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Ketamine Derivatives

20190169113 ยท 2019-06-06

    Inventors

    Cpc classification

    International classification

    Abstract

    pa The present invention relates to ketamine derivatives of the formula (I), pharmaceutical compositions comprising them, and methods for treating pain comprising administering them, and their use in the manufacture of medicaments for treating pain. The present invention also relates to methods for anaesthetizing and methods for sedating a subject comprising administering ketamine derivatives of the formula (II).

    Claims

    1. A method for anaesthetizing or sedating a subject in need thereof, the method comprising administering a therapeutically effective amount of a compound of formula (I) or a pharmaceutically acceptable salt or solvate thereof to the subject, wherein: ##STR00013## wherein Y.sup.1 is C.sub.2-6aliphaticC(O)OR.sup.1, C.sub.2-6aliphaticOC(O)R.sup.1, C.sub.1-6aliphaticC(O)OC.sub.1-6aliphaticC(O)OR.sup.1, or C.sub.1-6aliphaticC(O)OC.sub.1-6aliphaticOR.sup.3, wherein each aliphatic is optionally substituted with one or more R.sup.2; R.sup.1 is C.sub.1-6aliphatic, optionally substituted with one or more halo, CN, NO.sub.2, NH.sub.2, NHR.sup.11, NR.sup.11-R.sup.12, C.sub.1-6haloalkyl, C.sub.1-6haloalkoxy, C(O)NH.sub.2, C(O)NHR.sup.11, C(O)NR.sup.11R.sup.12, SO.sub.2R.sup.11, OR.sup.11, C(O)R.sup.11, and C.sub.1-6aliphatic; R.sup.2 is C.sub.1-6aliphatic, optionally substituted with one or more halo, OR.sup.11, or CN; R.sup.3 is hydrogen or R.sup.1; R.sup.11 and R.sup.12 are each independently C.sub.1-6aliphatic; or R.sup.11 and R.sup.12 together with the nitrogen atom to which they are attached are a heteroaryl or heterocyclyl ring; Y.sup.2 is hydrogen or R.sup.2; X.sup.1 and X.sup.2 are each independently hydrogen, R.sup.2, halo, NO.sub.2, NH.sub.2, NHR.sup.11, NR.sup.11R.sup.12, C.sub.1-6haloalkyl, C.sub.1-6haloalkoxy, C(O)NH.sub.2, C(O)NHR.sup.11, C(O)NR.sup.11R.sup.12, SO.sub.2R.sup.11, OR.sup.11, C(O)R.sup.11, C.sub.1-6aliphaticY.sup.1, OY.sup.1, C(O)Y.sup.1, SO.sub.2Y.sup.1, or C(O)NHY.sup.1 at any of the available 2-5 positions; or a pharmaceutically acceptable salt or solvate thereof.

    2. The method of claim 1, wherein: Y.sup.1 is C.sub.2-6alkylC(O)OR.sup.1, C.sub.2-6alkylOC(O)R.sup.1, C.sub.1-6alkylC(O)OC.sub.1-6alkylC(O)OR.sup.1, or C.sub.1-6alkylC(O)OC.sub.1-6alkylOR.sup.3, wherein each alkyl is optionally substituted with one or more R.sup.2; R.sup.1 is C.sub.1-6aliphatic, optionally substituted with one or more halo, CN, NO.sub.2, NH.sub.2, NHR.sup.11, NR.sup.11-R.sup.12, C.sub.1-6haloalkyl, C.sub.1-6haloalkoxy, C(O)NH.sub.2, C(O)NHR.sup.11, C(O)NR.sup.11R.sup.12, SO.sub.2R.sup.11, OR.sup.11, C(O)R.sup.11, and C.sub.1-6aliphatic; R.sup.2 is C.sub.1-6aliphatic, optionally substituted with one or more halo, OR.sup.11, or CN; R.sup.3 is hydrogen or R.sup.1; R.sup.11 and R.sup.12 are each independently C.sub.1-6aliphatic; or R.sup.11 and R.sup.12 together with the nitrogen atom to which they are attached are a heteroaryl or heterocyclyl ring; Y.sup.2 is hydrogen or R.sup.2; X.sup.1 and X.sup.2 are each independently hydrogen, R.sup.2, halo, NO.sub.2, NH.sub.2, NHR.sup.11, NR.sup.11R.sup.12, C.sub.1-6haloalkyl, C.sub.1-6haloalkoxy, C(O)NH.sub.2, C(O)NHR.sup.11, C(O)NR.sup.11R.sup.12, SO.sub.2R.sup.11, OR.sup.11, C(O)R.sup.11, C.sub.1-6aliphaticY.sup.1, OY.sup.1, C(O)Y.sup.1, SO.sub.2Y.sup.1, or C(O)NHY.sup.1 at any of the available 2-5 positions; or a pharmaceutically acceptable salt or solvate thereof.

    3. The method of claim 2, wherein Y.sup.1 is C.sub.2-6alkylC(O)OR.sup.1 or C.sub.2-6alkylOC(O)R.sup.1, wherein each alkyl is optionally substituted.

    4. The method of claim 2, wherein Y.sup.1 is C.sub.2-6alkylC(O)OR.sup.1, wherein the alkyl is optionally substituted.

    5. The method of claim 2, wherein R.sup.1 is C.sub.1-6alkyl, C.sub.2-6alkenyl, cycloalkyl, or cycloalkenyl, wherein each alkyl and cycloalkyl are optionally substituted with one or more halo, CN, NO.sub.2, NH.sub.2, NHR.sup.11, NR.sup.11R.sup.12, C.sub.1-6haloalkyl, C.sub.1-6haloalkoxy, C(O)NH.sub.2, C(O)NHR.sup.11, C(O)NR.sup.11R.sup.12, SO.sub.2R.sup.11, OR.sup.11, and C(O)R.sup.11; and each alkyl is optionally substituted with cycloalkyl or cycloalkenyl; and each cycloalkyl is optionally substituted with C.sub.1-6alkyl or C.sub.2-6alkenyl.

    6. The method of claim 5, wherein R.sup.1 is C.sub.1-6alkyl or cycloalkyl, wherein each alkyl and cycloalkyl is optionally substituted.

    7. The method of claim 6, wherein R.sup.1 is C.sub.1-6alkyl, wherein each alkyl is optionally substituted.

    8. The method of claim 2, wherein R.sup.2 is C.sub.1-6alkyl or cycloalkyl, optionally substituted with one or more halo, OR.sup.11, or CN.

    9. The method of claim 8, wherein R.sup.2 is C.sub.1-6alkyl, optionally substituted with one or more halo, OR.sup.11, or CN.

    10. The method of claim 2, wherein Y.sup.2 is hydrogen or C.sub.1-6alkyl, wherein the alkyl is optionally substituted.

    11. The method of claim 2, wherein X.sup.1 and X.sup.2 are each independently hydrogen, R.sup.2, halo, NO.sub.2, NH.sub.2, NHR.sup.11, NR.sup.11R.sup.12, C.sub.1-6haloalkyl, C.sub.1-6haloalkoxy, C(O)NH.sub.2, C(O)NHR.sup.11, C(O)NR.sup.11R.sup.12, SO.sub.2R.sup.11, OR.sup.11, or C(O)R.sup.11; or X.sup.2 is C.sub.1-6alkylY.sup.1, OY.sup.1, C(O)Y.sup.1, SO.sub.2Y.sup.1, or C(O)NHY.sup.1 at any of the available 2-5 positions.

    12. The method of claim 11, wherein X.sup.1 and X.sup.2 are each independently hydrogen, R.sup.2, halo, C.sub.1-6haloalkyl, C.sub.1-6haloalkoxy, SO.sub.2R.sup.11, or OR.sup.11 at any of the available 2-5 positions.

    13. The method of claim 12, wherein X.sup.1 is 2-chloro; and X.sup.2 is hydrogen, R.sup.2, halo, C.sub.1-6haloalkyl, C.sub.1-6haloalkoxy, SO.sub.2R.sup.11, or OR.sup.11 at any of positions 3-5.

    14. The method of claim 2, wherein Y.sup.1 is (CR.sup.AR.sup.B).sub.m(CR.sup.CR.sup.D).sub.nC(O)OR.sup.1, (CR.sup.AR.sup.B).sub.m(CR.sup.CR.sup.D).sub.nOC(O)R.sup.1, (CR.sup.AR.sup.B).sub.m-1(CR.sup.CR.sup.D).sub.nC(O)O(CR.sup.GR.sup.H).sub.p(CR.sup.ER.sup.F).sub.oC(O)OR.sup.1, or (CR.sup.AR.sup.B).sub.m-1(CR.sup.CR.sup.D).sub.nC(O)O(CR.sup.GR.sup.H).sub.p(CR.sup.ER.sup.F).sub.oOR.sup.3; m is an integer from 2 to 6; o is an integer from 1 to 6; n and p are each independently 0 or 1; the sum of m and n and the sum of o and p is 6 or less; and R.sup.A, R.sup.B, R.sup.C, R.sup.D, R.sup.E, R.sup.F, R.sup.G, and R.sup.H at each instance of m, n, o, and p are each independently hydrogen or R.sup.2.

    15. The method of claim 14, wherein Y.sup.1 is (CR.sup.AR.sup.B).sub.m(CR.sup.CR.sup.D).sub.nC(O)OR.sup.1.

    16. The method of claim 14, wherein R.sup.A, R.sup.B, R.sup.E, and R.sup.F at each instance of m and o are each independently hydrogen; and R.sup.C, R.sup.D, R.sup.G, and R.sup.H at each instance of n and p are each independently hydrogen or R.sup.2.

    17. The method of claim 2, wherein the compound is 3-((1-(2-chlorophenyl)-2-oxocyclohexyl)amino)propyl acetate, ethyl 3-((1-(2-chlorophenyl)-2-oxocyclohexyl)amino) propanoate, iso-propyl 3-((1-(2-chlorophenyl)-2-oxocyclohexyl)amino) propanoate, n-propyl 3-((1-(2-chlorophenyl)-2-oxocyclohexyl)amino) propanoate, ethyl 4-((1-(2-chlorophenyl)-2-oxocyclohexyl)amino) butanoate, isopropyl 4-((1-(2-chlorophenyl)-2-oxocyclohexyl)amino) butanoate, n-propyl 4-((1-(2-chlorophenyl)-2-oxocyclohexyl)amino) butanoate, methyl 5-((1-(2-chlorophenyl)-2-oxocyclohexyl)amino) pentanoate, ethyl 5-((1-(2-chlorophenyl)-2-oxocyclohexyl)amino) pentanoate, isopropyl 5-((1-(2-chlorophenyl)-2-oxocyclohexyl)amino) pentanoate, n-propyl 5-((1-(2-chlorophenyl)-2-oxocyclohexyl)amino) pentanoate, ethyl 3-((1-(2-chlorophenyl)-2-oxocyclohexyl)(methyl)amino) propanoate, ethyl 4-((1-(2-chlorophenyl)-2-oxocyclohexyl)(methyl)amino) butanoate, or methyl 5-((1-(2-chlorophenyl)-2-oxocyclohexyl)(methyl)amino) pentanoate, or a pharmaceutically acceptable salt or solvate thereof.

    18. The method of claim 2, wherein X.sup.1 is 2-halo and X.sup.2 is hydrogen.

    19. The method of claim 2, wherein Y.sup.2 is hydrogen or methyl.

    20. The method of claim 2, wherein R.sup.1 is C.sub.1-6alkyl.

    21. The method of claim 2, wherein X.sup.1is 2-chloro and X.sup.2 is hydrogen.

    22. The method of claim 2, wherein the compound is methyl 5-((1-(2-chlorophenyl)-2-oxocyclohexyl)amino)pentanoate, or a pharmaceutically acceptable salt or solvate thereof.

    23. The method of claim 2, wherein the compound is isopropyl 3-((1-(2-chlorophenyl)-2-oxocyclohexyl)amino)propanoate, or a pharmaceutically acceptable salt or solvate thereof.

    24. A compound of formula (I): ##STR00014## wherein Y.sup.1 is C.sub.2-6aliphaticC(O)OR.sup.1, C.sub.2-6aliphaticOC(O)R.sup.1, C.sub.1-6aliphaticC(O)OC.sub.1-6aliphaticC(O)OR.sup.1, or C.sub.1-6aliphaticC(O)OC.sub.1-6aliphaticOR.sup.3, wherein each aliphatic is optionally substituted with one or more R.sup.2; R.sup.1 is C.sub.1-6aliphatic, optionally substituted with one or more halo, CN, NO.sub.2, NH.sub.2, NHR.sup.11, NR.sup.11-R.sup.12, C.sub.1-6halalkyl, C.sub.1-6haloalkoxy, C(O)NH.sub.2, C(O)NHR.sup.11, C(O)NR.sup.11R.sup.12, SO.sub.2R.sup.11, OR.sup.11, C(O)R.sup.11, and C.sub.1-6aliphatic; R.sup.2 is C.sub.1-6aliphatic, optionally substituted with one or more halo, OR.sup.11, or CN; R.sup.3 is hydrogen or R.sup.1; R.sup.11 and R.sup.12 are each independently C.sub.1-6aliphatic; or R.sup.11 and R.sup.12 together with the nitrogen atom to which they are attached are a heteroaryl or heterocyclyl ring; Y.sup.2 is hydrogen or R.sup.2; X.sup.1 and X.sup.2 are each independently hydrogen, R.sup.2, halo, NO.sub.2, NH.sub.2, NHR.sup.11, NR.sup.11R.sup.12, C.sub.1-6haloalkyl, C.sub.1-6haloalkoxy, C(O)NH.sub.2, C(O)NHR.sup.11, C(O)NR.sup.11, R.sup.12, SO.sub.2R.sup.11, OR.sup.11, C(O)R.sup.11, C.sub.1-6aliphaticY.sup.1, OY.sup.1, C(O)Y.sup.1, SO.sub.2Y.sup.1, or C(O)NHY.sup.1 at any of the available 2-5 positions; or a pharmaceutically acceptable salt or solvate thereof.

    Description

    BRIEF DESCRIPTION OF THE DRAWINGS

    [0180] The invention will now be described with reference to the Figures in which:

    [0181] FIG. 1A and FIG. 1B are graphs showing time-course for anaesthesia (loss and recovery of righting reflex) with ketamine and rac-C2nPr (FIG. 1A) and rac-C4Me (FIG. 1B). The grey panel shows the duration of drug infusion (measurement taken every minute). .circle-solid..circle-solid..circle-solid..circle-solid.: test compound. .square-solid..square-solid..square-solid..square-solid.: ketamine.

    [0182] FIG. 2A and FIG. 2B are graphs showing time-course for analgesia (pedal withdrawal reflex score) with ketamine and rac-C2nPr (FIG. 2A) and rac-C4Me (FIG. 2B). The grey panel shows the duration of drug infusion (measurement taken every minute). Error bars are SEM. .circle-solid..circle-solid..circle-solid..circle-solid.: test compound. .square-solid..square-solid..square-solid..square-solid.: ketamine.

    [0183] FIG. 3 is a plot (log 10) of effective potency (dose [mg/kg] to LRR) vs. duration (time to RRR) for ketamine and compounds of the invention. The alkyl chain length of compounds is denoted by symbol: =C2; .circle-solid.=C3; .square-solid.=C4; .box-tangle-solidup.=ketamine. 7=rac-C3OAc, 7S=(S)-C3OAC, 832 rac-C2Et, 8S=(S)-C2Et, 9=rac-C2iPr, 9S=(S)-C2iPr, 9R=(R)-C2iPr, 10=rac-C2nPr, 1132 rac-C3Et, 12=rac-C3iPr, 13=rac-C3nPr, 14=rac-C4Me, 14S=(S)-C4Me, 15=rac-C4Et, 16=rac-C4iPr, and 17=rac-C4nPr.

    DETAILED DESCRIPTION OF THE INVENTION

    [0184] The present invention generally relates to ketamine derivatives and their use as anaesthetics, analgesics, or sedatives.

    [0185] The applicants have invented new ketamine derivatives of the formula (I) as defined above which can provide anaesthetic and/or analgesic effects similar to ketamine, but at least in some embodiments have the advantage of shortening the period of recovery after administration of the derivative has ceased.

    [0186] The applicants have also found that certain known ketamine derivatives, which are encompassed by the formula (II), can surprisingly be used as anaesthetics and have advantageous properties similar to those of the compounds of formula (I).

    [0187] Compounds of formula (I) or (II) may be prepared using methods of synthesis known in the art or methods analogous thereto.

    [0188] In one embodiment, the method comprises reacting a compound of the formula (III):

    ##STR00004##

    wherein Y.sup.2, X.sup.1, and X.sup.2 are as defined above with an alkylating agent of the formula Y.sup.1Z or Y.sup.11Z, wherein Z is a suitable leaving group and Y.sup.1 and Y.sup.11 are as defined above, to provide the compound of the formula (I) or (II), respectively.

    [0189] In one embodiment, Z is halo.

    [0190] In some embodiments, the reaction is carried out in the presence of a base. In certain embodiments, the reaction is carried out in the presence of an inorganic base, for example, a carbonate base.

    [0191] In some embodiments, the reaction is carried out in the presence of a suitable solvent, for example, an aprotic solvent.

    [0192] The reaction may be carried out at any suitable temperature. In some embodiments, the reaction is carried out in the presence of a suitable solvent at reflux. In other embodiments, the reaction is carried out at ambient temperature.

    [0193] In some embodiments, the compound of formula (III) is prepared by a method comprising heating a compound of the formula (IV)

    ##STR00005##

    wherein X.sup.1 and X.sup.2 are as defined above in a suitable liquid reaction medium to provide a compound of the formula (III), wherein Y.sup.2 is hydrogen.

    [0194] In some embodiments, the method comprises heating the compound of the formula (IV) in a suitable solvent. In certain embodiments, the compound is heated at a temperature of 75, 100, 125, 150, 175, or 200 C. or more.

    [0195] In some embodiments, the compound of formula (IV) is prepared by a method comprising reacting a compound of the formula (V)

    ##STR00006##

    wherein X.sup.1 and X.sup.2 are as defined above and Z.sup.1 is halo with NH.sub.3/NH.sub.4OH.

    [0196] In some embodiments, the compound of formula (V) is prepared by a method comprising reacting a compound of the formula (VI)

    ##STR00007##

    wherein X.sup.1 and X.sup.2 are as defined above with a halogenating agent.

    [0197] In one embodiment, the halogenating agent is copper (II) bromide.

    [0198] In some embodiments, the reaction is carried out in a suitable solvent.

    [0199] Schemes 1 to 4 below illustrate the preparation of certain compounds of formula (I) and (II) wherein X.sup.1 is chloro and X.sup.2 is hydrogen from (2-o-chlorophenyl)-2-amino-cyclohexanone (norketamine).

    [0200] (S)-Norketamine (S-24) is synthesized following a reported procedure [Hong & Davisson. J. Pharm. Sci., 1982, 71, 912].

    [0201] Commercially available (2-chlorophenyl)(cyclopentyl)methanone (31) is brominated by refluxing with CuBr.sub.2 in EtOAc. The brominated intermediate (22) is converted to the corresponding imino cyclopentanol (23) by stirring in NH.sub.4OH solution saturated with NH.sub.3 gas. Thermal rearrangement of the hydrochloride salt of imino cyclopentanol in Dowtherm A at 200 C. affords racemic norketamine (rac-24).

    ##STR00008##

    [0202] The (S)-enantiomer of norketamine (S-24) is obtained by resolution with L-(R,R)-(+)-tartaric acid. The (R)-enantiomer of norketamine (R-24) may be obtained in an analogous fashion from D-(S,S)-()-tartaric acid.

    [0203] Compounds of formula (I) or (II) are synthesized by treatment of racemic or (S)-norketamine with alkyl halides corresponding to Y.sup.1. Enantiopure (R)-norketamine and non-racemic enantiomeric mixtures of norketamine may be also used.

    [0204] The compounds may be converted to hydrochloride salts using HCl gas.

    ##STR00009##

    ##STR00010##

    [0205] Alkyl halides corresponding to Y.sup.1 are commercially available or may be prepared by methods known in the art or analogous thereto.

    [0206] Compounds wherein Y.sup.2 is R.sup.2 may be prepared from compounds of formula (I) or (II) wherein Y.sup.2 is hydrogen by treatment with an alkylating agent corresponding to R.sup.2. Such compounds may also be prepared by reductive amination with an aldehyde (e.g. formaldehyde when R.sup.2 is methyl) or ketone corresponding to R.sup.2.

    ##STR00011##

    [0207] Compounds of formula (I) and (II) wherein the phenyl ring is substituted with different X.sup.1 and X.sup.2 may be prepared by, for example, using suitably substituted (phenyl)(cyclopentyl)methanones.

    [0208] Certain compounds of formula (II) and methods for their preparation are described in WO 2004/045601.

    [0209] Preparation of the compounds may involve the protection and deprotection of various chemical groups. The need for protection and deprotection, and the selection of appropriate protecting groups, can be readily determined by a person skilled in the art. Protecting groups and methods for protection and deprotection are well known in the art [see e.g. T. W. Greene and P. G. M. Wuts, Protective Groups in Organic Synthesis, 3.sup.rd Ed., Wiley & Sons, Inc., New York (1999)].

    [0210] The compounds of formula (I) and (II) have analgesic, anaesthetic, and/or sedative activity and are therefore useful for treating pain and/or anaesthetizing and/or sedating subjects.

    [0211] The term treatment, and related terms such as treating and treat, as used herein, in the context of treating pain, relates generally to treatment, of a human or a non-human subject, in which some desired therapeutic effect is achieved. The therapeutic effect may, for example, be inhibition, reduction, amelioration, halt, or prevention of the pain.

    [0212] Analgesia is the alleviation or elimination of the sensation of pain. As used herein the term pain encompasses a wide range of clinical manifestations, and it has a broad meaning. Pain perception is highly subjective, and different people experience pain in different ways and with greatly different intensities. The International Association for the Study of Pain defines pain as an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage. Non-limiting types and causes of pain include neuralgia, myalgia, hyperalgesia, hyperpathia, neuritis, and neuropathy. Pain may also be caused by physical trauma, such as burns or surgery. In one embodiment, the pain is pain resistant to treatment with opioids.

    [0213] The term anaesthetize and related terms such as anaesthetizing as used herein means to induce a loss of sensation and usually of consciousness without loss of vital functions artificially produced by the administration of one or more agents that block responses of the body to painful stimuli, for example the absence of a response to a surgical incision.

    [0214] The term sedate and related terms such as sedating as used herein means to induce a state of depressed consciousness in which a patient or subject retains the ability to independently and continuously maintain an open airway and a regular breathing pattern, and to respond appropriately and rationally to physical stimulation and verbal commands. Sedation may be evaluated using, for example, the Ramsay Sedation Scale.

    [0215] The methods of the present invention comprise administering compounds of formula (I) or (II) to a subject.

    [0216] The subject may be a human or non-human animal. Non-human animals include, for example, production animals, such as, cattle, sheep, swine, deer, and goats; companion animals, such as, dogs, cats, and horses; zoo animals, such as, zebras, elephants, giraffes, and large cats; research animals, such as, mice, rats, rabbits, and guinea pigs; fur-bearing animals, such as, mink; birds, such as, ostriches, emus, hens, geese, turkeys, and ducks; fresh- and salt-water fish, such as, trout, salmon, carp, and eels; and reptiles, such as lizards and snakes. In one embodiment, the subject is a human.

    [0217] The methods comprise administering a therapeutically effective amount of the compound to the subject. A therapeutically effective amount of a compound is an amount effective to demonstrate a desired therapeutic effect either alone or in combination with other agents.

    [0218] The therapeutically effective amount of the compound to be administered to a subject depends on, for example, the purpose for which the compound is administered, mode of administration, nature and dosage of any co-administered compounds, and characteristics of the subject, such as general health, other diseases, age, sex, genotype, body weight and tolerance to drugs. A person skilled in the art will be able to determine appropriate dosages having regard to these any other relevant factors.

    [0219] In one embodiment, the dose of administered is from about 0.01 mg per kg of body weight (0.01 mg/kg) to about 100 mg/kg.

    [0220] The compounds may be administered by any suitable route. The route may depend on the therapeutic purpose for which the compound is administered.

    [0221] In one exemplary embodiment, the compound is administered intravenously.

    [0222] In one specifically contemplated embodiment, the compound is administered by intravenous bolus. In another specifically contemplated embodiment, the compound is administered intravenously by continuous infusion.

    [0223] In certain embodiments, the compound is administered as an intravenous bolus and by intravenous infusion. In one embodiment, the compound is administered as an intravenous bolus and by continuous intravenous infusion.

    [0224] In some embodiments, the compound is administered as an intravenous bolus at a dose from about 0.01 mg per kg of body weight (0.01 mg/kg) to about 100 mg/kg.

    [0225] In some embodiments, the compound is administered by continuous intravenous infusion at a dose from about 0.1 mg/kg/min to about 10 mg/kg/min.

    [0226] In one specifically contemplated embodiment, the compound is administered for anesthesia as an intravenous bolus at a dose from about 0.01 mg per kg of body weight (0.01 mg/kg) to about 100 mg/kg and as a continuous intravenous infusion at a dose from about 0.1 mg/kg/min to about 10 mg/kg/min. Smaller doses would be used for sedation and analgesia.

    [0227] The compounds of formula (I) and (II) are generally prepared in a formulation or pharmaceutical composition appropriate for administration by a particular route. Examples of administration route include transdermal, transmucosal (e.g. nasal, transbuccal, sublingual, vaginal, and rectal), oral, pulmonary (i.e. inhalation), and parenteral (e.g. intravenous, intraarterial, intraperitoneal, intradermal, intramuscular, intraventricular, or subcutaneous).

    [0228] The formulations generally comprise a pharmaceutically acceptable diluent, excipient, or carrier. Any suitable diluent, excipient, or carrier can be used provided that it is non-toxic and compatible with the other ingredients of the composition. The diluent, excipient, or carrier used depends on the intended route of administration.

    [0229] The formulation or pharmaceutical composition may be manufactured by any method known in the art, for example, by conventional mixing, dissolving, granulating, levigating, emulsifying, encapsulating, entrapping, or compression. Numerous diluents, excipients, and carriers and methods for preparing pharmaceutical compositions are known in the art [see e.g. Remington's Pharmaceutical Sciences, Mack Publishing Co., (2000)].

    [0230] Suitable formulations for administering the compounds include, for example, tablets, capsules, suppositories, solutions, and powders etc.

    [0231] The content of the pharmaceutically active compound(s) is typically in the range from 0.05 to 90 wt.-% of the composition as a whole. In one embodiment, the content is from 0.1 to 50 wt.-% of the composition as a whole.

    [0232] Suitable compositions include for example tablets, capsules, suppositories, solutions and powders etc. Tablets may comprise a solid carrier or diluent. Liquid pharmaceutical compositions may comprise a liquid carrier, for example, water, petroleum, animal or vegetable oils, mineral oil or synthetic oil. Liquid compositions may also comprise physiological saline solution, dextrose or other carbohydrate solution, glycols e.g. ethylene glycol, propylene glycol or polyethylene glycol, etc. Capsules may comprise a solid carrier e.g. gelatin. Such formulations will be well known to a person skilled in the art.

    [0233] The pharmaceutical composition may be formulated for intravenous, cutaneous or subcutaneous injection. The active ingredient is generally in the form of a parenterally acceptable aqueous solution, which is pyrogen-free and has a suitable pH, isotonicity and stability. Those skilled in the art will be able to prepare suitable solutions. The solutions may comprise isotonic vehicles e.g. sodium chloride injection, Ringer's injection, etc. Preservatives, stabilisers, buffers antioxidants and/or other suitable additives may be included as required.

    [0234] The composition of the present invention comprises a compound of formula (I) or a pharmaceutically acceptable salt or solvate thereof, and a pharmaceutically acceptable diluent, excipient, or carrier. The composition may be formulated as described above.

    [0235] The formulations may comprise or be used or administered in combination, for example sequentially or simultaneously, with one or more additional therapeutic agents, for example alpha-2 adrenergic drugs such as clonidine or dexmedetomidine.

    [0236] In one embodiment, the composition further comprises a buffer, stabiliser, or adjuvant.

    [0237] The uses of the present invention involve the manufacture of medicaments. The medicaments are also formulated as described above.

    EXAMPLES

    [0238] The following non-limiting examples are provided to illustrate the present invention and in no way limit the scope thereof.

    [0239] The structures and physicochemical properties of selected compounds representative of the invention are given in Table 1.

    [0240] Lipophilicities (clogP) were calculated using ChemBioDraw v12.02 (CambridgeSoft, UK). pKa values were calculated using ACD/PhysChem Suite v12 (ACD/Labs, Toronto, Canada).

    TABLE-US-00001 TABLE 1 Details of representative compounds (I) [00012]embedded image Purity Compd. X.sup.1 X.sup.2 Y.sup.1 Y.sup.2 Form (%).sup.a clogP.sup.b pKa.sup.c rac-C3OAc 2-Cl H (CH.sub.2).sub.3OAc H R/S 97.2 2.86 6.20 (S)-C3OAc 2-Cl H (CH.sub.2).sub.3OAc H S 95.8 2.86 6.20 rac-C2Et 2-Cl H (CH.sub.2).sub.2CO.sub.2Et H R/S 97.2 3.05 4.35 (S)-C2Et 2-Cl H (CH.sub.2).sub.2CO.sub.2Et H S 99.1 3.39 4.35 rac-C2iPr 2-Cl H (CH.sub.2).sub.2CO.sub.2.sup.iPr H R/S 99.0 3.36 4.35 (S)-C2iPr 2-Cl H (CH.sub.2).sub.2CO.sub.2.sup.iPr H S 99.5 3.36 4.35 (R)-C2iPr 2-Cl H (CH.sub.2).sub.2CO.sub.2.sup.iPr H R 99.5 3.36 4.35 rac-C2nPr 2-Cl H (CH.sub.2).sub.2CO.sub.2.sup.nPr H R/S 99.0 3.58 4.35 rac-C3Et 2-Cl H (CH.sub.2).sub.3CO.sub.2Et H R/S 95.3 3.39 5.86 rac-C3iPr 2-Cl H (CH.sub.2).sub.3CO.sub.2.sup.iPr H R/S 98.4 3.70 5.86 rac-C3nPr 2-Cl H (CH.sub.2).sub.3CO.sub.2.sup.nPr H R/S 97.2 3.92 5.85 rac-C4Me 2-Cl H (CH.sub.2).sub.4CO.sub.2Me H R/S 99.1 2.77 6.29 (S)-C4Me 2-Cl H (CH.sub.2).sub.4CO.sub.2Me H S 97.0 2.77 6.29 rac-C4Et 2-Cl H (CH.sub.2).sub.4CO.sub.2Et H S 94.4 3.29 6.29 rac-C4iPr 2-Cl H (CH.sub.2).sub.4CO.sub.2.sup.iPr H R/S 97.6 3.60 6.29 rac-C4nPr 2-Cl H (CH.sub.2).sub.4CO.sub.2.sup.nPr H R/S 95.4 3.82 6.29 19 2-Cl H (CH.sub.2).sub.2CO.sub.2Et Me R/S 93.0 3.69 4.77 20 2-Cl H (CH.sub.2).sub.3CO.sub.2Et Me R/S 94.0 3.48 5.51 21 2-Cl H (CH.sub.2).sub.4CO.sub.2Me Me R/S 94.8 3.32 5.74 .sup.aPurity by reverse-phase HPLC; .sup.bClogP calculated using ChemBioDraw Ultra v12.02; .sup.cpKa calculated using ACD/PhysChem Suite v12.

    [0241] Ketamine has a measured (Volgyi, G. et al. Anal. Chim. Acta 2007, 583, 418-428) aqueous pKa of 7.49 and a calculated clogP of 2.22. The closest match to this were the acetates (rac-C3OAc and (S)-C3OAc). Next closest in physicochemical properties were the C4 methyl esters (rac-C4Me and (S)-C4Me). The esters overall showed a range of both pKa values (from 4.35 to 6.29) and lipophilicities (from 2.77 to 3.92).

    [0242] General Details

    [0243] All reagents and solvents were obtained from commercial suppliers and used without further purification unless otherwise stated. Reactions requiring anhydrous conditions were performed under nitrogen atmospheres. Reactions were monitored by thin layer chromatography (TLC) on preloaded silica gel F254 plates (Sigma-Aldrich) with a UV indicator. Column chromatography was performed with Merck 230-400 mesh silica gel. .sup.1H and .sup.13C NMR spectra were obtained with a Bruker Avance 400 spectrometer at 400 MHz for .sup.1H and 100 MHz for .sup.13C spectra. Spectra were obtained in CDCl.sub.3 or (CD.sub.3)SO. The chemical shifts are reported in parts per million () downfield using tetramethylsilane (SiMe.sub.4) as internal standard. Spin multiplicities are given as s (singlet), d (doublet), dd (double doublet), br (broad), m (multiplet), and q (quartet). Coupling constants (J values) were measured in hertz (Hz). All LC/MS data were gathered by direct injection of methanolic solutions into a Surveyor MSQ mass spectrometer using an atmospheric pressure chemical ionization (APCI) with a corona voltage of 50 V and a source temperature of 400 C. Final products were analyzed by reverse-phase HPLC (Alltima C18 5 m column, 150 mm3.2 mm; Alltech Associated, Inc., Deerfield, Ill.) using an Agilent HP1100 equipped with a diode array detector. The mobile phase was 80% CH.sub.3CN/20% H.sub.2O (v/v) in 45 mM HCO.sub.2NH.sub.4 at pH 3.5 and 0.5 mL/min. The purity was determined by monitoring at 272 nm and was 95% for final products unless otherwise stated. The enantiomeric purity was analyzed by chiral HPLC (Chiralcel OJ-H column, 0.46 cm45 cm). The mobile phase was 85% hexanes/15% EtOH with a flow rate of 0.6 mL/min. The purity was determined by monitoring at 254 and 280 nm and was 95% unless otherwise stated. The final product purity was also assessed by combustion analysis carried out in the Campbell Micro analytical Laboratory, University of Otago (Dunedin, New Zealand). Melting points were determined on an Electrothermal 2300 Melting Point Apparatus and are uncorrected. DCM refers to dichloromethane, DMF refers to N,N-dimethylformamide, EtOAc refers to ethyl acetate, EtOH refers to ethanol.

    Example 1

    [0244] rac-3-((1-(2-Chlorophenyl)-2-oxocyclohexyl)amino)propyl acetate hydrochloride (rac-C3OAc). (Scheme 2). (2-chlorophenyl)(cyclopentyl)methanone [US 20080268071] (21) (10 g, 48.0 mmol) was dissolved in ethyl acetate (100 mL) followed by addition of Cu(II)Br.sub.2 (27 g, 120.9 mmol). The solution was refluxed for 2.5 h and cooled to 25 C. The solid was filtered and the filtrate was evaporated under reduced pressure. Some solid began to form while evaporating solvent under reduced pressure. DCM (100 mL) was added to the solid formed and solution cooled to 0 C. in an ice bath. After standing for 10 min. the solution was filtered and the filtrate concentrated under reduced pressure to obtain (1-bromocyclopentyl)(2-chlorophenyl)methanone (22) as a yellow oil (12.3 g, 89%). .sup.1H NMR (400 MHz, CDCl.sub.3) 7.70 (dd, J=7.4, 1.8 Hz, 1H), 7.43 (dd, J=7.9, 1.3 Hz), 7.37 (td, J=7.4, 1.8 Hz, 1H), 7.30 (td, J=7.4, 1.3 Hz, 1H), 2.45-2.27 (m, 4H), 2.09-2.01 (m, 2H), 1.89-1.82 (m, 2H); .sup.13C NMR (101 MHz, CDCl.sub.3) 6 199.47, 138.87, 130.83, 130.55, 130.16, 128.33, 126.49, 74.29, 40.42, 23.26. MS m/z 289.3 (M2H.sup.+, 24%) 207.4 (MBr.sup., 100%)

    [0245] Ammonium hydroxide (200 mL) was cooled to 0 C. in an ice bath and was saturated with NH.sub.3 gas for 5 min. The solution was added to a flask containing 22 (12.74 g, 44.5 mmol) and stirred vigorously at 25 C. for 5 days. The brown clumps formed were separated from the solvent and resuspended in hexanes (150 mL). After stirring in hexanes for 4 h, the precipitate formed was filtered and dried to obtain 23 (8.15 g, 81%) as a pale yellow solid. This was suspended in 8 mL of 2-propanol and cooled to 0 C. in an ice bath. HCl gas was bubbled through the solution for 2 min. and diethyl ether (16 mL) was added. Upon standing at 0 C. for 3 h a pale yellow precipitate was formed which was filtered, dried under vacuum to obtain 1-((2-chlorophenyl)(imino)methyl)cyclopentanol hydrochloride (23-HCl) [Parcell, R. F. & Sanchez, J. P. J. Org. Chem.1981, 46, 5055]. (7.21 g). .sup.1H NMR (400 MHz, CDCl.sub.3) 14.05 (br, 1H), 12.28 (br, 1H), 7.61-7.32 (m, 4H), 2.23 (br, 2H), 1.98 (m, 4H), 1.69 (br, 2H); .sup.13C NMR (101 MHz, CDCl.sub.3) 195.76, 132.74, 131.42, 130.57, 128.99, 128.85, 126.82, 85.56, 39.47, 38.78, 24.46, 23.85. MS m/z 224.4 (MH.sup.+).

    [0246] To Dowtherm A (142 mL) heated to 200 C. was added in portions 23 (18 g, 69.2 mmol). The heating was continued for 12 min. and cooled to 0 C. in an ice bath. The reaction mixture along with precipitate formed was poured into diethyl ether (500 mL) and allowed to stand overnight. The white precipitate formed was filtered and washed with diethyl ether (100 mL). The precipitate was dissolved in water (200 mL) and neutralized with 2 N NaOH. The water layer was extracted with DCM (3100 mL), dried over Na.sub.2SO4 and solvent evaporated. The residue obtained was purified by passing through a short silica gel column eluting with DCM (100%) to 10% MeOH/DCM to give racemic 2-amino-2-(2-chlorophenyl)cyclohexanone (norketamine) (rac-24) [Parcell, R. F. & Sanchez, J. P. J. Org. Chem.1981, 46, 5055] (9.2 g, 59%). .sup.1H NMR (400 MHz, CDCl.sub.3) 7.69 (dd, J=7.8, 1.7 Hz 1H), 7.39-7.33 (m, 2H), 7.26 (td, J=7.6, 1.6 Hz, 1H), 2.79-2.72 (m, 1H), 2.63-2.56 (m, 1H), 2.51-2.43 (m, 1H), 2.08-2.0 (m, 1H), 1.88 (br, 1H), 1.81-1.75 (m, 2H), 1.72-1.63 (m, 1H).

    [0247] A solution of rac-24 (200 mg, 0.89 mmol), 3-bromopropyl acetate [Demko, Z. P. & Sharpless K. B. Org. Lett. 2001, 3, 4091] (194 mg, 1.07 mmol), KI (45 mg, 0.27 mmol), K.sub.2CO.sub.3 (371 mg, 2.7 mmol) was dissolved in CH.sub.3CN (5 mL). The reaction mixture was heated to reflux for 24 h. After completion of reaction the reaction mixture was cooled to room temperature and solvent evaporated under reduced pressure. The residue was purified by column chromatography on silica gel eluting with hexanes (100%), EtOAc/hexanes (40%). The solvent was evaporated under reduced pressure to obtain the desired product as yellow oil (173 mg, 59%). The yellow oil was dissolved in diethyl ether (5 mL) and was cooled to 0 C. in an ice bath. Dry HCl gas was bubbled through the solution at 0 C. for 2 min. The solvent was evaporated under reduced pressure to obtain a yellow solid. The yellow solid was dissolved in EtOAc (1 mL) and sonicated at 25 C. for 2 min. The white precipitate formed was diluted with EtOAc (5 mL) and filtered, washed with EtOAc and dried under vacuum to give rac-C3OAc.HCl (107 mg, 33%), mp 180-183 C. .sup.1H NMR (400 MHz, CDCl.sub.3) 11.71 (br, 1H), 8.19 (d, J=7.6 Hz, 1H), 8.09 (br, 1H), 7.58 (m, 1H), 7.46 (d, J=4.0 Hz, 2H), 4.15 (m, 1H), 4.08 (m, 1H), 3.81 (dm, J=12.0 Hz, 1H), 3.19 (br, 1H), 2.74 (d, J=12.0 Hz, 1H), 2.68-2.60 (m, 2H), 2.47 (br, 1H), 2.28 (t, J=14 Hz, 1H), 2.12 (br, 2H), 2.09 (s, 3H), 1.84 (br, 2H), 1.54 (br, 1H); .sup.13C NMR (101 MHz, CDCl.sub.3) 206.20, 171.04, 135.14, 132.56, 132.34, 131.79, 129.16, 128.92, 77.49, 62.22, 41.87, 40.63, 40.01, 29.91, 25.84, 21.82, 21.02. MS m/z 324.2 (MH.sup.+). MS m/z 324.2 (MH.sup.+). Anal. calcd for C.sub.17H.sub.23Cl.sub.2NO.sub.3: C, 56.67; H, 6.43; N, 3.89; Cl, 19.68. Found: C, 56.49; H, 6.61; N, 3.69.

    Example 2

    [0248] (S)-3-((1-(2-Chlorophenyl)-2-oxocyclohexyl)amino)propyl acetate hydrochloride [(S)-C3OAc] (Scheme 2). Resolution of norketamine was achieved by following a published procedure [Hong & Davisson. J. Pharm. Sci., 1982, 71, 912]. A solution of rac-24 (13.2 g, 59.1 mmol) in MeOH (33 mL) was treated with L-(R,R)-(+)-tartaric acid (8.9 g, 59.1 mmol) in MeOH (118 mL). The reaction mixture was stirred overnight at 25 C. and filtered to remove any solid impurities. The filtrate was evaporated and the white solid obtained washed with 2-butanone (264 mL). The white solid was suspended in acetone (1750 mL) and heated to reflux until most of the solid was dissolved. The solution was cooled to room temperature and allowed to stand for 2 days. The crystals formed were filtered and recrystallized two additional times in acetone (1750 mL and 800 mL respectively) to obtain (S)-2-amino-2-(2-chlorophenyl)cyclohexanone, (S)-norketamine [(S)-24] as the tartrate salt. .sup.1H NMR (400 MHz, DMSO-d.sub.6) 7.85 (d, J=7.8 Hz), 7.39 (t, J=7.4 Hz, 2H), 7.34 (d, J=7.5 Hz, 1H), 4.21 (s, 2H), 2.78-2.70 (m, 1H), 2.32 (dt, J=15.1, 4.4 Hz, 1H), 1.96-1.81 (m, 3H), 1.73-1.60 (m, 2H), one proton submerged with DMSO-d6 peak; .sup.13C NMR (101 MHz, DMSO-d.sub.6) 208.6, 173.320, 131.96, 130.28, 129.1 (2), 128.93, 127.09, 71.93, 64.84, 38.31, 37.5, 25.79, 20.84. MS m/z 224.2 (MH.sup.30 ). Mp: 190-191 C.

    [0249] The (S)-norketamine tartrate salt was dissolved in water (200 mL) and neutralized with 2 N NaOH. The aqueous layer was extracted with DCM (3100 mL). The combined DCM layer was washed with brine (100 mL) and dried over Na.sub.2SO.sub.4. Evaporation of solvent under reduced pressure afforded (S)-norketamine free base [(S)-24] (4.96 g) as a pale yellow viscous oil. .sup.1H NMR (400 MHz, CDCl.sub.3) 7.70 (dd, J=7.8, 1.7 Hz), 7.38-7.31 (m, 2H), 7.28-7.23 (m, 1H), 2.79-2.71 (m, 1H), 2.63-2.56 (m, 1H), 2.51-2.43 (m, 1H), 2.08-2.02 (m, 1H), 1.89-1.74 (m, 3H), 1.71-1.63 (m, 1H); .sup.13C NMR (101 MHz, CDCl.sub.3) 212.75, 140.49, 133.02, 131.0, 128.97, 128.32, 127.20, 66.42, 41.25, 38.98, 28.32, 22.16. MS m/z 224.2 (MH.sup.+).

    [0250] A solution of (S)-24 (1 g, 4.47 mmol), 3-bromopropyl acetate [Demko, Z. P. & Sharpless K. B. Org. Lett. 2001, 3, 4091] (971 mg, 5.36 mmol), KI (223 mg, 1.34 mmol), K.sub.2CO.sub.3 (1.85 g, 13.4 mmol) was dissolved in CH.sub.3CN (12 mL). The reaction mixture was heated to reflux for 24 h. After completion of reaction the reaction mixture was cooled to room temperature and solvent evaporated under reduced pressure. The residue was purified by column chromatography on silica gel eluting with hexanes (100%), EtOAc/hexanes (40%). The solvent was evaporated under reduced pressure to obtain the desired product as yellow oil (695 mg, 48%). The yellow oil was dissolved in diethyl ether (20 mL) and was cooled to 0 C. in an ice bath. Dry HCl gas was bubbled through the solution at 0 C. for 2 min. The white precipitate formed was filtered and resuspended in EtOAc (20 mL) and stirred for 10 min at room temperature. The white precipitate was filtered to give (S)-C3OAc hydrochloride(512 mg, 29%), mp 169-172 C. .sup.1H NMR (400 MHz, CDCl.sub.3) 11.87 (br, 1H), 8.20 (d, J=8.2 Hz, 1H), 7.62-7.54 (m, 1H), 7.48 (d, J=3.8 Hz, 2H), 7.39 (br, 1H), 4.12 (q, J=7.1 Hz, 2H), 3.83 (dm, J=14.4 Hz, 1H), 3.11-3.02 (m, 1H), 2.75 (d, J=12.5 Hz, 1H), 2.70-2.61 (m, 1H), 2.51 (br, 1H), 2.32 (t, J=7.3 Hz, 2H), 2.24 (t, J=11.1 Hz, 1H), 2.05 (br, 1H), 1.99-1.88 (m, 2H), 1.83 (d, J=14.5 Hz, 2H), 1.76-1.61 (m, 3H), 1.24 (t, J=7.1 Hz, 3H); .sup.13C NMR (101 MHz, CDCl.sub.3) 205.41, 173.07, 135.21, 132.58, 132.06, 131.67, 129.34, 128.99, 73.20, 60.57, 43.59, 40.82, 39.62, 33.65, 29.68, 26.07, 22.27, 21.77, 14.31. MS m/z 352.2 (MH.sup.+). Anal. calcd for C.sub.19H.sub.27Cl.sub.2NO.sub.3: C, 58.77; H, 7.01; N, 3.61; Cl, 18.26. Found: C, 58.81; H, 7.1, N, 3.51; Cl, 18.31.

    [0251] General Procedure for Synthesis of N-Alkylated Norketamine Esters (Scheme 3)

    [0252] A solution of rac-24 or (S)-24 (1 eq.), the appropriate alkyl halide (1.2 eq. or 6 eq. in case of ethyl-3-bromo propionate), KI (0.3 eq.) and K.sub.2CO.sub.3 (3 eq.) was dissolved in CH.sub.3CN (4.5 mL/mmol). The solution was heated to 80 C. in a sealed tube for 24 h (72 h in case of ethyl-3-bromo propionate). The reaction mixture was cooled to room temperature and solvent evaporated. The residue was purified by column chromatography on silica gel eluting with hexanes (100%), EtOAc/hexanes (20-35%). The solvent was evaporated under reduced pressure to obtain the desired product as yellow oil. This was dissolved in diethyl ether (5 mL) and was cooled to 0 C. in an ice bath. Dry HCl gas was bubbled through the solution at 0 C. for 2 min. The solvent was evaporated under reduced pressure to obtain a yellow solid. The yellow solid was dissolved in EtOAc (2 mL) and sonicated at 25 C. for 2 min. The white precipitate formed was diluted with EtOAc (10 mL) and filtered, washed with EtOAc and dried under vacuum to obtain the product as hydrochloride salt.

    [0253] The following compounds were prepared according to this general procedure.

    Example 3

    [0254] Ethyl 3-((1-(2-chlorophenyl)-2-oxocyclohexyl)amino)propanoate hydrochloride (rac-C2Et). From rac-24 and ethyl 3-bromopropionate (33% yield), mp 199-202 C. .sup.1H NMR (400 MHz, CDCl.sub.3) 12.24 (br, 1H, NH.sub.2), 8.13 (d, J=8.0 Hz, 2H, ArH, NH.sub.2), 7.61-7.54 (m, 1H, ArH), 7.49 (d, J=3.8 Hz, 2H,), 4.23 (q, J=7.2 Hz, 2H), 3.78 (dm, J=14.3 Hz, 1H), 3.59-3.45 (m, 1H), 3.25 (q, J=5.4 Hz, 1H), 2.73 (br, 2H), 2.68-2.54 (m, 2H), 2.23 (td, J=13.7, 2.5 Hz, 1H), 2.14-2.02 (m, 1H), 1.89-1.82 (m, 2H), 1.65-1.59 (m, 1H), 1.28 (t, J=7.2 Hz, 3H, CH.sub.2CH.sub.3); .sup.13C NMR (101 MHz, CDCl.sub.3) 206.10, 171.94, 135.27, 132.57, 132.40, 131.85, 129.05, 128.57, 73.42, 61.67, 40.30, 39.71, 39.63, 30.38, 29.93, 21.86, 14.18; MS m/z 324.2 (MH.sup.+). Anal. calcd for C.sub.17H.sub.23Cl.sub.2NO.sub.3: C, 56.67; H, 6.43; N, 3.89; Cl, 19.68. Found: C, 56.65; H, 6.57; N, 3.89; Cl, 19.90

    Example 3A

    [0255] (S)-Ethyl 3-((1-(2-chlorophenyl)-2-oxocyclohexyl)amino)propanoate hydrochloride[(S)-C2Et]. From (S)-24 and ethyl 3-bromopropanoate (54%), mp 208-210 C. .sup.1H NMR (400 MHz, CDCl.sub.3) 12.08 (br, 1H), 8.25 (br, 1H), 8.13 (d, J=8.0 Hz, 1H), 7.61-7.56 (m, 1H), 7.49 (br, 2H), 4.21 (q, J=7.2 Hz, 2H), 3.76 (dm, J=14.3, 3.2 Hz, 1H), 3.55-3.46 (m, 1H), 3.28 (q, J=9.97 Hz, 1H), 2.75-2.56 (m, 4H), 2.26 (td, J=14.14 Hz, 1H), 2.08 (br, 1H), 1.90-1.78 (m, 2H), 1.61 (br, 1H), 1.28 (t, J=7.2 Hz, 3H); .sup.13C NMR (101 MHz, CDl.sub.3) 206.35, 172.38, 135.08, 132.39, 132.33, 131.71, 128.91, 128.27, 73.32, 61.75, 40.08, 39.57, 29.91, 29.89, 21.69, 14.02 (1C overlapping). MS m/z 324.2 (MH.sup.+). HRMS calculated for C.sub.17H.sub.23ClNO.sub.3 (MH.sup.+) 324.1361, found 324.1370.

    Example 4

    [0256] Iso-Propyl 3-((1-(2-chlorophenyl)-2-oxocyclohexyl)amino)propanoate hydrochloride (rac-C2iPr) From rac-24 and isopropyl 3-bromopropanoate (48%), mp 203-205 C. .sup.1H NMR (400 MHz, CDCl.sub.3) 12.0 (br, 1H), 8.27 (br, 1H), 8.14 (d, J=8.0 Hz, 1H), 7.61-7.55 (m, 1H), 7.49 (br, 2H), 5.13-5.04 (m, 1H), 3.79 (dm, J=14.3 Hz, 1H), 3.52-3.44 (m, 1H), 3.28 (br, 1H), 2.74 (br, 2H), 2.65-2.56 (m, 2H), 2.24 (td, J=13.8 Hz, 3.2 Hz, 1H), 2.07 (br, 1H), 1.89-1.78 (m, 2H), 1.65-1.62 (m, 1H), 1.26 (d, J=5.01 Hz, 6H); .sup.13C NMR (101 MHz, CDCl.sub.3) 206.57, 172.2, 135.23, 132.63, 132.49, 131.84, 129.07, 129.03, 73.51, 69.86, 40.23, 39.85, 30.27, 30.08, 21.93, 21.84. MS m/z 338.2 (MH.sup.+). HRMS calculated 338.1517, found 338.1529.

    Example 4A

    [0257] (S)-Isopropyl 3-((1-(2-chlorophenyl)-2-oxocyclohexyl)amino)propanoate hydrochloride [(S)-C2iPr]. From (S)-24 and isopropyl 3-bromopropanoate (29%), mp 208-211 C. .sup.1H NMR (400 MHz, CDCl.sub.3) 12.22 (br, 1H), 8.14 (dbr, J=8.1 Hz, 2H), 7.61-7.55 (m, 1H), 7.49 (br, 2H), 5.12-5.06 (m, 1H), 3.79 (dm, J=14.4 Hz, 1H), 3.52-3.43 (m, 1H), 3.26 (q, J=11.9 Hz, 1H), 2.71 (br, 2H), 2.67-2.55 (m, 2H), 2.21 (td, J=14.1, 3.3 Hz, 1H), 2.07 (br, 1H), 1.89-1.78 (m, 2H), 1.63 (br, 1H), 1.27 (app. dd, J=4.93, 1.25 Hz, 6H); .sup.13C NMR (101 MHz, CDCl.sub.3) 206.62, 172.23, 135.24, 132.62, 132.48, 131.84, 129.08, 128.42, 73.48, 69.86, 40.24, 39.87, 30.28, 30.09, 21.93, 21.87, 21.84. MS m/z 338.2 (MH.sup.+). HRMS calculated for C.sub.18H.sub.25ClNO.sub.3 (MH.sup.+) 338.1517, found 338.1524.

    Example 4B

    [0258] (R)-Isopropyl 3-((1-(2-chlorophenyl)-2-oxocyclohexyl)amino)propanoate hydrochloride [(R)-C2iPr]. From (R)-24 and isopropyl 3-bromopropanoate (29%), mp 216-219 C. .sup.1H NMR (400 MHz, CDCl.sub.3) 12.20 (br, 1H), 8.14 (dbr, J=8.1 Hz, 2H), 7.60-7.56 (m, 1H), 7.49 (br, 2H), 5.14-5.04 (m, 1H), 3.80 (dm, J=13.6 Hz, 1H), 3.51-3.44 (m, 1H), 3.26 (br, 1H), 2.73 (br, 2H), 2.64-2.56 (m, 2H), 2.21 (t, J=13.2 Hz, 1H), 2.06 (br, 1H), 1.89-1.79 (m, 2H), 1.64 (br, 1H), 1.26 (app. dd, J=4.81, 1.40 Hz, 6H); .sup.13C NMR (101 MHz, CDCl.sub.3) 206.71, 172.36, 135.23, 132.67, 132.51, 131.85, 129.11, 128.39, 73.5, 69.94, 40.24, 39.95, 30.26, 30.13, 21.95, 21.89, 21.85. MS m/z (MH.sup.+). HRMS calculated for C.sub.18H.sub.25ClNO.sub.3 (MH.sup.+) 338.1517, found 338.1521.

    [0259] (R)-24 was prepared by a procedure analogous to that described above for the preparation of (S)-24 using D-(S,S)-()-tartaric acid, rather than L-(R,R)-(+)-tartaric acid.

    Example 5

    [0260] n-Propyl 3-((1-(2-chlorophenyl)-2-oxocyclohexyl)amino)propanoate hydrochloride (rac-C2nPr). From rac-24 and propyl 3-bromopropanoate (44%) mp 163-165 C. .sup.1H NMR (400 MHz, CDCl.sub.3) 11.68 (br, 1H), 8.69 (br, 1H), 8.14 (d, J=8.0 Hz, 1H), 7.61-7.54 (m, 1H), 7.49 (br, 2H), 4.07 (t, J=6.8 Hz, 2H), 3.74 (dm, J=14.3 Hz, 1H), 3.53-3.43 (m, 1H), 3.38 (br, 1H), 2.81-2.71 (m, 3H), 2.64-2.57 (m, 1H), 2.35 (td, J=13.8, 3.2 Hz, 1H), 2.07 (br, 1H), 1.92-1.80 (m, 2H), 1.68-1.54 (m, 3H), 0.92 (t, J=7.4 Hz, 3H); .sup.13C NMR (101 MHz, CDCl.sub.3) 206.03, 172.0, 135.28, 132.48, 132.37, 131.84, 128.99, 128.6, 73.4, 67.22, 40.31, 39.57, 30.28, 29.9, 21.9, 21.81, 10.42. MS m/z 338.2 (MH.sup.+). HRMS calculated 338.1517, found 338.1526.

    Example 6

    [0261] Ethyl 4-((1-(2-chlorophenyl)-2-oxocyclohexyl)amino)butanoate hydrochloride (rac-C3Et). From rac-24 and ethyl 4-bromobutanoate (37% yield), mp 186-189 C. .sup.1H NMR (400 MHz, CDCl.sub.3) 11.14 (br, 1H, NH.sub.2), 9.14 (br, 1H, NH.sub.2), 8.26 (d, J=8.1 Hz, 1H), 7.62-7.49 (m, 1H), 7.45 (d, J=3.8 Hz, 2H), 4.11 (q, J=7.1 Hz, 2H), 3.75 (dm, J=14.4 Hz, 1H), 3.38-3.26 (m, 1H), 2.75-2.64 (m, 2H), 2.64-2.58 (m, 1H), 2.43-2.26 (m, 2H), 2.45-2.28 (m, 2H), 2.14-2.07 (m, 1H), 1.98(br, 2H), 1-91-1.79 (m, 1H), 1.58-1.44 (m, 1H), 1.23 (t, J=7.1 Hz, 3H); .sup.13C NMR (101 MHz, CDC.sub.3) 206.03, 173.16, 135.11, 132.76, 132.08, 131.61, 129.19, 129.02, 73.17, 61.04, 43.54, 40.86, 40.00, 32.24, 29.72, 21.64, 14.27. MS m/z 338.2 (MH.sup.+). Anal. calcd for C.sub.18H.sub.25Cl.sub.2NO.sub.3: C, 57.76; H, 6.73; N, 3.74; Cl, 18.94. Found: C, 57.55; H, 6.92; N, 3.64; Cl, 18.73.

    Example 7

    [0262] Isopropyl 4-((1-(2-chlorophenyl)-2-oxocyclohexyl)amino)butanoate hydrochloride(rac-C3iPr). From rac-24 and isopropyl 4-bromobutanoate [Fox, M. E., et al. J. Org. Chem. 2005, 70, 1227] (24% yield), mp 167-169 C. .sup.1H NMR (400 MHz, CDCl.sub.3) 11.41 (br, 1H), 8.94 (br, 1H), 8.26 (d, J=8.1 Hz, 1H), 7.68-7.50 (m, 1H), 7.45 (d, J=3.9 Hz, 2H), 4.99 (m, 1H), 3.79 (dm, J=14.4 Hz, 1H), 3.31-3.21 (m, 1H), 2.75-2.68 (m, 1H), 2.66-2.59 (m, 2H), 2.58-2.49 (m, 1H), 2.42-2.48 (m, 1H), 2.34 (t, J=10.8 Hz, 2H), 2.11-1.98 (m, 2H), 1.84 (d, J=10.2 Hz, 2H), 1.58-1.46 (m, 1H), 1.22 (dd, J=6.28, 2.2 Hz, 6H) ; .sup.13C NMR (101 MHz, CDCl.sub.3) 206.29, 173.46, 135.04, 132.84, 132.13, 131.62, 129.08, 129.06, 73.11, 68.81, 43.70, 40.84, 40.21, 32.79, 29.90, 21.91, 21.68. MS m/z 352.2 (MH.sup.+). Anal. calcd for C.sub.19H.sub.27Cl.sub.2NO.sub.3: C, 58.77; H, 7.01; N, 3.61. Found: C, 58.57; H, 7.2; N, 3.54.

    Example 8

    [0263] n-Propyl 4-((1-(2-chlorophenyl)-2-oxocyclohexyl)amino)butanoate hydrochloride (rac-C3nPr). From rac-24 and n-propyl 4-bromobutanoate (19%), mp 160-161 C. .sup.1H NMR (400 MHz, CDCl.sub.3) 11.10 (br, 1H), 9.23 (br, 1H), 8.27 (d, J=8.1 Hz, 1H), 7.59-7.52 (m, 1H), 7.44 (d, J=5.1 Hz, 2H), 4.01 (t, J=6.8 Hz, 2H), 3.76 (dm, J=14.4 Hz, 1H), 3.39-3.28 (m, 1H), 2.70 (t, J=7.8 Hz, 1H), 2.66 (t, J=6.9 Hz, 1H), 2.62-2.54 (m, 1H), 2.51 (td, J=7.0, 2.8 Hz, 2H), 2.47-2.41 (m, 1H), 2.39-2.30 (m, 1H), 2.15-2.06 (m, 1H), 2.0 (br, 1H), 1.85 (td, J=8.0, 3.9 Hz, 2H), 1.57-1.66 (m, 2H), 1.50 (q, J=14.4Hz, 1H), 0.91 (t, J=7.4 Hz, 3H); .sup.13C NMR (101 MHz, CDCl.sub.3) 205.92, 173.47, 135.12, 132.78, 132.05, 131.59, 129.23, 129.0, 73.16, 66.62, 43.54, 40.86, 39.99, 32.19, 29.77, 22.0, 21.78, 21.70, 10.48. MS m/z 352.2 (MH.sup.+).

    Example 9

    [0264] rac-Methyl 5-((1-(2-chlorophenyl)-2-oxocyclohexyl)amino)pentanoate hydrochloride (rac-C4Me). From rac-24 and ethyl 5-bromopentanoate, followed by purification by preparative HPLC (41%). .sup.1H NMR (400 MHz, CDCl.sub.3) 7.53 (dd, J=7.8, 1.6 Hz, 1H), 7.36 (dd, J=7.8, 1.4 Hz, 1H), 7.31 (dt, J=7.8, 7.6, 1.5 Hz, 1H), 7.25-7.21 (m, 1H), 3.64 (s, 3H), 2.77-2.69 (m, 1H), 2.55-2.42 (m, 2H), 2.36-2.30 (m. 1H), 2.26 (t, J=7.4 H, 2H), 2.09-1.73 (m, 7H), 1.66-1.58 (m, 2H), 1.55-1.40 (m, 2H). HPLC 99%.

    Example 10

    [0265] (S)-Methyl 5-((1-(2-chlorophenyl)-2-oxocyclohexyl)amino)pentanoate hydrochloride [(S)-C4Me]. From (S)-24 and ethyl 5-bromopentanoate (42%), mp (MeOH/EtOAc) 188-191 C., .sup.1H NMR (400 MHz, CDCl.sub.3) 7.52 (dd, J=7.82, 1.68 Hz, 1H), 7.36 (dd, J=7.8, 1.4 Hz, 1H), 7.31 (dt, J=7.8, 7.60, 1.45 Hz, 1H), 7.23 (dt, J=8.0; 1.7 Hz, 1H), 3.65 (s, 3H), 2.76-2.68 (m, 1H), 2.55-2.42 (m, 2H), 2.36-2.30 (m, 1H), 2.26 (t, J=7.4 Hz, 2H), 2.08-1.74 (m, 7H), 1.66-1.58 (M, 2H), 1.57-1.37 (m, 3H), Analysis Calc. for C.sub.18H.sub.25Cl.sub.2NO.sub.3: C, 57.8; H, 6.7, Cl, 18.9, N, 3.7; found C, 57.7, H, 6.8 Cl, 18.9 N, 3.7.

    Example 11

    [0266] rac-Ethyl 5-((1-(2-chlorophenyl)-2-oxocyclohexyl)amino)pentanoate hydrochloride (rac-C4Et). From rac-24 and ethyl 5-bromopentanoate (29%), mp 169-172 C. .sup.1H NMR (400 MHz, CDCl.sub.3) 11.87 (br, 1H), 8.20 (d, J=8.2 Hz, 1H), 7.62-7.54 (m, 1H), 7.48 (d, J=3.8 Hz, 2H), 7.39 (br, 1H), 4.12 (q, J=7.1 Hz, 2H), 3.83 (dm, J=14.4 Hz, 1H), 3.11-3.02 (m, 1H), 2.75 (d, J=12.5 Hz, 1H), 2.70-2.61 (m, 1H), 2.51 (br, 1H), 2.32 (t, J=7.3 Hz, 2H), 2.24 (t, J=11.1 Hz, 1H), 2.05 (br, 1H), 1.99-1.88 (m, 2H), 1.83 (d, J=14.5 Hz, 2H), 1.76-1.61 (m, 3H), 1.24 (t, J=7.1 Hz, 3H); .sup.13C NMR (101 MHz, CDCl.sub.3) 205.41, 173.07, 135.21, 132.58, 132.06, 131.67, 129.34, 128.99, 73.20, 60.57, 43.59, 40.82, 39.62, 33.65, 29.68, 26.07, 22.27, 21.77, 14.31. MS miz 352.2 (MH.sup.+). Anal. calcd for C.sub.19H.sub.27Cl.sub.2NO.sub.3: C, 58.77; H, 7.01; N, 3.61; Cl, 18.26. Found: C, 58.81; H, 7.1, N, 3.51; Cl, 18.31.

    Example 12

    [0267] Isopropyl 5-((1-(2-chlorophenyl)-2-oxocyclohexyl)amino)pentanoate hydrochloride (rac-C4iPr) From rac-24 and isopropyl 5-bromovalerate (40%), mp 161-163 C. .sup.1H NMR (400 MHz, CDCl.sub.3) 11.04 (br, 1H), 8.78 (br, 1H), 8.24 (d, J=8.0 Hz, 1H), 7.59-7.53 (m, 1H), 7.47 (br, 2H), 5.01-4.92 (m, 1H), 3.74 (dm, J=14.4 Hz, 1H), 3.29-3.21 (m, 1H), 2.73 (d, J=12.2 Hz, 1H), 2.64 (td, J=13.3 Hz, 6.3, 1H), 2.54-2.42 (m, 2H), 2.26-2.21 (m, 2H), 2.10-1.99 (m, 2H), 1.94-1.83 (m, 2H), 1.78 (d, J=17.6 Hz, 1H), 1.71-1.47 (m, 3H), 1.20 (dd, J=6.3, 1.2 Hz, 6H); .sup.13C NMR (101 MHz, CDCl.sub.3) 205.7, 172.68, 135.18, 132.61, 132.13, 131.72, 129.26, 129.04, 73.25, 67.95, 43.66, 40.80, 39.76, 33.95, 29.78, 26.12, 22.25, 21.97, 21.8. MS miz 366.2 (MH.sup.+). HRMS calculated 366.1830, found 366.1842.

    Example 13

    [0268] n-Propyl 5-((1-(2-chlorophenyl)-2-oxocyclohexyl)amino)pentanoate hydrochloride (rac-C4nPr). From rac-24 and propyl 5-bromopentanoate (45%), .sup.1H NMR (400 MHz, CDCl.sub.3) 11.23 (br, 1H), 8.49 (br, 1H), 8.23 (d, J=8.0 Hz, 1H), 7.59-7.52 (m, 1H), 7.46 (br, 2H), 4.0 (t, J=6.8 Hz, 2H), 3.76 (dm, J=14.3 Hz, 1H), 3.24-3.18 (m, 1H), 2.74 (br, 1H), 2.69-2.61 (m, 1H), 2.46 (t, J=14.0 Hz, 2H), 2.29 (td, J=7.5, 2.9 Hz, 2H), 2.04-1.95 (m, 1H), 1.92-1.89 (m, 1H), 1.87-1.83 (m, 1H), 1.79 (dbr, J=15.3 Hz, 1H), 1.73-1.57 (m, 5H), 1.54-1.47 (m, 1H), 0.91 (t, J=7.4 Hz, 3H); .sup.13C NMR (101 MHz, CDCl.sub.3) 205.98, 173.29, 135.14, 132.6, 132.19, 131.74, 129.17, 129.08, 73.28, 66.31, 43.68, 40.77, 39.88, 33.58, 29.85, 26.16, 22.16, 22.06, 21.81, 10.5. MS m/z 366.2 (MH.sup.+). HRMS calculated 366.1830, found 366.1839.

    [0269] General Procedure for Reductive Methylation of N-Alkylated Norketamine Esters (Scheme 4)

    [0270] Norketamine ester (0.9 mmol) was dissolved in MeOH (20 mL) and cooled to 0 C. in an ice bath. Acetic acid (0.2 mL, 3.6 mmol) and NaCNBH.sub.3(112 mg, 1.8 mmol) was added to the above solution and stirred at 0 C. for 5 min. Formaldehyde (37% in H.sub.2O, 2.2 mmol) was added at 0 C. and reaction mixture allowed to stir at 25 C. for 24 h. The reaction mixture was quenched with NaHCO.sub.3 and diluted with water. The aqueous layer was extracted with CH.sub.2Cl.sub.2 (320 mL), washed with brine and dried over Na.sub.2SO.sub.4. The solvent was evaporated under reduced pressure to obtain the product as yellow oil. The yellow oil was dissolved in Et.sub.2O (5 mL), cooled to 0 C. in an ice bath and treated with HCl gas for 1 min. Solvent was evaporated and the residue was resuspended in EtOAc (2 mL) and sonicated. The precipitate formed was diluted with EtOAc (10 mL) and filtered, dried to give the product as the HCl salt.

    Example 14

    [0271] Ethyl 3-4-((2-chlorophenyl)-2-oxocyclohexyl)(methyl)amino)propanoate (19). From reductive methylation of rac-C2Et, (97%). .sup.1H NMR (400 MHz, CDCl.sub.3) 7.38 (dd, J=7.8, 1.4 Hz, 1H), 7.36-7.33 (m, 1H), 7.30 (td, J=7.9, 1.4 Hz, 1H), 7.25-7.21 (m, 1H), 4.10 (q, J=7.2 Hz, 2H), 3.11-3.04 (m, 1H), 2.97-2.90 (m, 1H), 2.80-2.73 (m, 1H), 2.58 (t, J=6.7 Hz, 2H), 2.49-2.45 (m, 2H), 2.43 (s, 3H), 2.05-1.91 (m, 2H), 1.89-1.72 (m, 2H), 1.65-1.56 (m, 1H), 1.24 (t, J=7.2 Hz, 3H); .sup.13C NMR (101 MHz, CDCl.sub.3) 208.1, 172.7, 138.0, 134.07, 131.68, 129.86, 18.64, 126.65, 74.58, 60.37, 47.76, 41.19, 36.97, 36.14, 34.73, 27.28, 22.33, 14.27. MS m/z 338.5 (MH.sup.+). HRMS calculated for C.sub.18H.sub.25ClNO.sub.3 (MH.sup.+) 338.1517, found 338.1514.

    Example 15

    [0272] Ethyl 4-((1-(2-chlorophenyl)-2-oxocyclohexyl)(methyl)amino)butanoate hydrochloride (20). From reductive methylation of rac-C3Et (97%). Mixture of rotamers. .sup.1H NMR (400 MHz, CDCl.sub.3) 11.97 (br, 1H), 11.79 (br, 1H), 8.46 (d, J=8.0 Hz, 1H), 7.93 (d, J=7.6 Hz, 1H), 7.64-7.46 (m, 6H), 4.12-4.04 (m, 4H), 3.96 (t, J=9.3 Hz, 1H), 3.69 (d, J=14.8 Hz, 1H), 3.47 (1H), 3.25 (d, J=14.5 Hz, 1H), 3.16 (s, 3H), 2.78 (br, 6H), 2.69-2.55 (m, 5H), 2.48-2.34 (m, 3H), 2.14 (br, 3H), 1.97 (br, 3H), 1.84 (br, 5), 1.48-1.39 (m, 2H), 1.31-1.19 (m, 6H); .sup.13C NMR (101 MHz, CDCl.sub.3) 205.26, 204.28, 172, 136.05, 135.91, 133.57, 132.87, 132.77, 132.65, 132.55, 132.11, 129.2, 128.53, 127.69, 60.85, 53.32, 52.16, 42.65, 41.99, 37.37, 37.17, 36.59, 35.39, 31.49, 29.16, 22.22, 22.13, 20.64, 20.55, 14.3 (some C not seen for both rotamers). MS m/z 352.2 (MH.sup.+). HRMS calculated for C.sub.19H.sub.27ClNO.sub.3 (MH.sup.+) 352.1674, found 352.1687.

    Example 16

    [0273] Methyl 5-((1-(2-chlorophenyl)-2-oxocyclohexyl)(methyl)amino)pentanoate (21). From reductive methylation of rac-C4Me, (97%). .sup.1H NMR (400 MHz, CDCl.sub.3) 7.41 (d, J=7.5 Hz, 2H), 7.38-7.29 (m, 2H), 3.66 (s, 3H), 2.83 (br, 2H), 2.61-2.57 (m, 3H), 2.49 (br, 3H), 2.30 (t, J=7.1 Hz, 2H), 2.10-1.94 (m, 3H), 1.88-1.77 (m, 3H), 1.62-1.59 (m, 3H); .sup.13C NMR (101 MHz, CDCl.sub.3) 206.75, 173.94, 134.77, 133.19, 132.01, 131.14, 130.12, 127.44, 52.02, 51.62, 41.63, 37.0, 35.86, 33.66, 28.04, 27.07, 22.58, 22.27 (1C overlapping). MS m/z 352.2 (MH.sup.+). HRMS calculated HRMS calculated for C.sub.19H.sub.27ClNO.sub.3 (MH.sup.+) 352.1674, found 352.1683.

    [0274] Biological Activity

    [0275] All animal experiments were conducted at the Ruakura Research Centre, Hamilton, New Zealand, using experimental protocols reviewed and approved by the Ruakura Animal Ethics Committee (ethics ref 12604).

    [0276] Following acquisition of baseline physiologic parameters (heart rate, respiratory rate, PWR, and righting reflex (RR)) adult female Sprague-Dawley rats of approximately 350-450 g were put under non-traumatic restraint and the marginal vein of the tail was cannulated. Ketamine or a compound of the invention at 10 mg/ml was administered via a minibore extension tube adequately secured to the tail. Infusions were commenced at a rate (weight-adjusted) to deliver 20 mg/kg/min initially (until the pedal withdrawal reflex score PWR=1), then were reduced to a rate of 6.7 mg/kg/min. Infusion rate was then titrated in an up-and-down fashion to maintain dorsal recumbency and a PWR=1 to 10 minutes before cessation. Three rats were used in each study, with each group of rats also acting as their own ketamine control. The order of study drug administration was determined by prior odds/evens randomisation with a recovery interval of at least one hour afforded between experiments. PWR and RR were recorded at 1 minute intervals throughout. The times from cessation of infusion to return of righting reflex (RRR), and from cessation of infusion to the animals displaying independent locomotion (walk) were recorded.

    [0277] The results are provided in Tables 2 and 3 below.

    [0278] Pedal Withdrawal Reflex (PWR) scoring: Nociceptive testing in animals was conducted via 1 second application of constant pressure (firm digital pressure) over the forepaw of the animal. Pedal withdrawal reflex testing is primarily used to assess analgesic effect, and responses are graded accordingly: 0, absent; 1, flicker; 2, moderate withdrawal; 3, fast withdrawal; 4, Fast withdrawal with cry/preceding apnoea (modified from Buitrago, S. et al. J. Amer. Assoc. Lab. Animal. Sci. 2008, 47, 11-17).

    [0279] Loss of Righting Reflex (LRR): This is primarily used to assess anaesthetic hypnotic effect. Righting reflex is judged absent when the rat fails to right from a position of dorsal recumbency to a position of sternal recumbency on three attempts performed in rapid succession. Dose to LRR is termed effective potency.

    TABLE-US-00002 TABLE 2 Anaesthetic effects of ketamine and compounds of the invention in a rat infusion study LRR.sup.a PWR = 1.sup.b RRR.sup.c Walk.sup.d Time.sup.e Dose.sup.f Time.sup.e Dose.sup.f Time.sup.e Time.sup.e Compd (sec) (mg/kg) (sec) (mg/kg) (sec) (sec) rac-ketamine 59 5 20 2 93 8 31 2 863 153 1918 518 (S)-C3OAc 81 10 26 3 104 7 34 1 566 30 983 93 rac-ketamine 77 10 27 4 95 13 38 10 1602 549 2536 250 rac-C2Et 135 61 48 23 154 68 55 25 177 51 253 68 rac-ketamine 53 1 20 1 73 3 26 1 1315 215 2163 722 (S)-C2Et 171 54 59 19 185 55 62 20 62 8 80 8 rac-ketamine 62 7 22 2 71 9 24 3 760 144 1100 144 rac-C2iPr 103 17 33 6 127 13 37 6 83 19 153 33 rac-ketamine 65 10 30 4 77 12 34 4 900 60 1200 180 (S)-C2iPr 222 18 74 9 247 13 84 4 15 15 224 90 rac-ketamine 53 24 69 26 1170 1629 (R)-C2iPr 170 71 190 82 0 900 rac-ketamine 51 3 18 1 63 3 21 1 1060 221 1500 5 rac-C2nPr 404 196 131 62 420 180 136 67 0 0 rac-ketamine 59 6 17 2 76 7 24 4 1523 131 2122 131 rac-C3Et 70 6 24 2 137 14 44 5 95 12 170 17 rac-ketamine 69 7 23 2 84 4 28 2 874 81 1384 374 rac-C3iPr 125 21 42 9 192 47 66 17 37 22 110 45 rac-ketamine 69 7 23 2 84 4 28 2 874 81 1384 374 rac-C3nPr 329 106 137 48 558 42 209 20 10 5.5 65 33 rac-ketamine 70 28 20 5 81 23 22 4 1104 95 1462 113 rac-C4Me 92 14 34 7 124 21 44 10 99 16 126 32 rac-ketamine 56 6 17 2 76 7 23 4 1523 131 2122 107 rac-C4Et 97 8 34 4 172 36 57 12 134 22 158 22 rac-ketamine 54 19 66 22 1281 1499 rac-C4iPr 122 38 122 38 180 320 rac-ketamine 65 10 23 3 77 12 26 4 900 60 1200 180 rac-C4nPr 271 97 82 34 277 97 83 34 45 15 90 30 rac-ketamine 60 21 69 25 1230 1475 19 280 95 290 99 0 0 rac-ketamine 75 25 86 29 1500 1920 20 600 196 600 196 0 0 rac-ketamine 57 20 82 28 2040 2340 21 420 145 435 148 0 201 .sup.aLRR: (Loss of righting reflex) assesses anaesthetic effect. Righting reflex is considered absent when the animal fails to right from a position of dorsal recumbency to a position of sternal recumbency on three attempts performed in rapid succession. .sup.bPWR (Pedal withdrawal reflex) assesses analgesic effect, and is conducted by a 1 second application of firm constant pressure (for rats, firm digital pressure) over the forepaw of the animal. A PWR = 1 (a flicker of response) indicates a satisfactory level of analgesia (nociception). .sup.cRRR (Recovery of righting reflex; ability to right from dorsal recumbency). .sup.dWalk (ability to sustain independent locomotion). .sup.eTime: the time from onset of the infusion of drug to achieve LRR or PWR the end of the infusion of drug to achieve RRR or Walk. .sup.fDose: The total drug administered to achieve LRR or PWR no errors are given the results are from a single animal.

    TABLE-US-00003 TABLE 3 Head-to-head ratios of anaesthetic effects of compounds of the invention to ketamine LRR.sup.a PWR = 1.sup.b RRR.sup.c Walk.sup.d Compd Time.sup.e Dose.sup.f Time.sup.e Dose.sup.f Time.sup.e Time.sup.e (S)-C3OAc 1.37 1.30 1.12 1.10 0.65 0.51 rac-C2Et 1.75 1.78 1.62 1.45 0.11 0.10 (S)-C2Et 3.22 2.95 2.53 2.38 0.05 0.04 rac-C2iPr 1.66 1.50 1.79 1.54 0.11 0.14 (S)-C2iPr 3.41 2.46 3.14 2.47 0.02 0.19 (R)-C2iPr 3.20 2.96 2.75 3.15 NA.sup.g 0.06 rac-C2nPr 7.92 7.28 6.67 6.48 NC.sup.h NC.sup.h rac-C3Et 1.19 1.41 1.80 1.83 0.062 0.08 (S)-C3Et 3.23 2.95 2.53 2.38 0.05 0.04 rac-C3iPr 1.81 1.83 2.29 2.36 0.042 0.08 rac-C3nPr 4.77 5.95 6.64 7.46 0.012 0.05 rac-C4Me 1.31 1.70 1.53 2.00 0.090 0.086 (S)-C4Me 1.94 1.80 1.81 1.76 0.07 0.51 rac-C4Et 1.73 2.00 2.26 2.48 0.09 0.05 (S)-C4Et 1.73 2.00 2.26 2.48 0.088 0.074 rac-C4iPr 2.26 2.00 1.85 1.73 1.78 1.17 rac-C4nPr 4.17 3.56 3.60 3.19 0.05 0.08 19 4.67 4.50 4.20 3.96 NC.sup.h NC.sup.h 20 8.00 7.84 6.98 6.76 NC.sup.h NC.sup.h 21 7.37 7.25 5.30 5.29 NC.sup.h 0.09 .sup.a-fAs for Table 2. .sup.gNA: not active. .sup.hNC: not calculable.

    [0280] The results of Tables 2 and 3 clearly show that compounds of the invention show ketamine-like anaesthetic effects with similarly rapid onset and potency, but with much more rapid (up to 10-fold faster than ketamine) recovery following discontinuation of infusion.

    [0281] The average values of the parameters measured for the ketamine standard over the various experiments is shown below in Table 4. Given the complexity of the experimental protocol, the pre-sedation data (time and total dose for LRR; Table 2) are very consistent, with ranges of only 1.5-fold. The consistency of the post-sedation recovery times are expectedly lower, with ranges of about 2.5-fold.

    [0282] Representative plots of the performance of two representative compounds of the invention compared to ketamine in are shown in FIGS. 1 and 2. Loss of righting (anaesthesia) for rac-C2nPr and rac-C4Me are shown in FIGS. 1A and 1B, respectively, and pedal withdrawal scores are shown in FIGS. 2A and 2B.

    [0283] FIG. 3 shows a scatter-plot of effective potency (dose [mg/kg] to loss of righting reflex) versus duration (time to return of righting reflex) for ketamine and representative compounds of the invention.

    TABLE-US-00004 TABLE 4 Average parameters determined for the ketamine standard Property Average Range Time to achieve LRR (sec) 61 8 51-75 Total dose to LRR (mg/kg) 21 7 17-27 Time to PWR = 1 (sec) 76 9 60-95 Total dose to LRR (mg/kg) 26 4 21-34 Time to RRR (sec) 1212 318 863-2040 Time to walking (sec) 1709 400 1100-2340

    DISCUSSION

    [0284] Acetate (S)-C3OAc was the most potent of the compounds (about as potent as ketamine), but showed only moderately faster recoveries (1.5-2 fold) than ketamine itself. Without wishing to be bound by theory, the applicant believes that this is most likely not due to slow acetate hydrolysis, but to the fact that the corresponding alcohol product is itself a potent hypnotic/analgesic.

    [0285] Of the remaining norketamine esters, the more potent compounds (up to 2-fold less dose-potent than ketamine itself) rac-C2Et, rac-C2iPr, rac-C3Et, rac-C3iPr, rac-C4Me, rac-C4Et and rac-C4iPr comprised a mixture of chain lengths (thus a range of pKas) and a variety of Me, Et and iPr esters.

    [0286] The less dose-potent compounds (from 2-6 fold less than ketamine) rac-C2nPr, rac-C3nPr and rac-C4nPr were also a mixture of chain lengths, but were all n-Pr esters, and at the higher end of the lipophilicity range. Since dose-potency and rapidity of recovery from both LRR and PWR are broadly reciprocal, it is not surprising that these less potent compounds resulted in the fastest recoveries (20-25 fold faster than ketamine).

    [0287] Most of the norketamine esters were racemic, but several enantiomers were evaluated, since (S)-ketamine is known to be as active but about twice as potent as its racemate. Two of the S-enantiomers ((S)-C2Et, (S)-C2iPr), while active, were only half as potent and showed faster recoveries than the corresponding racemates, suggesting more rapid hydrolysis of the S-enantiomer esters. The (R)-C2iPr enantiomer had similar potency and kinetics of recovery to (S)-C2iPr. rac-C4Me and enantiopure (S)-C4Me had broadly equivalent properties.

    [0288] Exploratory studies were done (mostly single-animal evaluations) using ketamine esters 19-21. The racemic C2 ethyl ester 19 was about as potent as the n-Pr norketamine esters, but had a very weak sedative effect, with very rapid recovery. Longer chain length C3 ethyl and C4 methyl esters 20 and 21, were less potent, with weak sedative activity.

    [0289] There was no clear effect of pKa on anaesthetic activity, although the weakest bases were among the least potent of the esters.

    [0290] In summary, the above results show that short-chain aliphatic ester analogues of ketamine broadly retain its desirable anaesthetic and analgesic activities, yet are metabolised to the more polar and inactive acids sufficiently rapidly to minimise the drawbacks of ketamine itself in this capacity.

    [0291] Although the invention has been described by way of example and with reference to particular embodiments, it is to be understood that modifications and/or variations may be made without departing from the scope of the invention.

    [0292] All publications referenced in this specification are incorporated herein in their entirety.