This invention is in the field of pharmaceutical agents exhibiting central nervous system (CNS) activities. More specifically, the invention relates to novel in¬ dole derivatives, to a process for their preparation, to pharmaceutical compositions comprising the compounds, and to methods of treating therewith. The novel indole derivatives are potentially suitable for counteracting (including preventing, relieving and curing) certain CNS disorders.

It has long been known that serotonin (5-hydroxy-tryp- tamine, hereinafter referred to as 5-HT) is a neuro- transmitter in the central nervous system. In particu¬ lar, over the last decade intensive pharmacological research directed to serotonergic neurotransmitter functions has taken place; It is now generally accept¬ ed that in the CNS there are at least five different subtypes of 5-HT binding sites or receptors, which ty¬ pes are identifiable as 5-HT _1A , 5- HT _1B , 5-HT- ' 5-HT ₂ and 5-HT ₃ , respectively. Differentiation of the 5-HT receptor subtypes is mainly based on their binding characteristics as characterized by specific radio li- gands. For example, the ligand 8-hydroxy-2-(di-n-pro- pylamino)tetralin (8-OH-DPAT) binds with high affinity to 5-HT- receptors, while another ligand, a 2,4(1H,3H)- quinazolinedione derivative (adopted name: ketanserin) exhibits high affinity for the 5-HT ₂ receptor subtype. It is worth noting that none of these synthetic ligands have any chemical resemblance whatsoever to the physio¬ logical binding partner, i.e. 5-HT. For a recent review

of 5-HT receptor- ligand interactions reference is ma¬ de to J.R. Fozard: Trends in Pharmacol.Sci. *J (1987), 501-506.

A variety of indole derivatives which are chemically closer related to 5-HT, such as RU 24969, which is a 3-(tetrahydropyridin-4-yl)-indole (Ann.Reports Med.Chem. 21 (1986), 42-43) have high affinity for 5-HT ₁ recogni¬ tion sites, but generally they show only limited capa¬ city to discriminate between the 5-HT _1A and 5-HT. re¬ ceptor subtypes.

It has now surprisingly been observed that compounds of the general formula (I) hereinafter bind with high affinity to 5-HT receptors and, furthermore, that some of the compounds exhibit substantially higher affinity for the 5-HT- _A subtype than many of the synthetic li¬ gands known heretofore. Based on their binding specifi¬ city these compounds may be classified as extremely po- tent and specific 5-HT- agonists and, as such, of po¬ tential utility for the treatment of disorders asso¬ ciated with serotonergic dysfunctions. Such dysfunc¬ tions may be involved in the impairment of thermoregu- lation, memory function, sleep and satiety control of the consumption of feed and/or beverage, which may in¬ clude alcohol. They may also play a role in the develop¬ ment of hypertension, hyperemesis, and of such mental states as depression, anxiety or psychosis.

Thus the present invention provides novel indole deri¬ vatives of the general formula (I):

(I)

wherein R1, R2, R3 and R4, which may be the same or different, each is selected from the group consisting of hydrogen; lower alkyl containing from 1 to 4 carbon atoms, in which one or more hydrogen atoms may be sub- stituted by halogen, e.g. CF„; OR 7 or -COOR7 in which R 7 is hydrogen, C, .-alkyl, aryl or aralkyl; halogen, e.g. chlorine; and the group

,8

-CO-N

\

R-

wherein R 8 and R9 may be the same or different, each representing hydrogen or lower alkyl containing from 1 to 4 carbon atoms; A represents a straight or branch¬ ed alkylene chain containing from 2 to 4 carbon atoms;

5 R is hydrogen or a straight or branched C. .--alkyl group; A 2 is a straight or branched saturated or unsa¬ turated hydrocarbon chain containing from 2 to 6 car- bon atoms; and R is selected from the group consisting of

wherein R and R , which may be the same or diffe¬ rent, each represents a C, ,,-alkyl group, or R and R 11 together represent a tetra- or pentamethylene chain, thereby forming together with the heterocyclic ring an azaspiro- decanedione/trione or -undecanedione/trione ring structure;

wherein R 12 and R13, which may be the same or different, each represents a C ₁ _ -alkyl group, or R 12 and R13 to¬ gether with their neighbouring carbon atoms form a 5- or 6-membered saturated or nonsaturated ring fused to the 5-membered ring;

wherein E is -CH ₂ ~, -CH ₂ -CH ₂ ~, -CH=CH-, -0- or -S- and the dotted line represents optional unsaturation; R 14 and R 15 , which may be the same or different, each repre- sents hydrogen, a C ₁ _ ₃ -alkyl group, or R 14 and R15 to¬ gether with their neighbouring carbon atoms form a cyc¬ lopropane, cyclobutane, cyclobutene, cyclohexane or cyclohexene ring fused to the bicyclic ring structure.

The compounds of formula I may be converted into any physiological acceptable salts thereof.

The invention includes within its scope all optical isomers of compounds of the general formula (I) and their mixtures including racemic mixtures thereof.

Compounds of the general formula (I) were tested for binding to 5-HT receptors and compared with known li¬ gands by the following procedure:

Rat brain tissue (as specified in the table hereinaf¬ ter) was homogenized using a Pblytron homogenizer. The final pellet was resuspended in 125 vol (tissue wet weight) of buffer.

In all assays incubation was carried out for 10 min at 37°C.

Labelling of the 5-HT-_, receptor was complicated by the fact that the available ligand 3H-5-HT is nonselec- tive. However, by inclusion of the 5-HT _1A selective agent 8-OH-DPAT in the assay, labelling of the 5-HT. receptor could be avoided and a relatively selective labelling of the 5-HT _1R receptor could be accomplished.

Detailed conditions for the receptor binding assay in vitro are tabulated below.

Receptor type 5-HT

Ligand H-80H-DPAT ^J H-5-HT "Η-ketanserin Tissue frontal cortex frontal cortex frontal cortex Hippocampus Hippocampus striatu

Buffer 50 rtiM Tris-Citrate 50 mM Tris-HCl 50 mM Tris-Citrate (pH 7.4, 30°C) (pH 7.4, 37°C) (pH 7.4, 30°C) 120 mM NaCl, 120 mM NaCl, 4 mM 120 mM NaCl, 4 mM 4 mM MgCl, CaCl ₂ , 4 mM MgCl ₂ MgCl ₂

Monspec. binding defined with 10 μM serotonin 10 μM serotonin 1 μM cyproheptadine

Level of nonspec binding 20-30% 20-25% 12-18%

The following results were obtained:

Receptor binding IC _5Q (nM)

The present invention also provides a process for pre¬ paring the compounds of the general formula (I) and physiologically acceptable salts thereof, which process is outlined hereinafter.

A compound of the general formula (II)

wherein R R , R , R , and A are as defined for for- mula (I), and Z represents R ,5 of formula (I) or a group convertible into hydrogen (during such an alkylation process the indole nitrogen and any free hydroxy groups in the benzene ring may be protected, e.g. by benzyla- tion), e.g. benzyl, may be reacted with a compound of

the general formula

L-A ² -R ⁶ (III)

wherein L represents a leaving group, of which halogen,

7 fi in particular bromine, is preferred, and A and R are defined as in connection with formula (I).

Many representatives of compounds of formula (II) are commercially available or known from the literature. Other compounds falling within the scope of formula (II) may be prepared by methods, which are generally analogous to those of said literature. General methods for the preparation of compounds of formula

L-A ² -R ⁶

are described in British Patent Publication 2,174,703A wherefrom by analogy alternative methods for establish- ing the

chain can be derived.

The reaction may conveniently be effected in an organic solvent, such as an aprotic solvent, e.g. acetonitrile or dimethylformamide in the presence of a base, for ex¬ ample potassium carbonate. When the leaving group L is different from iodine, being e.g. bromine, the reaction can be conducted in the presence of a salt of hydrogen iodide, e.g. potassium iodide. Usually, the reaction is completed with stirring at a temperature above am¬ bient. The reaction product obtained following, if ne¬ cessary, after the conversion of Z into hydrogen, may

be recovered by conventional means and, if desirable, subjected to purification, e.g. by suitable chromato- graphic procedures.

The purified reaction product may be converted into a physiologically acceptable salt. Such salts include acid addition salts formed with inorganic or organic acids, for example hydrochlorides, hydrobromides, sul¬ phates, nitrates, oxalates, phosphates, tartrates, ci- trates, fumarates, maleates, succinates, and sulphona- tes e.g. mesylates.

If desirable, selected salts may be subjected to fur¬ ther purification by recrystallization.

The compound of the invention, together with a conven¬ tional adjuvant, carrier, or diluent, and if desired in the form of a pharmaceutically-acceptable acid addi¬ tion salt thereof, may be placed into the form of phar- maceutical compositions and unit dosages thereof, and in such form may be employed as solids, such as tablets or filled capsules, or liquids, such as solutions, sus¬ pensions, emulsions/ elixirs, or capsules filled with the same, all for oral use, in the form of suppositori- es for rectal administration; or in the form of steri¬ le injectable solutions for parenteral (including sub¬ cutaneous) use. Such pharmaceutical compositions and unit dosage forms thereof may comprise conventional in¬ gredients in conventional proportions, with or without additional active compounds or principles, and such unit dosage forms may contain any suitable effective central nervous system ailment alleviating amount of the active ingredient commensurate with the intended daily dosage range to be employed. Tablets containing one (1) milligram of active ingredient or, more broad¬ ly, one (1) to thirty (30) milligrams, per tablet, are accordingly suitable representative unit dosage forms.

The compounds of this invention can thus be used for the formulation of pharmaceutical preparations, e.g., for oral and parenteral administration to mammals in¬ cluding humans, in accordance with conventional methods of galenic pharmacy.

Conventional excipients are such pharmaceutically ac¬ ceptable organic or inorganic carrier substances suit¬ able for parenteral or oral application which do not deleteriously react with the active compound.

Examples of such carriers are water, salt solutions, alcohols, polyethylene glycols, polyhydroxyethoxylated castor oil, gelatin, lactose, amylose, magnesium stea- rate, talc, silicic acid, fatty acid monoglycerides and diglycerides, pentaerythritol fatty acid esters, hydroxymethylcellulose and polyvinylpyrrolidone.

The pharmaceutical preparations can be sterilized and mixed, if desired, with auxilliary agents, such as lu¬ bricants, preservatives, stabilizers, wetting agents, emulsifiers, salt for influencing osmotic pressure, buffers and/or coloring substances and the like, which do not deleteriously react with the active compound.

For parenteral application, particularly suitable are injectable solutions or suspensions, preferably aqueous solutions with the active compound dissolved in poly- hydroxylated castor oil.

Ampoules are convenient unit dosage forms.

For oral application, particularly suitable are tablets, dragees, or capsules having talc and/or a carbohydrate carrier or binder or the like, the carrier preferably being lactose and/or corn starch and/or potato starch. A syrup, elixir or like can be used when a sweetened

vehicle can be employed. Generally, as to broader ran¬ ges, the compound of the invention is dispensed in unit dosage form comprising 0.05-100 mg in a pharmaceutical- ly-acceptable carrier per unit dosage.

A typical tablet which may be prepared by conventional tabletting techniques contains:

Active compound 1.0 mg Lactosum 67.8 mg Ph.Eur.

Avicel 31.4 mg

Amberlite IRP 88 1.0 mg

Magnesii stearas 0.25 mg Ph.Eur.

Due to their high degree of affinity for the 5-HT re¬ ceptors, the compounds of the invention are extremely useful in the treatment of central nervous system ail¬ ments or disorders, when administered in an amount effective for the alleviation, amelioration, or elimi- nation thereof. The important CNS activity of the com¬ pounds of the invention as mentioned above, along with a low toxicity, together presenting a most favorable therapeutic index. The compounds of the invention may accordingly be administered to a subject, e.g., a liv- ing animal body, including a human, in need of the sa¬ me for the treatment, alleviation, amelioration, ^v or elimination of an indication, associated with the cen¬ tral nervous system and the 5-HT receptors, which re¬ quires such psychopharmaceutical treatment, if desired in the form of a pharmaceutically acceptable acid addi¬ tion salt thereof (such as the hydrobromide, hydrochlo- ride, or sulfate, in any event prepared in the usual or conventional manner, e.g., evaporation to dryness of the free base in solution together with the acid), ordinarily concurrently, simultaneously, or together with a pharmaceutically-acceptable carrier or diluent, especially and preferably in the form of a pharmaceuti-

cal composition thereof, whether by oral, rectal, or parenteral (including subcutaneous) route, in an effec¬ tive psychopharmaceutical central nervous system ail¬ ment alleviating amount, and in any event an amount which is effective for the alleviation of such a cen¬ tral nervous system ailment due to their 5-HT receptor affinity. Suitable dosage ranges are 1-200 milligrams daily, 1-100 milligrams daily, and especially 1-30 mil¬ ligrams daily, depending as usual upon the exact mode of administration, form in which administered, the in¬ dication toward which the administration is directed, the subject involved and the body weight of the subject involved, and the preference and experience of the phy¬ sician or veterinarian in charge.

The following examples serve to illustrate the present invention.

EXAMPLE 1

1-(4-(1,3-Dioxo-4,7-etheno-l,3,3a,4,4a,6a,7,7a-octa- hydro-2H-cyclobut[f]isoindol-2-yl)butyl-l-amino)-2- (3-indolyl)-ethane, oxalate

A mixture of tryptamine (480 mg; 3.0 mmol), 2-(4-bromo- butyl)-1,3-dioxo-4,7-etheno-l,3 ,3a,4,4a ,6a,7,7a-octa- hydro- 2H-cyclobut[f]isoindole (Abou-Gharbia et al., J.Med.Chem. 1988, 31, 1382-1392) (1.0 g; 3.0 mmol), po- tassium carbonate (830 mg; 6.0 mmol) in acetonitrile (20 ml) was stirred and heated at 60°C for 40 h. The solvent was removed under reduced pressure. Ethyl ace¬ tate (30 ml) was added to the residue followed by wa¬ ter (30 ml) and the organic phase was separated. The aqueous phase was extracted with ethyl acetate (2 x 30 ml) and the combined organic phases were dried (MgSO.), filtered and evaporated to give an oil, which was flash-

chromatographed on silica gel 60 with ethyl acetate graduated to ethyl acetate/methanol 4:1. The title com¬ pound was isolated as the oxalate. M.p. 209- 210°C. MS (70 eV): m/z 416 (2%, M+l) 415 (2%, M ⁺ ), 285 (100), 256 (7), 214 (4), 130 (27).

EXAMPLE 2

1-(4-Phthalimidobutyl-l-amino)-2-(3-indolyl)-ethane, oxalate

A mixture of tryptamine (1.28 g; 8.0 mmol), N-(4-bromo- butyl)phthalimide (2.25 g; 8.0 mmol), potassium carbo- nate (2.2 g; 16 mmol) in acetonitrile (60 ml) was stirr¬ ed and heated at 60°C for 40 h. The solvent was remov¬ ed under reduced pressure. Ethyl acetate (75 ml) was added to the residue followed by water (75 ml) and the organic phase was separated. The aqueous phase was ex- tracted with ethyl acetate (2 x 75 ml) and the combin¬ ed organic phases were dried (MgSO.), filtered and eva¬ porated to give an oil, which wa& flashchromatographed on silica gel 60 with ethyl acetate. The title compound was isolated as the oxalate. M.p. 215- 218°C. MS (70 eV): m/z 362 (2%, M+l), 361 (1%, M ⁺ ), 231 (100), 202 (8), 160 (30), 130 (31).

EXAMPLE 3

l-(4-(Cis-4-cyclohexen-l,2-dicarboximido)butyl-l- amino)-2-(3-indolyl)-ethane, oxalate

A mixture of tryptamine (620 mg; 3.9 mmol), N-(4-bromo- butyl)-cis-4-cyclohexen-l,2-dicarboximide (1.1 g; 3.9 mmol), potassium carbonate (1.1 g; 8.0 mmol) in aceto¬ nitrile (30 ml) was stirred and heated at 60°C for 40

h. The solvent was removed under reduced pressure. Ethyl acetate (50 ml) was added to the residue follow¬ ed by water (50 ml) and the organic phase was separat¬ ed. The aqueous phase was extracted with ethyl acetate (2 x 50 ml) and the combined organic phases were dried (MgSO.), filtered and evaporated to give an oil, which was flashchromatographed on silica gel 60 with ethyl acetate. The title compound was isolated as the oxala¬ te. M.p. 166-167°C. ¹ H MR (DMSO + D ₂ 0, 400 MHz) 7.60- 6.95 (m, 5H), 5.85 (m, 2H), 3.35 (m, 2H), 3.20-3.10

(m, 4H), 3.10-3.00 (m, 2H), 3.00- 2.90 (m, 2H), 2.45- 2.10 (m, 4H), 1.50 (m, 4H).

EXAMPLE 4

l-(4-(7,9-Dioxo-8-azaspiro[4,5]decan-8-yl)butyl-l- amino)-2-(5-methoxy-3-indolyl)-ethane, oxalate

A mixture of 5-methoxytryptamine, hydrochloride (500 mg; 2.2 mmol), 8-(4-bromobutyl)-8-azaspiro[4,5]decane- 7,9-dione (665 mg; 2.2 mmol), potassium carbonate (550 mg; 40 mmol) in acetonitrile (20 ml) was stirred and heated at 60 C for 40 h. The solvent was removed under reduced pressure. Ethyl acetate (30 ml) was added to the residue followed by water (30 ml) and the organic phase was separated. The aqueous phase was extracted with ethyl acetate (2 x 30 ml) and the combined orga¬ nic phases were dried (MgSO.), filtered and evaporated to give an oil, which was flashchromatographed on si¬ lica gel 60 with ethyl acetate graduated to ethyl ace- tate/methanol (4:1). The title compound was isolated as the oxalate. M.p. 109.5-110°C. ¹ H NMR (DMSO + D ₂ 0, 400 MHz) 7.30-6.70 (m, 4H), 3.75 (s, 3H), 3.60 (m, 2H), 3.15-3.05 (m, 2H), 3.00-2.90 (m, 4H), 2.60 (s, 4H), 1.65-1.35 (m, 12H).

EXAMPLE 5

l-(4-(1,3-Dioxo-4,7-etheno-l,3,3a,4,4a,6a,7,7a-octa- hydro-2H-cyclobut[f]isoindol-2-yl)butyl-l-amino)-2- (5-methoxy-3-indolyl)-ethane, oxalate

A mixture of 5-methoxytryptamine, hydrochloride (500 mg; 2.2 mmol), 2-(4-bromobutyl)-l,3-dioxo-4,7-etheno- 1,3,3a,4,4a,6a,7,7a-oσtahydro-2H-cyclobut[f]isoindole (740 mg; 2.2 mmol), potassium carbonate (550 mg; 4.0 mmol) in acetonitrile (20 ml) was stirred and heated at 60 C for 16 h. The solvent was removed under reduc¬ ed pressure. Ethyl acetate (30 ml) was added to the re- sidue followed by water (30 ml) and the organic phase was separated. The aqueous phase was extracted with ethyl acetate (2 x 30 ml) and the combined organic pha¬ ses were dried (MgSO.), filtered and evaporated to give an oil, which was flashchromatographed on silica gel 60 with ethyl acetate graduated to ethyl acetate/metha- nol (4:1). The title compound was isolated as the oxa¬ late. M.p. 122-123°C. MS (70 eV): m/z 445 (1%, M ⁺ ), 285 (100), 256 (7), 174 (6), 160 (28), 146 (4).

EXAMPLE 6

4-(7,9-Dioxo-8-azaspiro[4,5]decan-8-yl)butyl-2-(5- methoxy-3-indolyl)ethyl-methylamine, oxalate

A mixture of 3-(2-methylaminoethyl)indole (1.0 g, 5.7 mmol), 8-(4-bromobutyl)-8-azaspiro[4,5]decane-7,9-dione (1.7 g, 5.7 mmol) and potassium carbonate (1.4 g, 10 mmol) was stirred and refluxed for 8 h and then concen- trated in vacuo. The residue was dissolved in water and extracted with ethyl acetate (three times). The combined organic phases were dried over MgSO. and eva-

porated to give an oil, which was flash chromatograph- ed on silica 60 with ethyl acetate. The product was dissolved in acetone and oxalic acid (500 mg in 5 ml acetone) added to precipitate the desired product. M.p. > 80°C, dec. MS (70 eV): m/z 396 (2%, M+l), 395 (M ⁺ , 1%), 265 (100%), 222 (17%), 180 (5%), 130 (30%).