USPatent N° 5,462,956
| United States Patent |
5,462,956 |
| Daly , et al. |
October 31, 1995 |
Epibatidine
and derivatives,
compositions and methods of treating pain
Abstract
The present invention is directed to compounds,
compositions and methods of treating pain, and derivatives that have potent
analgetic activity. The compounds have the formula: ##STR1## wherein R.sup.1
is selected from H, lower alkyl, C.sub.3 -C.sub.9 cycloalkyl, acyl, C.sub.3 -C.sub.9
cycloalkylalkyl, haloalkyl, alkenyl, alkynyl, hydroxyalkyl, C.sub.3 -C.sub.8
cycloalkenyl C.sub.3 -C.sub.8 cycloalkynyl and phenyl; and wherein R is
selected from cycloalkyl, aryl, heteroaryls (selected from the group
consisting of pyridyl, thienyl, furanyl, imidazolyl, pyrazinyl, and pyrimidyl)
or phenoxy and wherein said R groups can be substituted with hydroxyl, C.sub.1
-C.sub.6 lower alkyl, C.sub.2 -C.sub.6 alkenyl, C.sub.1 -C.sub.6 lower alkoxyl,
halo, C.sub.1 -C.sub.6 haloalkyl, amino, C.sub.1 -C.sub.6 alkylamino and C.sub.2
-C.sub.10 dialkylamino, and sulfonamido or a pharmaceutically acceptable salt
thereof.
|
Inventors: |
Daly; John W. (Washington, DC); Spande;
Thomas F. (Bethesda, MD); Garraffo; Hugo M. (Rockville, MD)
|
|
Assignee: |
The United States of America as represented
by the Department of Health (Washington, DC) |
|
Appl. No.: |
248314 |
|
Filed: |
May 23, 1994 |
|
U.S. Class: |
514/397; 514/413; 548/466; 548/312.1
|
|
Intern'l Class: |
A61K 031/40; C07D 403/04 |
|
Field of Search: |
548/466,312.1 514/413,397 |
References Cited
[Referenced By]
U.S. Patent Documents
|
4499099 |
Feb., 1985 |
Watts |
548/452.
|
|
5015655 |
May., 1991 |
Galliani et al. |
548/452.
|
Primary Examiner: Fan; Jane
Attorney, Agent or Firm: Leydig, Voit & Mayer, Ltd.
Parent Case Text
This is a divisional of application Ser. No. 07/845,042, filed on Mar. 3,
1992, now U.S. Pat. No. 5,314,899. Parent Case Text
This is a divisional of application Ser. No. 07/845,042, filed on Mar. 3,
1992, now U.S. Pat. No. 5,314,899.
Claims
1. A compound having the formula: ##STR8## wherein
R.sup.1 is selected from the group consisting of H, C.sub.1 -C.sub.6 alkyl,
C.sub.3 -C.sub.9 cycloalkyl, C.sub.2 -C.sub.8 acyl, C.sub.4 -C.sub.9
cycloalkylalkyl, C.sub.1 -C.sub.6 haloalkyl, C.sub.2 -C.sub.20 alkenyl, C.sub.2
-C.sub.20 alkynyl, C.sub.1 -C.sub.10 hydroxyalkyl, C.sub.3 -C.sub.8
cycloalkenyl, C.sub.3 -C.sub.8 cycloalkynyl, and phenyl; and wherein R is
selected from the group consisting of thienyl, furanyl, and imidazolyl, where
said R groups are unsubstituted or substituted with one or more substituents
selected from the group consisting of hydroxyl, C.sub.1 -C.sub.6 alkyl, C.sub.2
-C.sub.6 alkenyl, C.sub.1 -C.sub.6 alkoxyl, halo, C.sub.1 -C.sub.6 haloalkyl,
amino, C.sub.1 -C.sub.6 alkylamino, C.sub.2 -C.sub.10 dialkylamino, and
sulfonamido; or a pharmaceutically acceptable salt thereof.
2. The compound of claim 1, wherein R.sup.1 is selected from the group
consisting of H, C.sub.1 -C.sub.6 alkyl, C.sub.3 -C.sub.8 cycloalkyl, C.sub.2
-C.sub.8 acyl, C.sub.4 -C.sub.9 cycloalkylalkyl, C.sub.1 -C.sub.6 haloalkyl,
C.sub.2 -C.sub.10 alkenyl, C.sub.2 -C.sub.10 alkynyl, C.sub.1 -C.sub.10
hydroxyalkyl, C.sub.3 -C.sub.8 cycloalkenyl, C.sub.3 -C.sub.8 cycloalkynyl,
and phenyl.
3. The compound of claim 2, wherein R.sup.1 is selected from the group
consisting of H, C.sub.1 -C.sub.6 alkyl, C.sub.3 -C.sub.8 cycloalkyl, C.sub.2
-C.sub.8 acyl, C.sub.4 -C.sub.9 cycloalkylalkyl, C.sub.1 -C.sub.6 haloalkyl,
C.sub.2 -C.sub.6 alkenyl, C.sub.2 -C.sub.6 alkynyl, C.sub.1 -C.sub.10
hydroxyalkyl, C.sub.3 -C.sub.8 cycloalkenyl, C.sub.3 -C.sub.8 cycloalkynyl,
and phenyl.
4. The compound of claim 3, wherein R.sup.1 is selected from the group
consisting of C.sub.1 -C.sub.6 alkyl, C.sub.3 -C.sub.8 cycloalkyl, and phenyl.
5. The compound of claim 4, wherein said R groups are unsubstituted.
6. The compound of claim 1, wherein R.sup.1 is selected from the group
consisting of methyl, vinyl, allyl, propargyl, n-pentyl, cyclohexyl, and
phenyl; and wherein R is selected from the group consisting of thienyl,
furanyl, and imidazolyl.
7. The compound of claim 3, wherein R.sup.1 is H.
8. The compound of claim 7, wherein said R groups are unsubstituted.
9. The compound of claim 8, wherein R is selected from the group consisting of
2-thienyl, 3-thienyl, and 2-furanyl.
10. A composition comprising an effective analgetic amount of a compound of
claim 1 and a pharmaceutically acceptable carrier therefor.
11. The composition of claim 10, wherein said carrier is suitable for oral
administration.
12. The composition of claim 11, wherein said composition is in the form of a
tablet or capsule.
13. A composition comprising an effective analgetic amount of a compound of
claim 5 and a pharmaceutically acceptable carrier therefor.
14. A composition comprising an effective analgetic amount of a compound of
claim 8 and a pharmaceutically acceptable carrier therefor.
15. A method of treating pain which comprises administering to a host in need
thereof an effective amount of a compound having the formula: ##STR9## wherein
R.sup.1 is selected from the group consisting of H, C.sub.1 -C.sub.6 alkyl,
C.sub.3 -C.sub.9 cycloalkyl, C.sub.2 -C.sub.8 acyl, C.sub.4 -C.sub.9
cycloalkylalkyl, C.sub.1 -C.sub.6 haloalkyl, C.sub.2 -C.sub.20 alkenyl, C.sub.2
-C.sub.20 alkynyl, C.sub.1 -C.sub.10 hydroxyalkyl, C.sub.3 -C.sub.8
cycloalkenyl, C.sub.3 -C.sub.8 cycloalkynyl, and phenyl; and wherein R is
selected from the group consisting of thienyl, furanyl, and imidazolyl, where
said R groups are unsubstituted or substituted with one or more substituents
selected from the group consisting of hydroxyl, C.sub.1 -C.sub.6 alkyl, C.sub.2
-C.sub.6 alkenyl, C.sub.1 -C.sub.6 alkoxyl, halo, C.sub.1 -C.sub.6 haloalkyl,
amino, C.sub.1 -C.sub.6 alkylamino, C.sub.2 -C.sub.10 dialkylamino, and
sulfonamido; or a pharmaceutically acceptable salt thereof.
16. The method of claim 15, wherein R.sup.1 is selected from the group
consisting of H, C.sub.1 -C.sub.6 alkyl, C.sub.3 -C.sub.8 cycloalkyl, C.sub.2
-C.sub.8 acyl, C.sub.4 -C.sub.9 cycloalkylalkyl, C.sub.1 -C.sub.6 haloalkyl,
C.sub.2 -C.sub.10 alkenyl, C.sub.2 -C.sub.10 alkynyl, C.sub.1 -C.sub.10
hydroxyalkyl, C.sub.3 -C.sub.8 cycloalkenyl, C.sub.3 -C.sub.8 cycloalkynyl,
and phenyl.
17. The method of claim 16, wherein R.sup.1 is selected from the group
consisting of H, C.sub.1 -C.sub.6 alkyl, C.sub.3 -C.sub.8 cycloalkyl, C.sub.2
-C.sub.8 acyl, C.sub.4 -C.sub.9 cycloalkylalkyl, C.sub.1 -C.sub.6 haloalkyl,
C.sub.2 -C.sub.6 alkenyl, C.sub.2 -C.sub.6 alkynyl, C.sub.1 -C.sub.10
hydroxyalkyl, C.sub.3 -C.sub.8 cycloalkenyl, C.sub.3 -C.sub.8 cycloalkynyl,
and phenyl.
18. The method of claim 17, wherein R.sup.1 is selected from the group
consisting of C.sub.1 -C.sub.6 alkyl, C.sub.3 -C.sub.8 cycloalkyl, and phenyl.
19. The method of claim 18, wherein said R groups are unsubstituted.
20. The method of claim 17, wherein R.sup.1 is selected from the group
consisting of methyl, vinyl, allyl, propargyl, n-pentyl, cyclohexyl, and
phenyl; and wherein R is selected from the group consisting of thienyl,
furanyl, and imidazolyl.
21. The method of claim 17, wherein R.sup.1 is H.
22. The method of claim 21, wherein said R groups are unsubstituted.
23. The method of claim 22, wherein R is selected from the group consisting of
2-thienyl, 3-thienyl, and 2-furanyl.
Description
FIELD OF THE INVENTION
The present invention is directed to epibatidine and its
derivatives, compositions and methods of treating pain.
BACKGROUND OF THE INVENTION
The control of pain is at present primarily through the use of opioid-like
analgetics, such as morphine, fentanyl, pentazocine, etc., or through non-steroidal
antiinflammatories. There are limitations to the usefulness of such agents,
and other classes of analgetics for the control and amelioration of pain are
needed. A trace alkaloid epibatidine from skins of a neotropical
frog is two-hundred fold more potent than morphine administered subcutaneously
to mice in a standard analgetic test. In addition the analgesia elicited by
epibatidine is not antagonized by the opioid antagonist naloxone,
indicating that the analgesia is not due to actions of epibatidine
at opioid receptors. In support of this conclusion is the very low affinity of
epibatidine for dihydromorphine binding sites in rodent brain
membranes. Epibatidine at higher doses causes a marked Straub-tail
response, as does morphine, an effect linked to activation of dopamine
pathways in the spinal cord. However, the Straub-tail response to
epibatidine, unlike the Straub tail response to morphine, is not
blocked by the opioid-antagonist naloxone.
SUMMARY OF THE INVENTION
The present invention is directed to a purified and isolated compound having
the formula: ##STR2## or a pharmaceutically acceptable salt therof.
The present invention is also directed to a compound having the formula:
##STR3## wherein R.sup.1 is selected from H, lower alkyl, C.sub.3 -C.sub.9
cycloalkyl, acyl, C.sub.3 -C.sub.9 cycloalkylalkyl, haloalkyl, alkenyl,
alkynyl, hydroxyalkyl, C.sub.3 -C.sub.8 cycloalkenyl C.sub.3 -C.sub.8
cycloalkynyl and phenyl; and wherein R is selected from cycloalkyl, aryl,
heteroaryls (selected from the group consisting of pyridyl, thienyl, furanyl,
imidazolyl, pyrazinyl, and pyrimidyl) or phenoxy and wherein said R groups can
be substituted with hydroxyl, C.sub.1 -C.sub.6 lower alkyl, C.sub.2 -C.sub.6
alkenyl, C.sub.1 -C.sub.6 lower alkoxyl, halo, C.sub.1 -C.sub.6 haloalkyl,
amino, C.sub.1 -C.sub.6 alkylamino and C.sub.2 -C.sub.10 dialkylamino, and
sulfonamido or a pharmaceutically acceptable salt thereof with the proviso
that R is not 6-chloro-3-pyridyl and R.sup.1 is not H.
The present invention is also directed to analgetic compositions which
comprise an effective amount of the above compounds, and a pharmaceutically
acceptable carrier and a method for treating analgesia which comprises
administering to a host in need thereof a analgetic effective amount of the
compounds described above.
Typical alkenyl and alkynyl groups may have one unsaturated bond, such as an
allyl group, or may have a plurality of unsaturated bonds, with such plurality
of bonds either adjacent, such as allene-type structures, or in conjugation,
or separated by several saturated carbons.
The term "pharmaceutically-acceptable salts" embraces commonly used alkali
metal salts and addition salts of free acids or free bases. Since the
compounds contain basic nitrogen atoms, such salts are typically acid addition
salts, or quaternary ammonium salts with one or more C.sub.1 -C.sub.6 alkyl or
cycloalkyl groups.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Where the term "alkyl" is used, either alone or within other terms, such as "haloalkyl"
and "hydroxyalkyl", the term "alkyl" embraces linear or branched radicals
having one to about twenty carbon atoms or, preferably, one to about ten
carbon atoms.
By lower alkyl, straight or branched, is meant structured monovalent radicals
having from 1 to 6 carbon atoms. Examples of lower alkyl include, but are not
limited to, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl,
tertiary-butyl, n-pentyl, iso-pentyl, methylbutyl, dimethylbutyl, neopentyl
and n-hexyl.
By cycloalkyl is meant radicals originating from cycloalkanes having from 3 to
8 carbon atoms. Examples of cycloalkyls, include, but are not limited to,
cyclopropyl, cyclobutyl, cyclopentyl and cyclohexyl. The cycloalkyl groups can
be further substituted with a halogen atom such as bromine, fluorine or
chlorine.
By cycloalkylalkyl is meant radicals originating from an alkane of 1 to 6
carbon atoms and which are further substituted by cycloalkyls having 3 to 8
carbon atoms. Examples of cycloalkylalkyl include, but are not limited to,
cyclopropylmethyl, cyclobutylmethyl, 1-cyclopentylethyl, cyclohexylmethyl, 2-cyclohexylethyl
and 3-cyclohexylpropyl.
By acyl is meant an organic radical derived from an organic acid by the
removal of the hydroxyl group, i.e., a radical having the formula R.sup.2 C(O)--,
wherein R.sup.2 is a lower C.sub.1 -C.sub.6 alkyl, C.sub.3 -C.sub.7 cycloalkyl,
a phenyl, a benzyl or phenethyl group. Examples of acyl groups, include, but
are not limited to, formyl, acetyl, propionyl and butyryl.
By arylacyl is meant an acyl group as described above wherein R.sup.2 is an
aromatic radical, i.e., phenyl and naphthyl. The aromatic radical can be
further substituted by C.sub.1 -C.sub.6 lower alkyl, halogen, lower haloalkyl,
lower mono- and di-alkylamino and sulfonamido groups.
By lower haloalkyl is meant a C.sub.1 -C.sub.6 alkyl radical which is
substituted with one or more, same or different, halogen atoms selected from
the group consisting of bromine, chlorine and fluorine and preferred are mono-
or di-halo substituted C.sub.1 -C.sub.6 alkyl. Examples of lower haloalkyl
include, but are not limited to, dibromomethyl, dichloromethyl,
bromochloromethyl and trifluoromethyl.
The term "hydroxyalkyl" embraces linear or branched alkyl groups having one to
about ten carbon atoms, any one of which may be substituted with one or more
hydroxyl groups. The terms "alkenyl" and "alkynyl" embraces linear or branched
radicals having two to about twenty carbon atoms, preferably two to about ten
carbon atoms, and containing at least one carbon-carbon double- or triple-bond.
By C.sub.2 -C.sub.6 alkenyl is meant a univalent linear or branched aliphatic
radical having at least one double-bond or a plurality of bonds either
adjacent, such as allene-type structures, or in conjugation or separated by
several saturated carbons. Examples of alkenyl groups include, but are not
limited to, ethenyl, 2-propenyl, 1-butenyl, 2-butenyl, 3-butenyl, 1-pentenyl,
2-pentenyl, 3-pentenyl, 1-hexenyl, 2-hexenyl and 3-hexenyl.
By C.sub.2 -C.sub.6 alkynyl is meant a univalent linear or branched radical
having at least 1 triple-bond. Examples of C.sub.2 -C.sub.6 alkynyl groups
include, but are not limited to, ethynyl, 1-propynyl, 2-propynyl, 1-butynyl,
2-butynyl, 3-butynyl, 1-pentynyl, 2-pentynyl, 3-pentynyl, 1-hexynyl, 2-hexynyl
and 3-hexynyl.
The terms "cycloalkenyl" and "cycloalkynyl" embrace cyclic radicals having
three to about ten ring carbon atoms including, at least one double- or
triple-bond involving, respectively, adjacent ring carbons. The term "alkoxyl"
embraces linear or branched oxy-containing radicals each having alkyl portions
of one to about ten carbon atoms, such as a methoxyl group. The "alkoxyl" or "alkoxyalkyl"
radicals may be further substituted with one or more halogen atoms, such as
fluorine, chlorine or bromine, to provide haloalkoxyl or haloalkoxyalkyl
groups. The term "heteroaryl" embraces aromatic ring systems containing one,
two or three hetero atoms selected from oxygen, nitrogen and sulfur in a ring
system having five, six or seven ring members. Examples of heteroaryl groups
include, but are not limited to, thienyl, furanyl, pyridinyl, thiazolyl,
pyrimidyl and isoxazolyl.
Pharmaceutically acceptable salts useful in the present invention include
compounds capable of forming a salt, for example, at the nitrogen atom on the
ring and which are bio-compatible and are well known to those skilled in the
art. Examples of pharmaceutically acceptable salts include, but are not
limited to, oxalates, citrates, tartrates, hydrochloride salts and the like,
since the compounds contain basic nitrogen atoms, such salts can be acid
addition salts or quaternary ammonium salts with 1 or more C.sub.1 -C.sub.6
alkyl or cycloalkyl groups.
The compounds and compositions of the present invention are useful in treating
pain.
By pain is meant acute and chronic pain, due to illness, trauma or associated
with inflammation or postoperative recovery.
All percentages are by weight unless otherwise stated.
EXAMPLE 1
Isolation of Epibatidine
Skins from 750 Epipedobates tricolor from southwestern Ecuador were minced and
extracted by trituration three times with methanol (total volume 1.5 L). After
concentration of the methanol extract in vacuo to 500 mL and dilution with an
equal volume of water, alkaloids were extracted three times into equal volumes
of chloroform. The chloroform-soluble alkaloids were then extracted four times
into one-half volumes of 0.1N HCl. The combined 0.1N HCl solutions were
adjusted to pH 9 with 1N aqueous ammonia, followed by extraction of alkaloids
three times into equal volumes of chloroform. The combined chloroform
solutions were dried over sodium sulfate and concentrated in vacuo to dryness
to yield 80 mg of crude alkaloids. Sixty milligrams of crude alkaloids from
Epipedobates tricolor were dissolved in 0.5 mL of chloroform and applied to a
prepacked silica gel 60 column (Merck 1.0.times.24 cm) and eluted with 500 mL
of chloroform-methanol-aqueous 6N ammonia (800:10:0.1) and then with 1 L of
chloroform-methanol-aqueous ammonia (1000:100:0.2). Five-milliliter fractions
were collected. Fractions 108-111 contained the bulk of the alkaloid
epibatidine that elicited the Straub-tail reaction in mice. The
estimated recovery of Straub-tail equivalents from the column was about 40%.
Fraction 108 in methanol was concentrated to 0.4 mL and further purified by
HPLC on Partisil PXS 10/25 PAC with a solvent of acetonitrile-0.01M (NH.sub.4).sub.2
CO.sub.3 at 4 mL/min. Fractions of 0.5 mL were extracted with chloroform, the
chloroform was dried over Na.sub.2 SO.sub.4 and evaporated. Fraction 4
contained almost exclusively epibatidine based upon thin-layer
and gas chromatographic analysis and was used for biological testing. Fraction
3 contained substantial amounts of epibatidine, along with other
alkaloids.
EXAMPLE 2
Preparation of N-Acetylepibatidine
A solution of epibatidine (.about.300 .mu.g) in 1 ml of CH.sub.3
OH was evaporated and treated with 2 drops of acetic anhydride for 2 hrs. at
room temperature, then saturated NaHCO.sub.3 was added and the aqueous
solution extracted with several one drop portions of EtOAc. The EtOAc layer
was extracted with three 200 .mu.l portions of 0.1N HCl to remove any
contaminating amines, dried and evaporated to dryness with a nitrogen stream.
The resulting N-acetylepibatidine was homogeneous by gas chromatographic
analysis and was obtained in near quantitative yield.
EXAMPLE 3
Synthesis of (.+-.) Epibatidine (8)
The synthesis of epibatidine is shown in Scheme 1. 3-pyridyl-2-cyclohexa-1,3-diene
(1) prepared from cyclohexane-1,2-dione by the steps of Scheme 2 is reacted
with tertiary butylnitrosoformate (2) in methylene chloride to provide the
Diels-Alder Adduct 3. Reagent 2 is generated in situ from tertiary-butyloxycarbonylhydroxylamine
and tetraethylammonium periodate. Adduct 3 (one of the two regioisomers is
shown; both produce the same cyclized product 6) is hydrogenated with a 5%
palladium-on-charcoal catalyst in methanol to the amino alcohol derivative 4.
The amino alcohol 4 is then treated with thionyl chloride in pyridine to give
the chloro amide 5 which is cyclized with base-treatment to give 6 . Free
radical chlorination of 6 (carbon tetrachloride, UV light source) provides 7,
which on deblocking with trifluoroacetic acid in methylene chloride gives (.+-.)
epibatidine (8). ##STR4##
As shown in Scheme 2, cyclohexane-1,2-dione is converted to 2-methoxy-cyclohex-2-enone
(9) with trimethyl orthoformate and acid, and reacted with the Grignard
derivative from 3-bromopyridine, 3-pyridylmagnesium bromile, in
tetrahydrofuran to produce 10, which is dehydrated with phosphorous
oxychloride in pyridine and hydrolyzed with dilute aqueous hydrochloric acid
to give 11. Compound 11 is reduced with sodium borohydride in methanol
containing cerium chloride to the allylic alcohol 12, which is dehydrated with
phosphorous oxychloride in pyridine at 0.degree. C. to give 1. ##STR5##
When phenylmagnesium bromide (a) or phenyllithium (b) is used in place of 3-pyridylmagnesium
bromide, the phenylcarbinol enol ether 13 arises (Scheme 3). This is refluxed
with acetic anhydride (c) or dehydrated with phosphorous oxychloride and
pyridine (d) and hydrolyzed with aqueous hydrochloric acid (e) to give 2-phenyl-2-cyclohexenone
(14). Reduction of 14 with sodium borohydride and cerium chloride in methanol
(f) provides the allylic alcohol 15 which is dehydrated (d) to 2-phenyl-1,3-cyclohexadiene
16. Reaction of 16 with tertiary butyl nitrosoformate (2) as in Scheme 1,
provides the Diels-Alder cycloadduct 17, which can be converted in four steps
to (.+-.) exo-2-phenyl-7-azabicyclo[2.2.1]heptane (18), the phenyl analog of
epibatidine. ##STR6##
If instead of a) or b) above, 2- or 3-thienylmagnesium bromide or 2-lithiofuran
is used, the analogous exo 2-(2-thienyl)-, 2-(3-thienyl)-, or 2-(2-furanyl)-7-azabicyclo[2.2.1]heptanes
(19) are produced (See Scheme 4) . ##STR7##
The exo 2-alkyl, 2-cycloalkyl or 2-aryl-substituted 7-azabicyclo[2.2.1]heptanes
(19) can be N-acylated to amides (20) with a variety of acyl chlorides or acid
anhydrides (see Scheme 5) as described for the conversion of epibatidine
to N-acetyl epibatidine (see Example 2 above). These in turn can
be reduced to N-alkyl, N-cycloalkylmethylene, or N-arylmethylene-2-substituted
7-azabicyclo [2.2.1]heptanes (21) using lithium aluminum hydride in
tetrahydrofuran.
BIOLOGICAL DATA
The assay of analgetic activity of epibatidine and comparison
with morphine was conducted by a standard procedure [Eddy N. B. and Leimbach,
D., J. Pharmacol. Exp. Therap. 107, 385-393, 1953]. NIH mice were dropped onto
a hot plate maintained at 55.degree. C. and the reaction time was determined.
The criterion for a reaction was kicking the hind leg, attempting to jump out,
or shaking a foot and turning and licking it. Reaction time for each mouse was
determined at least twice before and 5, 10, 20, 30, 45 and 60 min after
administration of compound. An analgetic effect was significant if the
reaction times over the 60 min assay exceeded the values calculated based on
preinjection time by 300 sec. A range of concentrations of a compound was used
to determine the ED.sub.50, i.e., the dose at which 50% of the mice would show
a significant analgetic effect.
Analgetic activity also was apparent for epibatidine in the
Nilsen assay [Nilsen, P. L., Acta Pharmacol. Toxicol. 18, 10-22, 1961].
TABLE 1
______________________________________
Comparison of Activity of Morphine and
Epibatidine as Analgetics.
ED.sub.50 Dose for
Effect of Naloxone
Hot Plate Analgesia
(5 mg/kg sc)
______________________________________
Morphine 1 mg/kg sc Blockade of Analgesia
Epibatidine
0.005 mg/kg sc No effect
______________________________________
The Straub-tail reaction was assayed by a standard
procedure [Aceto, M. D., et. al., Brit. J. Pharmacol. 36, 225-239, 1969].
Briefly the degree of Straub-tail reaction was observed after subcutaneous (sc)
injection of doses of morphine and epibatidine and the dose
required for a greater than 45.degree. arch of tail was determined. A dose of
10 mg/kg of morphine was required, while a dose of 20 .mu.g/kg of
epibatidine elicited a comparable Straub-tail reaction. Naloxone at 5
mg/kg administered 20 min prior to either morphine or epibatidine
prevented the Straub-tail reaction to 10 mg/kg morphine, but only slightly
reduced the Straub-tail reaction to 20 .mu.g/kg epibatidine.
The affinity of morphine and epibatidine for opioid-binding
sites in guinea pig brain preparations was conducted by a standard procedure
[Pert, C. P. and Snyder, S., Mol. Pharmacol., 10, 868-879, 1974]. Briefly,
cerebral tissue from brains of male Hartley guinea pigs was homogenized in 10
volumes of ice-cold 50 mM Tris-HCl buffer (pH 7.4) for 20 sec. in a Polytron
homogenizer at 3000 rpm. After centrifugation at 18,000 G for 10 min., the
pellet was reconstructed to the same volume in Tris buffer. Aliquots of the
suspension (1.9 ml) were incubated with 1 nM .sup.[3 H]dihydromorphine and
various concentrations of morphine or epibatidine in a final
volume of 2 ml for 30 min. at 25.degree. in the dark. Samples were chilled to
0.degree. and filtered through glass fiber filters, followed by two washes
with 5 ml of ice cold Tris buffer. Radioactivity retained on the filter was
determined with a liquid scintillation counter. Nonspecific binding of [.sup.3
H]dihydromorphine was determined in the presence of 100 nM naloxone. Morphine
had an IC.sub.50 of 1.1 nM, while epibatidine was nearly
inactive with an IC.sub.50 of 8,800 nM.
Embraced within this invention would be pharmaceutical compositions consisting
of the epibatidine-class compound in association with one or
more pharmaceutically-acceptable carriers and/or diluents and/or adjuvants (collectively
referred to herein as "carrier" materials) and, if desired, other active
ingredients. The compounds of the present invention may be administered by any
suitable route, preferably in the form of a pharmaceutical composition adapted
to such a route, and in an analgetic dose effective for the treatment intended.
Therapeutically effective analgetic doses of the compounds of the present
invention required to prevent or arrest the progress of the medical condition
will be readily ascertained by one of ordinary skill in the art. The compounds
and compositions may, for example, be administered parenterally, for example,
intravascularly, intraperitoneally, subcutaneously, intramuscularly; or
topically.
For oral administration, the pharmaceutical compositions may be in the form,
for example, of a tablet, capsule, suspension, or liquid. The pharmaceutical
composition is preferably made in the form of a dosage unit containing a
particular amount of the active ingredient. Examples of such dosage units are
tablets or capsules. The active ingredient may also be administered by
injection as a composition wherein, for example, saline or dextrose solutions
or water may be used as a suitable carrier. A suitable dose can be
administered, in multiple sub-doses per day. These sub-doses may be
administered in unit dosage forms.
By analgetic effective amount is meant the dosage regimen for treating chronic
or acute pain with the compounds and/or compositions of this invention and
would be selected in accordance with a variety of factors, including the type,
age, weight, sex and medical condition of the patient, the severity of the
disease, the route of administration, and the particular compound employed. An
analgetic effective amount would be considered between from about 0.1 to 20 .mu.g/kg
body weight per parenteral dose. A preferred dose would be from about 1-6 .mu.g/kg
body weight per parenteral dose.
For therapeutic purposes, the compounds of this invention are ordinarily
combined with one or more adjuvants appropriate to the indicated route of
administration. If administered per os, the compounds may be admixed with
lactose, sucrose, starch powder, cellulose esters of alkanoic acids, cellulose
alkyl esters, talc, stearic acid, magnesium stearate, magnesium oxide, sodium
and calcium salts of phosphoric and sulfuric acids, gelatin, acacia gum,
sodium alginate, polyvinylpyrrolidone, and/or polyvinyl alcohol, and then
tableted or encapsulated for convenient administration. Such capsules or
tablets may contain a controlled-release formulation as may be provided in a
dispersion of active compound in hydroxypropylmethyl cellulose. Formulations
of parenteral administration may be in the form of aqueous or non-aqueous
isotonic sterile injectable solutions or suspensions. These solutions and
suspensions may be prepared from sterile powders or granules having one or
more of the carriers or diluents mentioned for use in the formulations for
oral administration. The compounds may be dissolved in water, polyethylene
glycol, propylene glycol, ethanol, corn oil, cottonseed oil, peanut oil, or
various buffers. Other adjuvants and modes of administration are well and
widely known in the pharmaceutical art.
Although this invention has been described with respect to specific
embodiments, the details of these embodiments are not to be construed as
limitations. Various equivalents, changes and modifications may be made
without departing from the spirit and scope of this invention, and it is
understood that such equivalent embodiments are part of this invention.
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