NO883545L - DIETHYL-2- (N- (6-FLUOR-5-METHYL-1,2,3,4-TETRAHYDROKINALDINYL)) - METHYLENE MALONATE FOR USE AS OUTPUT MATERIAL FOR THE PREPARATION OF THERAPEUTIC ACTIVE COMPOUNDS. - Google Patents

Description

The present invention relates to derivatives of the heterocyclic system known as benzo-[ij]-quinolizine.

More specifically, the invention relates to 8-substituted 6,7-dihydro-5-methyl-1-oxo-1H,5H-benzo-£i jj-kyriolyzine-2-carboxylic acid and derivatives thereof. Use of the compounds in question as antimicrobial agents, pharmaceutical preparations containing the compounds as well as intermediate products for use in the manufacture of the compounds are also covered by the invention.

US Patent 3,896,131 describes a broad class

of 6,7-dihydro-5-methyl-9-fluoro-1-oxo-1H,5H-benzo-£± j^j -quinolizine-2-carboxylic acids for use as antimicrobial agents.

The patent specifically describes several compounds substituted with halogen and/or methyl in the benzo ring. The compound 6,7-dihydro-9-fluoro-5-methyl-1-oxo-1H,5H-benzo-£ijj-quinolizine-2-carboxylic acid (now known as flumequin), which is discussed in the aforementioned patent has been the subject for the greatest attention due to its antimicrobial activity. It has now been shown that the corresponding, hitherto unknown 8-methyl-9-fluoro compound exhibits far greater antimicrobial activity.

US Patent 4,301,289 describes the compounds 6-fluoroquinaldine, 6-fluoro-1,2,3,4-tetrahydroquinaldine and dialkyl-2-N-(6-fluoro-1,2,3,4-tetrahydroquinaldinyl)-methylenemalonates.

The present invention relates to the compound 6,7-dihydro-5,8-dimethyl-9-fluoro-1-oxo-1H,5H-benzo-[ij]-quinolizine-2-carboxylic acid and its carboxylate derivatives. The invention also relates to the pharmacological use of these compounds as antibiotics, and pharmaceutical preparations comprising these compounds. The invention also relates to synthesis intermediates which are useful for the preparation of the compounds. The invention specifically relates to the hitherto unknown compound 6,7-dihydro-5,8-dimethyl-9-fluoro-1-oxo-1H,5H-benzo-[ij]-quinolizine-2-carboxylic acid of formula or a pharmaceutically acceptable carboxylate thereof . These compounds are useful antimicrobial substances.

The compounds in question have an optically active carbon atom in the 5-position. All such optical isomers are covered by the invention.

It is well known in the art that pharmaceutically acceptable salts such as alkali metal, alkaline earth metal, aluminum, iron, silver and other metal salts and amine salts of pharmaceutically active acids are equivalent to the acids in terms of activity, and in some cases they can and with offering advantages in absorption, formulation and the like. Pharmaceutically acceptable carboxylate salts of the free acid compounds according to the invention are easily prepared by reacting the acid with a base, and subsequent evaporation to dryness. The base can be organic, e.g. sodium methoxide or an amine, or inorganic, e.g. sodium hydroxide. Alternatively, the cation of a carboxylate salt, e.g. sodium, is replaced with another cation such as calcium or magnesium when the salt of the other cation is more insoluble in a chosen solvent.

Other useful derivatives of the compound according to the invention include acyl chlorides, the esters and the alkylaminoalkyl ester salts thereof. In the acyl chloride derivative, the hydroxyl part of the carboxylic acid group has been removed and replaced with chlorine. In the ester derivatives, the hydrogen part in the carboxylic acid group is replaced with an optionally substituted alkyl group, preferably an alkylaminoalkyl group.

Esters and the acyl chloride of the compound according to the invention can be obtained as intermediate products during the preparation of the acidic compound. In some cases, the esters can be produced directly using standardized synthesis methods. These esters and the acyl chloride exhibit antimicrobial activity, but they are primarily of interest as synthesis intermediates, although hydrolyzable or salt-forming esters may in some cases be of interest as therapeutic agents. Preferred esters are alkyl esters and alkylaminoalkyl esters with 1-4 carbon atoms in the alkyl group. Particularly preferred are alkylaminoalkyl esters such as dimethylaminoethyl esters which form salts, e.g. hydrochlorides.

Ester derivatives are easily prepared by reacting the free acid of formula I with thionyl chloride to form the hitherto unknown acyl chloride derivative. The acyl chloride is reacted with the appropriate alcohol to form the desired ester.

The antimicrobial activity of the compounds produced according to the invention can be demonstrated by the known standard plate dilution method for testing the bacterial sensitivity of difficult microorganisms to antibiotics, sulfonamides and other chemotherapeutic agents. Tryptone soy agar (oxoid) with the following composition is the culture medium:

Using this test, the compounds produced according to the invention have been shown to have a broad-spectrum activity against Gram-positive and Gram-negative microorganisms.

The compounds produced according to the invention are active against microorganisms either in the absence or in the presence of 10% horse serum.

The test procedure used for determining the activity, as used in connection with the present invention, provides information on the amount of a compound which gives complete inhibition, partial inhibition or no inhibition of the microbial growth on the agar plates. In the experiment, the selected compound is added to the agar medium to achieve concentrations of 0, 1, 10 and 100 mg per litres. A number of plates with these concentrations are produced. 10% horse serum is added to a number of such plates. Aliquots of culture of any of 12 species of microorganisms are inoculated onto the agar plates containing the compound at various concentrations. The plates are incubated at 37°C in a 10% carbon dioxide atmosphere for 18-24 hours. The microbial growth on each plate is read visually, and the minimal inhibitory concentrations (for partial or complete inhibition) are recorded. Some of the microorganisms that have been used in this experiment are:

<*>Strains isolated from dental caries in rats or hamsters at the National Institute of Dental Health and cultured in PFY or API agar.

The compounds produced according to the invention have antimicrobial activity against one or more of the above-mentioned microorganisms. Of particular importance is the high level of activity of the compounds of formula I and its salts against pseudomonas aeruginosa, a particularly difficult species associated with many topical infections. This type of activity is very unusual in benzoquinolizine-type antimicrobials.

It should be understood that the species used are representative indicator species, as it would be impractical to carry out a test against all bacteria. It is well known in the art that broad-spectrum activity can be predicted on the basis of activity shown against selected representative bacterial species.

The compounds prepared according to the invention are active when administered orally to animals. They are excreted in the urine and are effective urinary tract antimicrobials for mammals. They can also be used in the treatment of lung infections, soft tissue infections, burn infections and bacteremia.

The compounds produced according to the invention are active against microorganisms in vitro or topically. In vitro activity is useful as such, as antimicrobial agents can be used for disinfection and sterilization, e.g. of medical and dental equipment, as ingredients in disinfectants.

The acute oral toxicity of the compounds prepared according to the invention is usually moderate to low compared to the effective oral dose, and they have an acceptable therapeutic ratio (LD^-q/EDj-q) of over 80.

The acidic compound prepared according to the invention is a white crystalline material when purified. It is mainly insoluble in water, lower alcohols or hydrocarbons, and is more soluble in halogenated solvents, N-N-dimethylformamide and the like. The salts, especially the alkali metal salts, are well soluble in water and lower alcohols.

The compounds produced according to the invention can be formulated by incorporating them into conventional pharmaceutical carrier materials, either organic or inorganic, which are suitable for oral or intraperitoneal administration. For use in vitro or topically, simple aqueous solutions or suspensions can be suitably used. For this purpose, concentrations in the order of 100 parts per 1,000,000 up to approx. 5 parts per 1 0 00 suitable, and the formulation is used by immersing the objects to be treated or by local application to an infected area.

The amount of a compound used for treatment, e.g. of a microbial urinary tract infection, by oral administration will be an effective amount below the toxic amount. The amount to be administered to control or combat an infection will depend on the species, sex, weight, physical condition and many other factors, but this judgment is within the realm of one skilled in the art of medicine. Usually the amount will be less than 100 mg per kg per dose. This is appropriately administered in the form of the usual pharmaceutical preparations such as capsules, tablets, emulsions, solutions etc. Excipients, fillers, coatings etc. are used in connection with tablets or capsules, which is well known in the art.

It is known that antimicrobial agents are used as growth activators for various animal and bird species. Although this has not yet been confirmed, it is assumed from their unique antimicrobial activity that the compounds produced according to the invention can also be used for this purpose. The compounds produced according to the invention can also be used to control or combat microbial (e.g. Erwinia amylovora) infections in plants, e.g. by spraying or dusting a preparation of these compounds on the infected area.

The acidic compound according to the invention can be prepared as described in the following reaction core:

wherein alk and each group R"'" are independent of each other and denote alkyl groups with 1-4 carbon atoms, preferably 1-2 carbon atoms.

In the first step in the reaction scheme, 5-amino-2-fluorobenzoic acid of formula II is reacted with the shown crotonaldehyde of formula III or a precursor of crotonaldehyde which forms crotonaldehyde under the acidic reaction conditions. Suitable precursors for crotonaldehyde which can be used in step (1) include acetaldehyde, acetal or paraldehyde. The product from step (1) is the hitherto unknown compound 5-carboxy-6-fluoroquinaldine of formula (IV). The reaction is carried out in the presence of a dilute aqueous acid such as sulfuric acid or hydrochloric acid, hydrochloric acid being preferred. The reaction is carried out at a temperature between approx. 50°C and the reflux temperature of the reaction mixture. It is advantageous to carry out the reaction in the presence of a reagent pair consisting of a weak oxidizing agent and a weak reducing agent. Suitable oxidizing agents include alkali metal-alkaline earth metal salts of the organic acid ineta-nitrobenzenesulfonic acid. The sodium and potassium salts are preferred. The free acids can also be used as oxidizing agents. Suitable reducing agents include ferrous sulphate, ferric sulphate, ferric chloride and the like. The currently preferred reagent pair is the sodium salt of m-nitrobenzenesulfonic acid as the oxidizing agent and ferrous sulfate as the reducing agent. Use of at least theoretical amounts of the oxidizing agent and reducing agent (ie at least 0.25 mol of each per mol of the aminobenzoic acid of formula II) is preferred. If catalytic amounts of the reducing agent are used, the reaction proceeds, but at a lower rate.

Steps (2) and (3) of the reaction scheme involve reduction of the carboxyl group in the intermediate of formula IV. The intermediate of formula IV is reduced in step (2) to form the hitherto unknown intermediate 1,2-dihydro-6-fluoro-5-hydroxy-methylquinaldine of formula V. This reduction is carried out using diborane in a suitable solvent such as tetrahydrofuran . The mixture is heated under reflux for several hours.

In step (3), the 1,2-dihydro-6-fluoro-5-hydroxy-methylquinaldine of formula V is reduced to form the hitherto unknown intermediate 6-fluoro-5-methyl-1,2,3,4-tetrahydro-quinaldine of formula VI. This reduction is carried out using hydrogen gas and a mixture of palladium on carbon and platinum on carbon. Alternatively, the reduction can be carried out in two consecutive steps, where the first step includes the use of one catalyst and the second step the other. In each case, the reduction is carried out in a solvent such as ethanol, using a Paar apparatus.

The 6-fluoro-5-methyl-1,2,3,4-tetrahydroquinaldine of formula VI is condensed with a dialkyl alkoxymethylene malonate of formula VII in step (4). The preferred dialkyl alkoxy methylene malonate is diethyl ethoxy methylene malonate, as this is the most readily available. The condensation reaction requires heating the reactants until the reaction is complete, as determined by chromatographic analysis. The reaction is carried out in the absence of solvent at a temperature of 100 - 200°C for several hours. It is preferred that the reaction is carried out at a temperature of 140 - 150°C for 2 hours. Alternatively, the reaction can be carried out in the presence of an inert organic solvent which forms an azeotropic mixture with the formed alcohol after condensation of dialkyl alkoxy methylene malonate (e.g. ethanol, where diethyl ethoxy methylene malonate is used in step (4)). The reaction mixture is heated to its reflux temperature and the azeotropic mixture comprising the alcohol and the organic solvent is collected, e.g. in a Dean-Stark trap. Fresh organic solvent is usually added to the reaction mixture as the solvent is used during distillation. Removal of the alcohol from the reaction mixture usually drives the condensation reaction completely and increases the yield. The product from step (4) is the hitherto unknown intermediate of formula VIII. This intermediate can be isolated, e.g. as an oil or a solid, or the product from step (4) can be used directly in step (5) without isolation of the intermediate product.

Alternatively, an N-cycloisopropylidenyl alkoxymalonate of formula in which alk is an alkyl group with 1-4 carbon atoms can be used as the diester of alkoxymethylenemalonic acid in step (4) instead of the shown dialkylalkoxymethylenemalonate of formula VII.

In step (5), the intermediate product of formula VIII is cyclized to form the ester of formula IX. The cyclization step is carried out by heating the intermediate of formula VIII in the presence of polyphosphoric acid. The reaction temperature is preferably 150 - 160°C. Alternatively, cyclization of the intermediate of formula VIII is carried out in the presence of phosphorus oxychloride under reflux for several hours, evaporation of excess phosphorus oxychloride and reflux in the presence of water.

The ester of formula IX is saponified in step (6) in the usual way to form 6,7-dihydro-5,8-dimethyl-9-fluoro-1-oxo-1H,5H-benzo-jijj-quinolizine-2-carboxylic acid of formula I.

When the above-mentioned N-cycloisopropylidenyl alkoxymalonate is used in step (4), step (5) usually results directly in the formation of 6,7-dihydro-5,8-dimethyl-9-fluoro-1-oxo-1H,5H-benzo-£ij" |-quinolizine-2-carboxylic acid and no separate hydrolysis step is required.

The invention is illustrated in the following examples.

Example 1

Preparation of 5-carboxyl-6-fluoroquinaldine

A mixture of 95.2 g 5-amino-2-fluorobenzoic acid (0.60 mol), 74.3 g (0.33 mol) sodium meta-nitrobenzenesulfonate, 46.2

g (0.17 mol) of ferrous sulfate heptahydrate and 660 ml of 9 N hydrochloric acid were heated to 90-95°C. 77 g (1.0 mol) of crotonaldehyde (96%) was added dropwise over 2.5 hours with vigorous stirring, keeping the temperature just below the reflux temperature. After further stirring for 0.5 hour, the hot solution was filtered through a plug of glass wool. The filtrate was cooled to 30°C, treated with decolorizing charcoal and filtered. The clear filtrate was cooled on ice with stirring to form a yellow solid. The solid was separated by filtration, washed with acetone and dried. The solid was then dissolved in 400 ml of hot water, and a solution of 50 g of sodium acetate in 100 ml of water was added. The product was 58.2 g of cream-colored crystals of 5-carboxyl-6-fluoroquinaldine. The structure

was confirmed by infrared analysis and nuclear magnetic resonance spectrum analysis.

Example 2

Preparation of the hitherto unknown intermediate 1,2-dihydro-6-fluoro-5-hydroxymethylquinaldine

To a stirred slurry of 20.0 g (97.6 mol) of 5-carboxyl-6-fluoroquinaldine in 400 ml of tetrahydrofuran, 300 ml of 1 M diborane in tetrahydrofuran (0.3 mol) was added dropwise. The solution was stirred at 20°C for 1 hour, was heated to the reflux temperature for 2 hours and then allowed to cool. A mixture of 150 ml of water and 100 ml of tetrahydrofuran was added and the mixture was stirred for 30 minutes on a steam bath and then cooled. The aqueous layer was saturated with sodium carbonate by stepwise addition of the salt. The organic layer was separated and the aqueous layer was extracted with 200 ml of diethyl ether. The extracts were combined with the organic and dried over magnesium sulfate. Evaporation of the solvent gave an oil which was dissolved in a solution of 400 ml of ethanol and 15 ml of concentrated hydrochloric acid. After heating this mixture under reflux for 1 hour, the solvent was evaporated to form a solid. The solid was dissolved in 200 ml of water and the solution basified with aqueous sodium hydroxide to give a solid which was predominantly 1,2-dihydro-6-fluoro-5-hydroxymethylquinaldine as determined by nuclear magnetic spectral analysis. Other isomers were also present.

Example 3

Preparation of the hitherto unknown intermediate 6-fluoro-5-methyl-1, 2, 3, 4- tetrahydroquinaldine

13.2 g of a solid which was mainly 1,2-dihydro-6-fluoro-5-hydroxymethylquinaldine, prepared according to Example 2, was dissolved in 300 ml of ethanol and 10 ml of concentrated hydrochloric acid. 1 g of 5% platinum on carbon and 3 g of 5% palladium on carbon were added to this solution. The solution was hydrogenated at 3.5 kg/cm 2 at 20°C on a Paar apparatus. After absorption of approx. 0.84 kg/cm 2 of hydrogen (the theoretically necessary amount), the solution was filtered, and the solvent was removed by evaporation, forming a solid.

Nuclear magnetic resonance spectral analysis showed a slightly incomplete reaction. Therefore, the solid was dissolved in 300 ml of aqueous (90%) ethanol, to which 2 g of platinum on carbon was added and the solution was hydrogenated at 3.5 kg/cm 2 on the Paar apparatus for approx. 16 hours. The solution was then filtered and the solvent was evaporated. The solid obtained was dissolved in 50 ml of water. This solution was basified with aqueous sodium hydroxide and then extracted with diethyl ether. Evaporation of the ether gave 6-fluoro-5-methyl-1,2,3,4-tetrahydroquinaldine as an oil.

Example 4

Alternative preparation of 6-fluoro-5-methyl-1,2,3,4-tetrahydro-quinaldine

7.0 g of a solid which was mainly 1,2-dihydro-6-fluoro-5-hydroxymethylquinaldine was dissolved in 200 ml of ethanol containing 1 ml of concentrated hydrochloric acid, 1.0 g of 5% palladium on carbon and 1, 0 g of 5% platinum on carbon, and the mixture was hydrogenated at 3.5 kg/cm 2 at 20°C for 5 hours. The solution was filtered and the filtrate was evaporated to give a white solid which according to nuclear magnetic resonance spectral analysis was 6-fluoro-5-hydroxymethyl-1,2,3,4-tetrahydroquinaldine.

The solid was dissolved in 350 ml of ethanol containing 3 ml of concentrated hydrochloric acid and 3.0 g of palladium on carbon,

and was hydrogenated at 3.5 kg/cm 2 overnight. The mixture was filtered and the filtrate was evaporated to give 6-fluoro-5-methyl-1,2,3,4-tetrahydroquinaldine hydrochloride as a white solid. The free base was separated by dissolving the solid in water, after which the solution was basified with 10% aqueous sodium hydroxide solution and extracted with diethyl ether, followed by evaporation of the ether to give a yellow solid.

Example 5

A mixture of 9.3 g of 6-fluoro-5-methyl-1,2,3,4-tetrahydroquinaldine and 17 ml of diethylethoxymethylene malonate was heated to 150-160°C for 3.5 hours and was then cooled to 100° C. 56 g of polyphosphoric acid were added to this solution, and the mixture was stirred for one hour while heating on a steam bath. The mixture was then cooled to room temperature and allowed to stand for approx. 72 hours. To. to this mixture containing ethyl 1,2-dihydro-5,8-dimethyl-9-fluoro-1-oxo-1H,5H-benzo-£ij J-quinolizine-2-carboxylate was added 250 ml of 20% aqueous sodium hydroxide to make the solution basic. The solution was then heated to reflux for 2 hours, cooled and acidified with concentrated hydrochloric acid. The solid was separated by filtration and recrystallized from aqueous N,N-dimethylformamide, washed with ethanol followed by drying, which gave 6,7-dihydro-5,8-dimethyl-9-fluoro-1-oxo-1H,5H -benzo- ^i jj -quinolizine-2-carboxylic acid as an off white solid with melting point 269 - 272°C.

Analysis calculated for: C15H14FN03

Calculated: C 65.4, H 5.1, N 5.1

Found: C 65.0, H 5.0, N 5.0.

Example 6

The antibacterial activity of the free acid compound according to the invention and the activity of several 6,7-dihydro-5-methyl-1-oxo-1H,5H-benzo-[ij]-quinolizine-2-carboxylic acids from the known technique were determined using the standard plate dilution method as described above. The experiments were carried out both in the absence (column A) and in the presence (column B) of horse serum as described above, and the amounts of the antimicrobial agent were as indicated. The results (indicated as the minimum concentrations in mg of the active antimicrobial agent per liter which gave partial or complete inhibition of the growth of the indicated microorganisms) are shown in the following table:

It appears that the compound according to the invention exhibits significantly greater activity than the known compounds.

Example 7

To a solution of 0.17 g (4.25 mmol) sodium hydroxide

1.3 g (4.73 mmol) of 1,2-dihydro-5,8-dimethyl-9-fluoro-1-oxo-1H,5H-benzo-quinolizine-2-carboxylic acid was added to 75 ml of water . The mixture was stirred for approx. 30 minutes and undissolved acid was removed by filtration. The solution was lyophilized to give 1.1 g of white fluffy solid sodium 1,2-dihydro-5,8-dimethyl-9-fluoro-1-oxo-1H,5H-benzo-£ijj-quinolizine-2-carboxylate.

Analysis calculated for:<C>15<H>13FNONa.0.5 H20

Calculated: C 58.8, H 4.6, N 4.6.

Found: C 58.9, H 4.6, N 4.4.

Claims (1)

Chemical connection, characterized in that this is diethyl-2-[N-(6-fluoro-5-methyl-1,2,3,4-tetrahydroquinaldinyl)]-methylene malonate.