WO1996001656A1

WO1996001656A1 - 5-ht1a ligands

Info

Publication number: WO1996001656A1
Application number: PCT/GB1995/001395
Authority: WO
Inventors: Ian Anthony Cliffe; Allan Fletcher; Alan Chapman White
Original assignee: John Wyeth & Brother Limited
Priority date: 1994-07-08
Filing date: 1995-06-15
Publication date: 1996-01-25
Also published as: AU2892495A; GB9413772D0

Abstract

5-HT1A receptor binding agents which are piperazine derivatives of specified formula are radiolabelled with ?123I, 125I or 18¿F. The radiolabelled compounds are useful in pharmacological screening procedures, in positron emission tomography studies and in single photon emission computed tomography studies.

Description

5-HT A Ligands

This invention relates to certain 5-HTIA ligands which are radioiabelled with ¹²³I, ¹²⁵I OΓ ISR

Our copending PCT application No PCT/GB 94/00324 discloses certain 5-HTIA ligands radioiabelled with ³H or C.

The compounds of the present invention are piperazine derivatives of formula

(I)

and the pharmaceutically acceptable acid addition salts thereof.

In formula (I)

R is hydrogen or lower alkyl,

Rl is a mono- or bicyclic aryl or heteroaryi radical containing a radionuciide selected from the group consisting of ^ 125j ^ 18p

and X is a group of formula

-(CH2)_nCR²R³CONR4R5 (Ha) or

-A-NR⁶COR⁷ (lib)

where

n is one of the integers 1 or 2, R2 is hydrogen or lower alkyl,

R3 is an aryl radical or an aryl(lower)alkyl radical,

R4 is hydrogen or lower alkyl,

R5 is hydrogen, an alkyl group of 1 to 8 carbon atoms, cycloalkyl of 3 to 12 carbon atoms or cycloalkyl(lower)alkyl,

or R4 and R together with the nitrogen atom to which they are attached represent an azetidino, pyrrolidino, piperidino, hexahydroazepino, morpholino or piperazino ring which may be optionally substituted by lower alkyl, aryl or aryl(lower)alkyl,

A is an alkylene chain of 2 to 4 carbon atoms optionally substituted by one or more lower alkyl groups,

R6 is a mono or bicyclic heteroaryi radical

and R7 is hydrogen, lower alkyl, cycloalkyl, cycloalkenyl, cycloalkyl(lower)alkyl, aryl, aryl(lower)alkyl, heteroaryi, heteroaryl(lower)alkyl, a group of formula -NR8R9 [where R8 is hydrogen, lower alkyl, aryl or aryl(lower)alkyl and R9 is hydrogen, lower alkyl, -CO(lower)alkyl, aryl, COaryl, aryl(lower)alkyl, cycloalkyl or cycloalkyl(lower)alkyl or R8 and R9 together with the nitrogen atom to which they are both attached represent a saturated heterocyclic ring which may contain a further hetero atom] or a group of formula ORlO [where RlO is lower alkyl, cycloalkyl, cycloalkyl(lower)alkyl, aryl, aryl(lower)alkyl, heteroaryi or heteroaryl-(lower)alkyl].

The term "lower" as used herein means that the radical referred to contains 1 to 6 carbon atoms. Preferably such radicals contain 1 to 4 carbon atoms. Examples of "lower alkyl" radicals are methyl, ethyl, propyl, isopropyl, butyl, tert-butyl, pentyl and isopentyl.

Examples of cycloalkyl groups are cyclopentyl, cyclohexyl and cycloheptyl. A preferred example is cyclohexyl. Cycloalkyl groups include bicyclic, tricyclic and tetracyclic groups, e.g. adamantyl. Preferably the cycloalkyl group contains 3 to 12 carbon atoms.

When used herein "aryl" means an aromatic radical having 6 to 12 carbon atoms (e.g. phenyl or naphthyl) which optionally may be substituted by one or more substituents. Preferred substituents are lower alkyl, lower alkoxy (e.g. methoxy, ethoxy, propoxy, butoxy), halogen, halo(lower)alkyl (e.g. trifluoromethyl), nitro, nitrile, amido, (lower)alkoxycarbonyl, amino, (lower)alkylamino or di(lower)alkylamino substituents. Two substituents on the aromatic ring may be connected together to form another ring system.

When Rl is an aryl radical it is preferably a phenyl radical containing a substituent in the ortho position. A preferred example of Rl is o-(lower)alkoxyphenyl e.g. o- methoxyphenyl. Rl can also be, for example a 1-naphthyl radical optionally substituted in the 2 or 7 positions by, for example, (lower)alkoxy.

Preferred examples of aryl(lower)alkyl are benzyl and phenethyl in which the phenyl rings may be substituted by substituents as given above.

The term "heteroaryi" refers to an aromatic radical containing one or more hetero atoms (e.g. oxygen, nitrogen, sulphur) and which may be optionally substituted by one or more substituents. Examples of suitable substituents are given above in connection with "aryl" radicals. The heteroaryi radical may, for example, contain up to 12 ring atoms. For example the heteroaryi radical may be a monocyclic radical containing 5 to 7 ring atoms or a bicyclic radical containing 8 to 12 ring atoms. Preferably the hetero ring contains one or two hetero atoms selected from nitrogen, oxygen and sulphur.

When Rl is a heteroaryi radical it is preferably an optionally substituted pyrimidyl (particularly 2-pyrimidyl), optionally substituted pyridyl (e.g. pyrid-2-yl), optionally substituted indolyl (particularly indol-4-yl and indol-7-yl), optionally substituted pyrazinyl (particularly 2-pyrazinyl), optionally substituted quinolinyl or isoquinolinyl (particularly 1 -isoquinolinyl) or optionally substituted benzofuran (particularly 4 and 7- benzofuranyl) where the substituents are given above in connection with aryl radicals.

When R6 is a bicyclic heteroaryi radical both rings of the radical may contain hetero ring atoms or only one ring may contain a hetero atom or atoms. In the latter instance the radical R6 is connected to the rest of the molecule of formula (I) via the ring containing the hetero atom(s).

Examples of the heteroaryi radical R6 include monocyclic radicals containing one hetero atom, e.g. optionally substituted pyridyl (particularly 2-pyridyl), monocyclic radicals containing two hetero atoms, e.g. thiazolyl (particularly 2-thiazolyl) and bicyclic radicals containing one or two hetero atoms e.g. quinolinyl or isoquinolinyl (particularly 2- quinolinyl).

Unlabelled piperazine derivatives of formula (I) (i.e. compounds in which the R-- group does not contain a radionuciide) are disclosed, for example, in

GB 2230780A

GB 2230781 A

GB 2248836A and GB 2255337 A

and the present invention particularly provides 1231, 1 5j ₀r 8F labelled derivatives of the compounds of the above mentioned specifications in particular 23l, 125j _or 18p labelled derivatives of the preferred compounds:

N-tert-butyl-3-[4-(2-methoxyphenyl)piperazin-l-yl]-2-phenylpropanamide and its (S)- enantiomer

2,3,4,5,6,7-hexahydro-l-[4-[l-[4-(2-methoxyphenyl)-piperazinyl]]-2-phenyl]butanoyl- lH-azepine

(-)-(R)-2,3 ,4,5,6,7-hexahydro- 1 -[4-[4-(2-methoxyphenyl)piperazin- 1 -yl]-2- phenyl]butanoyl- lH-azepine

N-[2-[4-(2-methoxyphenyl)-l-piperazinyl]ethyl]-N-(2- pyridinyl)cyclohexanecarboxamide

(R)-N-(l-methyl-2-(4-(2-methoxyphenyl)-l-piperazinylethyl-N-(2- pyridinyl)cyclohexanecarboxamide

(R)-N-[ 1 -[2-( l-(4-(2-methoxy)phenyl)piperazinyl)]propyl]-N-(2- pyridinyl)cyclohexanecarboxamide

and their pharmaceutically acceptable acid addition salts.

The radioiabelled compounds of formula I may be prepared by methods known in the art. For example a precursor of a compound of formula I in which Rl does not contain a radionuclide may be reacted with a reagent containing 123l, 125j _or 18p [_Q gj_{ve a} compound of formula I. Examples of precursors are given in the above mentioned GB specifications. In some cases, a compound of formula I where Rl does not contain a radionuciide may be reacted directly with a reagent containing 123ι. 1 5j _or 18p

Methods available for substituting radioactive iodine into a molecule include exchange, nucleophilic substitution or electrophilic substitution of hydrogen or other groups (see, for example, R. M. Baldwin, Appl. Radiat. Isotop., 1986, 37, 817-21). In the replacement of aromatic hydrogen by electrophilic iodine, the electrophilic iodine can be generated by a variety of oxidising agents e.g. chloramine-T. Reactive groups which will react with the iodine include, for example, phenols, imidazoles and indoles.

In one preferred method of introducing radio iodine into a molecule an aminophenyl precursor is diazotised and the diazonium salt is reacted with labelled iodide (e.g. K 125j or K 1 3l). An example of this process is illustrated below:

(ΠD (IV)

(where R and X are as defined above and Rl is lower alkoxy, e.g. methoxy).

In another preferred method an aromatic nucleus is lithiated (e.g. with butyl lithium) and then treated with an alkyl tin chloride (e.g. tributyl tin chloride). The resulting stanyl compound is stable and can, if necessary, be converted to a desired precursor and purified before treatment with a labelled iodide (e.g. Na 123j ₀r Na 125l) in presence of an oxidising agent (e.g. hydrogen peroxide). See J. Med. Chem., 1989, 32, 1431 and J. Med. Chem., 1991, 34, 877. The process is illustrated below: B

(V) (VI)

(vπ)

(where X, R and Rl2 are as defined above). The compounds of formula VI may be converted to those of formula VII by processes analogous to those described in the above mentioned GB specifications. For example the compound of formula (VI) may be reacted with a compound of formula

Z-(CH2)_nCR²R3cONR⁴R5 (Villa) or

where n, A, R2, R3, R4_? R5_? R6 _and R7 are as defined above and Z is a leaving group such as halogen or an alkyl- or aryl- sulphonyloxy group.

In a preferred method for preparing the compounds of formula I in which the radionuciide is l^F a stanyl compound (which may be prepared as described above by lithiating an aromatic nucleus and then treating with an alkyl tin chloride e.g. tributyl tin chloride) is cleaved with radioiabelled elemental fluorine or acetyl hypofluorite (see M. J. Adam et al, Can. J. Chem., 1983^ 61, 658; M. J. Adam et al, J. Fluorine Chem., 1984, 25, 329-337; M. Namavari, 207th ACS National Meeting, San Diego 1994, MEDI 51). For example a compound of formula VII may be reacted with radioiabelled acetyl hypofluorite.

As an illustration of an alternative method of preparing the compounds of the invention a compound of formula (VI) may be converted to a compound of formula

(where R and R 2 are as defined above and Y is 25l, 1 3ι _or 18p) by processes analogous to those described above and the compound of formula IX may then be converted into a compound of formula I by processes analogous to those described in the above mentioned GB specifications.

The unlabelled derivatives of the compounds of formula I which are described in the above mentioned GB specifications are potent ligands at the 5-HT i A sites and are selective for the 5-HTIA site over other monoamine receptor sites (e.g. the D2, o and 5-HT2 sites) in the CNS. Accordingly the labelled compounds of formula I are useful in, for example, pharmacological screening procedures, in positron emission tomography (PET) studies and in single photon emission computed tomography (SPECT) studies.

5-HTiA^-antag°ⁿ--^sts °f formula (I) radioiabelled with 125j re useful as standard ligands for studying 5-HTι A binding in pharmacological test procedures. For example they may be used in a similar manner to [3H]-8-OH-DPAT in measuring the binding properties of other potential 5-HTIA ligands. They have the advantage that they may be used in defining 5-WT A ligands as agonists or antagonists at an early stage of screening i.e. before having to do more time-consuming functional studies.

Compounds of formula I radioiabelled with 8F are useful as radioligands in Positron Emission Tomography (PET) studies and compounds labelled with 1²³I are suitable for SPECT studies. Such studies are carried out in vivo in animals and more preferably in humans. The 18F serves as a positron source producing gamma rays. These rays are detected by the PET scanner and the resulting data is processed by computer so as to give information on the distribution of the radioligand in the living subject. The 123j j_s a gamma emitter and can therefore be detected by a similar technique.

The F or 1 3l radioiabelled compounds may be used in the PET or SPECT studies as for example, research tools or as a diagnostic aids. For example, the potency and duration of an orally or parenterally administered unlabelled drug, which is a 5-HTι A ligand, can be measured by following the displacement of the 123i or &F labelled compound from the brain of humans. Furthermore PET or SPECT studies using 18F or 3i radioiabelled 5-HTIA ligands can be used to study the distribution and nature of 5- HTi A receptor sites as a function of disease states (e.g. Alzheimer's Disease or depression) and hence can be used to diagnose such disease states.

The compounds may be prepared with a high specific activity and may be purified by semipreparative HPLC and rendered sterile before use if for human study.

The following examples illustrate the invention.

Example 1

l-(2-Methoxy-5-nitrophenyl)-4-[2-(2-pyridyIamino)ethyI]piperazine

l-(2-Methoxyphenyl)-4-[2-(2-pyridylamino)ethyl]piperazine (20 mmol) was dissolved in cone sulphuric acid at 0°C (50 ml), and the stirred solution was treated with sodium nitrate (22 mmol) portionwise over ten minutes. Once the addition was complete, the mixture was stirred for 3 hours, poured into ice-water (500 ml), and the solution made basic with KOH. The product was extracted into dichloroethane and afforded 4.0g of a yellow solid. This was a 1:1 mixture of the title compound and l-(2-methoxy-5- nitrophenyl)-4-[2-(2- { 5-nitropyridyl } amino)ethyl]piperazine.

Example 2

N-[2-[4-(2-Methoxy-5-nitrophenyl)-l-piperazinyI]ethyI]-N(-2- pyridyl)cyclohexane carboxamide

A dichloromethane solution of the mixture from Example 1 (2.4g in 20 ml) was stirred at 0°C under argon, and was heated with triethylamine (2 equivalents). Cyclohexanoyl chloride (1.0 equivalents) was added dropwise over two minutes and the mixture left to stir for a further forty minutes. The solvent was removed in vacuo, water (100 ml) added and the product was extracted into ethyl acetate (2 x 150 ml). After drying over anhydrous sodium sulphate, filtration and concentration gave 3Jg of a yellow solid comprising the title compound and N-[2-[4-(2-methoxy-5-nitrophenyl)-l- piperazinyl]ethyl]-N(-2-(5-nitropyridyl)cyclohexane carboxamide. The product was purified by chromatography to give the title compound as the hydrochloride, m.p. 103°C. C25H33N5O4.HCI.1/2H2O requires: C, 58.53; H, 6.88; N, 13.65%. Found: C, 58.60; H, 6.79; N, 13.55%. Example 3

N-[2-[4-(2-Methoxy-5-aminophenyl)-l-piperazinyI]ethyl]-N(-2- pyridyI)cyclohexane carboxamide

Raney nickel (about 50 mg) was added to a stirred ethanolic solution of the product of

Example 2(1. Og in 10 ml) at ambient temperature, and this was treated with the dropwise addition of hydrazine hydrate (0.2 lg, two equivalents). After stirring for 15 minutes, the solution was filtered through celite and concentrated in vacuo to afford 0.98g of title compound as a yellow solid.

C25H35N5O2.O.33 EtOH requires: C, 68.07; H, 8.23; N, 15.47%.

Found: C, 67.71; H, 8.23; N, 15.57%. lHnmr:(CDCl3): 8.50 (lH,dd): 7.92 (1H, dt): 7.43 (1H, d) 7.35 (lH,dd): 6.60 (lH,d): 6J0 (2H,m)

Example 4

N-[2-[4-(2-Methoxy-5-bromophenyI)-l-piperazinyI]ethyl]-N(-2- pyridyl)cyclohexane carboxamide

A solution of sodium nitrite (0.01 mole) is added to a solution of the product of Example 3 (0.01 mol) in sulphuric acid (1J ml 0.02 mol) in water ( 20 ml) keeping the temperature below 10°C. On completion of the addition the diazotised solution is added with stirring to a suspension of copper (1) bromide (0.011 mol) in cone, hydrobromic acid (1 ml) and water (5 ml at 0°). On completion of the addition,the reaction is stirred at room temperature for 30 min, diluted with water and basified with sodium hydroxide solution. The precipitate is washed with water or extracted with dichloromethanol to afford the desired product. Example 5

N-[2-[4-(2-Methoxy-5-tributylstannylphenyl)-l-piperazinyI]ethyl]-N(-2- pyridyI)cycIohexane carboxamide

A mixture of the product from Example 4 (1 equiv.) and tributyl-n-tin chloride (1J equiv.) in dry tetrahydrofuran is treated with butyl lithium (1.2 equiv. in hexane) at -78 °C. The reaction is stirred for 5-10 minutes at this temperature and quenched with saturated ammonium chloride solution. After allowing to warm to room temperature the tetrahydrofuran is evaporated under reduced pressure. The mixture is extracted with dichloromethane, dried over MgSO4 and evaporated. The desired product is purified by chromatography.

Example 6

N-[2-[4-(2-Methoxy-5-¹²³I or ¹²⁵I iodophenyI)-l-piperazinyI]ethyl]-N(-2- pyridyI)cyc!ohexane carboxamide

Aqueous hydrogen peroxide (lOμL, 30% w/v) is added to a mixture of lOμL of the tributyl stannyl compound from Example 5 (lmg/mL), lOOμL of 50% EtOH/H2θ, lOμL of IM HCl and 5μL of ¹²³I or ¹²⁵I sodium iodide (2-3mCi) in a sealed vial. The reaction is allowed to proceed for 1-2 hr at 20°C and terminated by the addition of 0.5ml sodium bisulphate (lOOmg/ml). The reaction mixture is made basic by the addition of sodium bicarbonate and extracted with ethyl acetate (3xlml). The combined organic layers are passed through a column of anhydrous sodium sulphate, (0.2cm x 5cm) and evaporated to dryness in a stream of nitrogen. The required product is separated from unreacted compound and other impurities by reversed phase HPLC. Example 7

N-[2-[4-(2-Methoxy-5-[¹⁸F] fluorophenyI)-l-piperazinyl]ethyl]-N(-2- pyridyl )cyc!ohexane carboxamide

The tin product of Example 5 (100 μmol) is dissolved in CFCI3 (20ml), cooled to -78° in a narrow glass reaction vessel while passing helium gas throughout the mixture. Approximately 60 μmol of

gas (l-5mCi) is passed into the reaction mixture at about 50ml/m. On completion of the addition, helium gas is passed through the solution to remove any unreacted fluorine. The product is then purified by HPLC and assayed.

Claims

1. A piperazine derivative of formula

(I)

or the pharmaceutically acceptable acid addition salts thereof.

which

R is hydrogen or lower alkyl,

Rl is a mono- or bicyclic aryl or heteroaryi radical containing a radionuciide selected from the group consisting of 123^ 125j and 18p

and X is a group of formula

-(CH2)_nCR²R3C0NR⁴R5 (Ha) or

-A-NR6COR7 (lib)

where

n is one of the integers 1 or 2,

R2 is hydrogen or lower alkyl,

R3 is an aryl radical or an aryl(lower)alkyl radical,

R4 is hydrogen or lower alkyl,

R5 is hydrogen, an alkyl group of 1 to 8 carbon atoms, cycloalkyl of 3 to 12 carbon atoms or cycloalkyl(lower)alkyl, or R and R5 together with the nitrogen atom to which they are attached represent an azetidino, pyrrolidino, piperidino, hexahydroazepino, morpholino or piperazino ring which may be optionally substituted by lower alkyl, aryl or aryl(lower)alkyl,

R6 is a mono or bicyclic heteroaryi radical

and R7 is hydrogen, lower alkyl, cycloalkyl, cycloalkenyl, cycloalkyl(lower)alkyl, aryl, aryl(lower)alkyl, heteroaryi, heteroaryl(lower)alkyl, a group of formula -NR8R9 [where R8 is hydrogen, lower alkyl, aryl or aryl(lower)alkyl and R9 is hydrogen, lower alkyl, -CO(lower)alkyl, aryl, COaryl, aryl(lower)alkyl, cycloalkyl or cycloalkyl(lower)alkyl or R8 and R9 together with the nitrogen atom to which they are both attached represent a saturated heterocyclic ring which may contain a further hetero atom] or a group of formula OR 10 [where RlO is lower alkyl, cycloalkyl, cycloalkyl(lower)alkyl, aryl, aryl(lower)alkyl, heteroaryi or heteroaryl-(lower)alkyl].

2. A compound as claimed in claim 1 which is a 123l, 125j ₀r 18F labelled derivative of a compound selected from the group consisting of

(-)-(R)-2,3,4,5,6,7-hexahydro-l-[4-[4-(2-methoxyphenyl)piperazin-l-yl]-2- phenyl]butanoyl- lH-azepine

(R)-N-( 1 -methyl-2-(4-(2-methoxyphenyl)- 1 -piperazinylethyl-N-(2- pyridinyl)cyclohexanecarboxamide (R)-N-[l-[2-(l-(4-(2-methoxy)phenyl)piperazinyl)]propyl]-N-(2- pyridinyl)cyclohexanecarboxamide

and their pharmaceutically acceptable acid addition salts.

3. A compound as claimed in claim 1 which is N-[2-[4-(2-methoxy-5-123ι ₀r 125j iodophenyl)- 1 -piperazinyl]ethyl]-N(-2-pyridyl)cyclohexane carboxamide.