Title of Invention: PHARMACOLOGICALLY ACTIVE COMPOUNDS Abstract: The present invention relates to compounds of formula I shown below: wherein Q is as defined herein. The compounds of formula I act as selective positive allosteric modulators of strychnine-sensitive alpha 1-glycine receptors. The present invention further relates to the use of these compounds as therapeutic agents for the treatment and/or prevention of diseases or conditions in which strychnine-sensitive alpha 1-glycine receptor activity is implicated (such as, for example, chronic pain. The present invention also relates to processes for the preparation of these compounds and to pharmaceutical compositions comprising them. Detailed Description: REFERENCE TO RELATED APPLICATIONS This application is a continuation of U.S. application Ser. No. 15/107,653, filed Jun. 23, 2016, which is the U.S. National Stage of International Patent Application No. PCT/GB2014/053838, filed Dec. 23, 2014, which claims the benefit of and priority to Great Britain Patent Application No. 1322905.9, filed Dec. 23, 2013. Each of these applications is hereby fully incorporated by reference herein. INTRODUCTION The present invention relates to pharmacologically active compounds. More specifically, the present invention relates to compounds that act as selective positive allosteric modulators of strychnine-sensitive alpha 1-glycine receptors. The present invention further relates to the use of these compounds as therapeutic agents for the treatment and/or prevention of diseases or conditions in which strychnine-sensitive alpha 1-glycine receptor activity is implicated (such as, for example, chronic pain or neuropathic pain). The present invention also relates to processes for the preparation of these compounds and to pharmaceutical compositions comprising them. BACKGROUND OF THE INVENTION In many clinical settings there is a need for safe and effective pain control strategies. However the majority of developments in the pain control field have failed to deliver high efficacy products free of undesirable side effects and safety issues. The opiates are generally regarded as the most effective treatment available for severe pain, but the ultimate goal is to deliver a pain control agent with the efficacy of the opiates but without the sedation, dependence, gastric damage and general tolerability problems that are associated with opiate use. It has been postulated that phenol derivatives may have a number of neuromodulatory effects. However the only phenol derivative in widespread clinical use is the anaesthetic propofol (2,6-di-isopropyl phenol). Key features of anaesthesia are loss of consciousness, immobility in the presence of painful stimuli and absence of recall. Anaesthetics, such as propofol, are understood to mediate their anaesthetic effect by activating γ-aminobutyric acid (GABAA) receptors in the Central Nervous System (CNS). Analgesia is defined as the relief of pain. Among other peripheral and/or central nervous mechanisms, analgesia can arise as a result of enhanced inhibitory synaptic transmission within the dorsal horn of the spinal chord. It is understood that inhibitory postsynaptic transmission in the spinal chord involves mainly glycine receptors. Accordingly the glycine receptor family represents a target site for therapeutic agents aiming at inhibiting pain. Both, GABAA and glycine receptors belong to the ligand-gated ion channel superfamily. They have a common structure in which five subunits form an ion channel. α and β subunits assemble into a pentameric receptor with a proposed in vivo stochiometry of 3α:2β. Glycine receptors, like GABAA receptors, inhibit neuronal firing by opening chloride channels following agonist binding. Glycine receptors are mainly found in lower areas of the central nervous system and are involved in the control of motor rhythm generation, the coordination of spinal nociceptive reflex responses and the processing of sensory signals. Chronic pain is very different from acute pain. Acute pain can be considered as a useful early warning system informing us about noxious stimuli and thereby helping us to escape and prevent damage. Chronic pain, in contrast, is a disease in its own right. Experts regard it as a dys-equilibrium syndrome, where inhibitory neuronal activity which under normal circumstances suppresses the processing of pain is markedly reduced. Treatment of chronic inflammatory or neuropathic pain is still difficult, and there is currently no single treatment that works for all conditions. Increased neuronal excitability seen in chronic pain involves a loss of inhibition mediated by GABA- and/or glycinergic neurons in the superficial dorsal horn of the spinal cord that control the relay of nociceptive signals from the periphery to higher areas of the central nervous system. In the adult dorsal horn, the contribution of glycine to fast inhibitory postsynaptic transmission dominates. Glycine receptors are mainly found in lower areas of the central nervous system and are involved in the control of motor rhythm generation, the coordination of spinal nociceptive reflex responses and the processing of sensory signals. Their role in modulating ascending nociceptive pathways and pain makes them a potentially interesting target site for analgesic and spasmolytic agents. Microinjection of the glycine receptor agonist taurine into the anterior cingulate cortex—associated with the affective component of pain—relieves neuropathic pain, an effect that could be antagonized by the selective glycine receptor antagonist strychnine. There are four α-subunits and one β-subunit for the strychnine-sensitive glycine receptor, the α1-subunit is widely expressed in the adult spinal cord and brain stem, but also in higher centres of the brain involved in sensory processing. The glycine receptor α3-subunit has been identified as a target site underlying central inflammatory pain sensitization due to PGE2-induced receptor phosphorylation. α3-subunit knock-out mice do not develop inflammatory pain with otherwise normal response to acute pain. This phenomenon may be explained by the fact that al containing glycine receptor subunits which probably compensate for the lack in α3 do not possess the protein kinase A (PKA) phosphorylation site involved in the PGE2 signal transduction. Furthermore, phosphorylation of the α3 subunit is not necessarily involved in neuropathic pain. Based on this understanding, a need has been identified by the inventors for the development of drugs that target the predominant adult glycine receptor isoform containing the α1 subunit. Given the physiological role of glycine receptors and their relatively restricted expression (mainly in the spinal cord and lower brain areas), a selective glycine modulator should be of great interest therapeutically to increase inhibition at the level of the spinal cord dorsal horn. There exists a need to develop new and improved analgesics. Despite that fact that glycine receptors represent a good target for identifying such analgesics, there are no existing analgesics that effectively target these receptors. The inventors therefore decided to address this issue and exploited their knowledge of the pathophysiological mechanisms underlying anaesthesia and analgesia with a view to identifying new and improved drugs for controlling pain. Aspects of the invention were devised with the foregoing in mind. SUMMARY OF THE INVENTION In one aspect, the present invention provides a compound, or a pharmaceutically acceptable salt or solvate thereof, as defined herein. In another aspect, the present invention provides a pharmaceutical composition which comprises a compound as defined herein, or a pharmaceutically acceptable salt or solvate thereof, and one or more pharmaceutically acceptable excipients. In another aspect, the present invention provides a compound as defined herein, or a pharmaceutically acceptable salt or solvate thereof, or a pharmaceutical composition as defined herein, for use in therapy. In another aspect, the present invention provides a compound as defined herein, or a pharmaceutically acceptable salt or solvate thereof, or a pharmaceutical composition as defined herein, for use in the treatment of a disease or condition in which the selective, positive allosteric modulation of strychnine-sensitive alpha 1-glycine receptors is beneficial. In a particular aspect, the present invention provides a compound as defined herein, or a pharmaceutically acceptable salt or solvate thereof, or a pharmaceutical composition as defined herein, for use in the treatment of pain. In a particular embodiment, the pain is present in a human subject. In a particular aspect, the present invention provides a compound as defined herein, or a pharmaceutically acceptable salt or solvate thereof, or a pharmaceutical composition as defined herein, for use in the treatment of chronic pain. In a particular embodiment, the chronic pain is present in a human subject. In a particular aspect, the present invention provides a compound as defined herein, or a pharmaceutically acceptable salt or solvate thereof, or a pharmaceutical composition as defined herein, for use in the treatment of neuropathic pain. In a particular embodiment, the chronic pain is present in a human subject. In another aspect, the present invention provides a compound as defined herein, or a pharmaceutically acceptable salt or solvate thereof, or a pharmaceutical composition as defined herein, for use in the selective, positive allosteric modulation of strychnine-sensitive alpha 1-glycine receptors. In another aspect, the present invention provides the use of a compound as defined herein, or a pharmaceutically acceptable salt or solvate thereof, in the manufacture of a medicament for use in the treatment of a disease or condition in which the selective, positive allosteric modulation of strychnine-sensitive alpha 1-glycine receptors is beneficial. In a particular aspect, the present invention provides the use of a compound as defined herein, or a pharmaceutically acceptable salt or solvate thereof, in the manufacture of a medicament for use in the treatment of pain. Suitably, the medicament is for use in the treatment of pain in a human subject. In a particular aspect, the present invention provides the use of a compound as defined herein, or a pharmaceutically acceptable salt or solvate thereof, in the manufacture of a medicament for use in the treatment of chronic pain. Suitably, the medicament is for use in the treatment of chronic pain in a human subject. In a particular aspect, the present invention provides the use of a compound as defined herein, or a pharmaceutically acceptable salt or solvate thereof, in the manufacture of a medicament for use in the treatment of neuropathic pain. In a particular embodiment, the neuropathic pain is present in a human subject. In another aspect, the present invention provides the use of a compound as defined herein, or a pharmaceutically acceptable salt or solvate thereof, in the manufacture of a medicament for use in the selective, positive allosteric modulation of strychnine-sensitive alpha 1-glycine receptors. In another aspect, the present invention provides a method of selectively producing a positive allosteric modulation effect in strychnine-sensitive alpha 1-glycine receptors in vitro or in vivo, said method comprising contacting a cell with an effective amount of a compound as defined herein, or a pharmaceutically acceptable salt or solvate thereof. In another aspect, the present invention provides a method of treating a disease or condition in which the selective, positive allosteric modulation of strychnine-sensitive alpha 1-glycine receptors is beneficial in a patient in need of such treatment, said method comprising administering to said patient a therapeutically effective amount of a compound as defined herein, or a pharmaceutically acceptable salt or solvate thereof, or a pharmaceutical composition as defined herein. In another aspect, the present invention provides a method of treating pain in a patient in need of such treatment, said method comprising administering to said patient a therapeutically effective amount of a compound as defined herein, or a pharmaceutically acceptable salt or solvate thereof, or a pharmaceutical composition as defined herein. In another aspect, the present invention provides a method of treating chronic pain in a patient in need of such treatment, said method comprising administering to said patient a therapeutically effective amount of a compound as defined herein, or a pharmaceutically acceptable salt or solvate thereof, or a pharmaceutical composition as defined herein. In another aspect, the present invention provides a method of treating neuropathic pain in a patient in need of such treatment, said method comprising administering to said patient a therapeutically effective amount of a compound as defined herein, or a pharmaceutically acceptable salt or solvate thereof, or a pharmaceutical composition as defined herein. The present invention further provides a method of synthesising a compound as defined herein, or a pharmaceutically acceptable salt or solvate thereof. In another aspect, the present invention provides a compound as defined herein, or a pharmaceutically acceptable salt or solvate thereof, obtainable by, or obtained by, or directly obtained by any one of the methods of synthesis defined herein. In another aspect, the present invention provides novel intermediates defined herein which are suitable for use in any one of the synthetic methods set out herein. Preferred, suitable, and optional features of any one particular aspect of the present invention are also preferred, suitable, and optional features of any other aspect. DETAILED DESCRIPTION OF THE INVENTION Definitions Unless otherwise stated, the following terms used in the specification and claims have the following meanings set out below. It is to be appreciated that references to “treating” or “treatment” include prophylaxis as well as the alleviation of established symptoms of a condition. “Treating” or “treatment” of a state, disorder or condition therefore includes: (1) preventing or delaying the appearance of clinical symptoms of the state, disorder or condition developing in a human that may be afflicted with or predisposed to the state, disorder or condition but does not yet experience or display clinical or subclinical symptoms of the state, disorder or condition, (2) inhibiting the state, disorder or condition, i.e., arresting, reducing or delaying the development of the disease or a relapse thereof (in case of maintenance treatment) or at least one clinical or subclinical symptom thereof, or (3) relieving or attenuating the disease, i.e., causing regression of the state, disorder or condition or at least one of its clinical or subclinical symptoms. A “therapeutically effective amount” means the amount of a compound that, when administered to a mammal for treating a disease, is sufficient to effect such treatment for the disease. The “therapeutically effective amount” will vary depending on the compound, the disease and its severity and the age, weight, etc., of the mammal to be treated. The term “halo” refers to fluoro, chloro, bromo and iodo. The phrase “compound of the invention” means those compounds which are disclosed herein, both generically and specifically. Compounds of the Invention In one aspect, the present invention provides a compound of formula I shown below: wherein: Q is selected from: wherein: R1, R2a, R2b and R3 are each independently selected from hydrogen, halo, methyl, hydroxymethyl, CF3 and OCF3; or R2a and R2b are linked such that together they form a 4, 5 or 6-membered carbocyclic or heterocyclic ring; R4 and R5 are each independently selected from hydrogen, halo, methyl, hydroxymethyl, CF3 and OCF3; R6 and R7 are each independently selected from hydrogen, halo, methyl, hydroxymethyl, CF3 and OCF3; R8 and R9 are each independently selected from hydrogen, methyl, CF3 halo, hydroxymethyl and OCF3; R10 and R11 are each independently selected from hydrogen, methyl, CF3 halo, hydroxymethyl and OCF3; R12 is selected from hydrogen, (1-4C)alkyl or (1-4C)haloalkyl; or a pharmaceutically acceptable salt thereof. In another aspect, the present invention provides a compound of formula I shown below: wherein: Q is selected from: wherein: R1, R2 and R3 are each independently selected from hydrogen, halo, methyl, hydroxymethyl, CF3 and OCF3; R4 and R5 are each independently selected from hydrogen, halo, methyl, hydroxymethyl, CF3 and OCF3; R6 and R7 are each independently selected from hydrogen, halo, methyl, hydroxymethyl, CF3 and OCF3; R8 and R9 are each independently selected from hydrogen, methyl, CF3 halo, hydroxymethyl and OCF3; or a pharmaceutically acceptable salt thereof. In the compounds of formula I above, indicates the bond that attaches Q to the C(═O) moiety of the compound of formula I. In all cases, Q is a nitrogen linked heterocyclic ring of the formula (i), (ii), (iii), (iv) or (v) shown above. Particular compounds of the invention include, for example, compounds of the formula I, or pharmaceutically acceptable salts or solvates thereof, wherein, unless otherwise stated, each of Q, R1, R2a, R2b, R2, R3, R4, R5, R6, R7, R8, R9, R10, R11 and R12 has any of the meanings defined hereinbefore or in any one of paragraphs (1) to (33) hereinafter:— (1) Q is selected from: (2) Q is selected from: (3) Q is: (4) Q is of formula (i) and R1, R2, R2a, R2b and R3 are each independently selected from hydrogen, halo, methyl, hydroxymethyl, CF3 and OCF3; or R2a and R2b are linked such that together they form a 4 or 5 membered carbocyclic or heterocyclic ring; (5) Q is of formula (i) and one of R2a or R2b is hydrogen and the other is selected from hydrogen, fluoro, methyl, hydroxymethyl, CF3 and OCF3; or R2a and R2b are linked such that together they form a 4 membered heterocyclic ring comprising one N or O atom; (6) R1, R2a, R2b R2 and R3 are each independently selected from hydrogen, fluoro, methyl, hydroxymethyl, CF3 and OCF3; (7) R1, R2a, R2b R2 and R3 are each independently selected from hydrogen, fluoro, methyl, hydroxymethyl, CF3 and OCF3; (8) R1, R2a, R2b R2 and R3 are each independently selected from hydrogen, fluoro or methyl; (9) R1, R2a, R2b R2 and R3 are all hydrogen; (10) one or two of R1, R2a, R2b, R2 and R3 is a substituent other than hydrogen; (11) one of R1, R2a, R2b, R2 and R3 is a substituent other than hydrogen. (12) R1 and R3 are each independently selected from hydrogen, fluoro or methyl and R2a and R2b are hydrogen; (13) R2a and R2b are hydrogen and one of R1 and R3 is selected from hydrogen, fluoro or methyl and the other is hydrogen; (14) R1, R2a and R3 are hydrogen and R2b is selected from hydrogen, fluoro, methyl, hydroxymethyl, CF3 and OCF3; (15) R1, R2a and R3 are hydrogen and R2b is fluoro; (16) R1 and R3 are hydrogen and R2a and R2b are linked such that together they form a 4 membered carbocyclic or heterocyclic ring; (17) R4 and R5 are each independently selected from hydrogen, fluoro, methyl, hydroxymethyl, CF3 and OCF3; (18) R4 and R5 are each independently selected from hydrogen, fluoro or methyl; (19) R4 and R5 are both hydrogen; (20) one of R4 and R5 is fluoro or methyl and the other is hydrogen; (21) R6 and R7 are each independently selected from hydrogen, fluoro, methyl, hydroxymethyl, CF3 and OCF3; (22) R6 and R7 are each independently selected from hydrogen, fluoro or methyl; (23) R6 and R7 are both hydrogen; (24) one of R6 and R7 is fluoro or methyl and the other is hydrogen. (25) R8 and R9 are each independently selected from hydrogen or methyl; (26) R8 and R9 are both hydrogen; (27) one of R8 and R9 is methyl and the other is hydrogen; (28) R10 and R11 are each independently selected from hydrogen, fluoro or methyl; (29) R10 and R11 are both hydrogen; (30) one of R10 and R11 is methyl and the other is hydrogen; (31) R10 and R11 are both hydrogen and R12 is methyl; (32) R12 is selected from hydrogen or (1-4C)alkyl; (33) R12 is methyl. Suitably, Q is as defined in paragraphs (1), (2) or (3) above. In an embodiment, Q has the structural formula (i). In another embodiment, Q has the structural formula (ii). In an embodiment, Q has the structural formula (iii). In a particular embodiment, Q has the structural formula (iv). In a particular embodiment, Q is as defined in paragraph (3) above. Suitably when Q is of formula (i), it has the formula shown below: Suitably, R1, R2a, R2b and R3 are as defined in any one of paragraphs (4) to (16) above. Suitably, R4 and R5 are as defined in any one of paragraphs (17) to (20) above. In a particular embodiment, R4 and R5 are as defined in paragraph (20) above. Suitably, R6 and R7 are as defined in any one of paragraphs (21) to (24) above. In a particular embodiment, R6 and R7 are as defined in paragraph (23) or (24) above. Suitably, R8 and R9 are as defined in any one of paragraphs (25) to (27) above. In a particular embodiment, R6 and R7 are as defined in paragraph (26) or (27) above. Suitably, R10 and R11 are as defined in any one of paragraphs (28) to (30) above. In a particular embodiment, R6 and R7 are as defined in paragraph (29) or (30) above. In a particular group of compounds of the invention, Q is of the structural formula (iv) shown above. Such compounds have the structural formula IA below: wherein R8 and R9 each have any one of the definitions set out herein. In an embodiment of the compounds of formula IA, R8 and R9 are each independently selected from hydrogen or methyl. In a further embodiment of the compounds of formula IA, R8 and R9 are both hydrogen. In a further embodiment of the compounds of formula IA, one of R8 and R9 is methyl and the other is hydrogen. Particular compounds of the invention include any one of the following: (4-(hydroxy)-3,5-diisopropylphenyl)(morpholino)methanone; (R)-(4-(hydroxy)-3,5-diisopropylphenyl)(2-methylmorpholino)methanone; (3-fluoroazetidin-1-yl)(4-hydroxy-3,5-diisopropylphenyl) methanone; (4-(benzyloxy)-3,5-diisopropylphenyl)(piperidin-1-yl)methanone; (4-(hydroxy)-3,5-diisopropylphenyl)(morpholino)methanone; (4-Hydroxy-3,5-diisopropylphenyl)(2-oxa-6-azaspiro[3.3]heptan-6-yl)methanone; (4-Hydroxy-3-5-diisopropylphenyl)(4-methylpiperazin-1-yl)methanone; or a pharmaceutically acceptable salt or solvate thereof. In a particular embodiment, the compounds of the invention is: (4-(hydroxy)-3,5-diisopropylphenyl)(morpholino)methanone, or a pharmaceutically acceptable salt or solvate thereof. The various functional groups and substituents making up the compounds of the present invention are typically chosen such that the molecular weight of the compound does not exceed 1000. More usually, the molecular weight of the compound will be less than 750, for example less than 700, or less than 650, or less than 600, or less than 550. More preferably, the molecular weight is less than 525 and, for example, is 500 or less. Suitable or preferred features of any compounds of the present invention may also be suitable features of any other aspect. A suitable pharmaceutically acceptable salt of a compound of the invention is, for example, an acid-addition salt of a compound of the invention which is sufficiently basic, for example, an acid-addition salt with, for example, an inorganic or organic acid, for example hydrochloric, hydrobromic, sulfuric, phosphoric, trifluoroacetic, formic, citric or maleic acid. In addition a suitable pharmaceutically acceptable salt of a compound of the invention which is sufficiently acidic is an alkali metal salt, for example a sodium or potassium salt, an alkaline earth metal salt, for example a calcium or magnesium salt, an ammonium salt or a salt with an organic base which affords a physiologically-acceptable cation, for example a salt with methylamine, dimethylamine, trimethylamine, piperidine, morpholine or tris-(2-hydroxyethyl)amine. Compounds that have the same molecular formula but differ in the nature or sequence of bonding of their atoms or the arrangement of their atoms in space are termed “isomers”. Isomers that differ in the arrangement of their atoms in space are termed “stereoisomers”. Stereoisomers that are not mirror images of one another are termed “diastereomers” and those that are non-superimposable mirror images of each other are termed “enantiomers”. When a compound has an asymmetric center, for example, it is bonded to four different groups, a pair of enantiomers is possible. An enantiomer can be characterized by the absolute configuration of its asymmetric center and is described by the R- and S-sequencing rules of Cahn and Prelog, or by the manner in which the molecule rotates the plane of polarized light and designated as dextrorotatory or levorotatory (i.e., as (+) or (−)-isomers respectively). A chiral compound can exist as either individual enantiomer or as a mixture thereof. A mixture containing equal proportions of the enantiomers is called a “racemic mixture”. The compounds of this invention may possess one or more asymmetric centers; such compounds can therefore be produced as individual (R)- or (S)-stereoisomers or as mixtures thereof. Unless indicated otherwise, the description or naming of a particular compound in the specification and claims is intended to include both individual enantiomers and mixtures, racemic or otherwise, thereof. The methods for the determination of stereochemistry and the separation of stereoisomers are well-known in the art (see discussion in Chapter 4 of “Advanced Organic Chemistry”, 4th edition J. March, John Wiley and Sons, New York, 2001), for example by synthesis from optically active starting materials or by resolution of a racemic form. Some of the compounds of the invention may have geometric isomeric centres (E- and Z-isomers). It is to be understood that the present invention encompasses all optical, diastereoisomers and geometric isomers and mixtures thereof that possess activity. The present invention also encompasses compounds of the invention as defined herein which comprise one or more isotopic substitutions. For example, H may be in any isotopic form, including 1H, 2H(D), and 3H (T); C may be in any isotopic form, including 12C, 13C, and 14C; and O may be in any isotopic form, including 16O and 18O; and the like. It is also to be understood that certain compounds of the invention may exist in solvated as well as unsolvated forms such as, for example, hydrated forms. It is to be understood that the invention encompasses all such solvated forms that possess activity. It is also to be understood that certain compounds of the invention may exhibit polymorphism, and that the invention encompasses all such forms that possess activity. Compounds of the invention may exist in a number of different tautomeric forms and references to compounds of the invention include all such forms. For the avoidance of doubt, where a compound can exist in one of several tautomeric forms, and only one is specifically described or shown, all others are nevertheless embraced by compounds of the invention. Examples of tautomeric forms include keto-, enol-, and enolate-forms, as in, for example, the following tautomeric pairs: keto/enol (illustrated below), imine/enamine, amide/imino alcohol, amidine/amidine, nitroso/oxime, thioketone/enethiol, and nitro/aci-nitro. Compounds of the invention containing an amine function may also form N-oxides. A reference herein to a compound of the formula I that contains an amine function also includes the N-oxide. Where a compound contains several amine functions, one or more than one nitrogen atom may be oxidised to form an N-oxide. Particular examples of N-oxides are the N-oxides of a tertiary amine or a nitrogen atom of a nitrogen-containing heterocycle. N-Oxides can be formed by treatment of the corresponding amine with an oxidizing agent such as hydrogen peroxide or a per-acid (e.g. a peroxycarboxylic acid), see for example Advanced Organic Chemistry, by Jerry March, 4th Edition, Wiley Interscience, pages. More particularly, N-oxides can be made by the procedure of L. W. Deady (Syn. Comm. 1977, 7, 509-514) in which the amine compound is reacted with m-chloroperoxybenzoic acid (MCPBA), for example, in an inert solvent such as dichloromethane. The compounds of the invention may be administered in the form of a pro-drug which is broken down in the human or animal body to release a compound of the invention. A pro-drug may be used to alter the physical properties and/or the pharmacokinetic properties of a compound of the invention. A pro-drug can be formed when the compound of the invention contains a suitable group or substituent to which a property-modifying group can be attached. Examples of pro-drugs include in vivo cleavable ester derivatives that may be formed at a carboxy group or a hydroxy group in a compound of the invention and in-vivo cleavable amide derivatives that may be formed at a carboxy group or an amino group in a compound of the invention. Accordingly, the present invention includes those compounds of the formula I as defined hereinbefore when made available by organic synthesis and when made available within the human or animal body by way of cleavage of a pro-drug thereof. Accordingly, the present invention includes those compounds of the formula I that are produced by organic synthetic means and also such compounds that are produced in the human or animal body by way of metabolism of a precursor compound, that is a compound of the formula I may be a synthetically-produced compound or a metabolically-produced compound. A suitable pharmaceutically acceptable pro-drug of a compound of the formula I is one that is based on reasonable medical judgement as being suitable for administration to the human or animal body without undesirable pharmacological activities and without undue toxicity. Various forms of pro-drug have been described, for example in the following documents:— a) Methods in Enzymology, Vol. 42, p. 309-396, edited by K. Widder, et al. (Academic Press, 1985); b) Design of Pro-drugs, edited by H. Bundgaard, (Elsevier, 1985); c) A Textbook of Drug Design and Development, edited by Krogsgaard-Larsen and H. Bundgaard, Chapter 5 “Design and Application of Pro-drugs”, by H. Bundgaard p. 113-191 (1991); d) H. Bundgaard, Advanced Drug Delivery Reviews, 8, 1-38 (1992); e) H. Bundgaard, et al., Journal of Pharmaceutical Sciences, 77, 285 (1988); f) N. Kakeya, et al., Chem. Pharm. Bull., 32, 692 (1984); g) T. Higuchi and V. Stella, “Pro-Drugs as Novel Delivery Systems”, A.C.S. Symposium Series, Volume 14; and h) E. Roche (editor), “Bioreversible Carriers in Drug Design”, Pergamon Press, 1987. The in vivo effects of a compound of the formula I may be exerted in part by one or more metabolites that are formed within the human or animal body after administration of a compound of the formula I. As stated hereinbefore, the in vivo effects of a compound of the formula I may also be exerted by way of metabolism of a precursor compound (a pro-drug). It shall also be appreciated that compounds of formula I may also be covalently linked (at any suitable position) to other groups such as, for example, solubilising moieties (for example, PEG polymers), moieties that enable them to be bound to a solid support (such as, for example, biotin-containing moieties), and targeting ligands (such as antibodies or antibody fragments). Synthesis The compounds of the invention can be synthesised using chemistry techniques that are known in the art. In the description of the synthetic methods described below and in the referenced synthetic methods that are used to prepare the staring materials, it is to be understood that all proposed reaction conditions, including choice of solvent, reaction atmosphere, reaction temperature, duration of the experiment and workup procedures, can be selected by a person skilled in the art. It is understood by one skilled in the art of organic synthesis that the functionality present on various portions of the molecule must be compatible with the reagents and reaction conditions utilised. Necessary starting materials may be obtained by standard procedures of organic chemistry. The preparation of such starting materials is described in conjunction with the following representative process variants and within the accompanying Examples. Alternatively necessary starting materials are obtainable by analogous procedures to those illustrated which are within the ordinary skill of an organic chemist. It will be appreciated that during the synthesis of the compounds of the invention in the processes defined below, or during the synthesis of certain starting materials, it may be desirable to protect certain substituent groups to prevent their undesired reaction. The skilled chemist will appreciate when such protection is required, and how such protecting groups may be put in place, and later removed. For examples of protecting groups see one of the many general texts on the subject, for example, ‘Protective Groups in Organic Synthesis’ by Theodora Green (publisher: John Wiley & Sons). Protecting groups may be removed by any convenient method described in the literature or known to the skilled chemist as appropriate for the removal of the protecting group in question, such methods being chosen so as to effect removal of the protecting group with the minimum disturbance of groups elsewhere in the molecule. Thus, if reactants include, for example, groups such as amino, carboxy or hydroxy it may be desirable to protect the group in some of the reactions mentioned herein. By way of example, a suitable protecting group for an amino or alkylamino group is, for example, an acyl group, for example an alkanoyl group such as acetyl, an alkoxycarbonyl group, for example a methoxycarbonyl, ethoxycarbonyl or t-butoxycarbonyl group, an arylmethoxycarbonyl group, for example benzyloxycarbonyl, or an aroyl group, for example benzoyl. The deprotection conditions for the above protecting groups necessarily vary with the choice of protecting group. Thus, for example, an acyl group such as an alkanoyl or alkoxycarbonyl group or an aroyl group may be removed by, for example, hydrolysis with a suitable base such as an alkali metal hydroxide, for example lithium or sodium hydroxide. Alternatively an acyl group such as a tert-butoxycarbonyl group may be removed, for example, by treatment with a suitable acid as hydrochloric, sulfuric or phosphoric acid or trifluoroacetic acid and an arylmethoxycarbonyl group such as a benzyloxycarbonyl group may be removed, for example, by hydrogenation over a catalyst such as palladium-on-carbon, or by treatment with a Lewis acid for example BF3.OEt2. A suitable alternative protecting group for a primary amino group is, for example, a phthaloyl group which may be removed by treatment with an alkylamine, for example dimethylaminopropylamine, or with hydrazine. A suitable protecting group for a hydroxy group is, for example, an acyl group, for example an alkanoyl group such as acetyl, an aroyl group, for example benzoyl, or an arylmethyl group, for example benzyl. The deprotection conditions for the above protecting groups will necessarily vary with the choice of protecting group. Thus, for example, an acyl group such as an alkanoyl or an aroyl group may be removed, for example, by hydrolysis with a suitable base such as an alkali metal hydroxide, for example lithium, sodium hydroxide or ammonia. Alternatively an arylmethyl group such as a benzyl group may be removed, for example, by hydrogenation over a catalyst such as palladium-on-carbon. A suitable protecting group for a carboxy group is, for example, an esterifying group, for example a methyl or an ethyl group which may be removed, for example, by hydrolysis with a base such as sodium hydroxide, or for example a t-butyl group which may be removed, for example, by treatment with an acid, for example an organic acid such as trifluoroacetic acid, or for example a benzyl group which may be removed, for example, by hydrogenation over a catalyst such as palladium-on-carbon. Resins may also be used as a protecting group. In a particular aspect, the present invention provides a method of synthesising a compound of the formula I, or a pharmaceutically acceptable salt or solvate thereof, the method comprising: a) reacting a compound of formula A wherein X is a reactive group, such as chloro; and the hydroxyl group is optionally protected; with a compound of formula B: H-Q wherein Q is as defined hereinbefore and the H atom is attached to a nitrogen atom of the Q group; and b) optionally thereafter, and if necessary: i) removing any protecting groups present; ii) converting the compound formula I into another compound of formula I; and/or iii) forming a pharmaceutically acceptable salt or solvate thereof. X may be any suitable reactive group. Suitably X is a halogen, such as chlorine. Suitably the coupling reaction between compound A and compound B takes place in the presence of a suitable solvent. Any suitable solvent or solvent mixture may be used for this reaction. A person skilled in the art will know how to select suitable solvents or solvent mixtures for use in these reactions. An example of a suitable solvent is dichloromethane. A person skilled in the art will be able to select appropriate reaction conditions to use in order to facilitate this reaction. Suitably, the reaction is carried out in anhydrous conditions and in the presence of an inert atmosphere, such as argon or nitrogen. The reaction may also be carried out at room temperature or at an elevated temperature. The compound of formula A can be prepared by processes known in the art, and suitably by the processes described herein with reference to the examples. The compound of formula B can be prepared by processes known in the art, and suitably by the processes described herein with reference to the examples. The resultant compound of formula I can be isolated and purified using techniques well known in the art. The processes defined herein may further comprise the step of subjecting the compound of formula Ito a salt exchange, particularly in situations where the compound of formula I is formed as a mixture of different salt forms. The salt exchange suitably comprises immobilising the compound of formula I on a suitable solid support or resin, and eluting the compounds with an appropriate acid to yield a single salt of the compound of formula I. In a further aspect of the invention, there is provided a compound of formula I obtainable by any one of the processes defined herein. In a further aspect of the invention, there is provided a compound of formula I obtained by any one of the processes defined herein. In a further aspect of the invention, there is provided a compound of formula I directly obtained by any one of the processes defined herein. Pharmaceutical Compositions According to a further aspect of the invention there is provided a pharmaceutical composition which comprises a compound of the invention as defined hereinbefore, or a pharmaceutically acceptable salt or solvate thereof, in association with a pharmaceutically acceptable diluent or carrier. The compositions of the invention may be in a form suitable for oral use (for example as tablets, lozenges, hard or soft capsules, aqueous or oily suspensions, emulsions, dispersible powders or granules, syrups or elixirs), for topical use (for example as creams, ointments, gels, or aqueous or oily solutions or suspensions), for administration by inhalation (for example as a finely divided powder or a liquid aerosol), for administration by insufflation (for example as a finely divided powder) or for parenteral administration (for example as a sterile aqueous or oily solution for intravenous, subcutaneous, intramuscular, intraperitoneal or intramuscular dosing or as a suppository for rectal dosing). The compositions of the invention may be obtained by conventional procedures using conventional pharmaceutical excipients, well known in the art. Thus, compositions intended for oral use may contain, for example, one or more colouring, sweetening, flavouring and/or preservative agents. An effective amount of a compound of the present invention for use in therapy of proliferative disease is an amount sufficient to symptomatically relieve in a warm-blooded animal, particularly a human the symptoms of infection, to slow the progression of infection, or to reduce in patients with symptoms of infection the risk of getting worse. The amount of active ingredient that is combined with one or more excipients to produce a single dosage form will necessarily vary depending upon the host treated and the particular route of administration. For example, a formulation intended for oral administration to humans will generally contain, for example, from 0.5 mg to 0.5 g of active agent (more suitably from 0.5 to 100 mg, for example from 1 to 30 mg) compounded with an appropriate and convenient amount of excipients which may vary from about 5 to about 98 percent by weight of the total composition. The size of the dose for therapeutic or prophylactic purposes of a compound of the formula I will naturally vary according to the nature and severity of the conditions, the age and sex of the animal or patient and the route of administration, according to well-known principles of medicine. In using a compound of the invention for therapeutic or prophylactic purposes it will generally be administered so that a daily dose in the range, for example, 0.1 mg/kg to 75 mg/kg body weight is received, given if required in divided doses. In general lower doses will be administered when a parenteral route is employed. Thus, for example, for intravenous or intraperitoneal administration, a dose in the range, for example, 0.1 mg/kg to 30 mg/kg body weight will generally be used. Similarly, for administration by inhalation, a dose in the range, for example, 0.05 mg/kg to 25 mg/kg body weight will be used. Oral administration may also be suitable, particularly in tablet form. Typically, unit dosage forms will contain about 0.5 mg to 0.5 g of a compound of this invention. Therapeutic Uses and Applications In one aspect, the present invention provides a compound of formula I, or a pharmaceutically acceptable salt or solvate thereof, or a pharmaceutical composition as defined herein, for use in therapy. The compounds of the invention are capable of the selective, positive allosteric modulation of strychnine-sensitive alpha 1-glycine receptors. As will be evident from the example section, the compounds of the invention target the glycine receptor α1-subunit, which is known to be positively modulated by anaesthetics, alcohols and cannabinoids, but the compounds according to the present invention selectively target this receptor family with high affinity. In another aspect, the present invention provides a compound as defined herein, or a pharmaceutically acceptable salt or solvate thereof, or a pharmaceutical composition as defined herein, for use in the treatment of a disease or condition in which the selective, positive allosteric modulation of strychnine-sensitive alpha 1-glycine receptors is beneficial. In a particular aspect, the present invention provides a compound as defined herein, or a pharmaceutically acceptable salt or solvate thereof, or a pharmaceutical composition as defined herein, for use in the treatment of pain. In a particular embodiment, the pain is present in a human subject. In a particular aspect, the present invention provides a compound as defined herein, or a pharmaceutically acceptable salt or solvate thereof, or a pharmaceutical composition as defined herein, for use in the treatment of chronic pain, for example lower back pain or neuropathic pain. In a particular embodiment, the chronic pain is present in a human subject. In a particular aspect, the present invention provides a compound as defined herein, or a pharmaceutically acceptable salt or solvate thereof, or a pharmaceutical composition as defined herein, for use in the treatment of neuropathic pain. In a particular embodiment, the neuropathic pain is present in a human subject. In a particular aspect, the present invention provides a compound as defined herein, or a pharmaceutically acceptable salt or solvate thereof, or a pharmaceutical composition as defined herein, for use in the treatment of lower back pain. In a particular embodiment, the lower back pain is present in a human subject. In another aspect, the present invention provides a compound as defined herein, or a pharmaceutically acceptable salt or solvate thereof, or a pharmaceutical composition as defined herein, for use in the selective, positive allosteric modulation of strychnine-sensitive alpha 1-glycine receptors. In another aspect, the present invention provides the use of a compound as defined herein, or a pharmaceutically acceptable salt or solvate thereof, in the manufacture of a medicament for use in the treatment of a disease or condition in which the selective, positive allosteric modulation of strychnine-sensitive alpha 1-glycine receptors is beneficial. In a particular aspect, the present invention provides the use of a compound as defined herein, or a pharmaceutically acceptable salt or solvate thereof, in the manufacture of a medicament for use in the treatment of pain. Suitably, the medicament is for use in the treatment of pain in a human subject. In a particular aspect, the present invention provides the use of a compound as defined herein, or a pharmaceutically acceptable salt or solvate thereof, in the manufacture of a medicament for use in the treatment of chronic pain. Suitably, the medicament is for use in the treatment of chronic pain in a human subject. In a particular aspect, the present invention provides the use of a compound as defined herein, or a pharmaceutically acceptable salt or solvate thereof, in the manufacture of a medicament for use in the treatment of neuropathic pain. In a particular embodiment, the neuropathic pain is present in a human subject. In a particular aspect, the present invention provides the use of a compound as defined herein, or a pharmaceutically acceptable salt or solvate thereof, in the manufacture of a medicament for use in the treatment of lower back pain. In a particular embodiment, the lower back pain is present in a human subject. In another aspect, the present invention provides the use of a compound as defined herein, or a pharmaceutically acceptable salt or solvate thereof, in the manufacture of a medicament for use in the selective, positive allosteric modulation of strychnine-sensitive alpha 1-glycine receptors. In another aspect, the present invention provides a method of selectively producing a positive allosteric modulation effect in strychnine-sensitive alpha 1-glycine receptors in vitro or in vivo, said method comprising contacting a cell with an effective amount of a compound as defined herein, or a pharmaceutically acceptable salt or solvate thereof. In another aspect, the present invention provides a method of treating a disease or condition in which the selective, positive allosteric modulation of strychnine-sensitive alpha 1-glycine receptors is beneficial in a patient in need of such treatment, said method comprising administering to said patient a therapeutically effective amount of a compound as defined herein, or a pharmaceutically acceptable salt or solvate thereof, or a pharmaceutical composition as defined herein. In another aspect, the present invention provides a method of treating pain in a patient in need of such treatment, said method comprising administering to said patient a therapeutically effective amount of a compound as defined herein, or a pharmaceutically acceptable salt or solvate thereof, or a pharmaceutical composition as defined herein. In another aspect, the present invention provides a method of treating chronic pain in a patient in need of such treatment, said method comprising administering to said patient a therapeutically effective amount of a compound as defined herein, or a pharmaceutically acceptable salt or solvate thereof, or a pharmaceutical composition as defined herein. In another aspect, the present invention provides a method of treating neuropathic pain in a patient in need of such treatment, said method comprising administering to said patient a therapeutically effective amount of a compound as defined herein, or a pharmaceutically acceptable salt or solvate thereof, or a pharmaceutical composition as defined herein. Routes of Administration The compounds of the invention or pharmaceutical composition comprising the active compound may be administered to a subject by any convenient route of administration, whether systemically/peripherally or topically (ie. at the site of desired action). Routes of administration include, but are not limited to, oral (e.g, by ingestion); buccal; sublingual; transdermal (including, e.g., by a patch, plaster, etc.); transmucosal (including, e.g., by a patch, plaster, etc.); intranasal (e.g., by nasal spray); ocular (e.g., by eyedrops); pulmonary (e.g., by inhalation or insufflation therapy using, e.g., via an aerosol, e.g., through the mouth or nose); rectal (e.g., by suppository or enema); vaginal (e.g., by pessary); parenteral, for example, by injection, including subcutaneous, intradermal, intramuscular, intravenous, intraarterial, intracardiac, intrathecal, intraspinal, intracapsular, subcapsular, intraorbital, intraperitoneal, intratracheal, subcuticular, intraarticular, subarachnoid, and intrasternal; by implant of a depot or reservoir, for example, subcutaneously or intramuscularly. Combination Therapies The compounds of the invention may be administered as a sole therapy in order to treat the diseases or conditions identified herein. Alternatively, the therapy may involve the administration of one or more additional therapeutic agents (in addition to a compound of the invention). For example, the pain treatment defined hereinbefore may involve the use of a compound of the invention as a sole therapy or may involve, in addition to the compound of the invention, the administration of one or more additional analgesic and/or anti-inflammatory agents. Examples of suitable medicaments include non-steroidal anti-inflammatory drugs and opiate analgesics. Such conjoint treatment may be achieved by way of the simultaneous, sequential or separate dosing of the individual components of the treatment. Such combination products employ the compounds of this invention within the dosage range described hereinbefore and the other pharmaceutically-active agent within its approved dosage range. According to this aspect of the invention there is provided a combination suitable for use in the treatment of pain (e.g. chronic pain) comprising a compound of the invention as defined hereinbefore, or a pharmaceutically acceptable salt or solvate thereof, and another medicament. According to this aspect of the invention there is provided a combination suitable for use in the treatment of pain (e.g. chronic pain) comprising a compound of the invention as defined hereinbefore, or a pharmaceutically acceptable salt or solvate thereof, and another analgesic. In a further aspect of the invention there is provided a compound of the invention or a pharmaceutically acceptable salt or solvate thereof, in combination with another medicament for the treatment of pain (e.g. chronic pain). Herein, where the term “combination” is used it is to be understood that this refers to simultaneous, separate or sequential administration. In one aspect of the invention “combination” refers to simultaneous administration. In another aspect of the invention “combination” refers to separate administration. In a further aspect of the invention “combination” refers to sequential administration. Where the administration is sequential or separate, the delay in administering the second component should not be such as to lose the beneficial effect of the combination. According to a further aspect of the invention there is provided a pharmaceutical composition which comprises a compound of the invention, or a pharmaceutically acceptable salt or solvate thereof, another medicament (e.g. another analgesic) and a pharmaceutically acceptable diluent or carrier. BRIEF DESCRIPTION OF THE DRAWINGS The invention is described further in reference to the accompanying Figures, in which: FIG. 1 shows the fractional potentiation (y-axis) against concentration (nM; x-axis) for the compound LT-01-25 in the expression and electrophysiology study described in Example 7 [Y axis: fractional potentiation—e.g. 0.75 mean that if a response to glycine alone was 1 μA then the response to glycine in the present of drug
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