Pyrrolophthalazines

Abstract: Therapeutically useful pyrrolo[2,1- a ]phthalazine derivatives of the formula: wherein R¹ and R² represent cycloalkyl, optionally substituted alkyl, alkenyl, alkynyl, aryl or heteroaryl, X represents ethylene or vinylene, R³ represents a group of the formula: -Y-CH₂-CH(OH)-CH₂-COOR⁵ wherein Y represents carbonyl or hydroxymethylene and R⁵ represents hydrogen or optionally substituted alkyl, or R³ represents a lactone ring and the symbols R⁴ represent hydrogen, halogen, optionally substituted alkyl, alkenyl, alkynyl, aryl or heteroaryl, or R⁶O- wherein R⁶ represents alkyl, aryl or arylalkyl and salts thereof, processes for their preparation and compositions containing them are described.

Description: The present invention relates to new therapeutically useful pyrrolo[2,1- a ]phthalazine derivatives, to processes for their preparation, to pharmaceutical compositions containing them, and to their use as pharmaceuticals. The pyrrolo[2,1- a ]phthalazine derivatives are the compounds of general formula I shown hereinafter in the present specification, wherein R¹ and R², which may be the same or, preferably, different, each represents a cycloalkyl group containing from 3 to 8 carbon atoms, or represents a straight- or branched-chain alkyl, alkenyl or alkynyl group containing up to 6 carbon atoms, which may be substituted by up to three halogen, preferably chlorine or fluorine, atoms, or represents an optionally substituted aryl, preferably phenyl, or heteroaryl group, X represents an ethylene or vinylene group, preferably a vinylene group in the E -configuration, R³ represents a group of the general formula:- -Y-CH₂-CH(OH)-CH₂-COOR⁵ II wherein Y represents a carbonyl or hydroxymethylene group and R⁵ represents a hydrogen atom or an optionally substituted alkyl group containing up to 6 carbon atoms, or R³ represents a lactone ring of general formula III shown hereinafter in the specification, and the symbols R⁴ may be the same or different and each represents a hydrogen or halogen (i.e. fluorine, chlorine, bromine or iodine) atom, or represents an optionally substituted straight- or branched-chain alkyl, alkenyl or alkynyl group containing up to 6 carbon atoms, or an optionally substituted aryl, preferably phenyl, or heteroaryl group, or a group of the formula R⁶O- wherein R⁶ represents a straight- or branched-chain alkyl group containing up to 6 carbon atoms, an aryl, e.g. phenyl, group or an arylalkyl group containing 1 or 2 carbon atoms in the alkyl moiety, e.g. benzyl or phenethyl, and pharmaceutically acceptable salts thereof when R⁵ represents a hydrogen atom, for example alkali metal, alkaline earth metal, ammonium and amine salts. It is to be understood that, where in this specification reference is made to compounds of formula I, it is intended to refer also where the context so permits to their pharmaceutically acceptable salts. Substituted alkyl, alkenyl or alkynyl groups within the definition of formula I unless otherwise specified preferably carry up to three substituents selected from halogen, preferably fluorine or chlorine, atoms and straight- or branched-chain alkoxy and alkylthio groups each containing up to 6 carbon atoms. Substituted aryl and heteroaryl groups and moieties within the definition of formula I preferably carry one or more substituents selected from halogen, preferably fluorine or chlorine, atoms, cycloalkyl and cycloalkenyl groups each containing from 4 to 8 carbon atoms, and optionally substituted straight- or branched-chain alkyl, alkenyl or alkynyl groups each containing up to 6 carbon atoms. As will be appreciated by those skilled in the art, the compounds of formula I may exist in various isomeric forms, for example diastereoisomeric forms, and all such forms and mixtures thereof are included within the scope of the invention. However, when R³ represents a group of formula II and Y represents a hydroxymethylene group the erythro-form is the preferred form. When R³ represents a group of formula III the preferred form has the hydroxy group attached to the lactone ring in the trans-configuration with respect to the rest of the molecule. Preferably the lactone ring of formula III is the isomer which has the (4 R ,6 S )-configuration when X represents vinylene and the (4 R ,6 R )-configuration when X represents ethylene. The compounds of formula I possess useful pharmacological properties, and some are useful as intermediates for the preparation of other therapeutically useful compounds, for example other compounds of formula I, for example as described later in this specification. For example they lower the concentrations of cholesterol and of low density lipoproteins in the blood. Thus they are of utility in the prevention or treatment of hypercholesterolaemic and hyperlipoproteinaemic states, of atherosclerosis, and of associated conditions such as angina, myocardial infarction, cerebral vascular occlusion, arterial aneurism, peripheral vascular disease, recurrent pancreatitis, xanthomas and fungal infections, e.g. candidiasis. Particularly important classes of compounds of formula I include those which exhibit one or more of the following features:- (i) one of R¹ and R², preferably R², represents an optionally substituted aryl or heteroaryl group, more particularly a substituted or unsubstituted phenyl group, for example a phenyl group substituted by a halogen, e.g. fluorine, atom, especially in the 4-position of the phenyl group, and the other one of R¹ and R², preferably R¹, represents a cycloalkyl group containing from 3 to 8 carbon atoms, or a straight- or branched-chain alkyl, alkenyl or alkynyl group containing up to 6 carbon atoms, which may be substituted by up to 3 halogen, preferably chlorine or fluorine, atoms, more particularly a straight- or branched-chain alkyl group, for example an isopropyl group; (ii) X represents a trans-vinylene group; (iii) R⁵ represents a hydrogen atom or a methyl or ethyl group; and/or (iv) the symbols R⁴ all represent hydrogen atoms; the other symbols being as hereinbefore defined and, more especially, their pharmaceutically acceptable salts, particularly the alkali metal, e.g.sodium, salts. Important compounds of formula I include the following:- 3:2 mixture of erythro- and threo-diastereoisomers of ethyl ( E )-3,5-dihydroxy-7-(3-isopropyl-1-phenylpyrrolo[2,1- a ]phthalazin-2-yl)hept-6-enoate; A 3:2 mixture of erythro- and threo-diastereoisomers of sodium ( E )-3,5-dihydroxy-7-(3-isopropyl-1-phenylpyrrolo[2,1- a ]phthalazin-2-yl)hept-6-enoate; B 3:2 mixture of erythro- and threo-diastereoisomers of ethyl ( E )-7-{1-(4-fluorophenyl)-3-isopropylpyrrolo[2,1- a ]phthalazin-2-yl}-3,5-dihydroxyhept-6-enoate; C ethyl erythro-( E )-7-{1-(4-fluorophenyl)-3-isopropylpyrrolo[2,1- a ]phthalazin-2-yl}-3,5-dihydroxyhept-6-enoate; CA ethyl threo-( E )-7-{1-(4-fluorophenyl)-3-isopropylpyrrolo[2,1- a ]phthalazin-2-yl}-3,5-dihydroxyhept-6-enoate; CB 3:2 mixture of erythro- and threo-diastereoisomers of sodium ( E )-7-{1-(4-fluorophenyl)-3-isopropylpyrrolo[2,1- a ]phthalazin-2-yl}-3,5-dihydroxyhept-6-enoate; D sodium erythro-( E )-7-{1-(4-fluorophenyl)-3-isopropylpyrrolo[2,1- a ]phthalazin-2-yl}-3,5-dihydroxyhept-6-enoate; DA sodium threo-( E )-7-{1-(4-fluorophenyl)-3-isopropylpyrrolo[2,1- a ]phthalazin-2-yl}-3,5-dihydroxyhept-6-enoate; DB methyl ( E )-7-{1-(4-fluorophenyl)-3-isopropylpyrrolo[2,1- a ]phthalazin-2-yl}-3,5-dihydroxyhept-6-enoate; E methyl ( E )-7-{1-(4-fluorophenyl)-3-isopropylpyrrolo[2,1- a ]phthalazin-2-yl}-3-hydroxy-5-oxohept-6-enoate; and F sodium ( E )-7-{1-(4-fluorophenyl)-3-isopropylpyrrolo[2,1-a]phthalazin-2-yl}-3-hydroxy-5-oxohept-6-enoate. G The letters A to G are allocated to the compounds for easy reference later in this specification. Compounds B and, especially, D are of particular importance, especially their erythro-components, e.g. compound DA. In tests, the compounds of formula I show good results as competitive inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase and as a consequence are inhibitors of cholesterol biosynthesis. For example, in tests compounds of formula I produced inhibition in rat hepatic microsomal HMG CoA reductase activity in vitro as shown in the following Table I. In the table the concentrations of the test compounds are expressed in micrograms/ml. Compounds of formula I and intermediates for their preparation may be prepared by the application or adaptation of known methods, for example methods similar to those described hereinafter in the following Examples and Reference Examples. Optionally the reactions may be carried out in an inert atmosphere. For example, according to a feature of the invention, compounds of formula I wherein R³ represents a group of formula II, Y represents a hydroxymethylene group, R⁵ represents an optionally substituted alkyl group containing up to 6 carbon atoms and R¹, R², R⁴ and X are as hereinbefore defined, are prepared by the reduction of compounds of general formula IV shown hereinafter in the specification, wherein R¹, R², R⁴ and X are as hereinbefore defined and R⁷ represents a group of the general formula:- -CH(OH)-CH₂-CO-CH₂-COOR⁸ V wherein R⁸ represents an optionally substituted alkyl group containing up to 6 carbon atoms. The reduction may be carried out by means of sodium borohydride, preferably in a lower alkanol, e.g. methanol, and preferably below room temperature, e.g. at or near to 0°C. It should be noted that by prolonging the reaction time transesterification can also occur, if the alkyl group in the said lower alkanol does not correspond to the value of R⁵ in the starting material of formula V. According to a further feature of the invention, compounds of formula I wherein R³ represents a group of formula II wherein R⁵ represents a hydrogen atom (R¹, R², R⁴ and X being as hereinbefore defined), or salts thereof, are prepared from the corresponding compounds wherein R⁵ represents an optionally substituted alkyl group containing up to 6 carbon atoms by hydrolysis by known methods, for example by reaction with an aqueous solution of the corresponding base to form the salt, optionally followed by acidification to form the parent carboxylic acid. According to a further feature of the invention, compounds of formula I wherein R³ represents a group of formula II, wherein Y represents a carbonyl group, R¹, R², R⁴, R⁵ and X being as hereinbefore defined, are prepared by the oxidation of the corresponding compounds wherein Y represents a hydroxymethylene group. The oxidation may be carried out by reaction with activated manganese dioxide, preferably at or near room temperature. According to a further feature of the invention, compounds of formula I wherein X represents an ethylene group, R¹, R², R³ and R⁴ being as hereinbefore defined, are prepared from corresponding compounds wherein X represents a vinylene group, by catalytic hydrogenation. Suitable catalysts include those containing palladium, e.g. palladium on charcoal or on calcium carbonate, or mixtures thereof. According to a further feature of the invention, compounds of formula I wherein R³ represents a lactone ring of formula III, R¹, R², R⁴, and X being as hereinbefore defined, are prepared by the cyclisation of the corresponding compounds wherein R³ represents a group of formula II, wherein Y represents a hydroxymethylene group and R⁵ represents a hydrogen atom. Sometimes the cyclisation occurs spontaneously but sometimes it is preferable to warm or to heat the starting material. Conveniently the heating is carried out in a solvent such as toluene at temperatures up to the boiling point. Optionally the reaction is carried out in the presence of a trace of an acid, e.g. glacial acetic acid. The pharmaceutically acceptable salts may be prepared from parent compounds of formula I by known methods, for example by reaction of compounds of formula I (wherein R³ represents a group of formula II in which R⁵ represents a hydrogen atom) and the appropriate base, e.g. an alkali metal hydroxide or carbonate, an alkaline earth metal oxide, ammonia or an amine, in a suitable solvent which is preferably water in the case of the preparation of alkali and alkaline earth metal salts and water or isopropanol in the case of amine salts. As well as being useful in themselves as pharmaceutically useful compounds, salts of the compounds of formula I wherein R³ represents a group of formula II wherein R⁵ represents a hydrogen atom are useful for the purpose of purification of the parent acids of formula I, for example by exploitation of the solubility differences between the salts and the parent acids in water and in organic solvents, by techniques well known to those skilled in the art. The parent acids of formula I can be regenerated from their salts by known methods, for example by treatment with a mineral acid, e.g. dilute hydrochloric acid, or an organic acid, e.g. acetic acid. As will be readily appreciated by those skilled in the art, the compounds of formula I, including their aforementioned isomers, may be separated by the application or adaptation of known methods. For example, diastereoisomeric forms may be separated by chromatography using selective adsorption from solution or from the vapour phase onto suitable adsorbents, and enantiomeric forms of compounds of formula I wherein R³ represents a group of formula II in which R⁵ represents a hydrogen atom may be separated by formation of salts with an optically active base, followed by separation of the obtained pair of diastereoisomers by, for example, fractional crystallisation from a suitable solvent system, followed by separate regeneration of the enantiomeric acids. Compounds of formula IV may be prepared by the application or adaptation of known methods, for example methods illustrated in the following Reference Examples. By the term "known methods" as used in this specification is meant methods used heretofore or known in the literature. For example, compounds of formula IV wherein X represents an ethylene group and R¹, R², R⁴ and R⁷ are as hereinbefore defined, may be prepared by the catalytic reduction of corresponding compounds wherein X represents a vinylene group, under conditions similar to those described hereinbefore for the preparation of compounds of formula I wherein X represents an ethylene group by catalytic reduction. Compounds of formula IV, wherein R¹, R², R⁴, R⁷ and X are as hereinbefore defined, may be prepared from compounds of the general formula VI shown hereinafter in the specification, wherein R¹, R², R⁴ and X are as hereinbefore defined, by reaction with a dianion of a compound of the general formula:- CH₃COCH₂COOR⁸ VII wherein R⁸ is as hereinbefore defined, generated in situ by treatment with two equivalents of strong base, for example sodium hydride and/or butyl lithium, in a suitable solvent such as tetrahydrofuran and at between -50°C and 0°C. Compounds of formula VI, wherein R¹, R², R⁴ and X are as hereinbefore defined, may be prepared by the oxidation of compounds of the general formula VIII shown hereinafter in the specification, wherein R¹, R², R⁴ and X are as hereinbefore defined, under conditions similar to those described hereinbefore for the preparation of compounds of formula I wherein Y represents a carbonyl group by oxidation. Compounds of formula VIII, wherein R¹, R², R⁴ and X are as hereinbefore defined, may be prepared by the reduction of compounds of the general formula IX shown hereinafter in the specification, wherein R¹, R², R⁴ and X are as hereinbefore defined and R⁹ represents an alkyl group of 1 to 4 carbon atoms, for example by means of di-isobutylaluminium hydride in a suitable solvent such as tetrahydrofuran and between -30°C and +30°C. Compounds of formula IX wherein X represents a vinylene group, and R¹, R², R⁴ and R⁹ are as hereinbefore defined, may be prepared from a compound of the general formula X shown hereinafter in the specification, wherein R¹, R² and R⁴ are as hereinbefore defined, by a Wittig reaction, or variant thereof, for example by reaction with the anion of a trialkyl phosphonoacetate (generated in situ by treatment with a strong base, for example sodium hydride), in a suitable solvent such as tetrahydrofuran and at between -20°C and 50°C. Compounds of formula IX wherein X represents an ethylene group, and R¹, R², R⁴ and R⁹ are as hereinbefore defined, may be prepared by the catalytic reduction of corresponding compounds wherein X represents a vinylene group, under conditions similar to those described hereinbefore for the preparation of compounds of formula I wherein X represents an ethylene group by catalytic reduction. Compounds of formula X, wherein R¹, R² and R⁴ are as hereinbefore defined, may be prepared from a compound of the general formula XI shown hereinafter in the specification, wherein R¹, R² and R⁴ are as hereinbefore defined and R¹⁰ represents an alkyl group of 1 to 4 carbon atoms, by a series of reactions similar to those described hereinbefore for the preparation of compounds of formula VI from compounds of formula IX. Compounds of formula XI, wherein R¹, R², R⁴ and R¹⁰ are as hereinbefore defined, may be prepared from a compound of the general formula XII shown hereinafter in the specification, wherein R¹ and R⁴ are as hereinbefore defined, by reaction with a compound of the general formula:- R²C≡CCOOR¹⁰ XIII wherein R² and R¹⁰ are as hereinbefore defined in a suitable solvent, for example acetonitrile or 1,3-dimethylimidazolin-2-one, at 10-100°C. Compounds of formula XII, wherein R¹ and R⁴ are as hereinbefore defined, may be prepared from a compound of the general formula XIV shown hereinafter in the specification, wherein R¹ and R⁴ are as hereinbefore defined, by reaction with a mixture of acetic acid and fluoroboric acid at 10-80°C. Compounds of formula XIV, wherein R¹ and R⁴ are as hereinbefore defined, may be prepared from a compound of the general formula XV shown hereinafter in the specification, wherein R⁴ is as hereinbefore defined, by reaction with a compound of the general formula:- R¹COZ XVI wherein R¹ is as hereinbefore defined and Z represents a halogen atom, preferably a chlorine atom, in the presence of an alkali metal cyanide in a suitable solvent, for example dichloromethane, at 0-50°C or, preferably, in the presence of a trialkylsilylcyanide, for example trimethylsilylcyanide, preferably in the presence of a catalytic amount of a Lewis acid, for example aluminium chloride, in a suitable solvent, for example dichloromethane, at 0-50°C. Intermediate compounds of general formulae VII, XIII, XV and XVI, wherein the various symbols are as hereinbefore defined, are known or can be prepared by the application or adaptation of known methods. The following Examples illustrate the preparation of compounds according to the present invention, and the Reference Examples illustrate the preparation of intermediates. In the presentation of the nuclear magnetic resonance ("NMR") spectra, "DMSO-d₆" means "deuterated dimethylsulphoxide", "s", "d", "t", "q" and "m" mean "singlet", "doublet", "triplet", "quartet" and "multiplet" respectively, "dd" means "doublet of doublets" and "dt" means "doublet of triplets", and the positions of the signals are given in parts per million from the tetramethylsilane signal. EXAMPLE 1 Compound A A stirred solution of ethyl ( E )-5-hydroxy-7-(3-isopropyl-1-phenylpyrrolo[2,1- a ]phthalazin-2-yl)-3-oxohept-6-enoate [0.32g; prepared as described in Reference Example 1(i)] in methanol (10ml) under an atmosphere of argon was cooled to 0°C and treated with sodium borohydride (15.2mg). The solution was stirred for 15 minutes and then it was poured into a mixture of ice and water (50ml). The resulting mixture was extracted with diethyl ether (100ml) and then with ethyl acetate (2 x 50ml). The combined extracts were dried over magnesium sulphate, evaporated and subjected to flash chromatography on silica gel, using as eluant a mixture of petroleum ether (b.p. 40-60°C) and diethyl ether (1:1 v/v), to give ethyl ( E )-3,5-dihydroxy-7-(3-isopropyl-1-phenylpyrrolo[2.1- a ]phthalazin-2-yl)hept-6-enoate (0.26g) in the form of a yellow gum. [NMR (in a mixture of CDCl₃ and D₂O): 1.28 (3H, t, J = 7Hz), 1.4-1.7 (2H, m), 1.52 (6H, d, J = 7Hz), 2.40-2.48 (2H, m), 3.8 (1H, septet, J = 7Hz), 4.08-4.14 (3H, m), 4.28-4.42 (1H, m), 5.31 and 5.36 [1H, two dd, J = 16Hz, 6Hz), 6.63 and 6.65 (1H, two dd, J = 16Hz, 1Hz), 7.22-7.64 (9H, m), 8.24 (1H, s)]. The NMR spectrum indicated that the product was a 3:2 mixture of the erythro- and threo-diastereoisomers. EXAMPLE 2 Compound B A solution of a 3:2 mixture of the erythro- and threo-isomers of ethyl ( E )-3,5-dihydroxy-7-(3-isopropyl-1-phenylpyrrolo[2,1- a ]phthalazin-2-yl)hept-6-enoate (0.26g; prepared as described in Example 1) and sodium hydroxide (22mg) in water (1.0ml) and methanol (10 ml) was stirred at the ambient temperature under an atmosphere of argon for 3 hours. The solution was then evaporated in vacuo and the residue was dried by treatment twice with methanol (2 x 10ml) and once with diethyl ether (10ml) followed each time by evaporation in vacuo , finally drying under high vacuum, to give sodium ( E )-3,5-dihydroxy-7-(3-isopropyl-1-phenylpyrrolo[2,1- a ]phthalazin-2-yl)hept-6-enoate (0.21g) in the form of a yellow solid, m.p. 209-215°C. [Elemental analysis:- C, 65.8; H, 6.1; N, 5.4; H₂O, 4.9%; calculated for C₂₇H₂₇N₂O₄Na:1.5H₂O:- C, 65.7; H, 6.13; N, 5.7; H₂O, 5.5%; NMR (in a mixture of DMSO-d6 and D₂O):-1.10-1.32 (2H, m), 1.5 (6H, d, J = 7Hz), 1.7-2.1 (2H, m), 3.50-3.86 (2H, m), 4.02-4.16 (1H, m), 5.28 and 5.36 (1H, two dd, J = 16Hz, 6Hz), 6.46 (1H, dd, J = 16Hz, 1Hz), 7.16-7.60 (8H, m), 7.78-7.88 (1H, m), 8.57 (1H, s)]. The NMR spectrum indicated that the product was a 3:2 mixture of the erythro- and threo-diastereoisomers. EXAMPLE 3 Compound C By proceeding in a manner similar to that described hereinbefore in Example 1, but using as the starting material the appropriate quantity of ethyl ( E )-7-{1-(4-fluorophenyl)-3-isopropylpyrrolo[2,1- a ]phthalazin-2-yl}-5-hydroxy-3-oxohept-6-enoate [prepared as described in Reference 2(g)], there was prepared ethyl ( E )-7-{1-(4-fluorophenyl)-3-isopropylpyrrolo[2,1- a ]phthalazin-2-yl}-3,5-dihydroxyhept-6-enoate, in the form of a yellow gum. EXAMPLE 4 Compound D By proceeding in a manner similar to that described hereinbefore in Example 2, but using as the starting material the appropriate quantity of ethyl ( E )-7-{1-(4-fluorophenyl)-3-isopropylpyrrolo[2,1- a ]phthalazin-2-yl}-3,5-dihydroxyhept-6-enoate (prepared as described in Example 3), there was prepared sodium ( E )-7-{1-(4-fluorophenyl)-3-isopropylpyrrolo[2,1- a ]phthalazin-2-yl}-3,5-dihydroxyhept-6-enoate, in the form of a yellow solid, m.p. 226-230°C (with decomposition). [Elemental analysis:- C, 61.2; H, 5.8; N, 5.2%; calculated:- C, 61.2; H, 5.9; N, 5.3%; NMR (in a mixture of DMSO-d6 and D₂O):- 1.1-1.32 (2H, m), 1.47 (6H, d, J = 7Hz), 1.8-2.16 (2H, m), 3.56-3.86 (2H, m), 4.04-4.20 (1H, m), 5.28 and 5.37 (1H, two dd, J = 16Hz, 6Hz), 6.46 (1H, dd, J = 16Hz, 1Hz), 7.15-7.50 (7H, m), 7.80-7.88 (1H, m), 8.56 (1H, s)]. The NMR spectrum indicated that the product was a 3:2 mixture of the erythro- and threo-diastereoisomers. EXAMPLE 5 Compound E A stirred solution of ethyl ( E )-7-{1-(4-fluorophenyl)-3-isopropylpyrrolo[2,1- a ]phthalazin-2-yl}-5- hydroxy-3-oxohept-6-enoate (3.98g) in methanol (120ml) under an argon atmosphere at 0-5°C was treated with sodium borohydride (243mg). After 3 hours the solution was allowed to warm to room temperature, and was then evaporated to small volume (20ml). The solution was treated with water (300ml), and extracted with a mixture of diethyl ether and ethyl acetate (2 x 250ml; 1:1 v/v). The combined extracts were dried over magnesium sulphate and evaporated, to give methyl ( E )-7-{1-(4-fluorophenyl)-3-isopropylpyrrolo[2,1- a ]phthalazin-2-yl}-3,5-dihydroxyhept-6-enoate, in the form of an orange foam (3.16g). EXAMPLE 6 Compound F A solution of methyl ( E )-7-{1-(4-fluorophenyl)-3-isopropylpyrrolo[2,1- a ]phthalazin-2-yl}-3,5-dihydroxyhept-6-enoate (3.16g) in anhydrous diethyl ether (100ml) was treated with activated manganese dioxide (12.61g) and the mixture was stirred at room temperature under an argon atmosphere with the exclusion of light for 18 hours. The mixture was then filtered through diatomaceous earth. The filter pad was washed with diethyl ether (2 x 150ml) and the combined filtrate and washings were concentrated to give an orange foam. This foam was subjected to flash chromatography on silica gel, using a mixture of diethyl ether and hexane (4:1 v/v) as eluant, to give methyl ( E )-7-{1-(4-fluorophenyl)-3-isopropylpyrrolo[2,1- a ]phthalazin-2-yl}-3-hydroxy-5-oxohept-6-enoate (1.61g), in the form of an orange foam. [NMR (in CDCl₃):- 1.59 (6H, d, J = 8Hz), 2.55 (4H, m), 3.45-4.15 (5H, m), 4.40 (1H, m), 5.82 (1H, d, J = 16Hz), 7.05-7.70 (8H, m), 7.85 (1H, d, J = 16Hz), 8.30 (1H, s)]. EXAMPLE 7 Compound G By proceeding in a manner similar to that described hereinbefore in Example 2, but using as the starting material the appropriate quantity of methyl ( E )-7-{1-(4-fluorophenyl)-3-isopropylpyrrolo[2,1- a ]phthalazin-2-yl}-3-hydroxy-5-oxohept-6-enoate (prepared as described in Example 6), there was prepared sodium ( E )-7-{1-(4-fluorophenyl)-3-isopropylpyrrolo[2,1- a ]phthalazin-2-yl}-3-hydroxy-5-oxohept-6-enoate, thought to be in a hydrated form, m.p.150-157°C (with decomposition). EXAMPLE 8 Compounds CA and CB Ethyl ( E )-7-{1-(4-fluorophenyl)-3-isopropylpyrrolo[2,1- a ]phthalazin-2-yl}-3,5-dihydroxyhept-6-enoate (1:1g; prepared as described in Example 3) was subject to h.p.l.c. on a silica gel column using a mixture of hexane, chloroform and methanol (85:15:1 v/v) as eluant, to give ethyl erythro-( E )-7-{1-(4-fluorophenyl)-3-isopropylpyrrolo[2,1- a ]phthalazin-2-yl}-3,5-dihydroxyhept-6-enoate (0.62g) in the form of a yellow gum [NMR (in a mixture of CDCl₃ and D₂O):- 1.28 (3H, t, J = 7Hz), 1.36-1.7 (8H, m), 2.43-2.49 (2H, m), 3.8 (1H, septet, J = 7Hz), 4.10-4.26 (3H, m), 4.3-4.45 (1H, m), 5.33 (1H, dd, J = 16Hz, 7Hz), 6.64 (1H, dd, J = 16Hz, 1Hz), 7.12-7.48 (7H, m), 7.57-7.65 (1H, m), 8.26 (1H, s)], and ethyl threo-( E )-7-{1-(4-fluorophenyl)-3-isopropylpyrrolo[2,1- a ]phthalazin-2-yl}-3,5-dihydroxyhept-6-enoate (0.27g) in the form of a yellow gum [NMR (in a mixture of CDCl₃ and D₂O):- 1.28 (3H, t, J = 7Hz), 1.38-1.78 (8H, m), 2.41-2.48 (2H, m), 3.8 (1H, septet, J = 7Hz), 4.10-4.26 (3H, m), 4.34-4.48 (1H, m), 5.38 (1H, dd, J = 16Hz, 6Hz), 6.67 (1H, dd, J = 16Hz, 1Hz), 7.12-7.45 (7H, m), 7.58-7.66 (1H, m), 8.26 (1H, s)]. EXAMPLE 9 Compound DA By proceeding in a manner similar to that described hereinbefore in Example 2, but using as the starting material the appropriate quantity of ethyl erythro-( E )-7-{1-(4-fluorophenyl)-3-isopropylpyrrolo[2,1- a ]phthalazin-2-yl}-3,5-dihydroxyhept-6-enoate (prepared as described in Example 8), there was prepared sodium erythro-( E )-7-{1-(4-fluorophenyl)-3-isopropylpyrrolo[2,1- a ]phthalazin-2-yl}-3,5-dihydroxyhept-6-enoate in the form of a yellow solid, m.p. 218-222°C (with decomposition) [NMR (in a mixture of DMSO-d6 and D₂O):- 1.1-1.56 (8H, m), 1.78-2.1 (2H, m), 3.54-3.85 (2H, m), 4.04-4.18 (1H, m), 5.31 (1H, dd, J = 16Hz, 6Hz), 6.46 (1H, dd, J = 16Hz, 1Hz), 7.09-7.50 (7H, m), 7.82-7.9 (1H, m), 8.58 (1H, s)]. EXAMPLE 10 Compound DB By proceeding in a manner similar to that described hereinbefore in Example 2, but using as the starting material the appropriate quantity of ethyl threo-( E )-7-{1-(4-fluorophenyl)-3-isopropylpyrrolo[2,1- a ]-phthalazin-2-yl}-3,5-dihydroxyhept-6-enoate (prepared as described in Example 8), there was prepared sodium threo-( E )-7-{1-(4-fluorophenyl)-3-isopropylpyrrolo[2,1- a ]-phthalazin-2-yl}-3,5-dihydroxyhept-6-enoate in the form of a yellow solid, m.p. 218-225°C (with decomposition) [NMR (in a mixture of DMSO-d6 and D₂O):- 1.1-1.38 (2H, m), 1.48 (6H, d, J = 7Hz), 1.74-2.06 (2H, m), 3.66-3.85 (2H, m), 4.05-4.20 (1H, m), 5.35 (1H, dd, J = 16Hz, 6Hz), 6.6 (1H, dd, J = 16Hz, 1Hz), 7.15-7.50 (7H, m), 7.80-7.88 (1H, m), 8.58 (1H, s)]. REFERENCE EXAMPLE 1 (a) A stirred solution of phthalazine (3.25g) and trimethylsilylcyanide (4.96g) in dichloromethane (40ml), containing a catalytic amount of anhydrous aluminium chloride (10mg), was treated dropwise with isobutyryl chloride (5.3g), keeping the temperature of the mixture below 32°C. The mixture was then stirred at the ambient temperature for 18 hours and then it was washed successively with water (50ml), aqueous hydrochloric acid (1N; 2 x 30ml), water (50ml), aqueous sodium hydroxide solution (1N; 2 x 30ml) and water (50ml) and then it was dried over magnesium sulphate. The solution was evaporated and the resulting residue was triturated with a mixture of petroleum ether (b.p. 40-60°C) and diethyl ether (3:1 v/v; 30ml). The solid which separated was collected and dried, to give 1-cyano-2-isobutyryl-1,2-dihydrophthalazine (5.56g) in the form of a colourless solid, m.p. 144-146°C. [Elemental analysis : C, 68.9; H, 5.61; N, 18.4%; calculated : C, 68.7; H, 5.77; N, 18.5%; NMR (in CDCl₃) : 1.16 (3H, d, J = 7Hz), 1.27 (3H, d, J = 7Hz), 3.55 (1H, septet, J = 7Hz), 6.66 (1H, s), 7.36-7.44 (2H, m), 7.50-7.58 (2H, m), 7.73 (1H, s); Mass spectrum (electron impact) m/z = 227]. (b) A stirred solution of 1-cyano-2-isobutyryl-1,2-dihydrophthalazine (12.6g) in glacial acetic acid (50ml) at 60°C was treated with an aqueous solution of fluoroboric acid (48% w/v; 50ml). After stirring for 15 minutes the mixture was chilled to 15°C and stirring was continued for a further period of 1 hour. The solid which separated was collected, washed thoroughly with diethyl ether, and dried, to give 1-amino-3-isopropyloxazolo[4,3- a ]phthalazinium tetrafluoroborate (15.58g) in the form of a bright yellow solid, m.p. 180-182°C. [NMR (in DMSO-d₆) : 1.42 (6H, d, J = 7Hz), 3.74 (1H, septet, J = 7Hz), 7.50-7.60 (1H, m), 7.85-8.05 (3H, m), 8.12 (2H, broad singlet), 8.99 (1H, s)]. (c) A mixture of 1-amino-3-isopropyloxazolo[4,3- a ]phthalazinium tetrafluoroborate (1.58g) and ethyl phenylpropiolate (1.74g) in 1,3-dimethylimidazolin-2-one (30ml) was maintained at 40°C for 19 hours and then the resulting brown solution was poured into water (200ml), and the mixture was extracted with a mixture of petroleum ether (b.p. 40-60°C) and diethyl ether (1:1 v/v; 3 x 200ml). The extracts were combined, dried over magnesium sulphate, and evaporated, and the resulting residue was subjected to flash chromatography on silica gel, using as eluant a mixture of petroleum ether (b.p. 40-60°C) and diethyl ether (19:1 v/v), to give ethyl 3-isopropyl-1-phenylpyrrolo[2,1- a ]phthalazine-2-carboxylate (0.72g) in the form of a yellow solid, m.p. 141-142°C. [Elemental anaysis:- C, 77.1; H, 6.24; N, 7.8%; calculated:-C, 77.1; H, 6.19; N, 7.8%; NMR (in CDCl₃) : 0.93 (3H, t, J = 7Hz), 1.57 (6H, d, J = 7Hz), 4.08 (2H, q, J = 7Hz), 4.35 (1H, septet, J = 7Hz), 7.23-7.50 (8H, m), 7.60-7.66 (1H, m), 8.35 (1H, s); Mass spectrum (electron impact) m/z = 358]. (d) A stirred suspension of lithium aluminium hydride (1.0g) in diethyl ether (40ml) at 0°C under an atmosphere of argon was treated with a solution of ethyl 3-isopropyl-1-phenylpyrrolo[2,1- a ]phthalazine-2-carboxylate (2.35g) in diethyl ether (60ml). The reaction mixture was stirred at 0°C for 2 hours and then it was quenched by dropwise treatment with ethyl acetate (50ml). After stirring for a further period of 1 hour it was treated with saturated aqueous sodium sulphate solution (100ml) and the resulting mixture was then extracted with ethyl acetate (3 x 100ml). The combined extract was dried over magnesium sulphate and evaporated and the resulting residue was subjected to flash chromatography on silica gel, using as eluant a mixture of petroleum ether (b.p. 40-60°C) and diethyl ether (3:1 v/v), to give 2-hydroxymethyl-3-isopropyl-1-phenylpyrrolo[2,1- a ]phthalazine (1.22g) in the form of a yellow gummy solid. [NMR (in a mixture of CDCl₃ and D₂O):- 1.57 (6H, d, J = 7Hz), 3.86 (1H, septet, J = 7Hz), 4.62 (2H, s), 7.25-7.53 (8H, m), 7.58-7.64 (1H, m), 8.3 (1H, s); Mass spectrum (electron impact) m/z = 316]. (e) A mixture of 2-hydroxymethyl-3-isopropyl-1-phenylpyrrolo[2,1- a ]phthalazine (1.22g) and activated manganese dioxide (18g) in diethyl ether (200ml) was stirred at the ambient temperature under an atmosphere of argon for 24 hours. The suspension was then filtered and the solid was extracted with diethyl ether (3 x 50ml). The extracts and filtrate were combined and evaporated, and the resulting residue was triturated with a mixture of petroleum ether (b.p. 40-60°C) and diethyl ether (8ml; 3:1 v/v), to give 3-isopropyl-1-phenylpyrrolo[2,1- a ]phthalazine-2-carboxaldehyde (0.88g) in the form of a yellow solid, m.p. 163-164°C. [Elemental analysis:- C, 80.4; H, 5.78; N, 8.8%; calculated:- C, 80.2; H, 5.77; N, 8.9%; NMR (in CDCl₃):- 1.52 (6H, d, J = 7Hz), 4.41 (1H, septet, J = 7Hz), 7.30-7.35 (3H, m), 7.42-7.50 (5H, m), 7.58-7.66 (1H, m), 8.34 (1H, s), 9.83 (1H, s); Mass spectrum (electron impact) m/z = 314]. (f) A stirred suspension of sodium hydride (80% w/w dispersion in oil; 243mg; 8.1mmol) in dry tetrahydrofuran (20ml) at -5°C was treated dropwise with triethyl phosphonoacetate (1.82g) under an atmosphere of argon, maintaining the temperature at -5°C. The resulting mixture was then stirred for 30 minutes and then it was treated with a solution of 3-isopropyl-1-phenylpyrrolo[2,1- a ]]phthalazine-2-carboxaldehyde (0.85g) in tetrahydrofuran (10ml). The reaction mixture was stirred at 0°C for 30 minutes and then at 60°C for 2 hours and then it was quenched by treatment with saturated aqueous ammonium chloride solution (20ml). The organic layer was separated and the aqueous phase was extracted with diethyl ether (2 x 20ml). The combined organic layers were dried over magnesium sulphate and evaporated, and the residue was triturated with a mixture of petroleum ether (b.p. 40-60°C) and diethyl ether (10ml; 3:1 v/v). The solid which separated was collected, to give ethyl ( E )-3-(3-isopropyl-1-phenylpyrrolo[2,1- a ]phthalazin-2-yl)propenoate (0.86g) in the form of a yellow solid, m.p. 158-159°C. [Elemental analysis:- C, 77.7; H, 6.31; N, 7.2%; calculated:- C, 78.1; H, 6.29; N, 7.3%; NMR (in CDCl₃):- 1.24 (3H, t, J = 7Hz), 1.55 (6H, d, J = 7Hz), 3.88 (1H, septet, J = 7Hz), 4.14 (2H, q, J = 7Hz), 5.46 (1H, d, J = 16Hz), 7.14-7.33 (3H, m), 7.38-7.60 (6H, m), 7.86 (1H, d, J = 16Hz), 8.26 (1H, s); Mass spectrum (electron impact) m/z = 384]. (g) A stirred solution of ethyl ( E )-3-(3-isopropyl-1-phenylpyrrolo[2,1- a ]phthalazin-2-yl)propenoate (0.86g) in dry tetrahydrofuran (25ml) at 0°C under an atmosphere of argon was treated dropwise with a solution of diisobutyl aluminium hydride in tetrahydrofuran (1M; 6.7ml). The reaction mixture was stirred at 0°C for 1 hour and then it was quenched by dropwise treatment with saturated aqueous sodium sulphate solution (25ml). The resulting mixture was partitioned between water (100ml) and diethyl ether (100ml), and the organic layer was separated. The aqueous layer was extracted with diethyl ether (2 x 100ml) and the combined organic layers were dried over magnesium sulphate and evaporated, to give ( E )-3-(3-isopropyl-1-phenylpyrrolo[2,1- a ]phthalazin-2-yl)propen-1-ol (0.96g), in the form of a yellow oil. [NMR (in a mixture of CDCl₃ and D₂O):- 1.54 (6H, d, J = 7Hz), 3.82 (1H, septet, J = 7Hz), 4.15 (2H, dd, J = 7Hz, 1Hz), 5.55 (1H, dt, J = 16Hz, 7Hz), 6.62 (1H, dt, J = 16Hz, 1Hz), 7.21-7.32 (3H, m), 7.35-7.62 (6H, m), 8.23 (1H, s)]. (h) A mixture of activated manganese dioxide (2.18g) and ( E )-3-(3-isopropyl-1-phenylpyrrolo[2,1- a ]phthalazin-2-yl)propen-1-ol (0.77g) in anhydrous diethyl ether (50ml) was stirred at the ambient temperature under an atmosphere of argon for 2 hours. The suspension was then filtered and the solid was washed thoroughly with diethyl ether (4 x 25ml). The filtrate was evaporated, to give a yellow oil, which was triturated with a mixture of petroleum ether (b.p. 40-60°C) and diethyl ether (5ml; 3:1 v/v) and the solid which separated was collected, to give ( E )-3-(3-isopropyl-1-phenylpyrrolo[2,1- a ]phthalazin-2-yl)propenal (0.56g) in the form of a yellow solid, m.p. 162-164°C. [Elemental analysis:- C, 81.5; H, 6.07; N, 8.2%; calculated:- C, 81.1; H, 5.92; N, 8.2%; NMR (in CDCl₃):- 1.6 (6H, d, J = 7Hz), 3.89 (1H, septet J = 7Hz), 5.83 (1H, dd, J = 16Hz, 8Hz), 7.13-7.68 (10H, m), 8.29 (1H, s), 9.41 (1H, d, J = 8Hz); Mass spectrum (electron impact) m/z = 340]. (i) A stirred suspension of sodium hydride (80% dispersion in oil, 112mg; 3.7mmol) in dry tetrahydrofuran (15ml) was treated with ethyl acetoacetate (0.43g) under an atmosphere of argon, maintaining the temperature at -10°C. The mixture was stirred for 30 minutes and then it was treated with a solution of butyl lithium in hexane (2.5M; 1.38ml), still maintaining the temperature at -10°C. The mixture was stirred for a further period of 20 minutes and then it was treated dropwise with a solution of ( E )-3-(3-isopropyl-1-phenylpyrrolo[2,1- a ]phthalazin-2-yl)propenal (0.56g) in tetrahydrofuran (5ml) at -10°C, and the resulting mixture was stirred at -10°C for 1 hour. The reaction mixture was then quenched at -10°C by treatment with saturated aqueous ammonium chloride solution (15ml). The mixture was allowed to warm to the ambient temperature and then it was partitioned between water (20ml) and diethyl ether (50ml). The organic layer was separated and the aqueous layer was extracted with diethyl ether (50ml). The combined organic layers were dried over magnesium sulphate, evaporated and subjected to flash chromatography on silica gel, using as eluant a mixture of petroleum ether (b.p. 40-60°C) and diethyl ether (3:1 v/v), to give ethyl ( E )-5-hydroxy-7-(3-isopropyl-1-phenylpyrrolo[2,1- a ]phthalazin-2-yl)-3-oxohept-6-enoate (0.33g) in the form of an orange oil. [NMR (in a mixture of CDCl₃ and D₂O):- 1.27 (3H, t, J = 7Hz), 1.54 (6H, d, J = 7Hz), 2.52-2.62 (2H, m), 3.44 (2H, s), 3.78 (1H, septet, J = 7Hz), 4.21 (2H, q, J = 7Hz), 4.50-4.62 (1H, m), 5.3 (1H, dd, J = 16Hz, 7Hz), 6.65 (1H, dd, J = 16Hz, 1Hz), 7.22-7.62 (9H, m), 8.24 (1H, s)]. REFERENCE EXAMPLE 2 By proceeding in a manner similar to that described hereinbefore in Reference Example 1 sections (c) to (i), but replacing the ethyl phenylpropiolate, used as a starting material in section (c), by the appropriate quantity of methyl 4-fluorophenylpropiolate, there were prepared, respectively:- (a) methyl 1-(4-fluorophenyl)-3-isopropylpyrrolo[2,1- a ]phthalazine-2-carboxylate in the form of a yellow solid, m.p. 148-149°C. [Elemental analysis:-C, 73.1; H, 5.3; N, 7.8%; calculated:- C, 72.9; H, 5.29; N, 7.7%; NMR (in CDCl₃):- 1.54 (6H, d, J = 7JHz), 3.62 (3H, s), 4.29 (1H, septet, J = 7Hz), 7.09-7.40 (7H, m), 7.56-7.65 (1H, m), 8.32 (1H, s)]; (b) 1-(4-fluorophenyl)-2-hydroxymethyl-3-isopropylpyrrolo[2,1- a ]phthalazine in the form of a yellow gum. [NMR (in a mixture of CDCl₃ and D₂O):-1.55 (6H, d, J = 7Hz), 3.85 (1H, septet, J = 7Hz), 4.6 (3H, s), 7.13-7.50 (7H, m), 7.58-7.65 (1H, m), 8.29 (1H, s)]; (c) 1-(4-fluorophenyl)-3-isopropylpyrrolo[2,1- a ]phthalazine-2-carboxaldehyde in the form of a yellow solid, m.p. 153-155°C. [Elemental analysis:-C, 76.0; H, 5.15; N, 8.2%; calculated:- C, 75.9; H, 5.16; N, 8.4%; NMR (in CDCl₃):- 1.56 (6H, d, J = 7Hz), 4.38 (1H, septet, J = 7Hz); 7.13-7.47 (7H, m), 7.58-7.67 (1H, m), 8.34 (1H, s), 9.87 (1H, s); Mass spectrum (electron impact) m/z = 332]; (d) ethyl ( E )-3-{1-(4-fluorophenyl)-3-isopropylpyrrolo[2,1- a ]phthalazin-2-yl}propenoate in the form of a yellow solid, m.p. 157-158°C. [Elemental analysis:-C, 74.5; H, 5.91; N, 6.7%; calculated:- C, 74.6; H, 5.76; N, 7.0%; NMR (in CDCl₃):- 1.26 (3H, t, J = 7Hz), 1.57 (6H, d, J = 7Hz), 3.88 (1H, septet, J = 7Hz), 4.17 (2H, q, J = 7Hz), 5.50 (1H, d, J = 16Hz), 7.14-7.44 (7H, m), 7.56-7.65 (1H, m), 7.87 (1H, d, J = 16Hz), 8.28 (1H, s); Mass spectrum (electron impact) m/z = 402]; (e) ( E )-3-{1-(4-fluorophenyl)-3-isopropylpyrrolo[2,1- a ]phthalazin-2-yl}propen-1-ol in the form of an orange oil. [NMR (in a mixture of CDCl₃ and D₂O):- 1.57 (6H, d, J = 7Hz), 3.82 (1H, septet, J = 7Hz), 4.12 (2H, dd, J = 6Hz, 1Hz), 5.54 (1H, dt, J = 16Hz, 6Hz), 6.62 (1H, dt, J = 16Hz, 1Hz), 7.10-7.44 (7H, m), 7.54-7.63 (1H, m), 8.24 (1H, s)]; (f) ( E )-3-{1-[4-fluorophenyl)-3-isopropylpyrrolo[2,1- a ]phthalazin-2-yl)propenal in the form of a yellow solid, m.p. 195-197°C. [Elemental analysis:-C, 77.0, H, 5.41; N, 7.6%; calculated:- C, 77.1; H, 5.34; N, 7.82%; NMR (in CDCl₃):- 1.59 (6H, d, J = 7Hz), 3.89 (1H, septet, J = 7Hz), 5.84 (1H, dd, J = 16Hz, 8Hz), 7.12-7.43 (7H, m), 7.58-7.79 (2H, m), 8.31 (1H, s), 9.44 (1H, d, J = 8Hz); Mass spectrum (electron impact) m/z = 358]; and (g) ethyl ( E )-7-{1-(4-fluorophenyl)-3-isopropylpyrrolo[2,1- a ]phthalazin-2-yl}-5-hydroxy-3-oxohept-6-enoate in the form of a yellow gum. [NMR (in a mixture of CDCl₃ and D₂O):- 1.28 (3H, t, J = 7Hz), 1.53 (6H, d, J = 7Hz), 2.60-2.68 (2H, m), 3.45 (2H, s), 3.78 (1H, septet, J = 7Hz), 4.21 (2H, q, J = 7Hz), 4.50-4.64 (1H, m), 5.3 [1H, dd, J = 16Hz, 7Hz), 6.67 (1H, dd, J = 16Hz, 1Hz), 7.12-7.44 (7H, m), 7.54-7.63 (1H, m), 8.24 (1H, s)]. The present invention includes within its scope pharmaceutical compositions which comprise at least one of the compounds of formula I or a pharmaceutically acceptable salt thereof in association with a pharmaceutically acceptable carrier or coating. In clinical practice the compounds of the present invention may be administered parenterally, for example topically, especially when treating certain fungal infections, but are preferably administered rectally or, more preferably, orally. Solid compositions for oral administration include compressed tablets, pills, powders and granules. In such solid compositions, one or more of the active compounds is, or are, admixed with at least one inert diluent such as starch, sucrose or lactose. The compositions may also comprise, as is normal practice, additional substances other than inert diluents, e.g. lubricating agents, such as magnesium stearate. Liquid compositions for oral administration include pharmaceutically acceptable emulsions, solutions, suspensions, syrups and elixirs containing inert diluents commonly used in the art such as water and liquid paraffin. Besides inert diluents such compositions may comprise adjuvants, such as wetting and suspending agents, and sweetening, flavouring, perfuming and preserving agents. The compositions according to the invention for oral administration also include capsules of absorbable material such as gelatin, containing one or more of the active substances with or without the addition of diluents or excipients. Preparations according to the invention for parenteral administration include sterile aqueous, aqueous-organic, and organic solutions, suspensions and emulsions. Examples of organic solvents or suspending media are propylene glycol, polyethylene glycol, vegetable oils such as olive oil and injectable organic esters such as ethyl oleate. The compositions may also contain adjuvants such as stabilising, preserving, wetting, emulsifying and dispersing agents. They may be sterilised, for example, by filtration through a bacteria-retaining filter, by incorporation in the compositions of sterilising agents, by irradiation or by heating. They may also be manufactured in the form of sterile solid compositions, which can be dissolved in sterile water or some other sterile injectable medium immediately before use. Solid compositions for rectal administration include suppositories formulated in accordance with known methods and containing one or more of the compounds of formula I or a pharmaceutically acceptable salt thereof. Compositions in the form of solutions or suspensions, if desired together with additives as described above, in vegetable or other greases, paraffin or other waxes or lacquers or creams, to be applied topically, are also included in the invention. The percentage of active ingredient in the compositions of the invention may be varied, it being necessary that it should constitute a proportion such that a suitable dosage shall be obtained. Obviously, several unit dosage forms may be administered at about the same time. The dose, the route of administration and the duration of the treatment employed will be determined by the physician, and depend upon the desired therapeutic effect and the condition of the patient. In the adult, the doses are generally between 0.1 and 50, preferably between 0.2 and 8.5, mg/kg body weight per day by oral administration. The following Examples illustrate pharmaceutical compositions according to the present invention. COMPOSITION EXAMPLE 1 No. 2 size gelatin capsules each containing:- 3:2 mixture of erythro- and threo-diastereoisomers of sodium ( E )-7-{1-(4-fluorophenyl)-3-isopropylpyrrolo-[2,1- a ]phthalazin-2-yl}-3,5-dihydroxy-hept-6-enoate 20 mg lactose 100 mg starch 60 mg dextrin 40 mg magnesium stearate 1 mg were prepared in accordance with the usual procedure. COMPOSITION EXAMPLE 2 No. 2 size gelatin capsules each containing:- sodium erythro-( E )-7-{1-(4-fluorophenyl)-3-isopropylpyrrolo-[2,1- a ]phthalazin-2-yl}-3,5-dihydroxy-hept-6-enoate 20 mg lactose 100 mg starch 60 mg dextrin 40 mg magnesium stearate 1 mg were prepared in accordance with the usual procedure. The active ingredient may be replaced by the appropriate quantity of any other of the compounds of formula I.

Claims: A pyrrolo[2,1- a ]phthalazine derivative of the general formula: wherein R¹ and R², which may be the same or different, each represents a cycloalkyl group containing from 3 to 8 carbon atoms, or represents a straight- or branched-chain alkyl, alkenyl or alkynyl group containing up to 6 carbon atoms which may be substituted by up to three halogen atoms or represents an optionally substituted aryl or heteroaryl group, X represents an ethylene or vinylene group, R³ represents a group of the general formula: -Y-CH₂-CH(OH)-CH₂-COOR⁵ (II) wherein Y represents a carbonyl or hydroxymethylene group and R⁵ represents a hydrogen atom or an optionally substituted alkyl group containing up to 6 carbon atoms, or R³ represents a lactone ring of the formula: and the symbols R⁴ may be the same or different and each represents a hydrogen or halogen atom or represents an optionally substituted straight- or branched-chain alkyl, alkenyl or alkynyl group containing up to 6 carbon atoms, or an optionally substituted aryl or heteroaryl group, or a group of the formula R⁶O- wherein R⁶ represents a straight-or branched-chain alkyl group containing up to 6 carbon atoms, an aryl group or an arylalkyl group containing 1 or 2 carbon atoms in the alkyl moiety, and pharmaceutically acceptable salts thereof when R⁵ represents a hydrogen atom. A compound according to claim 1 wherein R¹ and R² are different. A compound according to claim 1 or 2 wherein X represents a vinylene group in the E configuration. A compound according to any one of the preceding claims wherein halogen substituents on alkyl, alkenyl or alkynyl groups represented by R¹ or R² are chlorine or fluorine atoms. A compound according to any one of the preceding claims wherein optionally substituted alkyl, alkenyl or alkynyl groups carry up to three substituents selected from halogen atoms and straight- or branched-chain alkoxy and alkylthio groups each containing up to 6 carbon atoms, and substituted aryl and heteroaryl groups carry one or more substituents selected from halogen atoms, cycloalkyl and cycloalkenyl groups each containing from 4 to 8 carbon atoms, and optionally substituted straight- or branched-chain alkyl, alkenyl or alkynyl groups each containing up to 6 carbon atoms. A compound according to any one of the preceding claims wherein, when R³ represents a group of formula (II) and Y represents a hydroxymethylene group, the compound is in the erythro-form. A compound according to claim 1 which exhibits one or more of the following features: (i) one of R¹ and R² represents an optionally substituted aryl or heteroaryl group and the other represents a cycloalkyl group containing from 3 to 8 carbon atoms, or a straight- or branched-chain alkyl, alkenyl or alkynyl group containing up to 6 carbon atoms, which may be substituted by up to three halogen atoms; (ii) X represents a trans-vinylene group; (iii) R⁵ represents a hydrogen atom or a methyl or ethyl group; and/or (iv) the symbols R⁴ all represent hydrogen atoms. A compound according to claim 1 which is a pharmaceutically acceptable salt of a pyrrolo[1,2- a ]phthalazine derivative according to any one of claims 1 to 7 wherein R³ represents a group of general formula (II) in which Y is as defined in claim 1 and R⁵ represents a hydrogen atom. A compound according to claim 1 which is ethyl ( E )-3,5-dihydroxy-7-(3-isopropyl-1-phenylpyrrolo[2,1- a ]phthalazin-2-yl)hept-6-enoate, ethyl ( E )-7-{1-(4-fluorophenyl)-3-isopropylpyrrolo[2,1- a ]phthalazin-2-yl}-3,5-dihydroxyhept-6-enoate, methyl ( E )-7-{1-(4-fluorophenyl)-3-isopropylpyrrolo[2,1- a ]phthalazin-2-yl}-3,5-dihydroxyhept-6-enoate, sodium ( E )-3,5-dihydroxy-7-(3-isopropyl-1-phenylpyrrolo[2,1- a ]-phthalazin-2-yl)hept-6-enoate, sodium ( E )-7-{1-(4-fluorophenyl)-3-isopropylpyrrolo[2,1- a ]-phthalazin-2-yl}-3,5-dihydroxyhept-6-enoate, or a threo or erythro diastereoisomer thereof; or methyl ( e )-7-{1-(4-fluorophenyl)-3-isopropylpyrrolo[2,1- a ]phthalazin-2-yl}-3-hydroxy-5-oxohept-6-enoate or sodium ( E )-7-{1-(4-fluorophenyl)-3-isopropylpyrrolo[2,1- a ]phthalazin-2-yl}-3-hydroxy-5-oxohept-6-enoate. A process for the preparation of a pyrrolo[2,1- a ]-phthalazine derivative of general formula (I) depicted in claim 1 wherein R³ represents a group of formula (II), Y represents a hydroxymethylene group, R⁵ represents an optionally substituted alkyl group containing up to 6 carbon atoms and R¹, R², R⁴ and X are as defined in claim 1, which process comprises the reduction of a compound of the general formula: wherein R¹, R², R⁴ and X are as defined in claim 1 and R⁷ represents a group of the general formula: -CH(OH)-CH₂-CO-CH₂-COOR⁸ (V) wherein R⁸ represents an optionally substituted alkyl group containing up to 6 carbon atoms, optionally followed by one or more of the following steps: (a) the hydrolysis of a compound of general formula (I) wherein R³ represents a group of formula (II) wherein R⁵ represents an optionally substituted alkyl group containing up to 6 carbon atoms and R¹, R², R⁴ and X are as defined in claim 1 to obtain a compound of general formula (I) wherein R³ represents a group of formula (II) wherein R⁵ represents a hydrogen atom and R¹, R², R⁴ and X are as defined in claim 1; (b) the oxidation of a compound of general formula (I) wherein R³ represents a group of formula (II) wherein Y represents a hydroxymethylene group and R¹, R², R⁴, R⁵ and X are as defined in claim 1 to obtain a compound of general formula (I) wherein R³ represents a group of formula (II) wherein Y represents a carbonyl group and R¹, R², R⁴, R⁵ and X are as defined in claim 1; (c) the reduction of a compound of general formula (I) wherein X represents a vinylene group and R¹, R², R³ and R⁴ are as defined in claim 1 to obtain a compound of general formula (I) wherein X represents an ethylene group and R¹, R², R³ and R⁴ are as defined in claim 1; d) the cyclization of a compound of general formula (I) wherein R³ represents a group of formula (II) wherein Y represents a hydroxymethylene group and R⁵ represents a hydrogen atom, and R¹, R², R⁴ and X are as defined in claim 1, to obtain a compound of general formula (I) wherein R³ represents a lactone ring of formula: and R¹, R², R⁴ and X are as defined in claim 1; e) the conversion of a compound of general formula (I) wherein R³ represents a group of general formula (II) wherein R⁵ represents a hydrogen atom into a pharmaceutically acceptable salt. A pharmaceutical composition which comprises, as active ingredient, a pyrrolo[2,1- a ]phthalazine derivative of general formula (I) as defined in claim 1, or a pharmaceutically acceptable salt thereof, in association with a pharmaceutically acceptable carrier or coating.

Inventors: ASHTON MICHAEL JOHN, BRIDGE ANDREW WILLIAM, DRON DONALD IAN, FENTON GARRY, LYTHGOE DAVID JOHN, NEWTON CHRISTOPHER GREGORY, RIDDELL DAVID, SMITH CHRISTOPHER, STUTTLE KEITH ALFRED JAMES, ASHTON, MICHAEL JOHN, BRIDGE, ANDREW WILLIAM, DRON, DONALD IAN, FENTON, GARRY, LYTHGOE, DAVID JOHN, NEWTON, CHRISTOPHER GREGORY, RIDDELL, DAVID, SMITH, CHRISTOPHER, STUTTLE, KEITH ALFRED JAMES
Applicants: MAY & BAKER LTD, MAY & BAKER LIMITED
Application year: 1988
Main classification: C07D487
IPC codes: C07D487, A61P9, A61K31, A61P43