are resistant to one or more known antibiotics and also because they provide "broad range" antibiotics that may be used to treat infections and diseases caused by more than one strain or species of pathogenic bacteria, e.g., various Gram positive, mycoplasma, and/or Gram negative bacteria.

Clearly any improvement in the ability to handle, preserve, or administer heterocyclic hybrid antibacterial compounds as described above will be highly valued as means to more fully develop and exploit the benefit of this new class of compounds. Summary of the Invention

The invention provides polar ester prodrugs, and pharmaceutically acceptable salts thereof, of heterocyclic hybrid antibacterial parent compounds, which hybrid parent compounds comprise a 6-anilinouracil-like (AU) moiety that inhibits DNA polymerase III (Pol III) and a fluoroquinolone (FQ) moiety that inhibits bacterial type II topoisomerase (Topo II). A polar ester prodrug described herein is a prodrug in that it exhibits no significant antibacterial activity until it is converted to the corresponding non-ester parent AU-FQ hybrid compound by an esterase activity present in the blood or other tissue of an individual (human or other mammal) after administration to the individual. The prodrug compounds described herein have a polar radical esterified to the carboxylic acid group at position 3 of the FQ moiety of the corresponding antibacterial hybrid parent compound. Polar ester prodrug compounds described herein may be uncharged polar esters or charged polar esters, such as quaternary aminoalkyl esters (e.g., choline esters), of the corresponding antibacterial hybrid parent compounds. The prodrug compounds may also be converted to corresponding salt forms. Pharmaceutically acceptable salts of polar ester prodrug compounds as described herein are significantly more soluble in water and aqueous buffers than the respective non- salt polar ester forms and also the corresponding non-ester hybrid parent compounds. Such

salts may be readily formed during synthesis. Alternatively, a salt of a polar ester prodrug compound may be prepared by placing the free base form of the polar ester prodrug in water and adjusting the pH downward with an acid (e.g., HCl or methanesulfonic acid) until the compound dissolves. An aqueous formulation comprising a pharmaceutically acceptable salt of a polar ester prodrug described herein is particularly useful in providing a patient with the antibacterial activity of the corresponding parent AU-FQ hybrid compound via parenteral administration.

In one embodiment, the invention provides polar ester prodrugs having the following formula (I):

(I) wherein:

Ri is selected from the group consisting of a lower (Ci _-6 ) alkyl, a lower (C _2-6 ) hydroxyalkyl, a C _3-6 cycloalkyl, a monofluorophenyl, or a difluorophenyl;

X is hydrogen (H), a halogen selected from the group consisting of fluorine (F) or chlorine

(Cl), or methoxy;

Y and Z are, independently, selected from the group consisting of hydrogen (H), lower (C ι-

C ₆ ) alkyl (preferably, methyl or ethyl), lower (C ₂ -C ₆ ) alkenyl, lower (C ₂ -C ₆ ) alkynyl, halomethyl, and halo; or Y and Z are each a terminal methylene in the trimethylene radical

-CH ₂ CH ₂ CH ₂ - that forms a 5-membered ring fused to the contiguous phenyl ring;

"LINKER" is a bivalent linker segment comprising 1-10 atoms in contiguous linear connectivity;

"DIAMINE" is an aliphatic mono- or polycyclic (e.g., bicyclic) bivalent diamine group wherein one amino nitrogen atom is covalently linked to the fluoroquinolone moiety of formula I and the other amino nitrogen atom is covalently linked to the LINKER moiety of formula I;

R ₃ is a polar radical selected from the group consisting of a hydroxyalkyl (C _2-6 ); a polyhydroxyalkyl (C _2-6 ), wherein "polyhydroxy" is 2-6 hydroxy groups; a ω- hydroxy(alkoxy) _n alkyl (C _2-4 ), where n = 1-10; a primary aminoalkyl (C _2-6 ); a secondary

aminoalkyl (C _2-6 ); a tertiary aminoalkyl (C _2-6 ); a cyclic aminoalkyl (C _2-6 ) (preferably wherein the cyclic aminoalkyl is N-piperidinyl-, N-morpholinyl-, or N-piperazinyl- alkyl); a quaternary aminoalkyl (preferably wherein the quaternary aminoalkyl is choline); and wherein any alkyl or alkoxy present in R ₃ that is greater than 3 carbons in length is a straight or a branched chain; and pharmaceutically acceptable salts thereof.

Preferably, the DIAMINE of a polar ester prodrug or salt thereof as shown in formula I is a diamine selected from the group consisting of:

More preferably, the bivalent diamine is a piperazinyl group. Even more preferably, the diamine is a 3-substituted piperazinyl group. Still more preferably, the diamine is a 3- methyl piperazinyl group or a 3-hydroxymethyl piperazinyl group. Most preferably, the diamine is a 3-methyl piperazinyl group. In another embodiment, the invention provides a polar ester prodrug of formula I, wherein Y is methyl, Z is methyl or ethyl, Ri is cyclopropyl, X is hydrogen (H) or fluorine (F), LINKER is -(CH ₂ ) ₄ - or -(CH ₂ ) ₅ -, DIAMINE is piperazinyl or a 3-substituted piperazinyl (wherein the 3-substituent is methyl or hydroxymethyl), and R ₃ is 2- (hydroxyethoxy)ethyl (i.e., -CH ₂ CH ₂ OCH ₂ CH ₂ OH) or 1 -methyl-2-hydroxyethyl (i.e., -CH(CH ₃ )CH ₂ OH); and pharmaceutically acceptable salts thereof.

In another embodiment, the invention provides a polar ester prodrug of formula I, wherein Y is methyl; Z is ethyl; R ₁ is cyclopropyl; X is H or F; LINKER is -(CH ₂ ) ₄ - or

-(CH ₂ ) _S -; DIAMINE is piperazinyl or a 3-substituted piperazinyl (wherein the 3-substituent is methyl or hydroxymethyl); and R ₃ is selected from the group consisting of 2-(N ,N- diethylamino)ethyl, 2-(N-piperidinyl)ethyl, 2-(N-morpholinyl)ethyl, and 2-(N- piperazinyl)ethyl; and pharmaceutically acceptable salts thereof. In still another preferred embodiment, the invention provides a polar ester prodrug of formula I, wherein Y is methyl; Z is methyl or ethyl; Ri is cyclopropyl; X is H or F; LINKER is -(CH ₂ ^- or -(CH ₂ ) _S -; DIAMINE is piperazinyl, 3-methylpiperazinyl, or 3- (hydroxymethyl)piperazinyl; and R ₃ is choline; and salts thereof.

In another preferred embodiment, polar ester prodrugs of the invention are in the form of a corresponding pharmaceutically acceptable salt selected from the group consisting of a mono hydrochloride, a bis-hydrochloride (di-hydrochloride), a sulfate, a mesylate (i.e., a methanesulfonate), a bis-mesylate (di-mesylate), a 2-furoate, a 3-furoate, fumarate or maleate. More preferably, the pharmaceutically acceptable salts of polar ester prodrugs that have a hydroxy or polyhydoxy ester are mesylates, and the pharmaceutically acceptable salts of polar ester prodrugs that have a basic (amino-containing) ester are bis-hydrochlorides or bis-mesylates. Pharmaceutically acceptable salts of the polar ester prodrugs are significantly more water-soluble than both the respective non-salt form of the polar ester prodrug as well as the non-ester parent AU-FQ hybrid antibacterial compound. Such pharmaceutically acceptable salts of polar ester prodrugs are particularly useful in preparing pharmaceutically acceptable compositions for administration to an individual (human or other mammal) by a parenteral route.

In another embodiment, the invention provides pharmaceutical compositions comprising a pharmaceutically acceptable salt of a polar ester prodrug described herein and a pharmaceutically acceptable buffer. Such pharmaceutical compositions may contain one or more other therapeutically active compounds, such as, another antibiotic, an anti-viral compound, an anti-cancer compound, and the like.

Pharmaceutically acceptable compositions may be administered to an individual parenterally or non-parenterally. Preferably, a pharmaceutical composition as described herein is administered by a parenteral route. Parenteral routes include, without limitation, intravenous (iv), subcutaneous (sc), intramuscular (im), intraperitoneal (ip), intrathecal (it), and epidural (ep).

Polar ester prodrugs and pharmaceutically acceptable salts thereof as described herein are antibiotics, which upon conversion to their corresponding non-ester AU-FQ hybrid parent compounds, are effective against one or more species of bacteria, such as species of Gram positive, mycoplasma, and/or Gram negative bacteria. Particularly preferred are polar ester prodrugs and pharmaceutically acceptable salts thereof that are effective against one or more species of Gram positive bacteria, including without limitation, species of Streptococcus, Enterococcus, Staphylococcus, Bacillus, Clostridium, Listeria, and combinations thereof.

The invention also provides methods for treating or preventing a bacterial infection or disease in an individual comprising administering to the individual a polar ester prodrug or pharmaceutically acceptable salt thereof as described herein to the individual. Preventative (prophylactic) administration of a polar ester prodrug or pharmaceutically acceptable salt thereof as described herein to an individual is useful when an exact diagnosis cannot be made or has not been made but the individual is considered to be at risk of infection by one or more pathogenic bacterial species or strains. Brief Description of the Drawings

Figure 1 shows the conversion of polar ester prodrug compound 4 ((S)-3-{4-[l-(l- cyclopropyl-3-carboxy-4-oxo-6,8-difluoro-7-quinolyl)-4-(3-me thylpiperazinyl)]butyl}-6-(3- ethyl-4-methylanilino)uracil, 2-(2-hydroxyethoxy)ethyl ester; diamonds) to its corresponding antibacterial hybrid parent compound ((S)-3-{4-[l-(l-cyclopropyl-3-carboxy- 4-oxo-6,8-difluoro-7-quinolyl)-4-(3-methylpiperazinyl)]butyl }-6-(3-ethyl-4- methylanilino)uracil; squares) as determined by HPLC when compound 4 was incubated in mouse plasma at room temperature (25°C). Y-axis indicates the concentration (mmol/L) of a compound in the plasma. X-axis indicates time (minutes) of incubation of compound 4 in the plasma. See, Example 3, infra, for details.

Figure 2 shows the effect of the cholinesterase inhibitor neostigmine (NS, 1 mg/mL) on mouse plasma-mediated conversion of polar ester prodrug compound 19 ((S)-3-{4-[l-(l- cyclopropyl-3-carboxy-4-oxo-6,8-difluoro-7-quinolyl)-4-(3-me thylpiperazinyl)]butyl}-6-(3- ethyl-4-methylanilino)uracil, 2-(N-morpholinyl)ethyl ester) to its corresponding hybrid antibacterial parent compound ((S)-3-{4-[l-(l-cyclopropyl-3-carboxy-4-oxo-6,8-difluoro-7- quinolyl)-4-(3-methylpiperazinyl)]butyl}-6-(3-ethyl-4-methyl anilino)uracil). Concentrations (mmol/L) of compounds were determined by HPLC at various times

(minutes) during incubation in mouse plasma. Open squares indicate the concentration of prodrug compound 19 in the absence of NS. Open diamonds indicate concentration of corresponding hybrid parent compound of compound 19 in the absence of NS. Filled squares indicate concentration of prodrug compound 19 in the presence of NS. Filled diamonds indicate the concentration of corresponding antibacterial hybrid parent compound of compound 19 in the presence of NS. See, Example 3, infra, for details.

Figure 3 shows plasma concentration (mg/L) of polar ester prodrug salt compound 18.Ms ₂ (3-{4-[l-(l-cyclopropyl-3-carboxy-4-oxo-6,8-difluoro-7-quino lyl)-4-(3- methylpiperazinyl)]butyl } -6-(3-ethyl-4-methylanilino)uracil, 2-(N-morpholinyl)ethyl ester dimesylate) and of the corresponding hybrid antibacterial parent of compound 18.Ms ₂ (3-{4- [l-(l-cyclopropyl-3-carboxy-4-oxo-6,8-difluoro-7-quinolyl)-4 -(3- methylpiperazinyl)]butyl}-6-(3 -ethyl -4-methylanilino)uracil) at various times (minutes) after compound 18.Ms ₂ was injected intravenously into mice (n = 6, at each point). Diamonds indicate the plasma concentration of compound 18.Ms ₂ . Squares indicate the plasma concentration of the antibacterial hybrid parent compound of compound 18.Ms ₂ . See, Example 6, infra, for details. Detailed Description of the Invention

The invention provides a new family of polar ester prodrug compounds and salts thereof, which are polar esters of heterocyclic 6-anilinouracil-fluoroquinolone (AU-FQ) hybrid antibacterial parent compounds. Various AU-FQ hybrid antibacterial parent compounds have been described (see, e.g., U.S. Patent No. 6,777,420; Zhi et al., J. Med. Chem., 49: 1455-1465 (2006)). Polar ester prodrug compounds and their corresponding pharmaceutically acceptable salts are converted in vivo from inactive ester compounds to the corresponding non-ester AU-FQ hybrid antibacterial parent compounds. It has been further discovered that certain pharmaceutically acceptable salts of the polar ester prodrug compounds are significantly more water-soluble than the corresponding non-salt polar ester prodrugs, the corresponding non-polar ester prodrugs, and the corresponding non-ester heterocyclic AU-FQ hybrid antibacterial parent compounds. The water-soluble pharmaceutically acceptable salts of polar ester prodrugs as described herein are particularly useful in the manufacture of pharmaceutical compositions that can be administered parenterally to an individual to treat or prevent an infection or disease caused by one or more species or strains of pathogenic bacteria. Such salts of polar ester prodrug compounds

described herein are readily made during synthesis. Alternatively, a salt of a polar ester prodrug compound may be made by placing the free base form of the polar ester prodrug into water and adding an acid (e.g., HCl or methanesulfonic acid) until the compound dissolves (or as much as possible dissolves in the water). If desired, the salt may be crystallized from solution by standard methods. Accordingly, the invention provides the means and methods to greatly expand and exploit the antibacterial activity of the class of AU-FQ hybrid antibacterial parent compounds for treating bacterial infection and disease in humans and other mammals.

In order that the invention may be more clearly understood, the following abbreviations and terms are used as defined below.

Abbreviations for various substiruents or side groups of organic molecules are those commonly used in the art. Such abbreviations include "shorthand" forms of such substiuents. For example, "Ac" is an abbreviation for an acetyl group, and "halo" or "halogen" indicates a halogen radical (e.g., F, Cl, Br, I). "Me" and "Et" are abbreviations used to indicate methyl (CH ₃ -) and ethyl (CH ₃ CH ₂ -) groups, respectively; and "MeO" and "EtO" indicate methoxy (CH ₃ O-) and ethoxy (CH ₃ CH ₂ O-), respectively. Hydrogen atoms are not always shown in organic molecular structures or may be only selectively shown in some structures, as the presence and location of hydrogen atoms in organic molecular structures are understood and known by persons skilled in the art. Likewise, carbon atoms are not always specifically abbreviated with "C", as the presence and location of carbon atoms, e.g., between or at the end of bonds, in structural diagrams are known and understood by persons skilled in the art. Amino acids may be indicated herein using conventional three or single letter abbreviations, with or without an indication of the L- or D- steroisomerism. For example, "Ala", "L-ala", and "A" are all acceptable abbreviations for L-alanine, one of the 20 naturally occurring L-amino acids (see, e.g., Lodish et al.,

Molecular Cell Biology. Fourth Edition (W. H. Freeman and Co., New York, 1999), p. 52). The term "alkyl" means a saturated straight chain or branched, primary, secondary, or tertiary hydrocarbon radical, typically Ci - Ci ₈ , e.g., Ci - Cio or Ci - C ₆ including, without limitation, methyl, ethyl, propyl, butyl, pentyl, hexyl, isopropyl, isobutyl, sec-butyl, t-butyl, isopentyl, amyl, and t-pentyl. Further, alkyl segments may optionally be substituted with one or more conventionally used alkyl substiruents, such as amino, alkylamino, alkoxy, alkylthio, oxo, halo, acyl, nitro, hydroxyl, cyano, aryl, alkylaryl, aryloxy, arylthio,

arylamino, carbocyclyl, carbocyclyloxy, carbocyclylthio, carbocyclylamino, heterocyclyl, heterocyclyloxy, heterocyclylamino, heterocyclylthio, and the like.

The term "cycloalkyl" means a mono- or polycyclic alkyl radical. "Pharmaceutically acceptable" means that a substance or composition is compatible with the physiology of an individual (human or other mammal) and is also compatible with and does not destroy any beneficial properties (e.g., solubility, antibacterial activity) provided by a polar ester prodrug or its corresponding salt as described herein or of any other desired ingredient that may be present in a composition to be administered to an individual. A "pharmaceutically acceptable salt" of a compound is a salt form of a compound (e.g., of a polar ester prodrug described herein) that is compatible with the desired pharmacological property of the parent compound and the physiology of an individual to whom such a salt form of the compound may be administered, as well as with the desired property of any other drug or compound that may also be administered to the individual. A "pharmaceutically acceptable carrier (or vehicle)" refers to any material (solid, semi-solid, liquid, or gas) that may be used to prepare compositions comprising a polar ester prodrug or salt thereof as described herein for administration to an individual. A "pharmaceutical acceptable buffer" is a broad term in that it includes pharmaceutically acceptable liquid carriers that have a true pH buffering capacity to maintain a particular pH in a composition or in the local environment in which a composition is administered as well as pharmaceutically acceptable liquid carriers, such as water, that do not have the capacity to maintain a particular pH. The terms "pharmaceutically acceptable composition" and a "pharmaceutical composition" are used interchangeably.

The term "antibacterial activity" (and equivalent terms used herein) of a compound or composition means the ability of the compound or composition to kill bacteria. Antibacterial activity may be determined as a measurable minimum inhibitory concentration (MIC) value in vitro against the growth of bacteria or by producing a clinically recognizable improvement of one or more symptoms of a bacterial infection or disease in vivo when administered to an individual. MIC may be measured by techniques known to those of skill in the art, e.g., determining the minimal concentration of a compound that is needed to prevent growth of one or more species of bacteria on a solid (e.g., agar plates) or liquid medium supplemented with varying concentrations of the prodrug test compound or salt thereof and a source of esterase activity. When a prodrug compound or corresponding salt

thereof as described herein is converted to its corresponding non-ester parent compound (either in vivo or in vitro), the parent compound possesses antibacterial activity that is effective against one or more strains or species of pathogenic bacteria, including but not limited to, one or more species or strains of Gram positive bacteria (such as Streptococcus, Enterococcus, Staphylococcus, Bacillus, Clostridium, and Listeria); one or more species or strains of mycoplasma bacteria; one or more species or strains of Gram negative bacteria (such as Escherichia coli, serovars of Salmonella enterica, and Vibrio species); and combinations thereof.

A "clinically recognizable improvement of one or more symptoms" of a bacterial infection or disease refers to any medically-recognized improvement in the health of an individual that presents one or more symptoms of a pathological bacterial infection or disease, including, but not limited to, survival or recovery of the individual from the bacterial infection or disease, reduction in fever, tissue or wound healing, decrease in pain, increase in physical or mental vigor, increase in appetite, restoration of normal heartbeat, restoration of normal breathing, restoration of normal gastrointestinal function; restoration of normal levels of circulating white blood cells, decrease in titer of antibodies to bacterial antigens in blood or other tissues, and reduction in titer of pathogenic bacteria in biological samples obtained from the individual.

"Antibiotic" is any compound that has antibacterial activity, i.e., is capable of killing one or more species or strains of bacteria. The polar ester prodrugs and salts thereof as described herein as well as their corresponding non-ester heterocyclic AU-FQ hybrid parent compounds are "antibiotics" as such compounds provide antibacterial activity under appropriate conditions.

"Bacteria" means any strain or species of prokaryotic cell as found in the classical kingdom Monera (more recently classified as the kingdoms/domains of Bacteria and

Archaea). The term "bacteria" generally includes, without limitation, Gram positive, Gram negative, Gram variable, and mycoplasma prokaryotes (which, owing to a lack of a cell wall, will Gram stain negative, but are phylogenetically more closely related to Gram positive bacteria). Examples of Gram positive bacteria include, without limitation, bacilli (such as Bacillus subtilis and Bacillus anthracis), Clostridia (such as Clostridium tetani), staphylococci (such as Staphylococcus aureus and Staphylococcus epidermidis), enterococci (such as Enterococcos fecium and Enterococcus fecalis), and streptococci (such as

Streptococcus pneumoniae). Examples of Gram negative bacteria include, without limitation, Escherichia coli, Pseudomonas aeruginosa, serovars of Salmonella enterica (e.g., S. typhimurium, S. typhi, S. paratyphi, etc.), Shigella dysenteriae, and Vibrio species (e.g., V. cholerae). The term "contiguous linear connectivity" means connected together so as to form an uninterrupted linear array or series of atoms. For example, a linker moiety (see, e.g., LINKER in formula I) of the polar ester prodrugs described herein having a specified number of atoms in contiguous linear connectivity has at least that number of atoms connected together so as to form an uninterrupted chain, but may also have additional atoms that are not so connected (e.g., branches or atoms contained within a ring system).

"DIAMINE" or "diamine" as a component of a polar ester prodrug compound, corresponding 6-anilinouracil-fluoroquinolone (AU-FQ) antibacterial hybrid parent compound, or salt thereof, as described herein, is an aliphatic mono- or polycyclic (e.g., bicyclic) bivalent diamine moiety, wherein one amino nitrogen atom is covalently linked to a fluoroquinolone (FQ) moiety and the other amino nitrogen atom is covalently linked to a LINKER moiety comprising 1-10 atoms in contiguous linear connectivity, and wherein at least one of the amino nitrogens is present in a ring and not more than one of the amino nitrogens is a ring substituent or covalently linked to a ring substituent (e.g., linked to an alkyl substituent). Preferred diamines useful in the prodrug compounds, corresponding hybrid parent compounds, and salts thereof, as described herein, include, but are not limited to:

More preferably, the diamine of a compound described herein is a piperazinyl group. Even more preferably, the diamine is a 3 -substituted piperazinyl group. Still more preferably, the 3-substituted piperazinyl group is a 3-methyl piperazinyl group or a 3-hydroxymethyl piperazinyl group. Most preferably, a diamine of a compound described herein is a 3- methyl piperazinyl group.

"Drug" is any compound that can provide an antibacterial activity or any other beneficial therapeutic or prophylactic pharmacological activity to an individual. Prodrug compounds, corresponding antibacterial hybrid parent compounds, and salts thereof, as described herein, are drugs. "DNA polymerase III" or "Pol III" means a bacterial enzyme having the activity of a bacterial DNA polymerase. This class of enzymes includes, but is not limited to, DNA polymerase HIC ("Pol HIC") of Gram-positive bacteria and DNA polymerase HIE of Gram- negative bacteria. The compounds described herein are particularly effective at inhibiting DNA polymerase IHC found in Gram positive bacteria and in mycoplasma bacteria. "Effective amount" of a polar ester prodrug compound or salt thereof or of a composition comprising a polar ester prodrug compound or salt thereof as described herein means an amount which, when administered to a patient in need of treatment thereof or when applied to an in vitro test, produces an antibacterial activity upon conversion to the non-ester parent AU-FQ hybrid compound (see above). "Halo" means a halogen radical, including but not limited to fluoro (F), chloro (Cl), bromo (Br), or iodo (I).

"Hydroxy(alkoxy) _n alkyl" means a group containing "n" number of repeating alkoxy units, where the alkoxy unit may be branched, culminating in a free hydroxy (OH) group on one end and connected to the oxygen of an acid group on the other end. "Hydroxyalkyl" means a group containing one or more hydroxyl (OH) groups attached to a straight or branched alkyl chain. Unless indicated otherwise, preferred hydroxyalkyl groups have 1 to 6 hydroxy (OH) groups and alkyl groups of 2-12 carbon atoms.

"LINKER" or "linker" means a diradical having from 1-10 atoms in contiguous linear connectivity (i.e., as defined above and excluding atoms present in any side chains and branches), and that covalently connects (links) one segment or moiety of a prodrug compound of this invention to the remaining portion of the compound. The atoms of the

linker in contiguous linear connectivity may be connected by saturated or unsaturated covalent bonds. Linkers are alkylidene, alkenylidene, alkynylidene, and cycloalkylidene (e.g., lower alkylidene, cycloalkylidene, alkylycloalkylidene and alkyl-substituted alkylidene) linkers wherein one or more (e.g., between 1 and 4, such as 1 or 2) carbon atoms may be optionally replaced with O, S, or N and wherein two or more (e.g., 2 to 4, such as 2 or 3) adjacent atoms may be optionally linked together to form a carbocyclic or heterocyclic moiety within the linker (which may be monocyclic, polycyclic, and/or fused, and which may be saturated, unsaturated, or aromatic). Examples of linkers useful in the compounds of the invention include (without limitation) diradicals of alkyl, alkenyl, alkynyl, alkoxy, alkoxyalkyl, alkylaminoalkyl, cycloalkyl, alkylcycloalkyl, and alkyl-substituted alkylcycloalkyl (wherein one or more carbon atoms in any of these linkers may be optionally replaced with O, S, or N).

"Lower" means the group to which it is applied has 6 or less atoms that define the group. For example, "lower" alkyl or alkoxy has 1 -6 carbon atoms, except in the case of rings (such as cycloalkyl), in which case "lower" signifies 3-6 ring members. Unless noted to the contrary, substituents to compounds described herein are "lower".

The terms "individual" and "patient" are synonymous and refer to a human or other mammal that receives or may be a candidate to receive a polar ester prodrug or pharmaceutically acceptable salt thereof as described herein to treat or prevent a bacterial infection or disease. As used herein, a "patient" or "individual" may or may not exhibit a recognizable symptom of a disease, but merely be at risk for infection by a pathogenic bacterial species that may cause a disease, e.g., due to exposure to a source of infection. A "prodrug" or "prodrug compound" is a compound that exhibits no significant pharmacological activity unless it is converted to a pharmacologically active "parent" compound. Pharmaceutically useful prodrugs are compounds that upon administration to an individual are converted in vivo to the corresponding pharmacologically active parent compound. Prodrugs may also be converted to the pharmacologically active parent drug in vitro in the presence of an exogenously provided converting activity, e.g., a converting enzyme. Prodrugs as described herein (see, formula I) are polar esters of heterocyclic AU- FQ hybrid antibacterial parent compounds (see, e.g., U.S. Parent No. 6,777,420) in which a polar radical is esterified to the C-3 carboxylic acid group of the FQ moiety of the AU-FQ hybrid parent compound. Such polar radicals include a quaternary aminoalkyl radical such

as choline (i.e., a 2-(trimethylammonium)ethanol radical). Accordingly, polar ester prodrug compounds described herein may be uncharged or charged depending on the particular polar radical esterified to the C-3 carboxylic acid group of the AU-FQ hybrid parent compound. The polar ester prodrugs described herein exhibit no significant pharmacological activity, i.e., no significant antibacterial activity, unless the ester group is removed, e.g., by an esterase activity present in the liver, blood, or other tissues of an individual who is administered the prodrug compound. Polar ester prodrugs described herein may also be described herein as "hydrophilic" to emphasize that the polar radical esterified at position 3 of the FQ moiety is required for the enhanced water solubility exhibited by the corresponding salts of such prodrugs.

A "quaternary ester prodrug" or "quaternary aminoalkyl ester prodrug" refers to a prodrug of the invention in which the radical esterified to the C-3 carboxylic acid group of the fluoroquinolone (FQ) moiety of a 6-anilinouracil-fluoroquinolone (AU-FQ) hybrid antibacterial parent compound (see, prodrug formula I) bears a permanent positive charge owing to the presence of a quaternary ammonium group. An example of such a radical is choline.

Non-quaternary aminoalkyl ester polar prodrug compounds described herein may exist as a non-salt form (uncharged "free base") or as a salt form, e.g., depending on the pH and ionic conditions of the environment in which the prodrug is situated (e.g., solutions, mixtures, suspensions, etc.). Various salt forms of a polar ester prodrug compound are readily obtained using standard methods to mix an inorganic acid (e.g., HCl, H ₂ SO ₄ ) or an organic acid (e.g., citric acid, methanesulfonic acid, 2-furoic acid, 3-furoic acid, fumaric acid, maleic acid) with the polar ester prodrug in a solvent in which both components are soluble, e.g. an alcohol, dioxane, tetrahydrofuran, and either evaporating the solvent or precipitating the salt with another solvent, e.g. diethyl ether, methyl t-butyl ether, hexane. A quaternary ammonium group, such as that in choline ester prodrug compounds, requires a counter anion, such as a chloride anion (CF) (see, e.g., compounds 29(.Cl) and 30(.Cl), infra), and, therefore, a quaternary ester prodrug compound, such as a choline ester prodrug compound, is already a salt. Accordingly, a "salt form" of such quaternary aminoalkyl ester prodrug compounds, such as a choline ester prodrug compound, is understood to mean the corresponding bis salt, e.g, a "chloride hydrochloride" (see, e.g., compounds 29.C1.HC1 and 30.C1.HC1, infra).

Preferred salts of prodrug compounds described herein are pharmaceutically acceptable salts. Suitable pharmaceutically acceptable salts include, but are not limited to, for example, acid addition salts such as hydrochloride, hydrobromide, hydroiodide, nitrate, sulfate, bisulfate, phosphate, acid phosphate, isonicotinate, acetate, lactate, salicylate, citrate, tartrate, pantothenate, bitartrate, ascorbate, succinate, maleate, gentisinate, fumarate, gluconate, glucaronate, saccharate, formate, 2-furoate, 3-furoate, benzoate, glutamate, methanesulfonate (mesylate), ethanesulfonate, benzensulfonate, p-toluenesulfonate, and pamoate (i.e., l,l'-methylene-bis-(2-hydroxy-3-naphthoate)) salts. See, e.g., Wermuth et al. (eds.), Pharmaceutical Salts: Properties, Selection, and Use, A Handbook (Verlag Helvetica Chimica Acta, Zurich 2002) [ISBN 3-906390-26-8] ; Bastin et al., Organic Proc. Res. Devel, 4:421-35 (2000).

Terms such as "parenteral", "parenterally", and the like, refer to any route or mode by which a compound or composition may be administered to an individual other than along the alimentary canal. Examples of parenteral routes of administration include, without limitation, intravenous (i.v.), subcutaneous (s.c), intravenous (i.v.), intramuscular (i.m.), intra-arterial (i.a.), intraperitoneal (i.p.), transdermal (absorption through the skin or dermal layers), nasal ("intranasal"; absorption across nasal mucosa), or pulmonary (e.g., inhalation for absorption across the lung tissue), vaginal, direct injections or infusions into body cavities or organs other than those of the alimentary canal, as well as by implantation of any of a variety of devices into the body, again, at sites other than those of the alimentary canal. Parenteral administration of a compound or composition described herein may thus be achieved by one or more of the following non-limiting examples: injection of a compound or composition, injection of a depot containing a compound or composition, and implantation of a device that provides active or passive release of a compound or composition into the body.

The terms "non-parenteral", "non-parenterally", "enteral", "enterally", "oral", "orally", and the like, refer to a mode or route by which a compound or composition may be administered to an individual at a site along the alimentary canal. Examples of enteral routes of administration include, without limitation, oral, as in swallowing solid (e.g., tablet) or liquid (e.g., syrup) dosage forms, sublingual (under the tongue for absorption through the mucosal membranes lining the floor of the mouth), buccal (absorption through the mucosal membranes lining the cheeks), nasojejunal or gastrostomy tubes (delivery into the stomach),

intraduodenal administration, as well as rectal administration (e.g., suppositories for release of a compound into and absorption by the lower intestinal tract of the alimentary canal).

"Pyridone", for the purposes of this invention, means a compound having the chemical structure of a 4-pyridone (including bicyclic structures such as quinolone, naphthyridone, benzoxazalone, pyridopyrimidone, pyrimidopyridone, and quinazolinone any of which may be optionally substituted with conventional substituents for compounds of those types (see substituents discussed and referenced in chapter 2 of The Quinolones, 2nd ed., Vincent T. Andriole, ed., 1998, Academic Press (San Diego, CA); chapter 2, The Quinolones, 3rd ed., Vincent T. Andriole, ed., 2000, Academic Press (San Diego, CA); and Q. Li et al., "The 2-Pyridone Antibacterial Agents: Bacterial Topoisomerase Inhibitors", Med. Res. Rev. 20: 231-293 (2000), which are hereby incorporated by reference in their entirety). Preferred pyridones of use in the invention are fluoroquinolones (FQ) as present in the hybrid antibacterial parent compounds and the corresponding polar ester prodrugs and salts thereof as described herein. The term "segment" means a portion of a parent compound that, when referred to apart from the parent compound, is capped with H, instead of being linked to the remainder of the parent compound. When referred to as a part of the parent compound, a segment shall be viewed as a radical of that segment. In addition, a "segment" of a compound described herein may also refer to a linked combination or grouping of two or more smaller contiguous segments of the compound. For example, a compound having linked segments A-B-C-D-E, also contains "segments" A-B, A-B-C, and B-C.

"Substituted", unless otherwise specified herein, means replacing one or more hydrogen radicals in a given structure or segment thereof with substituents (also called "ligands", "radicals", or "groups") conventionally used for structures or segments of the same general type. Conventional substituents for the structures and segments described herein may be found in the published literature and will be generally known to those of ordinary skill in the art of chemical synthesis.

"Type II topoisomerase", "Topo II", or an equivalent term means a bacterial enzyme having the activity of a type II bacterial topoisomerase (including both alpha and beta isozymes). These enzymes are characterized by the ability to cleave both strands of a bacterial double-stranded DNA molecule at the same time, passing a portion of the DNA duplex through the cut strands, and resealing the strands. Examples of type II

topoisomerases include, without limitation, bacterial DNA gyrase and bacterial topoisomerase IV.

Unless otherwise specified, the terms defined above shall have the meanings ascribed above even when such terms are used as a part (e.g., as a prefix or a suffix) of a different term (e.g., the definition of alkyl given above shall apply to the alkyl portion of an alkylamino group). Specific examples of chemical groups (radicals) falling within the general categories shown above are for the sake of convenience. It will be understood that these examples are not exhaustive and should not be viewed as limiting the scope of the invention in any way. Any radical defined above as being optionally substituted may be linked directly or indirectly through any of its substituents. Combinations and choices of substituents shall be selected so as to produce stable chemical compounds having the desired activity or property and which are available by conventional synthetic techniques. For any given substituent, stated examples may apply even if that substiruent is used in a different combination of variables. In all cases, functional oxygen, nitrogen, sulfur, or other chemically active segments may be protected as necessary or desired using conventional protecting groups. For compounds of this invention having one or more chiral centers, such compounds may be stereochemically pure, such as individual enantiomers (e.g., R or S enantiomers) or diastereomers, or may be present as a mixture of stereoisomers, such as a racemic or other ratio mixture of individual enantiomers or diastereomers. This choice will be made on a case-by-case basis, taking into account the observed activity of the mixture and of individual stereoisomers.

"Therapy" and "therapeutic" as understood and used herein refer to treatment of an individual for a bacterial infection or disease. For convenience, the terms are also understood to encompass prophylactic, preventative, or precautionary administration of a prodrug compound of the invention. Such precautionary or prophylactic use is exemplified, without limitation, by administration of an antibiotic to an immunocompromised or immunodeficient patient; to an individual who is suspected, but not proven, to have a bacterial infection; and to an individual who is susceptible to or at risk of contracting a pathogenic bacterial infection or disease due to exposure to infected individuals or contact with water, food, body fluids, corpses, or carcasses containing pathogenic bacteria.

A bacterial "infection" refers to the presence of a bacterial species or strain in an individual with or without presentation of clinical symptoms of pathology by the infected

individual. A bacterial "disease" refers to a bacterial infection in an individual in which the individual presents one or more symptoms of pathology that are known or suspected to be associated with infection by a strain or species of pathogenic bacteria.

A composition or method described herein as "comprising" one or more named elements or steps is open-ended meaning that the named elements or steps are essential, but other elements or steps may be added within the scope of the composition or method. To avoid prolixity, it is also understood that any composition or method described as "comprising" one or more named elements or steps also describes the corresponding, more limited, composition or method that "consists essentially of the same named elements or steps, meaning that the composition or method includes the named essential elements or steps and may also include additional elements or steps that do not materially affect the basic and novel characteristic(s) of the composition or method. It is also understood that ,- any composition or method described herein as "comprising" or "consisting essentially of one or more named elements or steps also describes the corresponding, more limited, and close-ended composition or method "consisting of the named elements or steps to the exclusion of any other unnamed element or step. In any composition or method disclosed herein, known or disclosed equivalents of any named essential element or step may be substituted for that element or step.

Unless stated otherwise, the meaning of other terms will be understood by their context or will be that known by persons skilled in this art, including those in the fields of organic chemistry, medicine, and antibiotics. Polar Ester ProdruRS of Heterocyclic (AU-FQ) Hybrid Antibacterial Parent Compounds

The invention provides polar ester prodrug compounds having the following formula

(I):

(I) wherein:

Ri is selected from the group consisting of a lower (Ci _-6 ) alkyl, a lower (Ci _-6 ) hydroxyalkyl, a Ci _-6 cycloalkyl, a monofluorophenyl, or a difluorophenyl;

X is hydrogen (H), a halogen selected from the group consisting of fluorine (F) or chlorine

(Cl), or methoxy;

Y and Z are, independently, selected from the group consisting of hydrogen (H), lower (Ci-

C ₆ ) alkyl (preferably, methyl or ethyl), lower (C ₂ -C ₆ ) alkenyl, lower (C ₂ -C ₆ ) alkynyl, and halo; or Y and Z are each a terminal methylene in the trimethylene radical -CH ₂ CH ₂ CH ₂ - that forms a 5-membered ring fused to the contiguous phenyl ring;

"LESIKER" is a bivalent linker segment comprising 1-10 atoms in contiguous linear connectivity;

"DIAMINE" is an aliphatic mono- or polycyclic (e.g., bicyclic) bivalent diamine group wherein one amino nitrogen atom is covalently linked to the fluoroquinolone (FQ) moiety of formula I and the other amino nitrogen atom is covalently linked to the LINKER moiety of formula I; and,

R ₃ is a polar radical selected from the group consisting of a hydroxyalkyl (C _2-6 ); a polyhydroxyalkyl (C _2-6 ), wherein "polyhydroxy" is 2-6 hydroxy groups; a ω- hydroxy(alkoxy) _n alkyl (C _2-4 ), where n = 1-10; a primary aminoalkyl (C _2-6 ); a secondary aminoalkyl (C _2-6 ); a tertiary aminoalkyl (C _2-6 ); a cyclic aminoalkyl (C _2-6 ) (preferably wherein the cyclic aminoalkyl is N-piperidinyl-, N-morpholinyl-, or N-piperazinyl- alkyl); a quaternary aminoalkyl (preferably, wherein the quaternary aminoalkyl is choline); and wherein any alkyl or alkoxy present in R ₃ that is greater than 3 carbons in length is a straight or a branched chain; and pharmaceutically acceptable salts thereof.

Preferably, the DIAMINE of a polar ester prodrug or salt thereof as shown in formula I is a diamine selected from the group consisting of:

More preferably, the diamine is a piperazinyl group. Even more preferably, the diamine is a 3 -substituted piperazinyl group. Yet more preferably, the diamine is a 3 -methyl piperazinyl group or a 3-hydroxymethyl piperazinyl group. Most preferably, the diamine is a 3 -methyl piperazinyl group.

Preferred hydroxylalkyl and polyhydroxyalkyl ester polar prodrugs of formula I include those wherein: Y is methyl, Z is methyl or ethyl, Ri is cyclopropyl, X is hydrogen (H) or fluorine (F), LINKER is (CH ₂ ) ₄ - or (CH ₂ ) ₅ -, DIAMINE is piperazinyl or a 3- substituted piperazinyl (wherein the 3-substituent is methyl or hydroxymethyl), and R ₃ is 2- (hydroxyethoxy)ethyl (i.e., CH ₂ CH ₂ OCH ₂ CH ₂ OH), l-methyl-2-hydroxyethyl (i.e., CH(CH ₃ )CH ₂ OH), or 2,3-dihydroxypropyl (i.e., CH ₂ CH(OH)CH ₂ OH); and pharmaceutically acceptable salts thereof.

Preferred basic polar ester prodrugs of formula I include those wherein: Y is methyl; Z is methyl or ethyl; Ri is cyclopropyl; X is H or F; LINKER is -(CH ₂ ) ₄ - or - (CH ₂ ) ₅ -; DIAMINE is piperazinyl or a 3 -substituted piperazinyl (wherein the 3-substituent is methyl or hydroxymethyl (-CH ₂ OH)), and R ₃ is selected from the group consisting of 2- (N,N-diethylamino)ethyl, 2-(N-piperidinyl)ethyl, 2-(N-morpholinyl)ethyl, and 2-(N- piperazinyl)ethyl; and pharmaceutically acceptable salts thereof. Preferred quaternary aminoalkyl polar ester prodrugs of formula I include those wherein: Y is methyl; Z is methyl or ethyl; Ri is cyclopropyl; X is H or F; LINKER is

-(CH ₂ ) ₄ - or -(CH ₂ ) ₅ -; DIAMINE is piperazinyl or a 3-substituted piperazinyl (wherein the 3-substituent is methyl or hydroxymethyl (-CH ₂ OH)), and R ₃ is choline (N,N,N- trimethylaminoethyl); and pharmaceutically acceptable salts thereof..

As indicated above, the polar ester prodrugs and salts thereof of formula I have a fluoroquinolone (FQ) moiety containing a polar radical (R ₃ ) esterified to the carboxylic acid function at position 3 (carbon 3; C-3). Preferred polar radicals esterified to the C-3 carboxylic acid of the FQ moiety include hydroxyalkyl radicals for "hydroxyalkyl ester prodrugs", such as a hydroxyalkyl (C _2-6 ), a polyhydroxyalkyl (C _2-6 ), and ω- hydroxy(alkoxy) _n alkyl (C _2-4 , where n = 1-10, e.g., esters of ethylene glycol, diethylene glycol, and also aminoalkyl radicals for "basic ester prodrugs", such as a primary aminoalkyl (C _2-6 ), a secondary aminoalkyl (C _2-6 ), a tertiary aminoalkyl (C _2-6 ), and a cyclic aminoalkyl (C _2-6 ), wherein the cyclic aminoalkyl is preferably N-piperidinyl-, N-morpholinyl-, or N- piperazinyl- alkyl, and also quaternary aminoalkyl radicals for "quaternary ester prodrugs", such as choline. Salts of the polar ester prodrug compounds are generally more water soluble than the corresponding "free base" form of the polar ester prodrug and the corresponding non-ester AU-FQ hybrid parent compound. Such salt forms of polar ester prodrugs are also more water soluble than other types of non-polar ester prodrugs in which the radical esterified to the C-3 carboxylic acid function of the FQ moiety is non-polar (e.g., an alkyl radical). Moreover, pharmaceutically acceptable salts of polar ester prodrugs of formula I are significantly more soluble in water than the corresponding non-salt polar ester prodrugs and the corresponding non-ester AU-FQ hybrid parent compounds. A salt of a polar ester prodrug described herein is easily prepared during synthesis of the compound. Alternatively, the free base form of a polar ester prodrug may be combined with a desired inorganic acid or organic acid in water or other aqueous solution. As the pH is lowered, the free base form is converted to the corresponding salt and becomes more soluble in the water or aqueous solution. Inorganic acids that may be used to prepare a soluble salt of a polar ester prodrug as described herein include, but are not limited to, hydrochloric acid and sulfuric acid. Organic acids that may be used to prepare a soluble salt of a polar ester prodrug as described herein may include, but are not limited to, methanesulfonic acid, 2- furoic acid (furan-2-carboxylic acid), 3-furoic acid (furan-3 -carboxylic acid), fumaric acid, and maleic acid. The resulting salt of the polar ester prodrug may then be dried or

crystallized using standard methods. The pH of a solution of a salt of a polar ester prodrug described herein may be considerably lower than pH 7 (neutral pH), however, such salts are sufficiently soluble (e.g., about 5 mg/ml or more in water) so that sufficiently low amounts or volumes of stock solutions can be safely employed for testing potency or efficacy of the prodrug and for preparing pharmaceutical compositions (including compositions for topical administration).

As noted above, a quaternary ester prodrug, such as a choline ester prodrug, has a permanent positive charge, and therefore requires an intrinsic counter anion, such as a chloride anion (CF) (see, e.g., compounds 29(.Cl) and 30(.Cl), infra). Thus, a quaternary ester prodrug compound is already a salt. Accordingly, a "salt form" of such quaternary ester prodrugs is understood to mean the corresponding bis salt, e.g., a "chloride hydrochloride" (see, e.g., compounds 29.C1.HC1 and 30.C1.HC1, infra). Such bis salts are readily prepared, e.g., by mixing a quaternary ester prodrug in an aqueous solution and adding a desired acid (e.g., HCl) and lyophilizing the solution to leave the bis salt. Preferred salts of prodrug compounds described herein are pharmaceutically acceptable salts. Preferred pharmaceutically acceptable salts of prodrug compounds as described herein include a mono-hydrochloride ("HCl"), a bis-hydrochloride ("di- hydrochloride", "(HCl) ₂ "), a citrate ("cit."), a sulfate, a mesylate (i.e., a methanesulfonate, "Ms"), a bis-mesylate ("di-mesylate", "Ms ₂ "), a 2-furoate (furan-2-carboxylate), a 3-furoate (furan-3-carboxylate), a fumarate, and a maleate. In the case where the polar ester prodrug contains a quaternary ammonium group in the ester moiety (e.g., choline), then the resulting compound can be a single salt (such as a chloride) or a bis salt (such as a "chloride hydrochloride", "C1.HC1"). More preferred as pharmaceutically acceptable salts useful in the invention are mesylates and hydrochlorides of hydroxy polar ester prodrugs and bis- hydrochlorides and bis-mesylates of basic polar ester prodrugs.

Polar ester prodrugs and pharmaceutically acceptable salts thereof as described herein may be formulated for administration to an individual by any of a variety of parenteral and non-parenteral routes. The enhanced water solubility of the pharmaceutically acceptable salts of polar ester prodrugs of formula I makes such salt forms particularly useful in preparing pharmaceutically acceptable compositions for administration to a patient by a parenteral route.

Synthesis and Characterization of Polar Ester Prodrugs

Polar ester prodrugs of heterocyclic AU-FQ hybrid parent compounds may be synthesized according to standard organic chemistry synthesis protocols, including combinatorial chemistry protocols. The structures of the compounds described herein may be viewed as essentially discrete segments. Accordingly, the simple alkyl esters of antibacterial heterocyclic compounds may be treated with alcohols in the presence of various catalysts to effect "transesterification" of said alkyl ester. Alternatively, the heterocyclic AU-FQ hybrid parent compounds may be esterified with an alcohol by

"condensation" in the presence of various catalysts. Solubility of a compound in water may be measured by a method comprising stirring an excess of a compound in water at room temperature, filtering an aliquot of the suspension, and analyzing the filtrate for the compound, e.g., using HPLC analysis.

Comparison with a standard curve of known concentrations allows calculation of the solubility of the compound. Representative polar ester prodrugs according to the invention include, but are not limited to, the following compounds.

Compound Name

1 3-{4-[l-(l-cyclopropyl-3-carboxy-4-oxo-6-fluoro-7-quinolyl)- 4- piperazinyl]butyl}-6-(3-ethyl-4-methylanilino)uracil, 2-(2- hydroxyethoxy)ethyl ester

2 3-{4-[l-(l-cyclopropyl-3-carboxy-4-oxo-6,8-difluoro-7-quinol yl)-4- piperazinyl]butyl}-6-(3-ethyl-4-methylanilino)uracil, 2-(2- hydroxyethoxy)ethyl ester

3 3-{4-[l-(l-cyclopropyl-3-carboxy-4-oxo-6,8-difluoro-7-quinol yl)-4- piperazinyl]butyl}-6-(3-ethyl-4-methylanilino)uracil, 2-[(2- hydroxyethoxy)ethoxy] ethyl ester

4 (S)-3-{4-[l-(l-cyclopropyl-3-carboxy-4-oxo-6,8-difluoro-7-qu inolyl)- 4-(3-methylpiperazinyl)]butyl}-6-(3-ethyl-4-methylanilino)ur acil, 2- (2-hydroxyethoxy)ethyl ester

5 (R)-3-{4-[l-(l-cyclopropyl-3-carboxy-4-oxo-6,8-difluoro-7- quinolyl)-4-(3-methylpiperazinyl)]butyl}-6-(3-ethyl-4- methylanilino)uracil, 2-(2-hydroxyethoxy)ethyl ester

6 3-{4-[l-(l-cyclopropyl-3-carboxy-4-oxo-6,8-difluoro-7-quinol yl)-4-

(3-methylpiperazinyl)]butyl}-6-(3-ethyl-4-methylanilino)u racil, 2-(2- hydroxyethoxy)ethyl ester

7 (S)-3- {4-[ 1 -( 1 -cyclopropyl-3-carboxy-4-oxo-6-fluoro-7-quinolyl)-4-

(3-methylpiperazinyl)]butyl}-6-(3-ethyl-4-methylanilino)u racil, 2-(2- hydroxyethoxy)ethyl ester

8 (R)-3-{4-[l-(l-cyclopropyl-3-carboxy-4-oxo-6-fluoro-7-quinol yl)-4- (3 -methylpiperazinyl)]butyl } -6-(3 -ethyl-4-methylanilino)uracil, 2-(2- hydroxyethoxy)ethyl ester

9 3-{4-[l-(l-cyclopropyl-3-carboxy-4-oxo-6-fluoro-7-quinolyl)- 4-(3- methylpiperazinyl)]butyl } -6-(3 -ethyl -4-methylanilino)uracil, 2-(2- hydroxyethoxy)ethyl ester

10 (S)-3- {4-[ 1 -( 1 -cyclopropyl-3-carboxy-4-oxo-6,8-difluoro-7-quinolyl)- 4-(3-methylpiperazinyl)]butyl}-6-(3,4-dimethylanilino)uracil , 2-(2- hydroxyethoxy)ethyl ester

11 (R)-3-{4-[l-(l-cyclopropyl-3-carboxy-4-oxo-6,8-difluoro-7- quinolyl)-4-(3 -methylpiperazinyl)]butyl } -6-(3 ,4- dimethylanilino)uracil, 2-(2-hydroxyethoxy)ethyl ester

12 3- {4-[ 1 -(I -cyclopropyl-3-carboxy-4-oxo-6,8-difluoro-7-quinolyl)-4-

(piperazinyl)]butyl}-6-(3,4-dimethylanilino)uracil, 2-(2- hydroxyethoxy)ethyl ester

13 (S)-3- {4-[ 1 -(I -cyclopropyl-3-carboxy-4-oxo-6,8-difluoro-7-quinolyl)- 4-(3-methylpiperazinyl)]butyl}-6-(3-chloro-4-methylanilino)u racil, 2-

(2-hydroxyethoxy)ethyl ester

14 (R)-3-{4-[l-(l-cyclopropyl-3-carboxy-4-oxo-6,8-difluoro-7- quinolyl)-4-(3-methylpiperazinyl)]butyl}-6-(3-chloro-4- methylanilino)uracil, 2-(2-hydroxyethoxy)ethyl ester

15 3- {4-[ 1 -(I -cyclopropyl-3-carboxy-4-oxo-6,8-difluoro-7-quinolyl)-4- piperazinyl]butyl}-6-(3-ethyl-4-methylanilino)uracil, 2-(N- moφholinyl)ethyl ester

16 3- {4-[ 1 -(I -cyclopropyl-3-carboxy-4-oxo-6-fluoro-7-quinolyl)-4- piperazinyl]butyl}-6-(3-ethyl-4-methylanilino)uracil, 2-(N- morpholinyl)ethyl ester

17 (S)-3- {4-[ 1 -( 1 -cyclopropyl-3-carboxy-4-oxo-6-fluoro-7-quinolyl)-4-

(3-methylpiperazinyl)]butyl}-6-(3-ethyl-4-methylanilino)u racil, 2-(N- morpholinyl)ethyl ester

18 3- {4-[ 1 -( 1 -cyclopropyl-3-carboxy-4-oxo-6-fluoro-7-quinolyl)-4-(3- methylpiperazinyl)]butyl } -6-(3 -ethyl-4-methylanilino)uracil, 2-(N- morpholinyl)ethyl ester

19 (S)-3- {4-[ 1 -(I -cyclopropyl-3-carboxy-4-oxo-6,8-difluoro-7-quinolyl)- 4-(3-methylpiperazinyl)]butyl}-6-(3-ethyl-4-methylanilino)ur acil, 2-

(N-moφholinyl)ethyl ester

20 (R)-3- {4-[ 1 -( 1 -cyclopropyl-3-carboxy-4-oxo-6,8-difluoro-7- quinolyl)-4-(3-methylpiperazinyl)]butyl}-6-(3-ethyl-4- methylanilino)uracil, 2-(N-morpholinyl)ethyl ester

21 3-{4-[l-(l-cyclopropyl-3-carboxy-4-oxo-6,8-difluoro-7-quinol yl)-

4-piperazinyl]butyl}-6-(3,4-dimethylanilino)uracil, 2-(N- moφholinyl)ethyl ester

22 (S)-3-{4-[l-(l-cyclopropyl-3-carboxy-4-oxo-6-fluoro-7-quinol yl)-

4-(3 -methylpiperazinyl)piperazinyl]butyl } -6-(3 ,4 dimethylanilino)uracil, 2-(N-morpholinyl)ethyl ester

23 3- {4-[ 1 -( 1 -cyclopropyl-S-carboxy^-oxo-όjδ-difluoro-T-quinolyl)^-

(3-methylpiperazinyl)]butyl}-6-(3,4-dimethylanilino)uraci l, 2-(N- morpholinyl)ethyl ester

24 (S)-3-{4-[l-(l-cyclopropyl-3-carboxy-4-oxo-6,8-difluoro-7-qu inolyl)- 4-(3-methylpiperazinyl)]butyl}-6-(3,4-dimethylanilino)uracil , 2-(N- morpholinyl)ethyl ester

25 (R)-3- {4-[ 1 -(I -cyclopropyl-S-carboxy^-oxo-ό.δ-difluoro-?- quinolyl)-4-(3-methylpiperazinyl)]butyl}-6-(3,4- dimethylanilino)uracil, 2-(N-morpholinyl)ethyl ester

26 3-{4-[l-(l-cyclopropyl-3-carboxy-4-oxo-6,8-difluoro-7-quinol yl)-4-

(3-methylpiperazinyl)]butyl}-6-(3-ethyl-4-methylanilino)u racil, 3-(N- moφholinyl)ρropyl ester

27 3-{4-[l-(l-cyclopropyl-3-carboxy-4-oxo-6,8-difluoro-7-quinol yl)-4-

(3-methylpiperazinyl)]butyl}-6-(3-ethyl-4-methylanilino)u racil, 2-(N- piperazinyl)ethyl ester

28 3-{4-[l-(l-cyclopropyl-3-carboxy-4-oxo-6,8-difluoro-7-quinol yl)-4- (3-methylpiperazinyl)]butyl}-6-(3-ethyl-4-methylanilino)urac il, 2- (PEG) ₄₅ ester, where "PEG" is polyethyleneglycol.

29(.Cl) 3-{4-[l-(l-cyclopropyl-3-carboxy-4-oxo-6,8-difluoro-7-quinol yl)-4- (3-methylpiperazinyl)]butyl}-6-(3-ethyl-4-methylanilino)urac il, choline ester chloride

30(.Cl) 3-{4-[l-(l-cyclopropyl-3-carboxy-4-oxo-6,8-difluoro-7-quinol yl)-4- (3-methylpiperazinyl)]butyl } -6-(3 ,4-dimethylanilino)uracil, choline ester chloride

The presence of a quaternary ammonium group in choline esters 29.Cl and 30.Cl necessitates the presence of an intrinsic counter anion, such as a chloride anion (CF) in such compounds.

Examples of preferred pharmaceutically acceptable salts of polar ester prodrugs that have significantly higher solubility in water than either the corresponding non-salt prodrug or the corresponding hybrid antibacterial parent compound include, but are not limited to, the following: Compound Name

1.Ms 3- {4-[ 1 -(I -cyclopropyl-S-carboxy^-oxo-ό-fluoro^-quinolyl)^- piperazinyl]butyl}-6-(3-ethyl-4-methylanilino)uracil, 2-(2- hydroxyethoxy)ethyl ester mesylate

2.Ms 3- {4-[ 1 -( 1 -cyclopropyl-3-carboxy-4-oxo-6,8-difluoro-7-quinolyl)-4- piperazinyl]butyl}-6-(3-ethyl-4-methylanilino)uracil, 2-(2- hydroxyethoxy)ethyl ester mesylate

3.Ms 3-{4-[l-(l-cyclopropyl-3-carboxy-4-oxo-6,8-difluoro-7-quinol yl)-4- piperazinyl]butyl}-6-(3-ethyl-4-methylanilino)uracil, 2-[(2- hydroxyethoxy)ethoxy] ethyl ester mesylate

4.HC1 (S)-3-{4-[l-(l-cyclopropyl-3-carboxy-4-oxo-6,8-difluoro-7-qu inolyl)- 4-(3-methylpiperazinyl)]butyl}-6-(3-ethyl-4-methylanilino)ur acil, 2- (2-hydroxyethoxy)ethyl ester hydrochloride

4.cit (S)-3-{4-[l-(l-cyclopropyl-3-carboxy-4-oxo-6,8-difluoro-7-qu inolyl)- 4-(3 -methylpiperazinyl)]butyl } -6-(3 -ethyl-4-methylanilino)uracil, 2- (2-hydroxyethoxy)ethyl ester citrate

4.Ms (S)-3-{4-[l-(l-cyclopropyl-3-carboxy-4-oxo-6,8-difluoro-7-qu inolyl)-

4-(3-methylpiperazinyl)]butyl}-6-(3-ethyl-4-methylanilino )uracil, 2- hydroxyethoxyethyl ester mesylate

5.Ms (R)-3- {4-[ 1 -( 1 -cyclopropyl-3-carboxy-4-oxo-6,8-difluoro-7- quinolyl)-4-(3 -methylpiperazinyl)]butyl } -6-(3 -ethyl-4- methylanilino)uracil, 2-(2-hydroxyethoxy)ethyl ester mesylate

6.Ms 3-{4-[l-(l-cyclopropyl-3-carboxy-4-oxo-6,8-difluoro-7-quinol yl)-4- (3-methylpiperazinyl)]butyl}-6-(3-ethyl-4-methylanilino)urac il, 2-(2- hydroxyethoxy)ethyl ester mesylate

7.Ms (S)-3-{4-[l-(l-cyclopropyl-3-carboxy-4-oxo-6-fluoro-7-quinol yl)-4- (3-methylpiperazinyl)]butyl}-6-(3-ethyl-4-methylanilino)urac il, 2-(2- hydroxyethoxy)ethyl ester mesylate

8.Ms (R)-3-{4-[l-(l-cyclopropyl-3-carboxy-4-oxo-6-fluoro-7-quinol yl)-4- (3-methylpiperazinyl)]butyl}-6-(3-ethyl-4-methylanilino)urac il, 2-(2- hydroxyethoxy)ethyl ester mesylate

9.Ms 3-{4-[l-(l-cyclopropyl-3-carboxy-4-oxo-6-fluoro-7-quinolyl)- 4-(3- methylpiperazinyl)]butyl } -6-(3 -ethyl-4-methylanilino)uracil, 2-(2- hydroxyethoxy)ethyl ester mesylate

16.(HCl) ₂ 3-{4-[l-(l-cyclopropyl-3-carboxy-4-oxo-6,8-difluoro-7-quinol yl)-4- piperazinyl]butyl}-6-(3-ethyl-4-methylanilino)uracil, 2-(N- morpholinyl)ethyl ester dihydrochloride

16.Ms ₂ 3-{4-[l-(l-cyclopropyl-3-carboxy-4-oxo-6,8-difluoro-7-quinol yl)-4- piperazinyl]butyl}-6-(3 -ethyl -4-methylanilino)uracil, 2-(N- morpholinyl)ethyl ester dimesylate

17.(HCl) ₂ (S)-3-{4-[l-(l-cyclopropyl-3-carboxy-4-oxo-6-fluoro-7-quinol yl)-4- (3-methylpiperazinyl)]butyl}-6-(3-ethyl-4-methylanilino)urac il, 2-(N- morpholinyl)ethyl ester dihydrochloride

17.Ms ₂ (S)-3-{4-[l-(l-cyclopropyl-3-carboxy-4-oxo-6-fluoro-7-quinol yl)-4- (3-methylpiperazinyl)]butyl}-6-(3-ethyl-4-methylanilino)urac il, 2-(N- morpholinyl)ethyl ester dimesylate

18.(HCl) ₂ 3-{4-[l-(l-cyclopropyl-3-carboxy-4-oxo-6,8-difluoro-7-quinol yl)-4- (3-methylpiperazinyl)]butyl}-6-(3-ethyl-4-methylanilino)urac il, 2-(N- morpholinyl)ethyl ester dihydrochloride

18.Ms ₂ 3-{4-[l-(l-cyclopropyl-3-carboxy-4-oxo-6,8-difluoro-7-quinol yl)-4-

(3-methylpiperazinyl)]butyl}-6-(3-ethyl-4-methylanilino)u racil, 2-(N- morpholinyl)ethyl ester dimesylate

19.(HCl) ₂ (S)-3-{4-[l-(l-cyclopropyl-3-carboxy-4-oxo-6,8-difluoro-7-qu inolyl)-

4-(3-methylpiperazinyl)]butyl}-6-(3-ethyl-4-methylanilino )uracil, 2- (N-morpholinyl)ethyl ester dihydrochloride

19.Ms ₂ (S)-3-{4-[l-(l-cyclopropyl-3-carboxy-4-oxo-6,8-difluoro-7-qu inolyl)-

4-(3-methylpiperazinyl)]butyl}-6-(3-ethyl-4-methylanilino )uracil, 2- (N-morpholinyl)ethyl ester dimesylate

20.(HCl) ₂ (R)-3- {4-[ 1 -(I -cyclopropyl-S-carboxy^-oxo-όjδ-difluoro-?- quinolyl)-4-(3-methylpiperazinyl)]butyl}-6-(3-ethyl-4- methylanilino)uracil, 2-(N-morpholinyl)ethyl ester dihydrochloride

20.Ms ₂ (R)-3- {4-[ 1 -( 1 -cyclopropyl-S-carboxy^-oxo-ό^-difluoro-?- quinolyl)-4-(3-methylpiperazinyl)]butyl}-6-(3-ethyl-4- methylanilino)uracil, 2-(N-morpholinyl)ethyl ester dimesylate

21.(HCl) ₂ 3-{4-[l-(l-cyclopropyl-3-carboxy-4-oxo-6,8-difluoro-7-quinol yl)-4- piperazinyl]butyl}-6-(3,4-dimethylanilino)uracil, 2-(N- morpholinyl)ethyl ester dihydrochloride

22.(HCl) ₂ 3- {4-[ 1 -(I -cyclopropyl-3-carboxy-4-oxo-6-fluoro-7-quinolyl)-4- piperazinyl]butyl}-6-(3,4-dimethylanilino)uracil, 2-(N- moφholinyl)ethyl ester dihydrochloride

23.(HCl) ₂ 3- {4-[ 1 -(I -cyclopropyl-3-carboxy-4-oxo-6,8-difluoro-7-quinolyl)-4- (3-methylpiperazinyl)]butyl}-6-(3,4-dimethylanilino)uracil, 2-(N- moφholinyl)ethyl ester dihydrochloride

24.(HCl) ₂ (S)-3-{4-[l-(l-cyclopropyl-3-carboxy-4-oxo-6,8-difluoro-7-qu inolyl)- 4-(3-methylpiperazinyl)]butyl}-6-(3,4-dimethylanilino)uracil , 2-(N- morpholinyl)ethyl ester dihydrochloride

25.(HCl) ₂ (R)-3-{4-[l-(l-cyclopropyl-3-carboxy-4-oxo-6,8-difluoro-7- quinolyl)-4-(3-methylpiperazinyl)]butyl}-6-(3,4- dimethylanilino)uracil, 2-(N-morpholinyl)ethyl ester dihydrochloride

26.(HCl) ₂ 3-{4-[l-(l-cyclopropyl-3-carboxy-4-oxo-6,8-difluoro-7-quinol yl)-4-

(3-methylpiperazinyl)]butyl}-6-(3-ethyl-4-methylanilino)u racil, 3-(N- morpholinyl)propyl ester dihydrochloride

27.(HCl) ₂ 3-{4-[l-(l-cyclopropyl-3-carboxy-4-oxo-6,8-difluoro-7-quinol yl)-4-

(3-methylpiperazinyl)]butyl}-6-(3-ethyl-4-methylanilino)u racil, 2-(N- piperazinyl)ethyl ester dihydrochloride

28.HC1 3-{4-[l-(l-cyclopropyl-3-carboxy-4-oxo-6,8-difiuoro-7-quinol yl)-4-

(3-methylpiperazinyl)]butyl}-6-(3-ethyl-4-methylanilino)urac il, 2- (PEG) ₄₅ ester hydrochloride.

29.C1.HC1 3-{4-[l-(l-cyclopropyl-3-carboxy-4-oxo-6,8-difluoro-7-quinol yl)-4-

(3-methylpiperazinyl)]butyl}-6-(3-ethyl-4-methylanilino)u racil, choline ester chloride hydrochloride

30.C1.HC1 3-{4-[l-(l-cycloproρyl-3-carboxy-4-oxo-6,8-difluoro-7-quino lyl)-4-

(3-methylpiperazinyl)]butyl}-6-(3,4-dimethylanilino)uraci l, choline ester chloride hydrochloride

Some compounds of the invention have one or more chiral centers. Such compounds may be provided as individual, pure species, such as individual enantiomers (see, e.g., compounds 4 and 5, 7 and 8, 10 and 11, 13 and 14, 19 and 20, 24 and 25) or diastereomers, or as mixtures of one or more species, including racemic mixtures of enantiomers (see e.g., compounds 6, 9, 14, 18, 23, and 26-30). Accordingly, chiral compounds and mixtures of chiral compounds may or may not be optically active as determined by standard methods known in the art for detecting optical activity of compounds having one or more chiral centers. Pharmaceutical compositions, routes of administration

As noted above, the polar ester prodrugs and their corresponding salts as described herein do not have significant antibacterial activity unless converted to the corresponding non-ester, antibacterial hybrid parent compounds. The polar ester moiety of a prodrug or its corresponding salt as described herein is readily hydrolyzed by esterase activity that is normally present in the blood or other tissues of an individual. Thus, an inactive polar ester prodrug compound or its corresponding salt may be used as the "active" ingredient in a pharmaceutical composition to treat a patient for a bacterial infection or disease. A pharmaceutically acceptable salt of a polar ester prodrug compound described herein is significantly more soluble in aqueous solutions, including in one or more pharmaceutically acceptable carriers, than the corresponding non-salt polar ester prodrug and the corresponding non-ester AU-FQ hybrid parent compound. Accordingly, pharmaceutically acceptable salt forms of the polar ester prodrug compounds described herein are particularly well-suited for use in aqueous compositions that can be administered parenterally to an individual to treat or prevent a bacterial infection or disease.

It will be appreciated that the amount (dose) of a particular prodrug compound or pharmaceutically acceptable salt thereof used to treat or prevent an bacterial infection in an individual may vary not only with the particular prodrug salt, but also with such factors as the route of administration, the nature of the condition or disease for which treatment is required, the age of the individual, and other medical conditions of the individual. Such factors are routinely considered by attending clinicians. In general, however, dosages are those that produce a sustained concentration at a level higher than the MIC ₉₀ value (i.e., the concentration of a compound that inhibits the growth of 90% of the strains of bacteria evaluated). The desired treatment dosage may conveniently be presented in a single dose or divided into portions that are administered at appropriate intervals, e.g., as two, three, four, or more portions per day.

A preferred route of administration of a salt form of a prodrug compound described herein is a parenteral route. Examples of parenteral routes of administration include, without limitation, intravenous (i.v.), subcutaneous (s.c), intravenous (i.v.), intramuscular (i.m.), intra-arterial (i.a.), intraperitoneal (i.p.), transdermal (absorption through the skin or dermal layers), nasal ("intranasal"; absorption across nasal mucosa), pulmonary (e.g., inhalation for absorption across the lung tissue), vaginal, direct injections or infusions into body cavities or organs other than those of the alimentary canal, as well as by implantation of any of a variety of devices into the body, again, other than those of the alimentary canal (e.g., of a composition, depot, or device that provides active or passive release of a prodrug compound or composition thereof into the body). An individual may be treated by i.v. injection of a pharmaceutical composition comprising a particular pharmaceutically acceptable salt of a prodrug compound and a pharmaceutically acceptable carrier. Desirable blood levels may be maintained by a continuous infusion or by intermittent infusions. While it is possible that a prodrug compound or salt thereof may be administered to an individual as the raw chemical, the compound or its salt is usually administered as an "active" ingredient in a pharmaceutical composition. The invention thus further provides a pharmaceutical composition comprising a polar ester prodrug compound or its salt as described herein and a pharmaceutically acceptable carrier (or vehicle). Preferred pharmaceutically acceptable carriers for parenteral administration of a prodrug compound or salt thereof as described herein include water, physiological buffers, and physiological saline solutions. Optionally, such compositions may also contain one or more other

therapeutic or beneficial agents, including but not limited to, another antibiotic, an anti- viral compound, an anti-cancer compound, a vitamin, a trace metal supplement, or an ion to restore or maintain proper ionic balance in blood or other tissues. Other examples of suitable therapeutic agents that may be used in combination with the prodrug compound or its salt as described herein include, without limitation, penicillins and other beta lactamase inhibitors, carbapenems, cephalosporins, macrolides (including erythromycin and ketolides), sulfonamides, aminoglycosides, quinolones (such as fluoroquinolones), oxazolidinones, lipopeptides (such as daptomycin), tetracyclines, vancomycin, erythromycin, streptomycin, efflux pump inhibitors, lactofeπϊns, and cationic peptides. Such agents may be administered together with or separately from a prodrug described herein. In addition, certain patients may suffer from or may be susceptible to simultaneous infections from a bacterial species and a virus. Such patients may benefit from co-administration (simultaneous or consecutive administration) of a prodrug or its salt as described herein and an antiviral agent. Examples of antiviral agents that may be co-administered with a prodrug described herein include, but are not limited to, an anti-influenza medication, such as zanamivir (e.g., Relenza) or oseltamivir (e.g., Tamiflu), or an anti-enteric virus drug such as pleconaril. Additional combination therapies may also include a prodrug or its salt as described herein and an anti-fungal agent, such as caspofungin acetate (e.g., Cancidas), fluconazole (e.g., Diflucan), and nystatin (e.g., Mycostatin). Clearly, the combination therapies described herein are merely exemplary and are not meant to limit possibilities for other combination treatments or co-administration regimens comprising a hydrophilic ester prodrug compound or its salt described herein and one or more other therapeutic agents.

Pharmaceutical compositions may, where appropriate, be conveniently presented in discrete dosage units and may be prepared by any of the methods well known in the art. Such methods include the step of bringing into association a prodrug compound or its salt with a liquid carrier or finely divided solid carrier, or both, and then, if necessary, shaping the product into a desired composition.

Pharmaceutical compositions suitable for oral administration may conveniently be presented as discrete units such as capsules, cachets, or tablets each containing a predetermined amount of a prodrug compound or its salt as described herein in a powder or granule form, in a solution, in a suspension, or as an emulsion. A prodrug compound or its salt may also be presented as a bolus, electuary, or paste. Tablets and capsules for oral

administration may contain conventional excipients such as binding agents, fillers, lubricants, disintegrants, or wetting agents. The tablets may be coated according to methods well known in the art. Oral liquid preparations may be in the form of, e.g., aqueous suspensions, oily suspensions, solutions, emulsions, syrups or elixirs, or may be presented as a dry product for constitution with water or other suitable vehicle before use. Such liquid preparations may contain conventional additives such as suspending agents, emulsifying agents, non-aqueous vehicles (which may include edible oils), or preservatives.

Compositions suitable for oral administration of a prodrug compound or its salt as described herein include, without limitation, lozenges comprising the prodrug compound, optionally, in a flavored base, usually sucrose and acacia or tragacanth and pastilles comprising the prodrug compound in an inert base such as gelatin and glycerin or sucrose and acacia.

As noted above, owing to their enhanced water solubility, pharmaceutically acceptable salt forms of prodrug compounds described herein are particularly well suited for formulation for parenteral administration (e.g., by injection or by continuous infusion). Such compositions for parenteral administration may be presented in unit dose form in ampoules, pre-fϊlled syringes, small volume infusion, or in multi-dose containers with an added preservative. The compositions may take such forms as solutions, suspensions, or emulsions in oily or aqueous vehicles, and may contain formulatory agents such as suspending, stabilizing, and/or dispersing agents. Alternatively, the prodrug compound may be provided in a powder form, obtained by aseptic isolation of sterile solid or by lyophilization from solution, for constitution with a suitable vehicle, e.g., sterile, pyrogen- free water, prior to use.

Compositions comprising a prodrug or salt thereof as described herein for topical administration to the epidermis or topical administration to a wound (topical intralesional administration) of an individual include, without limitation, solutions, suspensions, ointments, creams, gels, jellies, and lotions. A prodrug compound or salt thereof as described herein may also be incorporated into a transdermal patch. Such transdermal patches may contain penetration enhancers such as linalool, carvacrol, thymol, citral, menthol, t-anethole, and the like. Ointments and creams may be formulated with an aqueous or oily base comprising one or more suitable thickening and/or gelling agents. Lotions may be formulated with an aqueous or oily base and will in general also contain one

or more emulsifying agents, stabilizing agents, dispersing agents, suspending agents, thickening agents, and/or coloring agents.

Pharmaceutical compositions suitable for rectal administration wherein the carrier is a solid are presented as unit dose suppositories. Suitable carriers include cocoa butter and other materials commonly used in the art, and the suppositories may be conveniently formed by admixture of a prodrug compound or its salt as described herein with the softened or melted carrier(s) followed by chilling and shaping in molds.

Pharmaceutical compositions suitable for vaginal administration may be presented as pessaries, tampons, creams, gels, pastes, foams, or sprays containing a prodrug compound or its salt as described herein and such carrier(s) as known in the art to be appropriate.

For intra-nasal administration, a composition comprising a prodrug compound or its salt as described herein may be administered as a liquid spray or as a dispersible powder in the form of drops. Drops may be formulated with an aqueous or non-aqueous carrier that may also comprise one more dispersing agents, solubilizing agents, or suspending agents. Liquid sprays may conveniently be delivered from pressurized packs.

For administration by inhalation, the prodrug compounds described herein may conveniently be delivered from an insufflator, nebulizer, a pressurized pack, or other convenient means of delivering an aerosol spray. Pressurized packs may comprise a suitable propellant, such as dichlorodifluoromethane, trichlorofluoromethane, dichlorotetrafluoroethane, carbon dioxide or other suitable gas. In the case of a pressurized aerosol, the dosage unit may be determined by providing a valve to deliver a metered amount. Alternatively, for administration by inhalation or insufflation, compositions containing a prodrug compound or salt thereof as described herein may take the form of a dry powder composition, e.g., a powder mix of a compound of the invention and a suitable powder base such as lactose or starch. The powder composition may be presented in unit dosage form in, e.g., capsules, cartridges, or gelatin or blister packs from which the powder may be administered with the aid of an inhalator or insufflator.

A prodrug compound or its salt may also be formulated into a pharmaceutical composition for treating an eye or ear infection. Diseases of the eye that may be treated by administering a prodrug compound of the invention to a patient include, but are not limited to, bacterial keratitis, infectious keratoconjunctivitis, bacterial conjunctivitis, ocular tuberculosis, and suppurative uveitis. Diseases of ear that may be treated by administering a

compound of the invention include, but are not limited to, otitis externa and otitis media. Eye and ear diseases may be treated by administering a compound to a patient by any of the various routes described above or by direct administration to the infected eye or ear. Pharmaceutical compositions comprising a prodrug compound or salt thereof as described herein for treating an eye or ear disease may be a liquid or lotion, which may be administered directly into or on the infected eye or ear. Such compositions may be formulated in a manner similar to any of those known and used to administer an antibiotic to an eye or ear, such as compositions comprising fluoroquinolones (see, e.g., Am. Fam. Physician, 62: 1870-1876 (2000), and references cited therein). When desired, the above-described compositions may be adapted to give a sustained or time-delayed release of a selected prodrug compound or salt thereof as described herein using any of the sustained or time-delayed formats available in art.

In addition, the individual components of combinations of a prodrug compound or its salt and another therapeutic agent may be co-administered (either sequentially or simultaneously) in separate or combined pharmaceutical compositions. When a prodrug compound or its salt as described herein is used in combination with a second therapeutic compound, the dose of each compound may be either the same as or different from that when the compound is used alone. Appropriate doses will be readily appreciated by those skilled in the art. The ratio between a prodrug compound of the present invention and a second therapeutic compound for co-administration to a patient will be readily appreciated by those skilled in the art. For example, one may use a ratio in the range from about 1 : 1 to about 1: 50 (by weight) of prodrug compound or its salt as described herein to second therapeutic compound, hi additional embodiments, the ranges of ratios that may be used in preparing a composition for co-administration of a prodrug compound or salt thereof with a second therapeutic compound include, without limitation, about 1 : 1 to about 1:30 (by weight), about 1 : 1 to about 1 : 20 (by weight), about 1 : 1 to about 1:15 (by weight), about 1 : 1 to about 1 :10 (by weight), about 1 : 1 to about 1 :5 (by weight), and about 1 : 1 to about 1 :3 (by weight) of a prodrug compound or its salt to second therapeutic compound, or vice versa. If a further therapeutic compound is added, then ratios are adjusted accordingly. A prodrug compound or salt thereof according to the invention may be provided and packaged in any of a variety of forms as described above, including in a powder or lyophilized state for reconstitution with sterile water or buffer, in unit doses for convenient

administration, with one or more pharmaceutically acceptable buffers or salts, and/or with instructions for using the packaged compound as an antibiotic to treat a bacterial infection or as a enzyme inhibitor in polymerase IHC and/or type II topoisomerase assays.

Additional embodiments and features of the invention will be apparent from the following non-limiting examples. Examples Example 1. Synthesis of polar prodrug esters of heterocyclic antibacterial compounds.

Unless noted otherwise, representative polar ester prodrug compounds of corresponding heterocyclic hybrid antibacterial parent compounds were synthesized using methods described herein and/or standard organic synthesis methods known in the art. The compounds were then characterized for structure and/or various activities. The hybrid antibacterial compounds and their esters used as starting materials were prepared as described in US 6,777,420 and in Zhi et al. (J. Med. Chem., 49: 1455-1465 (2006)).

Abbreviations: DBU, diazabicylcloundecane; HATU, O-(7-azabenzotriazole-l-yl)- N,N,N',N'-tetramethyluronium hexafluorophosphate; DIPEA, di-isopropylethylamine; DMF, N,N-dimethylformamide; DMI, N,N'-dimethylimidazolidinone; DEG, diethyleneglycol; TEG, triethylene glycol; MorE, 2-(N-morpholinyl)ethanol; HPLC, high performance liquid chromatography; LC-MS, liquid chromatography-mass spectrometry; NMR, nuclear magnetic resonance spectroscopy. Method A - condensation

A solution of the hybrid antibacterial (AU-FQ parent) compound (1.5 mmol), HATU (3 mmol) and DIPEA (6 mmol) in DMI (5 mL) was stirred at room temperature under argon for 10 minutes, then slowly added to a stirred solution of 50% DEG, TEG or MorE in DMI (2 mL). After 5 hours at room temperature the reaction mixture was diluted with diethyl ether (50 mL) and vortexed briefly. The precipitate was separated by centrifugation, dissolved in chloroform (200 ml), and washed with 10% sodium carbonate solution. The organic layer was concentrated and the residue purified on a silica gel column with chloroform:methanol as eluent or by reverse phase HPLC on a Cl 8 column with a gradient of 0-50% acetonitrile in water containing 0.1% trifluoroacetic acid. Fractions from silica gel were evaporated, and the residue was dissolved in chloroform and washed with 10% sodium carbonate solution; the organic layer was dried over sodium sulfate, filtered and concentrated; the resulting products were crystallized from acetonitrile or other organic

solvent. Fractions from HPLC purification were lyophilized to give the products. LC-MS and H NMR were consistent with the structures in all cases.

It is understood that other conditions, catalysts, or reagents known in the art may also be employed to effect a condensation reaction to produce a desired polar ester prodrug of a corresponding parent heterocyclic hybrid antibacterial compound. Method B - transesterification

A mixture of the ethyl ester of a hybrid antibacterial (AU-FQ parent) compound (0.5 mmol) and DBU (0.6 mmol) in 50% solution of DEG, TEG or MorE in DMI (2 mL) was heated at 85°C under argon. After 24 hours the reaction mixture was diluted with diethyl ether (100 mL) and vortexed briefly. The precipitate was separated by centrifugation, mixed with chloroform (100 mL), and the mixture washed with 10% Na ₂ CO ₃ . The organic layer was concentrated and the residue purified on a silica gel column with chlorofornrmethanol as eluent or by reverse phase HPLC on a Cl 8 column with a gradient of 0-50% acetonitrile in water containing 0.1% trifluoroacetic acid. Fractions from silica gel were evaporated, and the residue was dissolved in chloroform and washed with 10% sodium carbonate solution; the organic layer was dried over sodium sulfate, filtered and concentrated; the resulting products were crystallized from acetonitrile or other organic solvent. Fractions from HPLC purification were lyophilized to give the products. LC-MS and ¹ H NMR were consistent with the structures in all cases. It is also understood that esters other than ethyl esters and other conditions, catalysts, or reagents known in the art may be employed to effect a transesterification reaction to produce a desired polar ester prodrug of a corresponding parent heterocyclic hybrid antibacterial compound. Syntheses Compound 1 - Compound 1 was synthesized by Method A and purified by silica gel chromatography in 84% yield.

Compound 2 - Compound 2 was synthesized by Method B, isolated by silica gel chormatography, and crystallized from acetonitrile in 77% yield.

Compound 3 - Compound 3 was prepared by Method B, and purified by reverse phase HPLC in 54% yield.

Compound 4 - Compound 4 was prepared by Method A, purified by silica gel chromatography, and crystallized from acetonitrile in 73% yield. The compound was also

prepared by Method B and isolated by reverse phase HPLC in 87% yield. Compound 4 from both methods was identical.

Compound 5 - Method A gave compound 5 in 61% yield (crystallized from acetonitrile). Compound 8 - Method B was used to prepare compound 8. The product was purified by silica gel chromatography to give 83% of 8 as an off-white powder.

Compound 10 - Method A and silica gel chromatography gave compound 10 in 88% yield.

Compound 15 - Method A and silica gel chromatography gave compound 15 in 65% yield.

Compound 16 - Method A and silica gel chromatography gave compound 16 in 57% yield.

Compound 17 - Method A and silica gel chromatography gave compound 17 in 66% yield. Compound 19 - Method A and silica gel chromatography gave compound 18 19 in

75% yield.

Compound 20 - Method B and reverse phase HPLC gave compound ¥£ 20 in 27% yield.

Compound 22 - Method A and silica gel chromatography gave compound 3A- 22 in 60% yield.

Compound 24 - Method A and silica gel chromatography gave compound 23- 24 in 58% yield.

Compound 25 - Method A and silica gel chromatography gave compound 3425 in 58% yield. Compound 26 - Method A and silica gel chromatography gave compound 26 in 60% yield.

Compound 27 - Method A and silica gel chromatography gave compound 27 in 88% yield.

Compound 28 - Method A and silica gel chromatography gave compound 28 in 18% yield.

Synthesis of salts

The salts of polar prodrug esters of heterocyclic antibacterial compounds were prepared by treatment of solutions of the polar prodrug esters in methanol with one equivalent of acid (DEG, TEG, choline esters) or two equivalents of acid (MorE esters). In each case, diethyl ether was added, and the precipitated product was filtered and dried under vacuum. Yields were quantitative.

Example 2. Solubility of polar ester prodrugs and their salts in water.

The water solubility of ester prodrugs and various parent hybrid antibacterial compounds in water was determined by stirring an excess amount of each compound in water at room temperature, filtering an aliquot of resulting suspension, and analyzing the filtrate for the compound using HPLC. A comparison was made with a standard curve of known concentrations in order to calculate the solubility of each compound.

Water solubility data for representative polar ester prodrugs of formula (II) are provided in Table 1 , below.

drug treatment using intravenous administration.

AU-FQ hybrid antibacterial compounds are themselves poorly soluble in water (< 1 mg/mL), as are simple alkyl esters of such compounds, such as methyl and ethyl esters (data not shown). Certain salts of polar ester prodrugs are significantly more water-soluble (> 25- 100 mg/mL) than the corresponding non-salt polar ester prodrug as well as the corresponding non-ester AU-FQ hybrid parent compound.

Example 3. Conversion of hybrid ester prodrugs to hybrid antibacterial compounds by mouse plasma.

Esters and salts thereof of heterocyclic antibacterial parent compounds were incubated with mouse plasma for various times, and aliquots were removed for analysis by HPLC. The conversion of polar ester prodrug compound 4 ((S)-3-{4-[l-(l-cyclopropyl-3- carboxy-4-oxo-6,8-difluoro-7-quinolyl)-4-(3-methylpiperaziny l)]butyl}-6-(3-ethyl-4- methylanilino)uracil, 2-(2-hydroxyethoxy)ethyl ester) to its corresponding hybrid antibacterial parent compound ((S)-3-{4-[l-(l-cyclopropyl-3-carboxy-4-oxo-6,8-difluoro-7- quinolyl)-4-(3-methylpiperazinyl)]butyl}-6-(3-ethyl-4-methyl anilino)uracil) at room temperature (25°C) is shown in Figure 1.

The dependence on cholinesterase activity of plasma conversion of prodrugs to the hybrid antibacterial parent compounds is illustrated by the results shown in Figure 2, which shows the effect of the cholinesterase inhibitor neostigmine (NS) on the rate of hydrolysis in mouse plasma of compound 19 ((S)-3-{4-[l-(l-cyclopropyl-3-carboxy-4-oxo-6,8-difluoro- 7-quinolyl)-4-(3-methylpiperazinyl)]butyl}-6-(3-ethyl-4-meth ylanilino)uracil, 2-(N- morpholinyl)ethyl ester) to its corresponding hybrid antibacterial parent compound ((S)-3- {4-[l-(l-cyclopropyl-3-carboxy-4-oxo-6,8-difluoro-7-quinolyl )-4-(3-methylpiperazinyl)] butyl }-6-(3 -ethyl -4-methylanilino)uracil). In the absence of NS, compound 19 (open squares) is readily converted to its corresponding hybrid parent compound (open diamonds), whereas the extent of hydrolysis of compound 19 in the presence of NS (filled squares) to its corresponding hybrid parent compound (filled diamonds) is clearly slower in the presence of NS than in its absence. These results indicate that the conversion of polar ester prodrug is, at least in part, a result of plasma cholinesterase activity.

Example 4. Measurement of in vivo antibacterial activity of prodrug compounds. Representative polar ester prodrugs and corresponding salts thereof of the heterocyclic antibacterial parent compounds can be tested for protection from lethal bacterial infection in vivo (see, e.g., Tarantino et al., Antimicrob. Agents Chemother., 43: 1982-1987 (1999); Zhi et al. J. Med. Chem., 49: 1455-1465 (2006)). Briefly, Swiss Webster mice, ca. 28 g each, were infected with Staphylococcus aureus (Smith strain) by the intraperitoneal route (ca. 4-8 x 10 cfu/mouse). (cfu = colony forming units) Test compounds were dissolved in 5% dextrose in water (D5W) to a concentration of 10 mg/ml. In the case of free bases of the prodrugs, the pH was adjusted to ca. 4-5 to effect solution. Daptomycin was used as positive control drug, i.e. to demonstrate protection from lethal infection. Fifteen minutes after infection, solutions of test compounds in D5W, daptomycin in D5W, or D5W (alone) were given intravenously via the tail vein to groups of 6-12 mice each. Animals were monitored for 48 hours, and the number of mice surviving was tabulated for each treatment.

Results of testing of intravenous administration of a single dose of representative prodrug ester salts of hybrid antibacterial compounds against intraperitoneal S. aureus (Smith) infections of mice are shown in Table 2.

Doses providing half maximal protection (ED ₅₀ ) by three polar ester prodrug compounds in the same model are presented in Table 3.

Example 5. Acute toxicity.

Polar ester prodrug compounds were evaluated for acute toxicity after intravenous dosing to assure that further testing will employ no higher than a maximum tolerated dose (MTD) of prodrug. Animals were six-week old (26-28 grams) specific pathogen- free Swiss- Webster mice. Each prodrug compound was dissolved in an appropriate vehicle, adjusted to pH ca 4 to dissolve the compound, and administered intravenously to the tail vein of each of three mice in a volume of 0.05-0.2 ml at single doses of 50 -250 mg/kg or vehicle-only controls. The animals were observed closely for 24 hours for signs of acute toxicity. An MTD was determined as the dose that produced no sign of overt toxicity. The MTD of representative prodrug esters are presented in Table 4.

Example 6. Pharmacokinetics and metabolism in vivo.

These experiments provided prodrug disposition data for selection of specific formulations or salts for further study, and to aid design of treatment regimens in the infection models. Six-week old (26-28 gram) specific pathogen-free ICR/Swiss mice were used. An appropriate dose (the MTD or lower) of each salt of a hybrid antibacterial compound was injected intravenously in a suitable carrier via a tail vein to mice, and at

selected times after injection, three mice were anesthetized with isoflurane, and blood was collected via cardiac puncture. The blood samples were centrifuged to yield clear plasma (0.4-0.6 mL per animal), and the plasma samples analyzed for prodrug and heterocyclic antibacterial compound content. The average plasma levels of compound for each time point were analyzed by the WinNonlin® software to estimate half-life (t _/2 ) and volume of distribution (Vj) for each species.

Representative results are shown in Figure 3 for compound 18 as its mesylate salt. The ester prodrug (diamonds) was converted rapidly in the mouse to the hybrid antibacterial compound (squares). The elimination ti _/2 of the latter was 17 minutes.

Example 7. Antibacterial efficacy in other murine models.

Groups of 6-10 male Swiss-Webster mice weighing 26-28 grams each are inoculated intraperitoneally (i.p.) with a LDg _O-100 dose (ca. 5 x 10 cfu) of S. aureus (Smith) or E. faecalis (ATCC strain 29412; 5 x 10 ⁸ cfu) suspended in brain-heart infusion broth. One hour after inoculation, test compounds are administered to groups of five mice by the iv, sc, or oral (po) route at three doses. Vancomycin (10-30 mg/kg, depending on route) or daptomycin (10 mg/kg) are used as a positive control and vehicle as negative control. Deaths occurring during the subsequent four days are recorded. If significant prevention of mortality (> 50%) is observed, the minimum effective dose (MED) or minimum dosing regimen (dose or regimen at which survival of > 50% is observed) will then be determined. Prodrug compounds are also tested in the same model with clinically relevant, drug- resistant strains, e.g. S. aureus (ATCC MRSA strain 1132) and E. faecalis (ATCC Vancomycin-resistant strain (VRE) B42762. In these experiments, vancomycin, daptomycin, ciprofloxacin, or other marketed antibiotics are used as appropriate controls, depending on the infecting organism, strain and route of administration.

All publications, patent applications, patents, and other documents cited herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting. Other variations and embodiments of the invention described herein will now be apparent to those of ordinary skill in art without departing from the scope of the invention or the spirit of the claims below.