GB1604045A - -(2-methyl-indol-3-yl)-acetic acid esters processes for its prepartion and pharmaceutical compositions incorporating the same - Google Patents

Description

(54) ANt-(2-METHYL-INDOL-3-YL)-ACETIC ACID ESTER, PROCESSES FOR ITS PREPARATION, AND PHARMACEUTICAL COMPOSITIONS INCORPORATING THE SAME (71) We, STERWIN A.G., a Swiss Company, of Zeughausgasse 9, CH-630O Zug, Switzerland, do hereby declare the invention, for which we pray that a patent may be granted to us., and the method by which it is to be performed, to be particu larly described in and by the following statement:- This invention concerns a pharmacologically-active ester, processes for its preparation and pharmaceutical compositions incorporating the same.

Analgesics are in widespread use today, and many compounds of different types have been proposed and marketed for use as such. For the relief of chronic conditions such as rheumatism and arthritis it is normally desirable to use an agent which displays an anti-inflammatory effect in addition to its analgesic activity. A number of antiinflammatory analgesic agents are known and it is normal practice at present to use one of these known agents for alleviation of the symptoms of chronic rheumatism, arthritis and similar conditions.

Some of the best-known, most effective and widely-used of the existing antiinflammatory analgesics are the 4 - alkyl - 3,5 - dioxo - pyrazolidine derivatives of the general formula:

wherein Alk represents an n-propyl or n-butyl group, and either one of W' and W" represents a phenyl group and the other represents a phenyl or a para-hydroxyphenyl group or W' and W" together with the intervening nitrogen atoms to which they are respect;vely attached represent a 3 - dimethylamino - 7 - methyl - [1,2,4] - benzotriazine ring-system fused with the pyrazolidine ring.

These compounds of general formula I may exist in the following tautomeric forms:

The following compounds are examples of these known anti-inflammatory analgesics of general formula I: 1,2 - diphenyl - 3,3 - dioxo - 4 - n - butylpyrazolidine; I - phenyl - 2 - (p - hydroxyphenyl) - 3,5 - dioxo - 4 - n - butylpyrazolidine (which may also be named 1 - (p - hydroxyphenyl) - 2 - phenyl - 3,5 - dioxo - 4n - butylpvrazolidine); and 5 - (dimethvlamino) - 9 - methyl - 2 - n - propyl - 1H - pyrazolo - [1,8-a] [ 1,2,41 benzotriazine - 1,3(2H) - dione.

Another class of existing anti-inflammatory analgesics, quite widely used at present are the well-known substituted a - (2 - methyl - ind [en/ol] - 3 - yl) - acetic acids of the general formula:

(wherein A represents a C.Cl, N, C.H or C.SO.CH, / / group; R represents a fluorine atom or a methoxy group; n is 0 or 1; and either X represents a nitrogen atom and Y represents a -CO- linkage [and the dotted line has no significance] or X represents a carbon atom, Y represents a CH group and the dotted line indicates a second CC bond) as well as their normal pharmacologically-acceptable salts.

The following compounds are examples of these known anti-inflammatory analgesics of general formula II: 1 - (para - chlorobenzoyl) - 2 - methyl - 5 - methoxy - indol - 3 - yl 1- acetic acid; 1 - (paramethylsulphinyl - benzylidene) - 2 - methyl - 5 - fluoro - indene - 3 - ylacetic acid; 1 - (3 - phenyl - acryloyl) - 2 - methyl - 5 - methoxy - indol - 3 - yl - acetic acid; and 1 - isonicotinoyl - 2 - methyl - 5 - methoxy - indol - 3 - yl - acetic acid.

Unfortunately, however, the desirable anti-inflammatory and analgesic properties of both of these compounds of general formula I and of the compounds of general formula II, are offset by their tendency to give rise to disturbances of the gastric tract.

In the case of the a - (2 - methyl - ind[en-/ol] - 3 - yl) - acetic acids of general formula X it has been suggested that this may be attributable to the acidic nature of their carboxyl functions; but that explanation is not altogether reliable, since there is little or no attenuation of this tendency when these anti-inflammatory analgesics are administered in the form of the a - 2 - methyl - ind[en/ol] - 3 - yl) - acetate salts, and furthermore there are no acidic carboxyl functions in the 4 - alkyl - 3,5 - dioxopyrazolidine derivatives of general formula I.

It is therefore particularly surprising to have found as we have done that when an ester linkage is formed between the carboxyl group present in a particular a - (2methyl - ind - [en/ol] - 3 - yl) - acetic acid of general formula X and the hydroxyl group present in the tautomeric forms of a particular 4 - alkyl - 3,5 - dioxopyrazolidine derivative of general formulae Ia and Ib, the resultant ester, although formed between gastrically-disturbing moieties, is nevertheless largely or substantially wholly free from unwanted side-effects upon the gut, while being an effective and indeed an outstanding anti-inflammatory analgesic.

Accordingly, the present invention provides, as a compound having anti inflammatory and analgesic activity, a 4 - alkyl - 3,5 - dioxo - pyrazolidinyl - a - (2 methyl - indol - 3 - yl) - acetate of the formula:

which is a solid compound having a melting point of from 1650C to 167"C.

The ester of the invention may be formed with either of the 3-oxo or 5-oxo groups of the corresponding compound of general formula I, since as indicated hereinbefore the compound may exist in tautomeric forms in which either one of the 3or 5-Dosition bears a hydroxy group.

We have moreover found that the compound of formula IV may be prepared conveniently and in good yield by reacting the corresponding 4 - alkyl - 3,5 - dioxopyrazolidine of general formula I with the appropriate a - (2 - methyl - indol - 3 - yl)acetic acid chloride.

Accordingly, in another aspect, the present invention provides a process for the preparation of a compound of the formula IV defined above, which process comprises reacting 1,2 - diphenyl - 3,5 - dioxo - 4 - n - butyl - pyrazolidine of the formula:

with 1 - para - chlorobenzoyl) - 2 - methyl - 5 - methoxy - indol - 3 - yl - acetic acid chloride of the formula:

in an anhydrous inert solvent at a temperature up to the reflux temperature of the solvent, but for no more than 10 minutes at reflux temperature. The inert solvent will normally be an organic solvent, and is advantageously a substituted aromatic hydrocarbon, such as toluene, one of the many halogenated aromatic solvents, an aliphatic hydrocarbon or a halogenated aliphatic hydrocarbon such as chloroform.

Being fairly vigorous, the reaction may be carried out at ambient temperature without heating or possibly, when the reaction is very vigorous as sometimes it is, even with cooling.

The reaction is preferably effected in the presence of a base, which is most conveniently a tertiary amine. The base currently preferred above all others is pyridine.

This process may also advantageously include the preliminary steps of preparing the acid chloride of formula III by reacting a solution or suspension in an anhydrous inert solvent of the corresponding acid or a salt thereof with thionyl chloride.

Where a salt of the acid is employed in this preliminary step it is preferably the pyridine salt.

The reaction with thionyl chloride may be conducted at any convenient temperature between ambient and the reflux temperature of the solvent; and usually will be carried out at a temperature within the range of from 40"C to 65 (:r.

The solvent used may be the same as that used in the above-described subsequent stage of the preparation. It will normally be an organic solvent and is advantageously a relatively low-boiling substituted aromatic hydrocarbon such as toluene, one of the many halogenated aromatic solvents, an aliphatic hydrocarbon or a halogenated aliphatic hydrocarbon such as chloroform or dichloromethane The solvent employed is preferably anhydrous dichloromethane, and then the reaction can be effected most conveniently under reflux at a temperature of 40--41"C.

The proportions of the reactants will preferably be about 1 mole of thionyl chloride per mole of acid and, when the acid is used in the form of a salt, e.g. the preferred pyridine salt, per mole of pyridine or other salt forming base.

It has been found advantageous to effect the reaction between the acid and the thionyl chloride in the presence of a catalytic amount of N,N-dimethy!formamide.

According to another aspect of the invention there is nrovided an alternative process for the preparation of a compound of the formula IV defined above, which process comprises reacting a compound of the formula II defined above with a mixed anhydride of the general formula:

wherein "Ayl" represents an alkyl group containing from 1 to 20 carbon atoms, an aryl group containing from 6 to 20 carbon atoms, an alkyl substituted aryl grout containing from 7 to 20 carbon atoms or an aralkyl group containing from 7 to 20 carbon atoms; m is 0 or 1; and Q represents a carbon atom or when m is zero a sulphinyl group, in an anhydrous inert solvent for a reaction time of no more than 20 minutes. The solvent is generally organic and is preferably ope of those solvents set out hereinbefore as preferable for nse in the first process of the invention Furthermore, the reaction may also be conducted without detriment in the presence of a base such as a tertiary amine like triethvlamine or pyridine.

The mixed anhydride of general formula V is convenientlv prepared bv reacting 1 - (para - chlorobenzyl) - 2 - methvl - 5 - methoxy - indol - 3 - yl - acetic acid or a salt thereof with a reactive organic chloride of general formula:

wherein Ayl, m and Q are as defined above, in the presence of a base.

The reactive organic chloride of general formula VI can for instance be: (a) an alkyl, aralkyl, aryl or alkyl substituted aryl chloroformate of the general formula:

or (b) a sterically-encumbered alkyl, aralkyl, aryl or alkyl substituted aryl acid chloride of the general formula:

or (c) an alkyl, aralkyl, aryl or alkyl substituted aryl sulphonyl chloride:

in which "Ayl" represents an alkyl, aralkyl, aryl or alkyl substituted aryl group having up to 20 carbon atoms therein, as defined above.

The reaction between the acid and the reactive chloride of general formula VI is most conveniently carried out in an anhydrous inert solvent, which is preferably an organic solvent such as is employed in the subsequent stage in the process.

This reaction must be performed in the presence of a base, which is advantageously, a tertiary amine, and most preferably either triethylamine or pyridine.

There is no need to isolate the mixed anhydride of general formula V from the reaction mixture in which it was prepared. Instead the solution of the mixed anhydride obtained from the first-stage reaction can be subjected to the second-stage reaction in the same reaction mixture withoue elimination of the base therefrom, and in the same reaction vessel.

According to a still further aspect of this invention there is also provided a third process for the preparation of a compound of the formula IV defined above, which process compr;ses reacting a compound of the formula II defined above with a solution in a water-immiscible solvent of symmetrical 1 - (para - chlorobenzyl) - 2 - methyl 5 - methoxy - indol - 3- yl - acetic acid anhydride in the presence of a strong aqueous base, so that the reaction mixture forms a two-phase system, which is agitated at ambient or near-ambient temperature not exceeding 30"C for up to 30 minutes to yield the desired product of formula IV.

The reaction between the compound of formula II and the symmetrical acid anhydride produces the corresponding acid as a side-product, and must therefore be effected in the presence of a strong base, which can be an organic base such as triethylamine but preferably will be aqueous sodium hydroxide. The anhydride is somewhat unstable in the presence of water, and is therefore brought to reaction in solution in a water-immiscible solvent and preferably an anhydrous inert organic solvent, conveniently for instance benzene, toluene, chloroform, dichloromethane or ethers such as diethyl ether. The reaction is conducted with agitation in a two-phase reaction system, and thus any breakdown of the anhydride before it has participated in the intended reaction is minimized.

This third process can moreover advantageously include the further preliminary step of preparing the symmetrical acid anhydride by reacting the corresponding acid with a carbodiimide in solution in an anhydrous, non-hydroxylic and otherwise inert organic solvent at ambient or near-ambient temperatures, usually not exceeding 300 C.

In principle any carbodiimide can be employed, but in practice the carboniim-de used must of course be stable, and accordingly we envisage that the carbodiimide used would best be an N,N'-di [alk/ar] yl-carbodiimide of general formula:

where Z' and Z" each represent an alkyl, cycloalkyl, alkyl substituted aryl, aryl or aralkyl group containing from 6 to 20 carbon atoms. Moreover, it must be added that at present the only carbodiimide commercially available (at least in Britain) at an economic price is N,N'-dicyclohexyl-carbodiimide, which therefore is preferred for use in this invention.

The compound of formula IV as shown below displays excellent anti-inflammatory and analgesic activities when tested by generally-accepted tests for anti-inflammatory drugs; and preliminary studies suggest that, when administered orally, the compound will be substantially free from gastric side-effects.

Naturally, however, for employment in human and veterinary medicine as an antiinflammatory analgesic the compound of formula IV should first be properly formulated into appropriate pharmaceutical compositions, by association with suitable pharmaceutical vehicles.

The term "pharmaceutical" is used herein to exclude any possibility that the nature of the vehicle (considered of course in relation to the route by which the composition is intended to be administered) could be harmful. The choice of a suitable vehicle for a chosen route and mode of presentation is believed to be within the competence of those accustomed to the preparation of pharmaceutical compositions.

Accordingly, in yet another aspect of the invention, there are provided pharmaceutical compositions comprising as active ingredient, a compound of formula IV in association with a pharmaceutical vehicle.

Although the comnositions of this invention are primarily designed for administration via the digestive tract, including rectally, they can also be administered parenterally. In respect of these various modes of presentation the "pharmaceutical" vehicle is desirably: (a) the ingestible excipient of a tablet, coated tablet sublingual tablet or pill; the ingestible container of a capsule or cachet; the ingestible pulverulent solid carrier of a powder, or the ingestible liquid medium of a syrup, solution, suspension or elixir; (b) the solid or liquid medium of a paste, lotion, salve, ointment or unguent or the propellant medium of an aerosol; (c) a sterile injectable liquid solution or suspension medium; or (d) a base material of a suppository.

Whilst the modes of presentation just listed represent those most likely to be employed, they do not necessarily exhaust the possibilities.

The preferred route for administration of the anti-inflammatory analgesic of formula IV, is orally, including perlingually, so that the compositons will most frequently be administered in the form of tablets, capsules and other solid dose forms.

Bearing in mind the presently-contemplated dosage rates, which are indicated bellow, the compositions will normally be presented in the form of unit doses containing usually from 10 mg to 700 mg.

Whilst the dosage of the anti-inflammatory analgesic of formula IV will to some degree depend upon the route by which the compositions are to be administered, and of course also upon the condition to be treated and the patient under treatment, as a general indication it may be said that the useful dose ranges from 25 mg to 5 g (in divided doses) of the active analgesic per day for an adult In order that the invention may be well understood the following Examples and Formulations are now given, though only by way of illustration, to show certain preferred aspects of the invention, and in particular to illustrate processes and compositions of the invention.

Example 1.

Preparation of 1,2 - diphenyl - 3 - oxo - 4 - n - butylpyrazolid - 4 - en - S - yl (para - chlorobenzoyl) - 2' - methyl - 5' - methoxy - indol - 3' - yl - acetate.

Stage A: Preparation of 1 - (para - chlorobenzovl) - 2 - methyl - 5 - methoxyindol - 3 - yl - acetic acid chloride.

A solution of 6.0 g of thionyl chloride in 10 ml of dichloromethane was slowly added to a stirred solution of 4.8 g of 1 - (para - chlorobenzoyl) o2 -. methyl - 5methoxy - indol - 3 - yl - acetic acid and 4.8 g of pyridine in 80 ml of dichloromethane. The resultant red solution was refluxed for 15 minutes, and contained the desired acid chloride which however was not isolated for use in the next stage, but when isolated for characterisation had a melting point of 107--1090C.

Stage B: Preparation of 1,2 - diphenyl - 3 - oxo - 4 - n - butylpyrazolid - 4en - 5 - yl - 1' - (para - chlorobenzoyl) - 2' - methyl - 5' - methoxy - indol - 3'yl - acetate.

A suspension of 15.4 g of 1,2 - diphenyl - 3,5 - dioxo - 4 - n - butyrazolidine and 5.0 g of pyridine in dichloromethane was cautiously added to the red solution obtained in Stage A. The mixture was refluxed for 10 minutes, cooled, washed twice with 2 M hydrochloric acid and once with 20% sodium carbonate solution, then dried over magnesium sulphate.

The resultant dichloromethane solution was concentrated under reduced pressure to give a yellow oil, which crystallised from ether/petroleum ether. Yield 13.5 g, (42%). M.pt. = 165-70C.

Example 2.

Alternative preparation of 1,2 - diphenyl - 3 - oxo - 4 - n - butylpvrazolid - 4 butylpyrazolid - 4 - en - 5 - yl - 1' - (para - chlorobenzoyl) -2' - methyl - 5' methoxy - indol - 3' - yl - acetate.

Stage A: Preparation of Mixed Anhydride.

3.58 g (0.01 mole) of 1 - (para - chlorobenzoyl) - 2 - methyl - 5 - methoxyindol - 3 - yl - acetic acid were dissolved in 25 ml of dichloromethane, and cooled to below about 100 C. 1.205 g (0.01 mole) of pivaloyl chloride were added to the solution, with stirring and cooling to maintain the temperature below about 10"C.

The stirring and cooling was continued while 1.01 g (0.01 mole) of triethy]amine were slowly added. When the addition had been completed, the reaction mixture was allowed to warm to room temperature. This contained the desired mixed anhydride, of general formula XXV, which was however not isolated but used directly in the next stage of the process.

In place of pivaloyl chloride it is possible instead to use an equimolar amount of another sterically-encumbered acid chloride such as isovaleryl chloride.

Alternatively one can in place of a sterically-encumbered acid chloride use an equimolar amount of either a chloroformate such as ethyl chloroformate, phenyl chloroformate, benzyl chloroformate or toluyl chloroformate, or a sulphonyl chloride such as methylsulphonyl chloride, phenylsulphonyl chloride, benzylsulphonyl chloride or toluylsulphonyl chloride.

Stage B: Preparation of 1,2 - diphenyl - 3 - oxo - 4 - n - butylpyrazolid - 4en - 5 - yl - 1' - (para - chlorobenzoyl) - 2' - methyl - 5' - methoxy - indol - 3'yl - acetate.

3.08 g (0.01 mole) of 1,2 - diphenyl - 3,5 - dioxo - 4 - n - butylpyrazolidine and 1.01 g (0.01 mole) of triethylamine were added to the reaction product from Stage A above. This reaction mixture was warmed to about 40"C for 20 minutes; and after cooling, the formed organic solution was washed with 2 M hydrochloric acid, then with either 20% sodium carbonate solution or 2 M sodium hydroxide solution.

The organic solution was finally dried over magnesium sulphate and then the solvent removed under reduced pressure.

The residue contained the desired product, which after being recrystallised from the appropriate solvents was indistinguishable from the product of Example 1.

If the starting material employed in Stage B derived from the use in Stage A either of another sterically-encumbered acid chloride or of a sulphonyl chloride, the procedures set out in Stage B above should be followed. If however the starting material in Stage B derived from the use in Stage A of a chloroformate, then the triethylamine used in Stage B (or any other base) should be omitted.

Example 3.

Preparation of 1,2 - diphenyl - 3 - oxo - 4 - n - butylpyrazolid - 4 - en - 5 - yl (para - chlorobenzoyl ) - 2' - methyl - 5' - methoxy - indol - 3 - yl - acetate.

Stage A: Preparation of the symmetrical anhydride of 1 - ( para - chlorobenzoyl) - 2 - methyl - 5 - methoxy - indol - 3 - yl - acetic acid.

16.5 g (0.08 mole) of N,N'-dicyclohexyl-carbodiimide were added to a solution of 28.62 g (0. 08 mole) of 1 - (para - chloro - benzoyl) - 2 - methyl - 5methoxy - indol - 3 - yl - acetate acid in 150 ml of tetrahydrofuran. The resultant mixture was left at room temperature overnight. It was then filtered, the filtrate was evaporated to dryness, and the residue taken up in ethanol and recrystallised to yield 6.5 g of the desired anhydride.

Stage B: Preparation of of 1,2 - diphenyl - 3,5- dioxo - 4 - n - butylpyrazolid 4 - en - 5 - yl' - (para - chlorobenzoyl) - 2' - methyl - 5 - methoxy. indol - 3 - yl- acetate.

3.08 g (0.01 mole) of 1,2 - diphenyl - 3,5 - dioxo - 4 - n - butyl - pyrrazolidine were dissolved in 20 ml of 1 M sodium hydroxide. To this solution there was added a solution of 6.98 g (0.01 mole) of the anhydride obtained in Stage A above, in 20 ml of benzene. The two-phase mixture was shaken vigorously for 30 minutes, and then filtered to give the desired product, which after being recrystallised from the appropriate solvents was indistinguishable from the product of Example 1.

Formulation I - Composition in the form of tablets.

A tabletting mixture was made up by intimately mixing together the following ingredients: 1,2-diphenyl-3-oxo-4-n-butylpyrazolid-4-en-5-yl-1'- (para-chlorobenzoyl ) -2'-methyl-5'-methoxy-indol-3'-yl acetate 114 g spray-dried lactose 429 g dicalcium phosphate 429 g granular microcrystalline cellulose 20 g magnesium stearate 8g 1000 g This mixture was then compressed by conventional tabletting machinery to form 350 mg tablets, each containing 40 mg of 1,2 - diphenyl - 3 - oxo - 4 - n - butyI- pyrazolid - 4 - en - 5 - yl - 1' - (para - chlorobenzoyl) - 2' - methyl - 5' - methoxyindol - 3' - yl - acetate.

Formulation II - Composition in the form of capsules.

A mixture was made by intimately mixing together the following ingredients: 1,2-diphenyl-3 -oxo-4-n-butylpyrazolid-4-en-5-yl- 1'- (para chlorobenzoyl ) -2'-methyl-5'-methoxy-indol-3'-yl-acetate 200 g lactose B.P. 385 g maize starch 390 g magnesium stearate 25 g 1000 g The mixture was then filled into capsules in an amount of 200 mg per capsule, corresponding to 40 mg of 1,2 - diphenyl - 3 - oxo - 4 - n - butylpyrazolid - 4 - en 5 - yl - 1' - (para - chlorobenzoyl) - 2' - methyl - 5' - methoxy - indol - 3' - ylacetate per capsule.

Formulation III - Composition in the form of injectable suspension.

(para-chlorobenzoyl ) -2'-methyl-5'-methoxy-indol 1,2-diphenyl-3 oxo-n-butylpyrazolid-4-en-5-yl- 1'- 3'-yl-acetate 5.00% w/v polysorbate 80 0.15% w/v thiomersal 0,005% w/v sodium chloride 0.18% w/v disodium phosphate 1.00% w/v phosphoric acid qs to pH 6.07.0 water for injection to 100% w/v The 1,2 - diphenyl - 3 - oxo - 4 - n - butylpyrazolid - 4 - en - 5- yl - 1' (para - chlorobenzoyl) - 2' - methyl - 5' - methoxy - indol - 3' - yl acetate was suspended in the injection vehicle. The pH was adjusted with the phosphoric acid, if necessary, and the suspension made up to volume. The bulk suspension was autoclaved under predetermined conditions and aseptically transferred into pre-sterilised multidose ampoules.

Formulation IV - Composition in the form of suppositories.

1,2-diphenyl-3 -oxo-4-n-butylpyrazolid-4-en-5-yl- 1'- (para chlorobenzoyl )-2'-methyl-5'-methoxyindol-3'-yl-acetate 100 g suppository base* 970 g g *Artificial wax, formed of mono-, di- and tri-glycerides, trade name "Suppocire AM" and available from Arthur Chemicals Limited of Staines, Middlesex, England.

The 1,2 - diphenyl - 3 - oxo - 4 - n - butylpyrazolid - 4 - en - 5 - yl - 1' - (para chlorobenzoyl) - 2' - methyl - 5' - methoxy - indol - 3' - yl - acetate, in finely divided form, was added to the melted Suppocire AM suppository base and the mixture was stirred until evenly dispersed. The mixture was poured into 1 g suppository moulds, left to solidify and then demoulded.

Finally the evaluations given below indicate the freedom from undesirable sideeffects of the compound of this invention, and its excellent anti-inflammatory and/or analgesic properties.

EVALUATION OF THE STABILITY OF THE ESTER OF THE INVENTION.

In order first to evaluate the stability (or otherwise) of the compound of this invention in the gastro-intestinal tract, simulated gastric and intestinal fluids were prepared as follows:- Preparation of Simulated Gastric Fluid.

2 g of sodium chloride were mixed with 7.0 ml of concentrated hydrochloric acid and the mixture was then made up to a volume of 1000 ml with distilled water, yielding a simulated gastric fluid with a pH value of about 1.2.

Preparation of Simulated Intestinal Fluid.

6.8 g of monobasic potassium phosphate were dissolved in 250 ml of water, and to this was added a mixture of 190 ml of 0.2 M sodium hydroxide solution and 409 ml of water. The pH of the resulting solution was adjusted to 7.5 with 0.2 M sodium hydroxide, and the solution was then diluted to 1000 ml with distilled water, yielding a simulated intestinal fluid.

Method of evaluation.

100 mg of the compound under test, namely the compound of structural formula IV were suspended in 5 ml of each of the simulated fluids, and shaken for 16 hours at 370C. After this, the mixture was allowed to stand; and the supernatant liquid was spotted onto silica TLC plates, and developed in 90:10 chloroform/methanol. The mixture was then extracted with 5 ml of chloroform, and the chloroform-containing mixture was filtered through phase-separating papers, which only allow the chloroform solution to pass through. The chloroform solution was also spotted onto silica TLC plates and developed in 90:10 chloroform methanol.

The results of this procedure, carried out for both the simulated gastric and simulated intestinal fluids, show that negligible breakdown occurs in either of these fluids. This indicates that the compound of formula IV tested should be largely or wholly free from gastric disturbance effects when administered per os.

EVALUATION OF THE GASTRIC TOLERANCE IN RATS.

Gastric intolerance being the major problem encountered in the oral administration of known compounds possessing analgesic and anti-inflammatory properties, the therapeutic index (or safety factor) of such compounds is best demonstrated via the gastric tolerance test in rats.

Accordingly the compound of this invention, namely 1,2 - diphenyl TABLE I

Number of rats with gastric lesions Number of Haemorrhage Total U. test v.

Dose Number of normal (mucosa) (submucosa) incidence control U. test v.

Substance mg/kg rats used stomachs See Note (a) See Note (a) of lesions group Compound In.

Control Group 1 - 8 8 0% Compound Ph. 80 8 2 2+1+1 1+1 75% P=0.005 Compound Ph. 120 8 1 2+1 1+3 87% P=0.002 Control Group II (A) - 8 8 - - 0% Control Group II (B) - 8 7 1 - 12% Control Group II (C) - 14 14 - - 0% Compound In. 7 8 1 3+3 1 87% P < 0.003 Compound In. 10 8 - 2+1+1 4 100% P=0.001 Compound In. 10 16 2 1+4 6+3 87.5% P < 0.001 Compound IV 12.7 8 7 1 - 12% NS P < 0.005 Compound IV 18.1 8 7 1 - 12% P=0.032 P=0.001 Notes to Table I.

(a) The numbers within these single columns are divided into sub-groups to show, from left to right, increasing severity of the specified symptoms.

(b) "Compound Ph" is used in the table and hereinafter to mean 1,2-diphenyl3,5-dioxo-4-n-butylpyrazolidine.

(c) "Compound In" is used in the table and hereinafter to mean l-(para-chloro benzoyl) -2-methyl-5-methoxy-indol-3 -yl-acetic acid.

(d) "Compound IV" is used in the table and hereinafter to mean 1,2 - diphenyl3 - oxo - 4 - n - butylpyrazolid - 4 - en - 5 - yl - 1' - (para - chlorobenzoyl) - 2'methyl - 5' - methoxy - indol - 3' - yl - acetate.

The results set out in Table I above show that, as compared either with 1,2diphenyl - 3,5 - dioxo - 4 - n - butylpyrazolidine or else with 1 - (para - chloro henzoyl) - 2 - methyl - 5 - methoxy - indol - 3 - yl - acetic acid, the compound of the present invention, namely 1,2 - diphenyl - 3 - oxo - 4 - n - butylpyrazolid - 4en - 5 - yl - 1' - (para - chlorobenzoyl) - 2' - methyl - 5' - methoxy - indol - 3'yl - acetate, Compound IV, is remarkably non-irritant to the gastric mucosa.

EVALUATION OF DESIRED PHARMACOLOGICAL EFFECTS.

Three tests are conventionally employed to evaluate the efficacy of analgesic and anti-inflammatory drugs, and all three of these tests were used in evaluating Compound IV, in comparison with one of its parent compounds. Compound In. In all the tests, which are reported below, the groups of rats used consisted of 10 rats each.

Adjuvant Arthritis Test (Inclined Screen) in Rats.

Adjuvant disease was induced in several groups of rats. When adjuvant arthritis is induced in rats (normally with mycobacterial adjuvant) the adjuvant produces inflamed lesions in areas of the body remote from the injection site, after a delay of 10 to 15 days; though the inflammation starts to subside by the 30th day.

One group were left untreated as controls; other groups were treated by oral administration, once per day for 18 days, with various amounts of the parent compound, Compound In, used as the standard of comparison, and of the compound to be evaluated, Compound IV.

The compound was in each case case administered to the rat in solution in 1 part of polyoxyethylene oleic glyceride, made up to 5 parts with 1% aqueous gum tragacanth, to which 1% ethanol was also added when required to bring about dissolution. The amount of this solvent vehicle administered was generally 5 ml per kg of rat. The same vehicle (but without the active ingredient) was also administered to the control group of rats.

Treatment was continued for 18 days, during which time the rats were intermittently tested by means of the conventional Inclined Screen Test. Brieflv stated, this evaluates the grip function of the rat, by placing it upon a wire-mesh screen which is pivoted up through an angle of 90" from the horizontal to the vertical, and if necessary then indeed beyond. The angle at which the rat being tested loses its grip and drops off the screen is recorded. Other things being equal, the larger the angle of inclination at which the rat drops off the screen the more powerful is its grip upon it-and thus the less its grip-function has suffered from the arthritis-like adjuvant disease; or, perhaps more strictly the greater the alleviation of the pain of that disease by the compound under test.

One group of rats to serve as controls received only vehicle in the appropriate amount per day from day 0 > 18 (17 doses). A second group of rats received 1 mg/kg per day of Compound In for 18 days. A third group received 2 m/k < = per day of Compound In. A fourth group of rats received 3.6 mg/kg of Compound IV.

The molar equivalent of a dosage rate of 3.6 mg/kg of Compound IV is a dosage rate of approximately 2 mg/kg of Compound In, and therefore to the extent that the former shows itself superior to the latter, its use is thereby indicated.

The results obtained in this way are shown graphically in Figure 1 of the accompanying drawings, where the line of progressive deterioration of the grip function in terms of the angle of inclination of the screen against time is shown for each of the various compounds tested and for the controls.

From Figure 1 it may be concluded that Compound IV, when tested at the 3.6 mg/kg level (equimolar with 2 mg/kg of Compound In) is about equiactive with 0.5 times its molar amount of Compound I in the grip function test. Bearing in mind that Compound In is a highly potent anti-inflammatory analgesic, the relatively reduced activity of Compound IV is still very acceptable, and especially so as to the extent that its gastric tolerance and/or toxicity are less than Compound In.

Adjuvant Arthritis Test (Body Weight) in Rats.

The experimental detection of unknown side-effects is more difficult than the detection of gastric irritation; but their existence can be suggested by a decrease in body weight. Therefore in order to ensure that the results secured in the Inclined Screen Tests were not rendered unreliable by other side-effects of the compound under test, the body weights of the rats suffering from the experimentally-induced adjuvant disease were also determined each day, and the average weight of each group of rats were recorded in Figure 2 of the accompanying drawings.

From Figure 2 it may be concluded that the systemic effect upon body weight of Compound IV is essentially similar to that of 0.5 times its molar amount of Compound In.

Antipyretic Test Against Yeast-induced Ilyperthermia in Rats.

Using the conventional procedure, groups of rats were injected with yeast.

Immediately after injection various dosages of Compound IV and of the parent Compound In, 1 - (para - chlorobenzoyl) - 2 - methyl - 5 - methoxy - indol - 3yl - acetic acid, were administered orally to different groups of rats, apart from the control group who received only the vehicle.

The body temperature of all the rats was carefully monitored for a period of 8 hours following oral administration of the compound under study. The results are shown in Figure 3 of the accompanying drawings.

It will be noted that Compound IV was tested at 7.2 mg/kg and compared with Compound In at 2 mg/kg and also at 4 mg/kg. It is thus shown as having a dose-dependent action which at the 4 mg/kg dose level of Compound In is better than that of Compound In in the later post-medication hours.

Randall-Selitto Test in Rats.

The tests were conducted upon male rats with an average weight of 150 170 g. Using the conventional techniques, the various compounds under test, as identified below, were administered orally to the rats in each group (except a control group, which received only the vehicle) and. 30 minutes later, each of the rats was injected in one hind-paw with yeast.

In order to evaluate the effect of the treatment upon pain thresholds, pressure was applied both to the injected hind-paw and to the other, non-injected hind-paw.

The pain threshold was noted as the pressure at which the rat flinched; and the readings taken for each rat were expressed as the percentage of the pain threshold pressure for the injected hind-paw as against the pain threshold pressure for the non injected hind-paw.

These pain threshold percentages were determined at intervals of 3 hours, 5 hours, 7 hours and 24 hours after the injection. Statistics: t-test versus the control group. The results of this test are summarised in Table II below: TABLE II

Time from: yeast injection (drug intake) 3 h 5 h 7 h 24 h Substance, dose (3 1/2 h) (5 1/2 h) 7 1i2 h) Control group 49 * 2.1 50 i 3.7 46 * 3.4 48 * 4.5 Compound In 2mg/kg 58 * 4.0 61 + 5.8 74 + 3.4 52 + 3.3 P < 0 .001 Compound In 4mg/kg 64 + 3.6 60 + 4.7 65 + 5.8 60 * 3.6 P < 0.01 P < 0.02 Compound IV 7.2mg/kg 60 + 4.0 65 + 3.2 71 + 3.5 50 * 5.0 P < o.05 P < 0.01 P < 0.001 It will be seen from Table II above that Compound IV was tested at 7.2 mg/kg and compared with Compound In at 2 mg/kg and 4 mg/kg per day. From the results thus obtained it appears to have as good an analgesic effect as Compound In if not indeed somewhat better.

EVALUATION OF THERAPEUTIC INDEX.

From the relative gastric tolerances appearing from Table I and the relative anti-inflammatory activities deduced from Figure I it is possible to work out the relative separation of the anti-inflammatory activity from the gastric toxicity of 1,2diphenyl - 3 - oxo - 4 - n - butylpyrazolid - 4 - en - 5 - yl - 1' - (para - chlorobenzoyl)2' - methyl - 5' - methoxy - indol - 3' - yl - acetate (Compound IV) as compared with 1' - (para - chlorobenzoyl) - 2 - methyl - 5 - methoxy - indol - 3 - yl - acetic acid (Compound In), as shown in Table III below: TABLE III

Relative gain in safety versus the reference drug Reference drug to Relative anti- relative activity which the substance inflammatory Relative gastric Substance is compared activity (a) toxicity (b) relative gastric toxicity Compound IV Compound In #0.5 x molar < molar ~2 (a) Rat adjuvant arthritis: 17 daily oral doses.

(b) Acute (4 hour, single, oral dose) gastric tolerance in rats.

It can thus be seen that the gastric tolerance of Compound IV is significantly improved as compared with that of Compound In. Indeed, comparasion with the gastric effects of 5 mg/kg of Compound In indicates that the gain in gastric tolerance, on a molar basis, is greater than x 4. This indication justifies great interest in the analgesic potential of Compound IV.

Claims (33)

WHAT WE CLAIM IS:

1. A 4 - alkyl - 3,5 - dioxo - pyrazolidinyl - a - (2 - methyl - indol - 3 - yl)acetate of the formula:

which is a solid compound having a melting point of from 1650C to 1670C.

2. A compound as claimed in claim 1 when prepared substantially as hereinbefore described in any one of the specific Examples.

3. A process for the preparation of a compound of the formula IV defined in claim 1, which process comprises reacting 1,2 - diphenyl - 3,5 - dioxo - 4 - n - butylpyrazolidine of the formula:

with 1 - (para - chlorobenzoyl) - 2 - methyl - 5 - methoxy - indol - 3 - yl - acetic acid chloride of the formula:

the reaction being effected in an anhydrous inert organic solvent at a temperature up to the reflux temperature of the solvent, but for no more than 10 minutes at reflux temperature.

4. A process as claimed in claim 3, in which the inert organic solvent is either a substituted aromatic hydrocarbon or a halogenated aliphatic hydrocarbon.

5. A process as claimed in claim 4, in which the solvent is toluene or chloroform.

6. A process as claimed in any one of claims 3 to 5, in which the reaction is effected in the presence of a tertiary amine.

7. A process as claimed in claim 6, in which the tertiary amine is pytidine.

8. A process as claimed in any one of claims 3 to 7, in which the acid chloride of formula III is prepared by reacting a solution and/or suspension in an anhydrous inert solvent of the corresponding acid or a salt thereof with thionyl chloride.

9. A process as claimed in claim 8, in which the pyridine salt of the acid is employed.

10. A process as claimed in claim 1 or claim 9, in which the reaction with thionyl chloride is conducted at a temperature within the range of from 400C to 650C.

11. A process as claimed in any one of claims 8 to 10, in which the solvent used is the same as that defined in any one of claims 3 to 5.

12. A process as claimed in claim 11, in which the solvent is anhydrous dichloromethane, and the reaction is effected under reflux at a temperature of 40 41 C.

13. A process as claimed in any one of claims 8 to 12, in which the proportions of the reactants are substantially 1 mole of thionyl chloride per mole of acid and (when appropriate) per mole of salt forming base.

14. A process as claimed in any one of claims 8 to 13, in which the reaction with thionyl chloride is effected in the presence of a catalytic amount of N,N-dimethylformamide.

15. A process for the preparation of a compound of the formula IV defined in claim 1, which process comprises reacting a compound of the formula II defined in claim 3 with a mixed anhydride of the general formula:

wherein "Ayl" represents an alkyl group containing from 1 to 20 carbon atoms, an aryl group containing from 6 to 20 carbon atoms, an alkyl substituted aryl group containing from 7 to 20 carbon atoms or an aralkyl group containing from 7 to 20 carbon atoms; m is 0 or 1; and Q represents a carbon atom or when m is zero a sulphinyl group, in an anhydrous inert solvent for a reaction time of no more than 20 minutes.

16. A process as claimed in claim 15, in which the solvent used is the same as that defined in any one of claims 3 to 5.

17. A process as claimed in cla;m 15 or claim 16, in which the reaction is carried out in the presence of a tertiary amine.

18. A process as claimed in claim 17, in which the tertiary amine is triethylamine or pyridine.

19. A Drocess as claimed in any one of claims 15 to 18 in which the moved anhvdr;ds of general formula V is preDared by reacting 1 - (para - b1nrobenz1)- 2 - methyl - 5 - methoxy - indol - 3 - v 1 - acetic acid or a salt thereof, with a reactive organic chloride of general formula:

wherein Ayl, m and Q are as defined in claim 15, in the presence of a base.

20. A process as claimed in claim 19, in which the reaction between the acid and the reactive chloride is carried out in an anhydrous inert solvent.

21. A process as claimed in claim 20 > in which the solvent used is the same as that defined in any one of claims 3 to 5.

22. A process as claimed in any one of claims 19 to 21, in which the base is a tertiary amine.

23. A process as claimed in claim 22, in which the tertiary amine is triethylamine or pyridine.

24. A process as claimed in any one of claims 19 to 23, in which the solution of the mixed anhydride obtained is reacted with the compound of formula II without elimination of the base therefrom, and in the same reaction vessel.

25. A process for the preparation of a compound of the formula IV defined in claim 1, which process comprises reacting a compound of the formula II defined in claim 3 with a solution in a water-immiscible solvent of symmetrical 1 - (para - chlorobenzyl) - 2 - methyl - 5 - methoxy - indol - 3 - yl - acetic acid anhydride in the presence of a strong aqueous base, so that the reaction mixture forms a two-phase system, which is agitated at ambient or a near-ambient temperature not exceeding 300C for up to 30 minutes to yield the desired product of formula IV.

26. A process as claimed in claim 25, in which the strong aqueous base is aqueous sodium hydroxide.

27. A process as claimed in claim 25 or claim 26, in which the water-immiscible solvent is benzene, toluene, chloroform, dichloromethane or diethyl ether.

28. A process as claimed in any one of claims 25 to 27, in which the symmetrical acid anhydride is prepared by reacting the corresponding acid with a carbodiimide in solution in an anhydrous, non-hydroxylic and otherwise inert organic solvent at ambient or near-ambient temperature.

29. A process as claimed in claim 28, in which the carbodiimide is N,N'-dicyclohexyl-carbodiimide.

30 . A process for preparing the compound of formula IV substantially as hereinbefore described with reference to any one of the specific Examples.

31. A compound of formula IV when prepared by a process as claimed in anv one of claims 3 to 30.

32. A pharmaceutical composition comprising, as active ingredient, a compound of formula IV as claimed in claim 1 in association with a pharmaceutical vehicle.

33. A composition as claimed in claim 32 in the form of a unit dose containing from 10 mg to 700 mg of the active ingredient.