HK1034456B - Use of 1-(3,3-diphenylpropionyl)-4-benzhydril piperazine in the treatemnt of pain - Google Patents

Description

Technical Field

The invention relates to a compound useful in treating conditions associated with calcium channel function. More specifically, the invention concerns a compound containing benzhydril and 6-membered heterocyclic moieties that is useful in treatment of pain.

Background Art

Native calcium channels have been classified by their electrophysiological and pharmacological properties as T, L, N, P and Q types (for reviews see McCleskey, E.W. et al. Curr Topics Membr (1991) 39:295-326, and Dunlap, K. et al. Trends Neurosci (1995) 18:89-98). T-type (or low voltage-activated) channels describe a broad class of molecules that transiently activate at negative potentials and are highly sensitive to changes in resting potential. The L, N, P and Q-type channels activate at more positive potentials (high voltage activated) and display diverse kinetics and voltage-dependent properties. There is some overlap in biophysical properties of the high voltage-activated channels, consequently pharmacological profiles are useful to further distinguish them. L-type channels are sensitive to dihydropyridine agonists and antagonists, N-type channels are blocked by the Conus geographus peptide toxin, ω-conotoxin GVIA, and P-type channels are blocked by the peptide ω-agatoxin IVA from the venom of the funnel web spider, Agelenopsis aperta. A fourth type of high voltage-activated calcium channel (Q-type) has been described, although whether the Q- and P-type channels are distinct molecular entities is controversial (Sather, W.A. et al. Neuron (1995) 11:291-303; Stea, A. et al. Proc Natl Acad Sci USA (1994) 91:10576-10580; Bourinet, E. et al. Nature Neuroscience (1999) 2:407-415). Several types of calcium conductances do not fall neatly into any of the above categories and there is variability of properties even within a category suggesting that additional calcium channels subtypes remain to be classified.

Biochemical analyses show that neuronal high voltage activated calcium channels are heterooligomeric complexes consisting of three distinct subunits (α₁, α₂δ and β) (reviewed by De Waard, M. et al. Ion Channels (1997) vol. 4, Narahashi, T. ed. Plenum Press, NY). The α₁ subunit is the major pore-forming subunit and contains the voltage sensor and binding sites for calcium channel antagonists. The mainly extracellular α₂ is disulfide-linked to the transmembrane δ subunit and both are derived from the same gene and are proteolytically cleaved in vivo. The β subunit is a nonglycosylated, hydrophilic protein with a high affinity of binding to a cytoplasmic region of the α₁ subunit. A fourth subunit, γ, is unique to L-type calcium channels expressed in skeletal muscle T-tubules. The isolation and characterization of γ-subunit-encoding cDNAs is described in U.S. Patent No. 5,386,025 which is incorporated herein by reference.

Recently, each of these α₁ subtypes has been cloned and expressed, thus permitting more extensive pharmacological studies. These channels have been designated α_1A-α_1I and α_1S and correlated with the subtypes set forth above. α_1A channels are of the P/Q type; α_1B represents N; α_1C, α'_1D, α_1F and α_1S represent L; α_1E represents a novel type of calcium conductance, and α_1G-α_1I represent members of the T-type family, reviewed in Stea, A. et al. in Handbook of Receptors and Channels (1994), North, R.A. ed. CRC Press; Perez-Reyes, et al. Nature (1998) 391:896-900; Cribbs, L.L. et al. Circulation Research (1998) 83:103-109; Lee, J.H. et al. Journal of Neuroscience (1999) 19:1912-1921.

U.S. Patent No. 5,646,149 describes calcium antagonists of the formula A-Y-B wherein B contains a piperazine or piperidine ring directly linked to Y. An essential component of these molecules is represented by A, which must be an antioxidant; the piperazine or piperidine itself is said to be important. The exemplified compounds contain a benzhydril substituent, based on known calcium channel blockers (see below). U.S. Patent No. 5,703,071 discloses compounds said to be useful in treating ischemic diseases. A mandatory portion of the molecule is a tropolone residue; among the substituents permitted are piperazine derivatives, including their benzhydril derivatives. U.S. Patent No. 5,428,038 discloses compounds which are said to exert a neural protective and antiallergic effect. These compounds are coumarin derivatives which may include derivatives of piperazine and other six-membered heterocycles. A permitted substituent on the heterocycle is diphenylhydroxymethyl. Thus, approaches in the art for various indications which may involve calcium channel blocking activity have employed compounds which incidentally contain piperidine or piperazine moieties substituted with benzhydril but mandate additional substituents to maintain functionality.

Certain compounds containing both benzhydril moieties and piperidine or piperazine are known to be calcium channel antagonists and neuroleptic drugs. For example, Gould, R.J. et al. Proc Natl Acad Sci USA (1983) 80:5122-5125 describes antischizophrenic neuroleptic drugs such as lidoflazine, fluspirilene, pimozide, clopimozide, and penfluridol. It has also been that fluspirilene binds to sites on L-type calcium channels (King, V.K. et al. J Biol Chem (1989) 264:5633-5641) as well as blocking N-type calcium current (Grantham, C.J. et al. Brit J Pharmacol (1944) 111:483-488). In addition, lomerizine, as marketed by Kenebo KK, is a known calcium channel blocker. A review of publications concerning lomerizine is found in Dooley, D., Current Opinion in CPNS Investigational Drugs (1999) 1:116-125.

ES 514 167 discloses certain compounds according to formula (I) below, including the compound of the invention. Such compounds are asserted to have vasodilatory activity.

The present invention is based on the recognition that the combination of a six-membered heterocyclic ring containing at least one nitrogen coupled optionally through a linker to a benzhydril moiety not only results in calcium channel blocking activity, but also enhanced specificity for N-type channels, thus making these compounds particularly useful for treating stroke and pain. By focusing on these moieties, compounds useful in treating indications associated with excessive calcium channel activity and combinatorial libraries that contain these compounds can be prepared.

Disclosure of the Invention

The invention relates to the use of 1-(3,3,-diphenylpropionyl-4-benzhydrid piperazine or a pharmaceutically active salt thereof in the manufacture of a medicament for treating pain. Although not claimed per se, 1-(3,3-diphenylpropionyl)-4-benzhydrid piperazine is referred to herein as "the compound of the invention." The compound of the invention is a benzhydril derivative of piperazine, with substituents which enhance the calcium channel blocking activity. The compound is a member of a group of compounds of the formula    wherein m is 0, 1 or 2;    wherein when m is 0, Z is O, when m is 1, Z is N, and when m is 2, Z is C;    Y is H, OH, NH₂, or an organic moiety of 1-20C, optionally additionally containing 1-8 heteroatoms selected from the group consisting of N, P, O, S and halo;    each 1¹ and 1² is independently 0-5;    1³ is 0 or 1;    each of R¹, R² and R³ is independently alkyl (1-6C), aryl (6-10C) or arylalkyl (7-16C) optionally containing 1-4 heteroatoms selected from the group consisting of halo, N, P, O, and S or each of R¹ and R² may independently be halo, COOR, CONR₂, CF₃, CN or NO₂, wherein R is H or lower alkyl (1-4C) or alkyl (1-6C);    n is 0 or 1;    X is a linker;    with the proviso that Y is not a tropolone, a coumarin, or an antioxidant containing an aromatic group and with the further proviso that if 1³ is 0, neither R¹ nor R² represents F in the para position.

Brief Description of the Drawings

• Figure 1 shows the structure of several known compounds which have been shown to exhibit calcium channel antagonistic activity.
• Figure 2 shows the structure of several known compounds which have been demonstrated to lack calcium channel blocking activity at acceptable concentrations.

Modes of Carrying out the Invention

The compounds of formula (I), exert their desirable effects through their ability to antagonize the activity of calcium channels.

While it is known that calcium channel activity is involved in a multiplicity of disorders, the types of channels associated with particular conditions is the subject of ongoing data collection. The association of, for example, N-type channels, as opposed to other types, in a specific condition would indicate that compounds of the invention which specifically target N-type receptors are most useful in this condition. Many of the members of the genus of compounds of formula (1) are likely to specifically target N-type channels. Other members of the genus may target other channels

Among the conditions associated in which blocking excessive calcium would be of therapeutic value are stroke, epilepsy, and chronic and acute pain. Other cardiovascular conditions include hypertension and cardiac arrhythmias. Calcium is also implicated in other neurological disorders such as migraine, epilepsy and certain degenerative disorders. These channels and receptors are also associated with conditions that are susceptible to treatment. Blockers of sodium channels, for example, are useful as local anesthetics, and in treating cardiac arrhythmias, as anticonvulsants, and in treating hyperkalemic periodic paralysis. Potassium channel blockers are useful in treating hypertension and cardiac arrhythmias; various other receptors are associated with psychoses, schizophrenia, depression, and apnea. Thus, the library of compounds of the invention is useful in standard screening techniques as a source of effective pharmaceutical compounds.

The compounds of formula (I) may be synthesized using conventional methods. Illustrative of such methods are Schemes 1 and 2:

Alternatively, a carboxylic acid containing the benzhydril moiety can be synthesized and then reacted with the piperazine (or piperidine) moiety and subsequently reduced. Under those circumstances, an ω-bromo carboxylic acid is refluxed with triphenylphosphine in the presence of methyl nitrile and then treated with lithium hexamethyldisilazide in a solvent such as THF. The resulting unsaturated carboxylic acid containing the two phenyl substituents is then reduced as shown in Scheme 1 with hydrogen on a palladium catalyst and then reacted with derivatized piperazine (or piperidine) to form the amide. The amide can then be reduced as shown above.

The compound of the invention may also be supplied as pharmaceutically acceptable salts. Pharmaceutically acceptable salts include the acid addition salts which can be formed from inorganic acids such as hydrochloric, sulfuric, and phosphoric acid or from organic acids such as acetic, propionic, glutamic, glutaric, as well as acid ion-exchange resins.

Utility and Administration

For use as treatment of animal subjects, the compound of the invention can be formulated as pharmaceutical or veterinary compositions. Depending on the subject to be treated, the mode of administration, and the type of treatment desired ― e.g., prevention, prophylaxis, therapy; the compounds are formulated in ways consonant with these parameters. A summary of such techniques is found in Remington's Pharmaceutical Sciences, latest edition, Mack Publishing Co., Easton, PA.

The compound of the invention may be used alone, as mixtures of two or more compounds of formula (1) or in combination with other pharmaceuticals. Depending on the mode of administration, the compounds will be formulated into suitable compositions to permit facile delivery.

Formulations may be prepared in a manner suitable for systemic administration or topical or local administration. Systemic formulations include those designed for injection (e.g., intramuscular, intravenous or subcutaneous injection) or may be prepared for transdermal, transmucosal, or oral administration. The formulation will generally include a diluent as well as, in some cases, adjuvants, buffers, preservatives and the like. The compounds can be administered also in liposomal compositions or as microemulsions.

For injection, formulations can be prepared in conventional forms as liquid solutions or suspensions or as solid forms suitable for solution or suspension in liquid prior to injection or as emulsions. Suitable excipients include, for example, water, saline, dextrose, glycerol and the like. Such compositions may also contain amounts of nontoxic auxiliary substances such as wetting or emulsifying agents, pH buffering agents and the like, such as, for example, sodium acetate, sorbitan monolaurate, and so forth.

Various Sustained release systems for drugs have also been devised. See, for example, U.S. Patent No. 5,624,677.

Systemic administration may also include relatively noninvasive methods such as the use of suppositories, transdermal patches, transmucosal delivery and intranasal administration. Oral administration is also suitable for compounds of the invention. Suitable forms include syrups, capsules, tablets, as in understood in the art.

For administration to animal or human subjects, the dosage of the compound of the invention is typically 0.1-100 µg/kg. However, dosage levels are highly dependent on the nature of the condition, the condition of the patient, the judgment of the practitioner, and the frequency and mode of administration.

The following examples are intended to illustrate but not to limit the invention.

Example 1 Correlation of Calcium Channel Blocking with the Presence of a Piperidine/Piperazine Ring

Antagonist activity was measured using nystatin patch recordings on human embryonic kidney cells either stably or transiently expressing rat α_1B+α_2b+β_1b channels with 5 mM barium as a charge carrier.

For transient expression, host cells, such as human embryonic kidney cells, HEK 293 (ATCC# CRL 1573) are grown in standard DMEM medium supplemented with 2 mM glutamine and 10% fetal bovine serum. HEK 293 cells are transfected by a standard calcium-phosphate-DNA coprecipitation method using the rat α_IB + β_1b + α₂δ N-type calcium channel subunits in a vertebrate expression vector (for example, see Current Protocols in Molecular Biology).

After an incubation period of from 24 to 72 hrs the culture medium is removed and replaced with external recording solution (see below). Whole cell patch clamp experiments are performed using an Axopatch 200B amplifier (Axon Instruments, Burlingame, CA) linked to an IBM compatible personal computer equipped with pCLAMP software. The external recording solution is 5-20 mM BaCl₂, 1 mM MgCl₂, 10 mM HEPES, 40 mM TEACI, 10 mM Glucose, 65 mM CsCl (pH 7.2). The internal pipette solution is 105 mM CsCl, 25 mM TEACl, 1 mM CaCl₂, 11 mM EGTA, 10 mM HEPES (pH 7.2). Currents are typically elicited from a holding potential of -100 mV to various test potentials. Data are filtered at 1 kHz and recorded directly on the hard drive of a personal computer. Leak subtraction is carried out on-line using a standard P/5 protocol. Currents are analyzed using pCLAMP versions 5.5 and 6.0. Macroscopic current-voltage relations are fitted with the equation I = {1/(1+exp(-(V_m-V_h)/S)} x G - (V_m-E_rev), where V_m is the test potential, V_h is the voltage at which half of the channels are activated, and S reflects the steepness of the activation curve and is an indication of the effective gating charge movement. Inactivation curves are normalized to 1 and fitted with I = (1/1+exp((V_m-V_h)/S) with V_m being the holding potential.

The results of three experiments were averaged. The structures of most of the compounds tested are shown in Figures 1 and 2. The compounds of Figure 1 showed effective blocking activity:

• Penfluridol has an IC50 of 5 µM; the block develops over 60-90 sec at 10 µM concentrations and is poorly reversible (pKa=9.0).

Pimozide shows an IC₅₀ of about 2-3 µM; the block develops in 90 sec at 10 µM and is completely reversible (pKa=7.32). More than 80% of the activity is blocked at 10 µM.

Haloperidol has an IC₅₀ of 90 µM and the block develops in less than 16 sec. It is reversible within 15 sec (pKa=8.3). At 10 µM concentrations, the block is about 10%.

Flunarizine has an IC₅₀ of <1 µM; the block develops over about 120 sec at 10 µM concentration and reverses over about 5 min. The block is 90-95% effective at 10 µM.

On the other hand, less activity was shown by prenylamine (IC₅₀ >40 µM); pridinol (IC₅₀ >400 µM); primidone (IC₅₀ >500 µM); and piperidolate (IC₅₀ >300 µM). Additional compounds which showed high values for IC₅₀ include bupivacaine, tolylpiperazine, piperine, trifluoromethylphenothiazine, morpholineacetophenone, morpholinebenzophenone and chloroethylpiperazine. As shown, the compounds of formula (1) which show activity comprise those wherein the CH attached to X is in turn bound to two phenyl rings and Y contains one phenyl ring, optionally substituted by halo.

Example 2 Synthesis of Illustrative Compounds of Formula (1) A. Synthesis of 6,6-Diphenyl Hexanoic Acid.

6-Bromohexanoic acid (7.08g, 36.3 mmole) and triphenylphosphine (10g, 38.2 mmole) were mixed in dry CH₃CN (40 ml), heated to reflux overnight and allowed to cool to RT. The solution was concentrated under reduced pressure to give a viscous gel. Approximately 75 ml of THF was added to the reaction mixture and the walls of the flask were scratched with a spatula to start crystallization. The resulting solid was filtered under vacuum, washed with THF and dried under reduced pressure and used without further purification.

This product (1.5g) was suspended in dry THF (10ml) and the flask purged with N₂ and cooled to -78°C. To the stirred reaction was added lithium hexamethyldisilazide (LiHMDS) (10ml, 1M in THF). The yellow solution was stirred at -78°C for 1h over which time the reaction darkened slightly. The cooling bath was removed and the reaction allowed to warm to RT. The reaction was kept at RT for 1h during which time the solution turned a dark red color and most of the solids went into solution. Benzophenone (0.54g in 3ml THF) was added to the reaction and allowed to react overnight. The yellow solution was concentrated under reduced pressure to give a yellow solid. The resulting solid was partitioned between ether and 10% HCl. The organic layer was washed with water (2x) and extracted with 10% NaOH (3x). The combined aqueous base fraction was acidified with conc. HCl to a pH of 4. The water layer was extracted with ether (3x) and the combined organic fractions dried over Na₂SO₄.

The ether was evaporated to dryness under reduced pressure to give a colorless oil which crystallized on standing to give a waxy solid, 6,6-diphenyl hex-5-enoic acid, which was dissolved in 30ml MeOH and mixed with 5% Pd-C and placed in a Parr hydrogenator. The reaction vessel was purged with hydrogen and pressurized to 60 PSIG and reacted at RT for 4h. The reaction mixture was sampled and analyzed by TLC. If the TLC when stained with KMnO₄ showed a positive test for alkenes the reaction mixture was resubjected to the reaction conditions. The solution was then filtered through a plug of celite and the methanol filtrate containing 6,6-diphenyl hexanoic acid was concentrated under vacuum.

B. Reaction with Substituted Piperazine.

6,6-Diphenylhexanoic acid (0.4 mmoles) was mixed with the desired N-alkylated piperazine (0.35 mmoles) in dry THF (7ml). EDC (0.5 mmoles) and DMAP (cat) were added and the mixture heated to 40°C with shaking overnight. The reaction was diluted with ethyl acetate and washed with water (4x) and 10% NaOH (3x) and dried over sodium sulfate and evaporated to dryness. The resulting residue was purified by column chromatography (silica gel, 1:1 hexane:EtOAc), and the products were characterized by HPLC-MS.

Piperazines used in the foregoing procedure include phenylpiperazine, benzylpiperazine, benzhydrilpiperazine, and piperazine substituted at the 1-position with BOC or Φ-CH=CH₂-.

The resulting compounds contain a carbonyl adjacent to the ring nitrogen of piperazine. These compounds are of formula (1) and exhibit calcium ion channel blocking activity.

C. Reduction of CO in X ¹ .

The compounds prepared in paragraph B were dissolved in dry THF (5ml) and reacted with LiAlH₄ (1M in THF) and allowed to react for 6h. The reactions were quenched with EtOAc (15ml) and extracted with water (5x) 10% NaOH (10x), brine (1x), dried over sodium sulfate and concentrated under reduced pressure. Most of the products at this stage were >80% pure. Those <80% were purified for running a short column (silica gel, 1:1 hex:EtOAc).

D. Preparation of Compounds of Formula (1) from Benzhydrylpiperazine Derivatives.

N-(Diphenylmethyl)piperazine (0.5 mmole) was dissolved in dry THF (10ml). To each reaction flask was added powdered K₂CO₃ and acid chloride of the formula Y'-CO-Cl (0.7 mmole). The reaction was stirred at RT for 2h and quenched with 105 NaOH (10ml) and extracted with EtOAc (10ml). The organic layer was washed with 10% NaOH (4x) and dried over sodium sulfate, concentrated, and purified by column chromatography (silica gel, 1:1 hex:EtOAc) to give the desired amide. Acyl halides used in this procedure included cyclohexyl COCl, ΦCOCl and ΦCH=CHCOCl.

To reduce the resulting amide, the above product was dissolved in dry THF (5ml) and reacted with LiAlH₄ (1M in THF) and allowed to react for 6h. The reaction was quenched with EtOAc (15ml) and extracted with water (5x) 10% NaOH (10x), brine (1x), dried over sodium sulfate and concentrated under reduced pressure. Most of the products at this stage were >80% pure. Those <80% were purified for running a short column (silica gel, 1:1 hex:EtOAc).

Example 3 Synthesis of Additional Compounds of Formula (1)

Following the general procedure described above in Reaction Schemes 1 and 2, the following compounds of formula (1) are synthesized as shown in Table A.

Example 4 Channel Blocking Activities of Various Compounds

Using the procedure set forth in Example 1, the compound of the invention (marked in Table 2 below with an asterisk) and various other compounds of formula (I) were tested for their ability to block N-type calcium ion channels. The results are shown in Tables 1-3, where IC₅₀ is given in µM (micromolar). Table 1 represents results for compounds of formula (1a) where Z is CH; Table 2 represents results for compounds of formula (1a) where Z is N; and Table 3 represents the results the results for compounds of formula (1b) where Z is N. In all cases, 1¹, 1² and 1³ are 0. Table 1

Formula (1a), Z is CH
				Ar		% reversibility
1		1		Φ	3	80
1		1		Φ	2	67

Table 2

Formula (1a), Z is N
				Ar		% reversibility
1		1		Φ	2-5	52
1		1		Φ	1-3	44
1		0	-	Φ	±10	83
1		1		Φ	±5	71
1		1			5-10	72
1		1		Φ	±5	66
1		1		Φ	2-3	58
1		1		Φ	5	78
1		1		Φ	2-6	84
1		1		Φ	2-5	39
1		0	-	Φ	3-5	13
1		1		Φ	±5	48
0	-	1		2Φ	2-5	40
0	-	1		2Φ	2-5	40
1		1	COCH	2Φ	±5	60
1	CO	1	COCH	2Φ	>20	90
1		1	CH	2Φ	2-5	40
1		1	CH	2Φ	2-5	40
1	CO	1	CH	2Φ	>50	-
0	-	1			±15	70
1		1		Φ	±50	0
1	CO	1		Φ	±50	85
1		1		Φ	±20	70
1	CO	0	-	Φ	±50	85
1	CO	1		Φ	±50	85
1	CO	1	CH	2Φ	>50	-
1	CO	1		Φ	±50	90
1		0	-	Φ	>50	90
1		1		Φ	±15	80
1		1		Φ	±20	80
1		0	-	Φ	>50	0
1		1		Φ	±50	0
1		1	CH	2Φ	>50	90
1		1		Φ	35	60
1		0	-	Φ	±9	11
1		1		Φ	±10	13
1		1	CH	2Φ	±23	28

Table 2

1		1		Φ	±5	20

Table 3

1		1	NHCH	cyclohexyl	3-4	62
1		1	NHCH	cyclohexyl	2-3	68
1		1		cyclohexyl	±1	5
1		1		cyclohexyl	5-10	66

Claims (1)

1. Use of 1-(3,3-diphenylpropionyl)-4-benzhydril piperazine or a pharmaceutically acceptable salt thereof in the preparation of a medicament for treating pain.