The present invention relates to a novel compound, to processes for its production, to pharmaceutical formulations containing it, and to its use in therapy, particularly in the treatment of microbial infections.

EP-A-0 259 804 describes the compound of formula (A):

(A)

(9-fluoro-3-methyl-10-(4-methyl-l-piperazinyl)-7-oxo-2,3- dihydro-7H- pyrido[3,2,l-ij]-l,3,4-benzadiazine-6-carboxylic acid). The compound of formula (A) is reported to have antibacterial activity.

The present invention provides a compound of formula (I):

(I) wherein R* and R^ are independently C _ft alkyl, such as methyl or ethyl. A parucular compound of formula (I) is 6-(diethoxycarbonyl)acetyl 9-fluoro-3-

methyl-10-(4-methyl-l-piperazinyl)-7-oxo-2,3-dihyuro-7H-pyri do[3,2,l-ij]-l,3,4- benzoxadiazine.

Compounds of formula (I) have antibacterial activity and are therefore of use in the treatment and prophylaxis of bacterial infections in humans and animals.

The invention in a second aspect, further provides a process for the production of a compound of formula (I), which comprises treating a compound of formula (LI):

(ID

wherein X is a leaving group, such as imidazole or halide, such as chlorine, with a carbanion derivable by treating a dialkyl malonate with a strong base, such as sodium hydride.

The compound of formula (II) can be obtained by treating the compound of formula (A) with, for example, an excess of carbonyl diimidazole. This reaction is typically carried out in an aprotic solvent such as chloroform at ambient or elevated temperature, eg at reflux, under dry conditions, e.g. in an argon, atmosphere.

Generation of the carbanion is typically carried out at between-70 and 70° C, for instance at ambient temperature, in an aprotic solvent such as THF. A solution of the compound of formula (LI) in THF is then added and the mixture is refluxed. After evaporation of solvent the residue is dissolved in water and the reaction quenched by neutralization to pH7. The product is extracted and purified by chromatography such as HPLC.

T e compound according to the invention is suitably provided in substantially pure form, for example at least 50% pure, suitable at least 60% pure, advantageously at least 75% pure, preferably at least 85% pure, more preferably

at least 95% pure, especially at least 98% pure, all percentages being calculated as weight/weight. An impure or less pure form of the compound according to the invention may, for example, be used in the preparation of a more pure form of the same compound.

The compound of the invention has antibacterial activity and is useful for the prophylactic and therapeutic treatment of bacterial infections in animals, especially mammals, including humans, in particular humans and domesticated animals (including farm animals). The compound may be used for the treatment of infections caused by, among other organisms, species of Staphylococcus, Streptococcus, Aerococcus, Enterococcus, Micrococcus, Kactobacillus, Bifidobacterium, Clostridium, Eubacterium, Peptococcus, Peptostreptococcus, Propionibacterium, Citrobacter, Campylobacter, Enterobacter, Klebsiella, Proteus, Pseudomonas, Serratia, Salmonella, Shigella, Vibrio, Aeromonas, Haemophilus, Neisseria, Acinetobacter, Alcaligenes, Bordetella, Bacteroids, Fusobacterium, Myocoplasma and other microorganisms.

Accordingly a third aspect of the invention provides the compound of formula (I) for use in medical therapy, in particular for use as an antibacterial agent

The invention further provides a method of treating a human or animal suffering from a bacterial infection by the administration of an effective amount of the compound of the invention.

A particular method of the invention comprises treating or preventing bacterial infections in non-human animals , more particularly domesticated mammals and birds, such as horses, cattle, swine, sheep, companion animals including dogs and cats, and poultry including chickens. The method comprises administering to the animal via the oral route an antibacterially effective amount of a compound of formula (I):

A further aspect of the invention provides use of a compound of formula (I) in the manufacture of a medicament for use in the treatment or prevention of bacterial infections in non-human animals by administration via the oral route.

The invention further provides a pharmaceutical composition comprising a compound of the formula (I) together with a pharmaceutically acceptable diluent or carrier.

The compound of the invention can be administered alone, but will generally be administered in admixture with a pharmaceutical carrier selected with regard to the intended route of administration and standard pharmaceutical practice. For

example, it may be administered orally in the form of a tablet containing such excipients as starch or lactose; or in a capsule or ovule either alone or in admixture with excipients, or in the form of an elixir or suspension containing a flavouring or colouring agent. It may be injected parenterally, for example, intravenously, intramuscularly or subcutaneously. For parenteral administration, it is best used in the form of a sterile solution which may contain other substances, for example, enough salts or glucose to make the solution isotonic.

For oral and parenteral administration , it is expected that the daily dosage level of the compound of formula (I) will be from 0.5 to 500, preferably 1 to 300 mg/kg (in divided doses) when administered by either the oral or parenteral route.

No unacceptable toxicological effects are expected when the compound is administered in the above mentioned dosage ranges.

The compounds and compositions according to the invention may be formulated for administration in any convenient way for use in human or veterinary medicine, by analogy with other antibacterial agents.

The tablets and capsules for oral administration may be in unit dosage form, and may contain conventional excipients including, for example, binding agents, for example, syrup, acacia, gelatin, sorbitol, tragacanth, or polyvinylpyrrollidone; fillers, for example lactose, sugar, maize-starch, calcium phosphate, sorbitol or glycine; tabletting lubricants, for example magnesium stearate, talc, polyethylene glycol or silica; disintegrants, for example potato starch; and pharmaceutically acceptable wetting agents, for example sodium lauryl sulphate. The tablets may be coated according to methods well known in normal pharmaceutical practice.

Oral liquid preparations may be in the form of, for example, aqueous or oily suspensions, solutions, emulsions, syrups or elixirs, or may be presented as a dry product for reconstitution with water or another suitable vehicle before use. Such liquid preparations may contain conventional additives, including, for example, suspending agents, for example sorbitol, methyl cellulose, glucose syrup, gelatin, hydroxyethyl cellulose, carboxymethyl cellulose, aluminium stearate gel or hydrogenated edible fats; emulsifying agents, for example lecithin, sorbitan monooleate or acacia; non-aqueous vehicles (which may include edible oils), for example almond oil, oily esters (for example glycerine), propylene glycol, or ethyl alcohol; preservatives, for example methyl or propyl p-hydroxybenzoate or sorbic acid; and, if desired, conventional flavouring and colour agents.

Compositions according to the invention intended for topical administration may,

for example, be in the form of ointments, creams, lotions, eye ointments, eye drops, ear drops, impregnated dressings, and aerosols, and may contain appropriate conventional additives, including, for example, preservatives, solvents to assist drug penetration, and emollients in ointments and creams. Such topical formulations may also contain compatible conventional carriers, for example cream or ointment bases, and ethanol or oleyl alcohol for lotions. Such carriers may constitute from about 1% to about 98% by weight of the formulation; more usually they will constitute up to about 80% by weight of the formulation.

Compositions according to the invention may be formulated as suppositories, which may contain conventional suppository bases, for example cocoa-butter or other glycerides.

Compositions according to the invention intended for parenteral administration may conveniently be in fluid unit dosage forms, which may be prepared utilizing the compound and a sterile vehicle, propyleneglycol. The compound, depending on the vehicle and concentration used, may be either suspended or dissolved in the vehicle. Parenteral suspensions may be prepared in substantially the same manner except that the compound is suspended in the vehicle instead of being dissolved and sterilisation cannot be accomplished by filtration. The compound may instead be sterilised by exposure to ethylene oxide before being suspended in the sterile vehicle. Advantageously, a surfactant or wetting agent is included in such suspensions in order to facilitate uniform distribution of the compound.

Compositions according to the invention may also be administered by inhalation. By "inhalation" is meant intranasal and oral inhalation administration. Appropriate dosage forms for such administration such as an aerosol formulation or a metered dose inhaler, may be prepared by conventional techniques.

Preferably, the compound of formula (I) is administered in admixture with the animal's feedstuff or drinking water. Thus, a further aspect of the invention provides feedstuff or drinking water having a compound of formula (I) mixed therewith, as well as a premix comprising a compound of formula (I) together with a veterinarily acceptable carrier. Suitable carriers include a mixture of a binder, such as polyvinylpyrrollidone, and a filler, such as lactose, which can be extruded, granulated and mixed with or sprinkled on the animals' food. For addition to drinking water, the active is first made up as a concentrate with a liquid carrier, such as gluconolactone.

The following example serves to illustrate the present invention.

EXAMPLE 1

6-(Diethoxycarbonyl)acetyl 9-fluoro-3-methyl-10-(4-methyl-l-piperazinyl)-7-oxo- 2,3-dihydro- 7H-pyrido[3,2, 1 -ij]- 1 , 3, 4-benzox diazine.

Sodium hydride (0.67g, 16.7mmol of a 60% suspension in oil) was added portionwise to a stirred solution of diethyl malonate (2.67g, 16.7mmol) in dry THF (50ml). The resulting effervescent mixture turned pale yellow after 5min and was allowed to stir at room temperature for 3h (solution A). A solution of carbonyl diimidazole (1.8g, 11.12mmol) and 9-fluoro-3-methyl-10-(4-methyl-l- piperazinyl)-7-oxo-2,3-dihydro-7H-pyrido[3,2,l-ij]- 1,3,4- benzoxadiazine-6- carboxylic acid (2.0g, 5.56mmol) in chloroform (50ml) was heated under reflux in an argon atmosphere for 12h. The chloroform was then evaporated in vacuo and the residue was dissolved in anhydrous THF (50ml) (solution B). Solution B was added to solution A in one portion under an argon atmosphere and the resulting mixture was heated under reflux for a period of 16h. The volatiles were then removed by evaporation in vacuo and the residue was dissolved in water (50ml). The aqueous solution was neutralised to pH 7 by careful addition of acetic acid and the resulting mixture was extracted with ethyl acetate (3 x 50ml). The combined organic extracts were dried (MgSO4) and evaporated in vacuo. The residue was purified by normal phase HPLC using a Dynamax 300A silica column with a flow rate of l .Oml/min and 5% methanol/dichloromethane as eluant to give the title compound, retention time 24.5min, m/z (FAB) 505 (M + 1).