This application is divided out of Indian Patent Application No.424/KOLNP/2004
dated 31/03/2004
BACKGROUND OF THE INVENTION
5 Pain has been characterized and described in various different ways in the
literature. For example, pain can be intense, localized, sharp or stinging, and/or dull,
aching, diffuse or burning in nature.' Pain can also be centralized, taking place in the
dorsal horn of the spinal cord, the brain stem and brain, or peripheral, taking place at
the injury site and surrounding tissue. Pain that occurs for extended periods of time
10 (i.e., persistent) is generally referred to as chronic pain. Examples of chronic pain
include neuropathic pain, inflammatory pain, and cancer pain. These pains can be
related to hyperalgesia and/or allodynia, where hyperalgesia refers to an increase in
sensitivity to a typically noxipus stimulus and allodynia refers to an increase in
sensitivity to a typically non-noxious stimulus.
15 A type of chronic pain that currently lacks adequate pharmacological
treatment is neuropathic pain. Neuropathic pain is generally thought of as a chronic
pain caused by damage to or pathological changes in the peripheral or central
nervous systems. Examples of pathological changes related to neuropathic pain
include prolonged peripheral or central neuronai sensitization, central sensitization
20 related damage to nervous system inhibitory and/or excitatory functions and
abnormal interactions between the parasympathetic and sympathetic nervous
systems. A wide range of clnical conditions may be associated with or form the
basis for neuropathic pain including for example diabetes, post traumatic pain of
amputation, lower back pain, cancer, chemical injury or toxins, other major surgeries
25 peripheral nerve damage due to traumatic injury compression, nutritional
deficiencies, or infections such as shingles or HIV.
There are various types of agents currently being used to treat pain such as
for example, non-narcotic analgesics such as aspirin, acetaminophen or ibuprofen;
non-steroida! anti-inflammatory drugs (NSAID): narcotic analgesics such as
30 morphine, hydromorphone, fentanyl, codeine or meperidine; steroids such as
prednisone or dexamethasone; tricyclic antidepressants such as amitriptyline,
desipramine, or imipramine; antiepileptics such as gabapentin, carbamazepine,
topiramate, sodium valproate or phenytoin; or combinations of these different agents.
2

However, these agents are typically unsatisfactory for treating pain of a chronic
nature, and can have adverse effects such as drowsiness, dizziness, dry mouth,
weight gain, memory impairment, and/or orthostatic hypotension.
Of more recent interest has been the use of inhibitors of the N-methyi-D-
5 aspartate ("NMDA") receptors to treat pain (hereinafter called "NMDA receptor
antagonists"). It has been shown that NMDA receptors are involved in a wide range
of processes including, neuronal death following ischemia, synaptic plasticity
associated with memory formation and centra! sensitization during persistent pain. it
is believed that glutamate, which regulates NMDA receptors, plays a key role in pain
10 and especially chronic pain.
NMDA receptors are localized throughout the central nervous system. NMDA
receptors are ligand-gated cation channels that modulate sodium, potassium and
calcium ions flux when they are activated by glutamate in combination with glycine.
Structurally, the NMDA receptor is thought to be comprised of heteromultimeric
15 channels containing two major subunits designated as NR1 and NR2. These
subunits contain a glycine binding site, a glutamate binding site and polyamine
binding site. For the NR1 subunit, multiple splice variants have been identified,
whereas for the NR2 subunit, four individual subunit types (NR2A, NR2B, NR2C,and
NR2D) have been identified. The NMDA receptor also contains a Mg++ binding site
20 located inside the pore of the ionophore of the NMDA receptor/channel complex,
which blocks the flow of ions. Phencyciidine, as well as other compounds, appear to
bind to this Mg** site. In order for PCP to gain access to the PCP receptor, the
channel must first be opened by glutamate and glycine (i.e., use dependence).
Various NMDA antagonists have been developed to inieract with these sites
25 of the NMDA receptor. For example, NMDA receptor glutamate site antagonists refer
to those antagonists that interact with the glutamate binding site of the NR2 subunit.
Examples of NMDA receptor glutamate site antagonists that have been shown in
preclinical models to suppress pain include CGS-19755 (Selfotel; cis-4-
phosphonomethyi-2-piperidine carboxylic acid), CPP (3-(2-carboxypiperazinyi-4-
30 yl)propyl-1-phosphonic acid) and AP5 (D-2 amino 5-phosphonopentanoic acid). See
e.g., Karlsten and Gordh, Drugs and Aging 11: 398-412, (1997). Other NMDA
receptor antagonists have been identified that interact at the strychinine-in-sensitive
glycine site (glycinep) such as L701324 (7-chloro-4-hydroxy-3-(3-phenoxy)phenyl-
-2A-

2(1H)-quino!ine) and at the polyamine site such as ifenprodil. Noncompetitve NMDA
receptor channel blocking antagonists that have beer, found effective in suppressing
pain include dextromethorphan, ketamine, memantine, and amantadine. See e.g.,
Hao et al., Pain 66:279-285 (1996); Chaplan et al., J. Pharmacol. Exper. Ther.
5 280:829-838 (1997); Suzuki et al., Pain 91:101-109, (2000); Bennett, J. Pain
Symptom Management 19: S2 (2000); Sang, J. Pain Symp. Manag. 19 (1): S21,
(2000).
NMDA receptor antagonists have been used in clinical settings to treat pain.
For example, ketamine has been used to treat postherpetic neuralgia pain, phantom
10 limb pain, post nerve injury pain, postoperative pain, and burn pain. Also, for
example dextromethorphan has been used to treat diabetic neuropathy pain, and
postoperative pain; and amantadine has been used to treat pain in cancer patients.
Clinical usefulness of these NMDA receptor antagonists have been limited by
adverse effects such as headache, disturbances of motor function such as ataxia,
15 sedation and/or psychotomimetic effects such as dizziness, hallucinations, dysphoria,
or disturbances of cognitive function at analgesic doses. See e.g., Hao et a!., Pain
66:279-285 (1996); Chaplan et ali., J. Pharmacol. Exper. Ther. 280:829-838 (1997);
Suzuki et al., Pain 91:101-109, (2000): Bennett, J. Pain Symptom Management 19:
S2 (2000); Sang, J. Pain Symp. Manag. 19 (1): S21, (2000). For example, the high
20 affinity NMDA receptor channel blockerketamine, which is occasionally used for burn
related pain has reported adverse effects that has limited its use in patients (Pa! et
a)., Bums 23: 404-412, 1997). Additionally, development of the NMDA receptor
channel blocking antagonist dizocilpine (MK-801) was terminated because of
psychotomimetic effects similar to those produced by phencydidine (i.e., PCP). It
25 has been suggested that lower affinity channei biockers such as dextromethorphan,
amantadine and memantine might have fewer adverse effects than the high affinity
biockers (Rogawski, Trends Pharmacol. Sci. 14:325, 1998). In support of this view,
dextromethorphan had analgesic effects in patients suffering from diabetic
neuropathy with fewer side effects than ketamine (Sang, J. Pain Symp. Manag. 19
30 (1): S21, 2000). Similarly, amantadine relieved surgical neuropathic pain in cancer
patients with fewer side effects (Hewitt, Clin. J. Pain 16: 573, 2000).
However, even with the lower affinity noncompetitve NMDA receptor channei
blocking antagonists, like the higher affinity noncompetitive antagonists, there have
-3-

been undesirable psychotomimetic effects which have hampered development. For
example, in preclinical models, NMDA receptor channel blockers of varying affinities
consistently produce PCP-Iike discriminative stimulus effects in rats trained to
discriminate between saline and PCP. Memantine, ketamine and dizocilpine all
5 substitute for the PCP-iike discriminative stimulus effects in rats (Nicholson et a!.,
Behav. Pharmacol. 9(3): 231-243, 1998; Mori et al., Behav. Brain Res. 119:33-40,
20 01). Moreover, like PCP, memantine maintains self-administration in monkeys
suggesting that it might have abuse potential in humans (Nicholson et al., Behav.
Pharmacol. 9(3): 231-243, 1998). Use dependent NMDA receptor channel blockers
10 can also increase heart rate and blood pressure, which can further limit their clinicai
utility.
Although NMDA receptor glutamate antagonists do not have the degree of
psychotomimetics side effects in human or PCP-like, discriminative stimulus effects in
non-humans (see e.g., Baron and Woods, Psychopharmacol. 118(1): 42-51, (1995);
15 Mori et al., Behav. Brain Res. 119:33-40, (2001); France et al., J. Pharmacol: Exper.
Ther. 257(2): 727-734, (1991); France et al., Eur. J. Pharmacol 159(2): 133-139,
(1989)), they have been shown to have many undesirable side effects. For example,
the NMDA glutamate antagonist CGS-19755 has been shown to have a transient,
reversible induction of vacuoies in some iayers of the cingulate and retrosplenial
20 cortices of mice and rats at behaviorly effective doses (i.e., effectiveness/-
vacuolization ratio of 1). See e.g., Herring et al., Excitatory Amino Acids Clinical
Results with Antagonists, published by Academic Press, Chptr 1 (1997). Although
the functional implications of vacuolization are unclear, previous studies suggest that
this vacuoiization correlates with the psychotomimetic effects produced by NMDA
25 receptor antagonists (see e.g... Olney et ai., Science, 244: 1630-1632,1989: Olney et
al., Science 254: 1515-1518, 1991) and might lead to limited neuronal cell death as
in the case of dizocilpine (Fix et al., Exp. Neurol. 123:204-215, 1993).
Thus, it would be desirable to find alternative compounds effective in treating
pain. Preferably these compounds would have reduced adverse side effects and/or
30 be more effective in treating pain.
U.S. Patent No. 5,168,103 to Kinney et al. (hereinafter "Kinney") discloses
certain [[2-(Amino-3,4-dioxo-1-cyclobuten-1-yl)amino]alkyl]-acid derivatives useful as
neuroprotectant and anticonvulsant agents. These [[2-(Amino-3,4-dioxo-1-
-4-

cyclobuten-1-yl)amino]alkyl]-acid derivatives are disclosed as competitive NMDA
antagonists useful to treat certain central nervous system disorders such as
convulsions, brain cell damage and related neurodegenerative disorders.
Side effects of one of the compounds disclosed in the Kinney patent, [2-(8,9-
5 dioxo-2,6-diazabicyclo[5.2.0]non-1(7-en-2-yl)ethyl]phosphonic acid, were previously
evaluated in healthy volunteers in a phase I study conducted in Europe. This study
was in connection with developing this compound for treating stroke-related ischemia
in patients (Bradford et al., Stroke and Cerebral Circulation abstract, 1998).
The present inventors have found that the cyclobutene derivatives in Kinney
10 are effective in treating pain in a variety of preclinical pain models. For example, the
present inventors have found that these cyclobutene derivatives can relieve pain
under conditions where comparitor NMDA receptor antagonists tested herein do not
Additionally, these cyclobutene derivatives surprisingly do not have the degree of
adverse side effects exhibited by known NMDA receptor antagonists at dosages
15 needed for pain relief.
For example, the present inventors, as described in more detail hereinafter,
have found that compounds disclosed in Kinney, such as [2-(8,9-dioxo-2,6-
diazabicyclo[5.2.0]non-1(7-en-2-yl)ethyI]phosphonic acid, did not produce ataxia or
sedation in comparison to other reported competitive glutamate antagonists (CGS-
20 19755), competitive polyamine antagonists (ifenprodii) and use dependent channel
blockers (MK-801, memantine; dizocilipine, ketamine) at doses needed to relieve
pain in preciinical models. Additionally, as mentioned previously, some NMDA
receptor antagonists, such as CGS-19755 were found to exhibit a transient,
reversible induction of vacuoles in some layers of the cingulate and retrospienial
25 cortices of mice and rats. In contrast to CGS-19755, which caused vacuolization at
behavioraliy effective doses, cyclobutene derivatives such as [2-(8,9-dioxo-2,6-
diazabicycio[5.2.0]non-1(7-en-2-yi)ethyi]phosphonic add had an effectiveness/-
vacuolization ratio as large as 16. Moreover, unlike the NMDA receptor channel
blocking antagonists previously mentioned herein, the cyclobutene derivatives such
30 as [2-(8,9-dioxo-2,6-dia2abicyclo[5.2.0]non-1 (7-en-2-yl}ethyl]phosphonic acid did not
substitute for PCP in rats, suggesting that this compound would not be associated
with PCP-like psychotomimetic effects or contain PCP-like abuse liability.
Additionally, [2-(8,9-dioxo-2,6-diazabicyclo[5.2.0]non-1(7-en-2-yl)ethyl]phosphonic
-5-

acid was devoid of many PCP-like effects up to doses 4-10 times higher than those
effective in an ischemia model.
SUMMARY OF INVENTION
5 The present invention provides a method of treating pain in a mammal that
includes administering to a mammal in need of such treatment a pain treating
effective amount of at least one compound having the formula (I):

where:
10 R1 is hydrogen, alkyl of 1 to 6 carbon atoms or phenylalkyi of 7 to 12 carbon
atoms;
R2 is hydrogen, alky! of 1 to 6 carbon atoms, alkenyl of 2 to 6 carbon atoms or
phenyialkyi of 7 to 12 carbon atoms; or
R1 and R2 taken together are Z, which is -CH2CH2—, —CH2C(R6)(R7}CH2—
15 or —CH2C(R8)(R9)—C(R10)(R11)CH2—, where R6, Rs and R10 are, independently,
hydrogen, alkyl of 1 to 6 carbon atoms or bydroxyl and R7, R9 and R11 are,
independently, hydrogen or alkyl of 1 to 6 carbon atoms;
A is alkylene of 1 to 6 carbon atoms or alkenylene of 2 to 6 carbon atoms;
X is CO2R3, P(O)(OR4)(OR5), 3,5-dioxo-1,2,4-oxadiazolidin-2-yi or 5-tetrazolyl
20 where R3, R4 and R5 are, independently, hydrogen or alkyl of 1 to 6 carbon atoms;
or a pharmaceutically acceptable salt thereof.
The present invention also provides a pharmaceutical composition that
contains: a pain treating effective amount of the compound of formula (i) or a
25 pharmaceutically acceptable salt thereof, where R1 and R2 taken together are Z and
the remaining variables are defined as before; and at least one pharmaceutical
carrier. In a preferred embodiment, this composition also contains a
pharmaceuticaily effective amount of at least one pain relieving agent. Also provided
is a pharmaceutical composition that contains a pain treating effective amount of the
-6-

compound of formula (I) or a pharmaceutically acceptable salt thereof, and a
pharmaceutically effective amount of at least one pain relieving agent.
The present invention also provides a pharmaceutical composition in unit
dosage form and a therapeutic package containing the compound of formula (I) in
5 unit dosage form for treating pain in a mammal.
DETAILED DESCRIPTION OF THE INVENTION
Compounds useful in the present invention for treating pain include
cyclobutene derivatives of formula (I)

R1 is hydrogen, aikyl of 1 to 6 carbon atoms or phenylalkyl of 7 to 12 carbon
atoms;
R2 is hydrogen, alky! of 1 to 6 carbon atoms, alkenyl of 2 to 6 carbon atoms or
15 phenylalkyl of 7 to 12 carbon atoms; or
R1 and R2 taken together are Z, which is -CH2CH2—, —CH2C(R6)(R7)CH2-
or —CH2C(R8)(R9)-C(R10)(R11)CHZ-where R8, R8 and R10 are, independently,
hydrogen, alky! of 1 to 6 carbon atoms or hydroxyl and R7, R9 and R11 are,
independently, hydrogen or alkyl of 1 to 6 carbon atoms;
20 A is alkylene of 1 to 6 carbon atoms or alkenylene of 2 to 6 carbon atoms;
X is CO2R3, P(O)(OR4)(OR5), 3,5-dioxD-1,2,4-oxadiazoiidin-2-yl or 5-tetrazolyl
in which R3, R4 and R5 are, independentiy, hydrogen or an alkyl of 1 to 6 carbon
atoms;
or a pharmaceuticaliy acceptable salt thereof.
25
Examples of alkyl for R1-11 and alkylene for A are straight or branched groups
such as methyl, ethyl, propyl (e.g., n-propyl, isopropyl), butyl (e.g., n-butyl, isobutyl),
pentyl (e.g., n-pentyl, isopentyl) or hexyl. Preferred alkyl groups of the present
invention have 1 to 4 carbon atoms. Examples of alkenyl for R2 and alkenylene for A
-7-

are straight or branched mono-, di-, or polyunsaturated groups such as vinyl, prop-1-
enyl, allyl, methallyl, but-1-enyl, but-2-eny] or but-3-enyI.
Examples of phenylalkyl groups for R1 and R2 are such groups wherein the
alkyl moiety is a straight or branched carbon chain having 1 to 6 carbon atoms such
5 as benzyl, phenylethyl, 3-phenyIpropyl, or 4-pheny! butyl.
Preferred values for R1 are hydrogen, methyl, ethyl or benzyl. Preferred
values for R2 are hydrogen, methyl, ethyl, allyl, methallyl or benzyl.
Other preferred values are when R1 and R2 are taken together to form a
moiety Z in the formula (II):

With respect to A, preferred examples of alkylene groups are straight or
branched chain groups having 1 to 4 carbon atoms such as: —CH2—, —CH2CH2—,
—CH(CH3)CH2-, —CH2CH(CH3)—, —(CH2)-, or —(CH2)4-. Preferred examples
of alkenylene groups for A are cis or trans groups preferably having 2 to 4 carbon
20 atoms such as —CH2-CH=CH— —CH=C(CH3)—, —C(CH3)=CH—, —CH=CH—
CH2-, —CH2-CH=CH—CH2— or —CH2-CH=C(CH3)—. Preferably A is alkylene
of 1 to 4 carbon atoms or trans-2-butylene. Preferred substituents for X are carboxyl,
phosphonyl or 5-tetrazolyl.
-8-

In a most preferred embodiment of the present invention, the compounds
useful in the present invention have the formula (III):

where A and X are defined as before.
5 The compounds useful in the present invention aiso include pharmaceutically
acceptable salts of the compounds of formula (1). By "pharmaceutically acceptable
salt", it is meant any compound formed by the addition of a pharmaceutically
acceptable base or acid and a compound of formula (I) to form the corresponding
salt. By the term "pharmaceuticaliy acceptable" it is meant a substance that is
10 acceptable for use in pharmaceutical applications from a toxicological perspective
and does not adversely interact with the active ingredient Preferably, the
pharmaceutically acceptable salts are alkali metal (sodium, potassium, iithium) or
alkaline earth metal (calcium, magnesium) salts of the compounds of formula (I), or
salts of the compounds of formula (I) with pharmaceutically acceptable cations
15 derived from ammonia or a basic amine. Examples of the iater include, but are not
limited to, ammonium, mono-, di-, or trimethylammonium, mono-, di-, or triethyl-
ammonium, mono-, di-, or tripropylammonium (iso and normal), ethyldimethyl-
ammoniurn, benzyldimethylammonium, cyclohexylammonium, benzylammonium,
dibenzylammonium, piperidinium, morphoiinium, pyrroiidinium, piperazinium,
20 1-methylpiperidinium, 1-isopropylpyrrolidinium, 1,4-dimethylpiperazinium, 1-n-butyl-
piperidinium, 2-methylpiperidinium, 1-ethyl-2-methylpiperidinium, mono-, di-, or
triethanolammonium, tris-(hydroxymethyl)methylammonium, or phenyimonoethanol-
ammonium.
The compounds described herein can be prepared by the methods described
25 in U.S. Patent No. 5,168,103 (Kinney et al.), issued December 1, 1992, the entire
contents of which are incorporated herein by reference. Compounds of this invention
can also be prepared by the methods described in U.S. Patent Nos. 5,240,946
-9-

(Kinney et al.), 5,990,307 (Asselin et al.), or 6,011,168 (Asselin et al.); the contents of
these patents are also entirely incorporated herein by reference.
Preferred compounds useful in the present invention include the following
5 compounds or their pharmaceutically acceptable salts:


or a pharmaceutically acceptable salt form thereof.
-10-

While in no way intending to be bound in theory, it is believed that the
cyclobutene derivatives of the present invention have a unique affinity and selectivity
for certain binding sites on the NMDA receptor. This unique affinity and selectivity is
believed to provide effective treatment of pain at lower doses and/or cause less side
5 effects at doses needed to relieve pain.
The cyclobutene derivatives described herein are useful for treating pain in
mammals in accordance with the methods of the present invention. By "treating", as
used herein, it is meant partially or completely alleviating, inhibiting, ameliorating
and/or relieving pain. For example, "treating" as used herein includes partially or
10 completely alleviating, inhibiting or relieving pain for a period of time. "Treating" also
includes completely ameliorating the pain.
The compounds useful in the present invention are useful for treating a
varity of different types of pains experienced by mammals, such as humans. For
example, the compounds of the present invention are effective in treating acute pain
15 (short duration) or chronic pain (regularly reoccurring or persistent). This pain may
also be centralized or peripheral.
Examples of pain that can be acute or chronic and that can be treated in
accordance with ihe methods of the present invention include inflammatory pain,
muscuioskeietai pain, bony pain, iurnbosacrai pain, neck or upper back pain, viscera!
20 pain, somatic pain, neuropathic pain, cancer pain, pain caused by injury or surgery
such as bum pain, or headaches such as migraines or tension headaches, or
combinations of these pains. One skilled in the art will recognize that these pains
may overlap one another. For example, a pain caused by inflammation may also be
visceral or musculoskeleta! in nature.
25 In a preferred embodiment of the present invention the compounds useful in
the present invention are administered in mammals to treat chronic pain such as
neuropathic pain associated for example with damage to or pathological changes in
the peripheral or central nervous systems; cancer pain; viscera! pain associated with
for example the abdominal, pelvic, and/or perinea! regions or pancreatitis;
30 muscuioskeietai pain associated with for example the lower or upper back, spine,
fibromylagia, temporomandibular joint, or myotascial pain syndrome; bony pain
associated with for example bone or joint degenerating disorders such as
osteoarthritis. rheumatoid arthritis, or spinal stenosis; headaches such migraine or
-11-

tension headaches; or pain associated with infections such as HIV, sickle ceil
anemia, autoimmune disorders, multiple sclerosis, or inflammation such as
osteoarthritis or rheumatoid arthritis.
In a preferred embodiment, the compounds useful in this invention are used
5 to treat chronic pain that is neuropathic pain, visceral pain, musculoskeletal pain,
bony pain, headache, cancer pain or inflammatory pain or combinations thereof, in
accordance with the methods described herein. Inflammatory pain can be
associated with a variety of medical conditions such as osteoarthritis, rheumatoid
arthritis, surgery, or injury. Neuropathic pain may be associated with for example
10 diabetic neuropathy, peripheral neuropathy, post-herpetic neuralgia, trigeminal
neuralgia, lumbar or cervical radiculopathies, fibromyalgia, glossopharyngeal
neuralgia, reflex sympathetic dystrophy, casualgia, thalamic syndrome, nerve root
avulsion, or nerve damage cause by injury resulting in peripheral and/or central
sensitization such as phantom limb pain, reflex sympathetic dystrophy or
15 postthoracotomy pain, cancer, chemica! injury, toxins, nutritional deficiencies, or viral
or bacterial infections such as shingles or HIV, or combinations thereof. The
methods of use for compounds of this invention further include treatments in which
the neuropathic pain is a condition secondary to metastatic infiltration, adiposis
dolorosa, burns or centra! pain conditions reiated to thalamic conditions.
20 As mentioned previously, the methods of the present invention may be used
to treat pain that is somatic and/or visceral in nature. For example, somatic pain that
can be treated in accordance with the methods of the present invention include pains
associated with structural or soft tissue injury experienced during surgery, dentai
procedures, bums, or traumatic body injuries. Examples of visceral pain that can be
25 treated in accordance with the methods of the present invention include those types
of pain associated with or resulting from maladies of the. internal organs such as
ulcerative colitis, irritable bowel syndrome, irritabie biadder, Crohn's disease,
rheumatologic (arthralgias), tumors, gastritis, pancreatitis, infections of the organs, or
biliary tract disorders, or combinations thereof One skilled in the art will also
30 recognize that the pain treated according to the methods of the present invention
may also be related to conditions of hyperalgesia, ailodynia, or both. Additionally, the
chronic pain may be with or without peripheral or central sensitization.
-12-

The compounds useful in this invention may also be used to treat acute
and/or chronic pains associated with female conditions, which may also be referred
to as female-specific pain. Such groups of pain include those that are encountered
solely or predominately by females, including pain associated with menstruation,
5 ovulation, pregnancy or childbirth, miscarriage, ectopic pregnancy, retrograde
menstruation, rupture of a follicular or corpus luteum cyst, irritation of the pelvic
viscera, uterine fibroids, adenomyosis, endometriosis, infection and inflammation,
pelvic organ ischemia, obstruction, intra-abdornina! adhesions, anatomic distortion of
the pelvic viscera, ovarian abscess, loss of pelvic support, tumors, pelvic congestion
10 or referred pain from non-gynecological causes.
The cyclobutene derivatives useful in the present invention can be
administered in a variety of ways including for example by oral, intramuscular,
intraperitoneal, epidural, intrathetic, intravenous, subcutaneous, intramucosal such
as sublingual or intranasal, or transdermal administration. in a preferred embodiment
15 of the present invention, the compounds useful [n the present invention are
administered orally, intramucosally or intravenously.
The compounds useful in the present invention are administered in a pain
treating effective amount to the mammal needing treatment for pain. As used herein
"a pain treating effective amount" is at least the minimal amount of the cyclobutene
20 derivative or a pharmaceuticaliy acceptable salt form thereof, which treats the pain in
question. To determine the pain treating effective amount of the compound to be
administered in the treatment of pain, the physician may. for example, evaluate the
effects of a given cyclobutene derivative in the patient by incrementally increasing the
dosage, such as an oral dosage, preferably from about 3 mg/kg to about 1000 mg/kg
25 until the desired symptomatic relief ieve! is achieved. The continuing dose regimen
may then be modified to achieve the desired result, with the range for oral dosage
being preferably from about 150 mg/day to about 900 mg/day. Similar techniques
may be followed by determining the effective dose range for other administration
routes such as by intravenous or intramuscular routes based on bioavaiiability data.
30 For example, it is estimated that intravenous dosages would preferably range from
about 3 mg/day to about 50 mg/day.
Although the cyclobutene derivatives may be administered in accordance with
the methods of the present invention as the sole active ingredient for treating pain,
-13-

the present inventors have found that the cyclobutene derivatives may also be
administered with one or more other pain relieving agents. By "pain relieving agents"
it is meant any agent that directly or indirectly treats pain symptoms. Examples of
indirect pain relieving agents include for example anti-inflammatory agents, such as
5 anti-rheumatoid agents.
The one or more other pain relieving agents may be administered
simultaneously (such as individually at the same time, or together in a
pharmaceutical composition), and/or successively with one or more cydobutene
derivatives useful in the present invention. Preferably, the cyclobutene derivative
10 and the one or more pain relieving agents are administered in a manner so that both
are present in the mammal body for a certain period of time to treat pain.
The method of administration of the other pain relieving agent may be the
same or different from the route of administration used for the cyclobutene derivative.
For example, the other pain relieving agent may be administered by oral,
15 intramuscular, intraperitoneal, epidural, intrathecal, intravenous, intramucosal such
as by intranasal or sublingual, subcutaneous or transdermal administration. The
preferred administration route will depend upon the particular pain relieving agent
chosen and its recommended administration route(s) known to those skilled in the
art. For example, opioids are preferably administered by oral, intravenous, or
20 intramuscular administration routes.
One skilled in the art will recognize that the dosage of the other pain relieving
agent administered to the mammal will depend on the particular pain relieving agent
in question and the desired administration route. Accordingly, the other pain relieving
agent may be dosed and administered according to those practices known to those
25 skilled in the art such as those disclosed in references such as the Physicians' Desk
Reference, 55 Edition, 2001, published by Medical Economics Co., Inc., Montvale,
NJ.
Examples of pain relieving agents that may be administered with the
cydobutene derivatives useful in the present invention include analgesics such as
30 non-narcotic analgesics or narcotic analgesics; anti-inflammatory agents such as non-
steroidal anti-inflammatory agents (NSAID), steroids or anti-rheumatic agents;
migraine preparations such as beta adrenergic blocking agents, ergot derivatives, or
isometheptene; tricyclic antidepressants such as arnitryptyline, desipramine. or
-14-

imipramine; anti-epileptics such as gabapentin, carbamazepine, topiramate, sodium
valproate or phenytoin; α2 agonists; or selective serotonin reuptake inhibitors/-
selective norepinepherine uptake inhibitors, or combinations thereof. One skilled in
the art will recognize that some agents described hereinafter act to relieve multiple
5 conditions such as pain and inflammation, while other agents may just relieve one
symptom such as pain. A specific example of an agent having multiple properties is
aspirin, where aspirin is anti-inflammatory when given in high doses, but at Sower
doses is just an analgesic. The pain relieving agent may include any combination of
the aforementioned agents, for example, the pain relieving agent may be a non-
10 narcotic analgesic in combination with a narcotic analgesic.
Non-narcotic analgesics useful in the present invention include, for example,
salicylates such as aspirin, ibuprofen (MOTRIN®, ADVIL®), ketoprofen (ORUDIS®),
naproxen(NAPROSYN®), acetaminophen, indomethacin or combinations thereof.
Examples of narcotic analgesic agents that may be used in combination with the
15 cyclobutene derivatives include opioid analgesics such as fentenyl, sufentanil,
morphine, hydromorphone, codeine, oxycodone, buprenorphine or pharmaceutically
acceptable saiis thereof or combinations thereof. Examples of anti-inflammatory
agents that may be used in combination with the cyclobutene derivatives include but
are not limited to aspirin; ibuprofen; ketoprofen; naproxen; etodoiac (LODINE®);
20 COX-2 inhibitors such as celecoxib (CELEBREX®), rofecoxib (VIOXX®), valdecoxib
(BEXTRA®), parecoxib, etoricoxib (MK663), deracoxib, 2-(4-ethoxy-phenyl)-3-
(4-rnethanesulfonyl-phenyl)-pyrazolo[1,5-b]pyridazine, 4-(2-oxo-3-phenyl-2,3-dihydro-
oxazol-4-yl)benzenesulfonamide, darbufelone, flosulide, 4-(4-cyclohexyl-2-methyl-5-
oxazolyl)-2-flucrobenzenesulfonamide), meloxicam, nimesulide, 1-.Methyleulfonyl-4-
25 (1,1-dimethyl-4-(4-fiuorophenyl)cyciopenta-2,4-dien-3-yl)benzene, 4-(1,5-Dihydro-6-
fluoro-7-methoxy-3-(trifluoromethyl)-(2)-benzothiopyrano(4,3-c)pyrazol-1-yi)benzene-
suifonamide, 4,4-dimethyl-2-phenyl-3-(4-methylsulfonyl)phenyl)cyciobutenone, . 4-
Amino-N-(4-(2-fluoro-5-trifluoromethyl)-thiazol-2-yl)-benzene sulfonamide, 1-(7-tert-
butylk-2,3-dihydro-3,3-dirnethyl-5-benzo-furanyl)-4-cyclopropyl butan-1-one, or their
30 physiologically acceptable salts, esters or solvates; sulindac (CLINORIL®); diclofenac
(VOLTAREN®); piroxicam (FELDENE®); diflunisal (DOLOBID®), nabumetone
(RELAFEN®), oxaprozin (DAYPRO®), indomethacin (INDOCIN®); or steroids such as
PEDIAPED® prednisol'one sodium phosphate oral solution, SOLU-MEDROL®
-15-

methylprednisolone sodium succinate for injection, PRELONE® brand prednisolone
syrup.
Further examples of anti-inflammatory agents preferably used for treating
rheumatoid arthritis include naproxen, which is commercially available in the form of
5 EC-NAPROSYN® delayed release tablets, NAPROSYN®, ANAPROX® and
ANAPROX® DS tablets and NAPROSYN® suspension from Roche Labs,
CELEBREX® brand of celecoxib tablets, VIOXX® brand of rofecoxib, CELESTONE®
brand of betamethasone, CUPRAMINE® brand peniciilamine capsules, DEPEN®
brand titratable peniciilamine tablets, DEPO-MEDROL brand of methyiprednisolone
10 acetate injectable suspension, ARAVA™ ieflunomide tablets, AZULFIDINE EN-tabs®
brand of sulfasalazine delayed release tablets, FELDENE® brand piroxicam
capsules, CATAFLAM® diclofenac potassium tablets, VOLTAREN® diclofenac
sodium delayed release tablets, VOLTAREN®-XR diclofenac sodium extended
release tablets, or ENBREL® etanerecept products.
15 Examples of other agents used to treat inflammations, especially rheumatoid
arthritis include immunosuppressants such as GENGRAF™ brand cyclosporine
capsules, NEORAL® brand cyclosporine capsules or oral solution, or IMURAN®
brand azathioprine tablets or IV injection: INDOCIN® brand indomethacin capsules,
oral suspension or suppositories; PLAQUENIL® brand hydroxychforoquine sulfate; or
20 REMICADE® infliximab recombinant for IV injection; or gold compounds such as
auranofin or MYOCHRISYINE® gold sodium thiomalate injection.
The cyclobutene derivatives useful in the present invention may aiso be
administered with one or more other pharmaceutical active agents such as those
agents being used to treat any other medical condition present in the mammal that is
25 related or unrelated to the pain being experienced by the mammal. Examples of
such pharmaceutical active agents include anti-anglogenic agents, anu-neoplasilc
agents, anti-diabetic agents, anti-infective agents, or gastrointestinal agents, or
combinations thereof.
A more complete listing of pharmaceutical active agents, including pain
30 relieving agents, can be found in the Physicians' Desk Reference, 55 Edition, 2001,
published by Medical Economics Co., Inc., Montvale, NJ. Each of these agents may
be administered according to the pharmaceuticaliy effective dosages and regimens
-16-

known in the art, such as those described for the products in the Physicians' Desk
Reference, 55 Edition, 2001, published by Medical Economics Co., Inc., Montvale,
NJ.
In a preferred embodiment of the present invention, at least one cyclobutene
5 derivative is administered with at least one opioid analgesic in accordance with the
methods previously described herein. It has surprisingly been found that the
cyclobutene derivatives useful in the present invention, when administered with at
least one opioid anaigesic such as morphine, have such beneficial effects as
synergistically decreasing pain perception, increasing the duration of pain relief,
10 and/or decreasing adverse side effects to a greater extent than other comparitor
NMDA antagonists.
The cyciobutene derivatives useful in the present invention may be
administration neat (i. e., as is ) or in a pharmaciutical composition. Pharmaciutical
compositions useful in the present invention may be in any form known to those
15 skilled in the art such as in liquid or solid form.
Pharmaceutical compositions, in addition to containing a pain treating
effective amount of one or more cyciobutene derivatives of the present invention,
may include one or more ingredients known to those skilled in the art for formulating
pharmaceutical compositions. Such ingredients include for example, carriers (e.g., in
20 solid or liquid form), flavoring agents, lubricants, solubilizers, suspending agents,
fillers, glidants, compression aids, binders, tablet-disintegrating agents,
encapsulating materials, ernulsifiers, buffers, preservatives, sweeteners, thickening
agents, coloring agents, viscosity regulators, stabilizers or osmo-reguiators, or
combinations thereof.
25 Solid pharmaceutical compositions preferably contain one or more solid
carriers, and optionally one or more other additives such as flavoring agents,
lubricants, soiubilizers, suspending agents, fillers, glidants, compression aids,
binders or tablet-disintegrating agents or an encapsulating material. Suitable solid
carriers include, for example, calcium phosphate, magnesium stearate. talc, sugars,
30 lactose, dextrin, starch, gelatin, cellulose, methyl cellulose, sodium carboxymethy!
cellulose, polyvinylpyrrolidine, low melting waxes or ion exchange resins, or
combinations thereof. In powder pharmaceutical compositions, the carrier is
preferably a finely divided solid which is In admixture with the finely divided active
-17-

ingredient In tablets, the active ingredient is mixed with a carrier having the
necessary compression properties in suitable proportions, and optionally, other
additives, and compacted into the desired shape and size. Solid pharmaceutical
compositions, such as powders and tablets, preferably contain up to 99% of the
5 active ingredient
Liquid pharmaceutical compositions preferably contain one or more
cyclobutene derivatives and one or more liquid carriers to form solutions,
suspensions, emulsions, syrups, elixirs, or pressurized compositions.
Pharmaceutically acceptable liquid carriers include for example water, organic
10 solvent, pharmaceutically acceptable oils or fat, or combinations thereof. The iiquid
carrier can contain other suitable pharmaceutical additives such as solubiiizers,
emulsifiers, buffers, preservatives, sweeteners, flavoring agents, suspending agents,
thickening agents, colors, viscosity regulators, stabilizers or osmo-regulators, or
combinations thereof.
15 Examples of liquid earners suitable for oral or parenteral administration
include water (preferably containing additives such as cellulose derivatives such as
sodium carboxymethyl cellulose), alcohols or their derivatives (including monohydric
alcohols or polyhydric alcohols such as glycois) or oils (e.g., fractionated coconut oil
and arachis oil). For parenterai administration the carrier can also be an oily ester
20 such as ethyl oleate and isopropyl myristate. The liquid carrier for pressurized
compositions can be halogenated hydrocarbons or other pharmaceutically
acceptable propellant
Liquid pharmaceutical compositions which are sterile solutions or
suspensions can be administered parenterally, for example by, intramuscular
25 intraperitoneai, epidurai, intrathecal, intravenous or subcutaneous injection.
Pharmaceutical compositions for oral or transmucosal administration may be either in
liquid cr solid composition form.
In a preferred embodiment of the present invention, the pharmaceutical
composition, in addition to containing the cydobutene derivative may also contain a
30 pharmaceutically effective amount of one or more pain relieving agents as previously
described herein, and/or a pharmaceutically effective amount one or more other
pharmaceutical active agents as previously described herein. Thus, the present
invention also provides a pharmaceutical composit'on for treating pain containing a
-18-

pain treating effective amount of at least one cyclobutene derivative useful in the
present invention and a pharrnaceuticaliy effective amount of at ieast one pain
relieving agent as previously described. In a more preferred embodiment, the pain
relieving agent includes an opioid analgesic.
5 Preferably the pharmaceutical composition is in unit dosage form, such as
tablets or capsules. In such form, the composition is sub-divided in unit dose
containing appropriate quantities of the active ingredient. The unit dosage forms can
be packaged compositions, for example packeted powders, vials, ampoules, pre-
filled syringes or sachets containing liquids. The unit dosage form can be, for
10 example, a capsule or tablet itself, or it can be the appropriate number of any such
compositions in package form.
Thus, the present invention also provides a pharmaceutical composition in
unit dosage form for treating pain in a mammal that contains a pain treating effective
unit dosage of at least one cyclobutene derivative of the present invention. As one
15 skilled in the art will recognize, the preferred pain treating effective unit dosage will
depend on for example the method of administration. For example, a unit dosage for
oral administration preferably ranges from about 75 mg to about 300 mg and more
preferably from about 100 mg to about 300 mg of the cyclobutene derivative useful In
the present invention.
20 The present invention also provides a therapeutic package for dispensing the
cyclobutene derivative useful in the present invention to a mammal being treated for
pain. Preferably, the therapeutic package contains one or more unit dosages of the
cyclobutene derivative and a container containing the one or more unit dosages and
labeling directing the use of the package for treating pain in a mammal. In a
25 preferred embodiment, the unit dose is in tablet or capsule form, in a preferred
embodiment, each unit dosage is a pain treating effective amount.
EXAMPLES
The cyclobutene derivatives useful in the present invention were evaluated for
30 their effectiveness to treat pain. NMDA receptor antagonists known to relieve pain
were also tested for comparison.
The test methods used herein have been used by others skilled in the art to
evaluate the effectiveness of compounds for relieving pain. See e.g., Bennett GJ
and the TK, A peripheral mononeuropathy in rat produces disorders of pain
-19-

sensation like those seen in man, Pain 33: 87-107 (1988); Chaplan SR, Bach RW,
Pogrei JW, Chung JM and Yaksh TL, Quantitative assessment of tactile ailodynia in
the rat paw, J. Neurosci. Methods 53: 55-63 (1994); and Mosconi T and Kruger L
Fixed-diameter polyethylene cuffs applied to the rat sciatic nerve induce a painful
5 neuropathy: ultrastructural morphometric analysis of axonal alterations Pain 64: 37-
57(1996).
Subjects
Individually housed Spraque-Dawley rats had free access to rat chow and
10 water. A 12-h light/12-h dark cycfe was in effect (lights on from 6:00 am to 6:00 pm).
Animal maintenance and research were conducted in accordance with the guidelines
provided by the National Institutes of Health Committee on Laboratory AnimaJ
Resources. These subjects were used in the tests below.
15 Compounds Tested
The cyclobutene derivatives tested in the examples were:
A. [2-(8,9-Dioxo-2,6-diazabicyclo[5.2.0]non-1(7)-en-2-yl)ethyl]phosphonic
acid (referred to as Compound A); and
B. 2-[(1H-Tetrazol-5-yi)methyl]-2,6-diazabicyclo[5.2.03-non-1-(7)-ene-8,9-
20 dione (referred to as Compound B).
Compounds A and B were produced according to synthesis methods
described in U.S. Patent No, 5,990,307 to Asselin and U.S. Patent No. 5,168,103 to
Kinney et al., respectively.
25 The cyciobutene derivatives of the present invention were compared to one or
more of the following NMDA antagonists known for relieving pain:
memantine, obtained from RBI (Natick, MA)
dizocilipine, obtained from RBI (Natick, MA)
ketamine. obtained from Fort Dodge (Fort Dodge, IO)
30 ifenprodil, obtained from Sigma (St. Louis, MO)
CGS-19755, obtained from Tocris (Ellisville, MO)
-20-

Ketamine and dizodlpine are high affinity use-dependent NMDA receptor channel
blockers, while memantine is a moderate affinity use-dependent NMDA receptor
channel blocker. CGS-19755 is a competitive NMDA antagonist and ifenprodii is a
competitive polyamine antagonist.
5
Test Method 1: Prostaglandin E2-induced thermal hypersensitivity.
The terminal 10 cm of the tail was placed into a thermos bottle containing
water warmed to 38,42, 46, 50, 54, or 58 °C. The latency in seconds for the animal
to remove the tail from the water was used as a measure of nociception. If the
10 animal did not remove the tail within 20 sec, the experimenter removed the tail and a
maximum latency of 20 sec was recorded.
Following the assessment of baseline thermal sensitivity, thermal
hypersensitivity was produced by a 50 µl. Injection of 0.1 mg prostaglandin E2 (PGE2)
into the terminal 1 cm of the tail. Temperature-effect curves were generated before
15 (baseline) and after (15, 30, 60, 90 and 120 min) the PGE2 injection. Previous
studies in other species (e.g.. monkeys; Brandt et al., J. Pharmacol. Exper. Ther.
296:939, 2001) and results from the current study demonstrate that PGE2 produces a
dose- and time-dependent thermal hypersensitivity that peaks 15 min after injection
and dissipates after 2 hr.
20 Single compound studies. The ability of drugs to reverse PGE2-induced
thermal hypersensitivity was assessed using a single dose time-course procedure.
under this procedure, a single dose of the compound to be tested was administered
intraperitoneaily (IP), orally (PO) or intranasally (IN) 30 min before the injection of
PGE2. Tactile sensitivity was assessed 30 min after PGE2 injection.
25 Combination compound studies. Combination studies with NMDA receptor
antagonists together with the mu opioid agonist morphine were conducted. A
minimally effective' dose of morphine (5.6 mg/kg) was administered alone and in
combination with ineffective doses of NMDA receptor antagonists in the thermal
warm-water tail withdrawal assay. Compounds were administered IP at the same
30 time 30 min before testing.
Combination studies with NMDA receptor antagonists together with the mu
opioid agonist morphine were also conducted in the PGE2-induced thermal
hypersensitivity assay. A dose of morphine (5.6 mg/kg) that completely reversed
-21-

thermal hypersensitivity (i.e., return to baseline) was administered alone and in
combination with doses of NMDA receptor antagonists in the PGE2-induced thermal
warm-water tail withdrawal assay. Compounds were administered !P at the same
time as PGE2, which was administered 30 min before testing.
5 Test Method 1 Data Analysis - The temperature that produced a half-
maximal increase in the tail-withdrawal latency (i.e., T10) was calculated from each
temperature-effect curve. The T10 was determined by interpolation from a line drawn
between the point above and the point below 10 sec on the temperature-effect curve.
For these studies, thermal hypersensitivity was defined as a leftward shift in the
10 temperature-effect curve and a decrease in the T10 value. Reversal of thermal
hypersensitivity was defined as a return to baseline of the temperature-effect curve
and the T10 value and was calculated according to the following equation:

in which T10drU9+PGH2 is the T10 after a drug in combination with PGE2r T10PGE2 is the T1C
after PGE2 alone, and T10baselins is the T10 under control conditions. A % MPE value of
100 indicates a complete return to the baseline thermal sensitivity observed without
20 the PGE2 injection. A value of greater than 100% indicates that the compound tested
reduced thermal sensitivity more than the baseline thermal sensitivity without the
PGE2 injection.
Test Method 2: Chronic Constriction Injury
25 Rats were anesthetized with 3.5% haioihane in O2 at i L/min and maintained
with 1.5% halothane in O2 during surgery. A modified chronic sciatic nerve
constriction injury (Mosconi & Kruger, 1988; Bennett S Xie, 1388) was produced by a
cutaneous incision and a blunt dissection through the biceps femoris to expose the
sciatic nerve. A PE 90 Polyethylene tubing (intramedic, Clay Adams; Becton
30 Dickinson Co.) cuff (2mm length) was placed around the sciatic nerve at the level of
the mid-thigh. The wound was closed in layers using 4-0 silk suture and wound clips.
Testing was conducted 6-10 days after surgery.
Animals were placed in elevated wire cages and allowed 45-60 minutes to
acclimate to the testing room. Baseline tactile sensitivity was assessed using a
-22-

series of calibrated von Frey monofilaments (Stoeiting; Wood Dale, 1L) 0-3 days
before surgery. Von Frey monofilaments were applied to the mid-piantar hind paw in
sequential ascending or descending order, as necessary, to hover as closely as
possible to the threshold of responses. The threshold was indicated by the lowest
5 force that evoked a brisk withdrawal response to the stimuli. Thus, a withdrawal
response led to the presentation of the next lighter stimulus and the lack of a
withdrawal response led to the presentation of the next stronger stimulus. Rats with
baseline thresholds < lOg force were excluded from the study. Approximately one
week following CCI surgery, tactile sensitivities were reassessed and animals that
10 exhibited motor deficiency (i.e. paw dragging) or failure to exhibit subsequent tactile
hypersensitivity (threshold > 10g) were excluded from further testing. Under
cumulative dosing conditions, compounds were administered !P every 30 minutes
with the cumulative dose increasinginin 1/2 log unit increments. Tactile hypersensitivity
was assessed 20-30 minutes following each drug administration.
15 Test Method 2 Data Analysis — The 50% threshold values (in gm force)
estimated by the Dixon non-parametric test (Chaplan et al, 1994) was calculated and
fifteen-grams of force was used as the maximal force. Dose-effect curves were
generated for each experimental condition for each rat. individual tactile
hypersensitivity threshold values were averaged to provide a mean (± 1 SEM).
20 Reversal of tactile hypersensitivity was defined as a return to baseline tactile
sensitivity and was calculated according to the following equation:

in which 50%dru9+ccl is the 50% value after compound in animals approximately one
week after CCI surgery, 50%ccl is the 50% value approximately one week after CCI
surgery alone, and 50%base"ne is the 50% value before CCi surgery. Maxima! effect of
100 % reversal represents a return to the mean pre-operative threshold value for
30 subjects in that experimental condition.
Test Method 3: Scheduled-controlled responding.
Rats were trained under a muitiple-cycle procedure during experimental
sessions conducted five days each week. Each training cycie consisted of a 10-min
-23-

pretreatment period followed by a 10-min response period. During the pretreatment
period, stimulus lights were not illuminated, and responding had no scheduled
consequences. During the response period, the left or right stimulus lights were
illuminated (counterbalanced among subjects), the response lever was extended and
5 subjects could respond under a fixed ratio 30 schedule of food presentation. Training
sessions consisted of 3 consecutive cycles. Testing sessions were identical to
training sessions except that a single dose of drug was administered at the start of
the first cycle.
Data analysis. Operant response rates from individual animals were
10 averaged for the three cycles during test sessions and were converted to percent of
control response rates using the average rate from the previous training day as the
control value (i.e., average of three cycles). Data are presented as the mean (± 1
SEM) response rate as a percent of control. Thus, for example, a test value of 100%
would indicate the response rate after administration of the compound to be tested
15 was the same as the control response rate and there was no adverse effect of the
compound tested.
Results
Test Method 1: Baseline thermal nociception and PGE2-induced thermal
20 hypersensitivity.
Under baseline conditions, maximal tail-withdrawal latencies (i.e., 20 sec)
were typically obtained with temperatures of 38, 42, and 46°C. When the- water
temperature was increased to 50°C, tail-withdrawal latencies for individual rats were
typically between 5 and 15 sec. The highest temperature of 54°C produced taii-
25 withdrawa! latencies below 10 sec in all rats. Average baseiine T10 values
(withdrawal in 10 seconds) were between 49°C and 51 °C.
A dose of 0.1 mg PGE2 produced a dose- and time-dependent thermal
hypersensitivity manifested as a leftward shift in the temperature-effect curve and a
decrease in the T10 value. Maximal decreases in tail-withdrawal latencies occurred
30 15 min after administration, and latencies returned to baseline by 120 rnin after
injection.
Table 1 below shows the effects of PGE2 in combination with comparative
NMDA antagonist compounds. Up to doses that produced observable signs of
-24-

sedation and ataxia (i.e., Comp. Ex. 1 - <10 mg/kg, Comp. Ex. 2 - <100 mg/kg,
Comp. Ex. 3 - <0.3 mg/kg, Comp. Ex. 4 to 6 - <30 mg/kg}, none of the comparative
compounds, including memantine (Comp. Example 1 and 2), dizocilpine (Comp.
Example 3), ketamine (Comp. Example 4}, ifenfrodil (Comp. Example 5) or CGS-
5 19755 (Comp. Example 6), produced greater than a 25% reversal of PGE2-induced
thermal hypersensitivity. in comparison, [2-(8,9-Dioxo-2,6-diazabicyclo[5.2.0]non-
1(7)-en-2-yl)ethyl]phosphonic acid, a cyclobutene derivative useful in the present
invention (Compound A), produced a 79% reversal following IP administration at 10
mg/kg and a 87% reversal following PO administration at 100 mg/kg. These doses
10 (as high as 178 mg/kg) were not associated with sedation or ataxia as seen with the
comparative compounds. In addition, 1 mg or 3 mg of Compound A administered
intranasally (IN) produced a 37% or 79% reversal, respectively. The mean dose
calculated from subject weight represents doses of 2.6 and 7.5 mg/kg, respectively.
Similarly, another cyclobutene derivative useful in the present invention, 2-[(1H-
15 Tetrazol-5-y/)methyl]-2,6-diazabicyclo[5.2.0]-non-1-(7)-ene-8,9-dione (Compound B)
produced a full reversal of PGE2-tnduced thermal hypersensitivity.
The effectiveness of the cyciobutene derivatives useful in the present
invention, such as Compounds A and B, in relieving pain, such as thermal
hypersensitivity, is surprising and unexpected. For example, a!! the compounds
20 tested according to test method 1 were NMDA receptor antagonists, however
Compounds A and B performed substantially and significantly better that the
comparative compounds. It is especially important to note that both Compounds A
and B, like the comparative compound CGS-19755 are competitive glutamate NMDA
receptor antagonists, but Compounds A and B performed significantly and
25 substantially better.
Table 1: Results of PGE2-induced thermal hypersensitivity
Example Compoundtested Method ofAdmin. % WIPEDose (mg/kg)
0.3 1 3 10 18 30 100
Comp. Ex. 1 memantine IP 13% 15%
Comp. Ex. 2 memantine PO -1% 11% 5%
Comp. Ex. 3 dizocilipine 18%
Comp. Ex. 4 ketamine IP 14% 9%
Comp. Ex. 5 ifenfrodil IP 1% 14%
Comp. Ex. 6 CGS-19755 IP 9% 25% 9%

Table 1 (cont'd.): Results of PGE2-induced thermal hypersensitivity
Example Compound tested Method of Admin. % WIPEDose (mg/kg)
0.3 1 3 10 18 30 100
Example 7 A IP -7% 66% 79%
Example 8 A PO 5% 23% 87%
Example 9 A IN 37%* 79%**
Example 10 B PO 16% 92% 101%
*displayed in column for approximation; actual mean dose is 2.6 mg/kg
**displayed in column for approximation; actual mean dose is 7.5 mg/kg
5
The cyclobutene derivatives useful in the present invention were also tested
with an opioid analgesic to determine the ability of the cydobutene derivative to
reduce thermal sensitivity in combination with an opioid analgesic, morphine. A
minimally effective dose of morphine was administered alone and in combination with
10 ineffective doses of the compounds to be tested. Table 1-2 shows examples in the
warm-water tail withdrawal assay. A dose of 5.6 mg/kg morphine IP (Comp. Ex 11)
produced a small yet significant increase in the T10 (51.2 ± 0.7) compared to the
vehicie T10 (48.9 ± 0.1). When administered in combination with 5.6 mg/kg morphine,
an ineffective dose of 18 mg/kg ketamine IP (Comp, Ex. 12) produced a non-
15 significant increase in the T10 (52.8 ± 0.5) compared to morphine alone (Comp. Ex.
13). In contrast, an ineffective dose of 10 mg/kg Compound A IP (Ex 14) in
combination with morphine significantly and surprisingly increased the T10 (55.8 ±
1.3) compared to morphine alone (Ex. 15).
20 Table 1-2: Warm-water tail withdrawal combination studies
Example CompoundTested H Dose(mg/kg) Change fromBaseline
Comp. Ex. 11 Morphine 5.6 + 2.3
Comp. Ex, 12 Ketamine 18.0 -0.3
Comp. Ex. 13 Morphine +Ketamine 5.6 +18.0 + 3.9
Ex. 14 A 10.0 -0.3
Ex. 15 Morphine +A 5.6 +10.0 + 6.9
The cydobutene derivatives useful in the present invention were also tested
with an opioid analgesic to determine the ability of the cyclobutene derivative to
-26-

reduce PGE2-induced thermal hypersensitivity in combination with an opioid
analgesic, morphine. Table 1-3 shows examples in the PGE2-induced thermal
hypersensitivity assay. PGE2 injected into the tail significantly decreased the T10
(44.8 ± 0.1) compared to the vehicle T10 (50.3 ± 0.4; Comp. Ex. 16). A dose of 5.6
5 mg/kg morphine (Comp. Ex. 17) significantly reversed the T10 to a value similar to
vehicle (50.6 ± 0.5). When administered in combination with 5.6 mg/kg morphine, an
ineffective dose of 18 mg/kg Example 3 IP (Comp. Ex. 18) produced a non-significant
increase in the T10 (51.7 ± 0.2) compared to morphine alone (Comp. Ex. 19). In
contrast, an effective dose of 10 mg/kg Example 6 IP (T10 = 48.8 ± 0.2; Ex. 20) in
10 combination with morphine significantly and surprisingly increased the T10 (55.3 ±
0.2) compared to morphine alone (Ex. 21).
Table-1-3-PGE2-induced-thermal-hypersensitivity-combination-studies
Example CompoundTested Dose(mg/kg) Change fromBaseline
Comp. Ex. 16 vehicle -5.6
Comp. Ex. 17 Morphine 5.6 + 0.3
Comp. Ex. 18 Ketamine 18.0 -5.5
Comp. Ex. 19 Morphine +Ketamine 5.6 +18.0 + 1.4
Ex.20 A 10.0 -1.5
Ex.21 Morphine +A 5.6 +10.0 + 5.0
15
Test Method 2 Results: Chronic Constriction Injury
Table 2 shows the effects of the cyclobutene derivatives useful in the present
invention to reverse CCl-induced tactile hypersensitivity in animals that had received
CCl surgery one week before testing. NMDA receptor antagonists memantine
20 (Comp. Ex 22) and CGS-19755 (Comp. Ex 23) were also tested for comparison. Up
to doses that produced observable signs of sedation and ataxia (i.e., Comp. Ex. 22 -
<10 mg/kg, Comp. Ex. 23- < 30 mg/kg), none of the comparative compounds
produced any reversal of CCl-induced tactile hypersensitivity. in comparison,
Compound A (Example 24) produced a 97% reversal following IP administration and
25 Compound B (Example 25) produced a 40% reversal following IP administration.
The doses for compounds A and B were not associated with sedation or ataxia as
was seen with the comparative compounds.
-27-

Table 2: Chronic Constriction Injury-induced tactile hypersensitivity
Example Compoundtested MethodofAdmin. % ReversalDose (mg/kg)
1 3 10 30
Comp. Ex. 22 memantine IP -25% -45%
Comp. Ex. 23 CGS-19755 IP -9% -5% -17%
Example 24 A IP 13% 45% 97%
Example 25 B IP 13% 14% 40% 12%
The effectiveness of the cyclobutene derivatives useful in the present
5 invention, such as Compounds A and B, in relieving pain, such as CCl-induced tactile
hypersensitivity, is surprising and unexpected. For example, Compounds A and B
performed significantly and substantially better than known NMDA receptor
antagonists memantine and CGS-19755.
10 Test Method 3 Results
To assess potential adverse effects of the cyclobutene derivatives useful in
the present invention, Compound A was administered to animals responding under a
schedule of food presentation. NMDA receptor antagonists memantine and
dizocilpine were also tested for comparison. Table 3 shows that rnemantine (Comp.
15 Ex. 26) and dizocilpine dose-dependently decreased rates of responding. These
were doses that also did not reverse PGE2-induced thermal hypersensitivity or CCl-
induced tactile hypersensitivity. In contrast, Compound A administered JP (Example
28) or PO (Example 29), unexpectedly did not significantly modify rates of
responding at doses that reversed PGE2-induced thermal hypersensitivity or CCl-
20 induced tactile hypersensitivity.
Table 3: Gperant responding
Example CompoundTested Method ofAdmin. Dose mg/kg
0.1 0.3 3 10 30 100
Comp. Ex. 26 memantine IP 93% 2%
Comp. Ex. 27 dizocilpine IP 63% 16%

Example 28 A IP 111% 86%
Example 29 A PO 112% 97% 100%
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WE CLAIM:
1. A process for the preparation of a pharmaceutical composition comprising
bringing into association:
a) a pain treating effective amount of at least one compound having the
formula (I):

wherein:
R1 is hydrogen, alkyl of 1 to 6 carbon atoms or phenylalkyl of 7 to 12 carbon
atoms;
R2 is hydrogen, alkyl of 1 to 6 carbon atoms, alkenyl of 2 to 6 carbon atoms or
phenylalkyl of 7 to 12 carbon atoms; or
R1 and R2 taken together as Z are -CH2CH2— —CH2C(R6)(R7)CH2— or
—CH2C(R8)(R9)—C(R10)(R11)CH2— where R6, R8 and R10 are, independently,
hydrogen, alkyl of 1 to 6 carbon atoms or hydroxyl and R7. R9 and R11 are,
independently, hydrogen or alkyl of 1 to 6 carbon atoms;
A is alkylene of 1 to 6 carbon atoms or alkenylene of 2 to 6 carbon atoms;
X is CO2R3, P(O)(OR4)(OR5), 3,5-dioxo-1,2,4-oxadiazolidin-2-yi or 5-tetrazoIyl
wherein R3, R4 and R5 are, independently, hydrogen or alkyl of 1 to 6 carbon atoms:
or a pharmaceutically acceptable sait thereof; and
b) at least one pharmaceutical carrier.
2. A process as claimed in Claim 1 wherein R1 is hydrogen, methyl, ethyl, or
benzyl.
3. A process as ciaimed in Claim 1 or Claim 2 wherein R2 is hydrogen, methyl,
ethyl, allyl, methallyl or benzyl.
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4. A process as claimed in any one of Claims 1 to 3 wherein R1 and R2 taken
together are Z.
5. A process as claimed in Claim 4 wherein Z is —(CH2)3—.
6. A process as cliam in any one of claims 1 to 5 WHEREIN A is a straight or
branched chain alkylene selected from —CH2—, —CH2CH2—, —CH(CH3)CH2—, —
CH2CH(CH3) —, —(CH2)3—, and — (CH2)4—.
7. A process as claimed in any one of Claims 1 to 6 whereinX is selected from
carboxyl, phosphonyl and 5-tetrazolyl.
8. A process as claimed in any one of Claims 1 to 7 wherein the compound of
formula (I) comprises at least one of:
N-(2-Amino-3,4,dioxo-1 -cyclobuten-1-yl)beta-alanine,
2-[2-[(2-Amino-3,4-dioxo-1-cyciobuten-1-yl)amino]ethyl]-1,2,4-oxadiazoiidine-
3,5-dione,
N-(2-Amino-3,4-dioxo-1-cyclobuten-1-yl)-N-(2-propenyl)glycine,
[2-[(2-Amino-3,4-dioxo-1 -cyclobuten-1 -yl)amino]ethyl]phosphonic acid,
[(E)-4-[(2-Amino-3,4-dioxo-1-cyclobuten-1-yl)amino]-2-butenyl]phosphonic
acid,
[2-[(2-Amino-3,4-dioxo-1-cyclobuten-1-yi)methylamino]ethy!]phosphonic acid;
[2-{7,8-Dioxo-2,5-diazabicyc!o[4.2.0]oct-1(6)-en-2-yl)ethyl]phosphonic acid,
[2-(8,9-Dioxo-2,6-diazabicyclo[5.2.0]non-1 (7)-en-2-yl)ethyl]phosphonic acid,
[2-(4-Hydroxy-8,9-dioxo-2,6-diazabicycio[5.2.0]non-1(7)en-2-
yl)ethyl]phosphonic acid,
8,9-Dioxo-2,6-diazabicyclo[5.2.0]non-1(7)-ene-2-acetic acid,
2-[(1H-Tetrazol-5-yl)methyl]-2,6-diazabicyclo[5.2.0]-non-1-(7)-ene-8,9-dione,
[2-(9,10-Dioxo-2,7-diazabicyclo[6.2.0]dec-1(8)-en-2-yl)ethyl]phosphonic acid,
or a pharmaceutically acceptable salt form of any of these.
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9. A process as claimed in any one of Claims 1 to 8 for the preparation of a
composition for the treatment of acute pain or chronic pain.
10. A process as claimed in Claim 9 wherein the pain is inflammatory pain,
musculoskeletal pain, bony pain, lumbosacral pain, neck or upper back pain, visceral
pain, somatic pain, neuropathic pain, cancer pain, pain caused by injury or surgery,
or headache pain, or combinations thereof.
11. A process as claimed in Claim 9 wherein the chronic pain is associated with
allodynia, hyperalgesia, or both.
12. A process as claimed in Claim 11 wherein the chronic pain is neuropathic
pain; cancer pain; visceral pain; musculoskeletal pain; bony pain; headache pain; or
pain associated with infections, sickle cell anemia, autoimmune disorders, multiple
sclerosis, or inflammation, or combinations thereof.
13 A process as claimed in Claim 9 wherein the pain comprises neuropathic
pain.
14. A process as claimed in Claim 13 wherein the neuropathic pain is associated
with diabetic neuropathy, peripheral neuropathy, post-herpetic neuralgia, trigemina!
neuralgia, lumbar or cervical radiculopathies, fibromyalgia, glossopharyngeai
neuralgia, reflex sympathetic dystrophy, casualgia, thalamic syndrome, nerve root
avulsion, phantom limb pain, reflex sympathetic dystrophy, postthoracotomy pain,
cancer, chemical injury, toxins, nutritional deficiencies, or viral or bacterial infections,
or combinations thereof.
15. A process as claimed in any one of Claims 1 to 14 for the preparation of a
composition further comprising a pharmaceutically effective amount of at least one
pain relieving agent.
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16. A process for the preparation of a pharmaceutical composition for treating
pain comprising bringing into association:
a) a pain treating effective amount of at least one compound of formula (I) as
claimed in any one of claims 1 to 8 or a pharmaceutically acceptable salt
thereof; and
b) a pharmaceutically effective amount of at least one pain relieving agent.
17. A process as claimed in Claim 15 or claim 16 wherein the pain relieving agent
comprises one or more analgesics; anti-inflammatory agents; migraine preparations;
tricyclic antidepressants; anti-epileptics; a2 agonists; or selective serotonin reuptake
inhibitors/selective norepinepherine uptake inhibitors; or combinations thereof.
18. A process as claimed in Claim 17 wherein the pain relieving agent comprises
an opioid analgesic.
19. A process for the preparation of a pharmaceutical composition, in unit dosage
form, for treating pain comprising bringing into association a pain treating effective
unit dosage of at least one compound of formula (I) as claimed in any one of claims 1
to 8 or a pharmaceutically acceptable salt thereof, to provide the composition in unit
dosage form.
20. A process as claimed in Claim 19 for the preparation of a composition in the
form of a tablet or capsule.
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21. A process for the preparation of a pharmaceutical
composition, substantially as herein described,
particularly with reference to the foregoing
examples.
Dated this 23rd day of April, 2007.

33

A process for the preparation of a pharmaceutical composition comprising
bringing into association:
a) a pain treating effective amount of at least one compound having the formula (I):
wherein:
R1 is hydrogen, alkyl of 1 to 6 carbon atoms or phenylalkyl of 7 to 12 carbon atoms;
R2 is hydrogen, alkyl of 1 to 6 carbon atoms, alkenyl of 2 to 6 carbon atoms or
phenylalkyl of 7 to 12 carbon atoms; or
R1 and R2 taken together as Z are
-CH2CH2—, —CH2C(R6)(R7)CH2— or
—CH2C(R8)(R9)—C(R10)(R11)CH2—, where R6, R8 and R10 are, independently, hydrogen, alkyl of 1 to 6 carbon atoms or hydroxyl and R7, R9 and R11 are, independently, hydrogen or alkyl of 1 to 6 carbon atoms; A is alkylene of 1 to 6 carbon atoms or alkenylene of 2 to 6 carbon atoms;
X is CO2R3, P(O)(OR4)(OR5), 3,5-dioxo-1,2,4-oxadiazolidin-2-yl or 5-tetrazolyl
wherein R3, R4 and R5 are, independently, hydrogen or alkyl of 1 to 6 carbon atoms;
or a pharmaceutically acceptable salt thereof; and
b) at least one pharmaceutical carrier.