Title of Invention: Pharmaceutically Active Compounds Abstract: The invention is directed to compounds of general formula (I) and pharmaceutical compositions containing such compounds. The compounds and compositions have valuable pharmaceutical properties. In particular, they may be used for the treatment of cancer. Novel intermediates and novel methods of preparation are also disclosed. Detailed Description: CROSS REFERENCE TO RELATED APPLICATIONS This application is a divisional of U.S. patent application Ser. No. 15/533,048, filed Jun. 5, 2017, which is a national phase entry pursuant to 35 U.S.C. § 371 of International Application No. PCT/EP2015/081168, filed Dec. 23, 2015, which claims the benefit of priority of Application No. GB 1423087.4, filed Dec. 23, 2014, Application No. GB 1508787.7, filed May 22, 2015, and Application No. GB 1519919.3, filed Nov. 11, 2015, each of which is incorporated by reference in its entirety for any purpose. This invention relates to pyridine, pyridazine and triazine derivatives that are useful in the treatment of cancer and/or other diseases. The compounds are believed to be inhibitors of serine/threonine kinase (Akt), and in particular selective inhibitors of Akt3, and hence are useful in the treatment of conditions associated with Akt3 activity, gene amplification or overexpression. Akt, also known as “protein kinase B” (PKB), is a family of serine/threonine kinases comprising, in humans, three members: Akt1, Akt2 and Akt3. These three isoforms are transcripted from different genes and have distinct subcellular localisation, expression patterns and knock-out phenotypes. The Akt family is known to be involved in diverse cellular processes including cell proliferation, motility, growth, glucose homeostasis, cell survival and cell death. Akt regulates cellular survival and metabolism by binding and regulating many downstream effectors, e.g. by activating Nuclear Factor-κB, resulting in the transcription of pro-survival genes, and by phosphorylating and thus deactivating BAD (a pro-apoptotic protein). These effects mean that Akt leads ultimately to cell growth and proliferation. The effects of Akt on the cell life cycle are not limited to normal, healthy cells. Activated Akt may also enable the proliferation and survival of potentially mutagenic cells, possibly contributing to the development of mutations in other genes. Akt has also been associated with angiogenesis and the development of tumours, particularly with tumour cell survival, proliferation and invasiveness. The roles for Akt1, Akt2 and Akt3 in normal development have been studied in knock-out mice, revealing that Akt1 is important for overall growth (knock-out mice are generally healthy but have reduced growth), Akt2 is primarily involved in glucose metabolism (knockout mice grow normally but show insulin resistance) and Akt3 is important in brain development (see e.g. Dummler B, Hemmings B A. Physiological roles of PKB/Akt isoforms in development and disease. Biochem Soc Trans 2007; 35:231-5). A more general role for Akt1 and Akt2 is suggested by their widespread expression throughout the body, while Akt3 has more restricted expression in the brain, kidney and heart. Although Akt1, Akt2 and Akt3 have approximately 80% sequence identity, they have been found to have distinct expression patterns, opposing roles in cell migration, invasion and metastasis (see e.g. Virtakoivu R et al, Distinct roles of Akt isoforms in regulating β1-integrin activity, migration, and invasion in prostate cancer. Mol Biol Cell 2012; 23(17):3357-69) and distinct target specificities. Despite this, the majority of research publications on Akt refer either to Akt1 or to Akt without specifying the family member, a consequence of the widespread use of pan-Akt antibodies which do not distinguish between the family members. Of the three isoforms, least is known about Akt3. Indeed, in a 2010 review article “Key signalling nodes in mammary gland development and cancer. Signalling downstream of PI3 kinase in mammary epithelium: a play in 3 Akts” (Wickenden J A and Watson C J, Breast Cancer Research 2010, 12, 202), Akt3 is mentioned just three times: once to establish its existence, once to note that it appears to have a minor role in normal mammary gland development and once to note that it does not affect Stat5a phosphorylation during pregnancy and lactation. Conventional cancer treatments such as chemotherapy act against all actively dividing cells, whether normal or cancerous. However, more recent research into cancer treatment has focused on the development of targeted therapies which interfere with specific molecules involved in cancer cell growth and survival, often seeking to prevent proliferation of cancer cells rather than simply seeking to destroy cancer cells which are already present. Due to this, targeted therapies have improved the treatment of cancer compared to traditional chemotherapeutic and immunosuppressive agents. Akt is considered an attractive target for cancer therapy, and inhibition of Akt alone or in combination with standard cancer chemotherapeutics has been postulated to reduce the apoptotic threshold and preferentially kill cancer cells (Lindley C W, Curr Top Med Chem, 10, 458, 2010). A recent review of attempts to inhibit Akt members pinpoints Akt2 as the most commonly mutated family member in cancers and suggests that inhibition of Akt1 and Akt2 would be optimal (Mattmann M E et al “Inhibition of Akt with small molecules and biologies: historical perspective and current status of the patent landscape”, Expert Opinion on Therapeutic Patents, 21, 1309, 2011). Many of the compounds covered in this review have poor selectivity for Akt compared to other kinases and generally focus on Akt1. Compounds reported in this review with selectivity between the different family members overwhelmingly inhibit Akt1 and/or Akt2, rather than Akt3. Despite the overwhelming focus on Akt1 in the literature, Akt3 overexpression has been linked to several cancers including melanoma (Cancer Res. 2004 Oct 1; 64(19):7002-10) and ovarian cancer (Cancer Discov. 2012 Jan. 1; 2(1):56-67). WO2013/164788 discusses the use of Akt3 as a biomarker for detecting the occurrence of Epithelial-Mesenchymal Transition (EMT) in a subject and the subsequent use of Akt3 inhibitors to treat cancer, but no examples of Akt3-specific inhibitors are provided. The Epithelial-Mesenchymal Transition (EMT) is a natural cellular program in which individual epithelial cells lose the gene expression patterns and behaviours characteristic of epithelial cells, and instead begin to look and behave like, and express genes typical of, mesenchymal cells. In so doing, they lose adhesion and apical-basal polarity and gain the ability to migrate and invade the extracellular matrix. EMT is not irreversible. A mirror process called Mesenchymal-Epithelial Transition (MET) results in the loss of mesenchymal characteristics and re-establishment of cell-cell adhesion and apical-basal polarity. EMT is especially important during embryonic development. It plays a fundamental role in gastrulation, where an embryo consisting of a single epithelial cell layer develops into one with the three classical germ layers: ectoderm, mesoderm and endoderm. Slightly later in vertebrate development, EMT gives rise to the neural crest cells. These cells migrate throughout the embryo and give rise to many different structures including ganglia of the peripheral nervous system, bone and cartilage of the face and head, pigment cells and glial cells. Further rounds of MET and EMT are essential for the formation of internal organs from both the mesoderm and endoderm. Epithelial tissues make up one of the four basic tissue types of the body, along with connective tissue, muscle and nervous tissue. Epithelial cells are characterised by a tendency to form into sheets of polarised cells held together by strong intercellular junctions. As a consequence of this, epithelial cells are not able to move freely and show little migration compared to other cell types. In contrast, mesenchymal-like cells (e.g. fibroblasts) lack strong intercellular junctions and can move as individual cells. They can be highly motile and able to migrate through the extracellular matrix. In contrast to its importance during embryonic development, the EMT program is seldom activated in healthy adults. It is, however, induced in response to inflammation following injury or disease: EMT plays a role in wound healing and tissue repair, and occurs during organ degenerative disease (e.g. renal fibrosis). EMT is also increasingly understood to play a key role in cancer metastasis. Carcinomas are epithelial cancers, and, in order for metastasis to occur, individual cells must escape the primary tumour and undergo a series of migrations. These include migration from the primary tumour into the local circulatory or lymphatic system, and extravasation from the vasculature and establishment at the site of metastasis. There is now good and growing evidence that interactions between tumour cells and their microenvironment can lead to induction of EMT in some of the tumour cells. The resulting increased cell migration and invasion potential of these cells then enhances the likelihood of a metastasis becoming established. The receptor tyrosine kinase Axl, which is a chronic myelogenous leukaemia-associated oncogene, has been shown to be an essential EMT-induced effector in the invasion-metastasis cascade (WO2010/103388). As well as this role in increasing metastatic potential, the EMT program has recently been linked with Cancer Stem Cells (CSCs). These cells have been postulated to represent a subset of tumour cells with stem cell characteristics, i.e. the ability to give rise to all the cell types found in a particular cancer, and thus the ability to form a new tumour. Although they may represent only a tiny fraction of the cells in a tumour, CSCs are thought to be particularly resistant to existing anti-cancer drugs. Even though drug treatment may kill the vast majority of cells in the tumour, a single surviving CSC can therefore lead to a relapse of the disease. Recent evidence suggests an overlap between EMT and CSC phenotypes, suggesting that EMT may also play a role in recurrence of cancer after chemotherapy and the development of drug-resistant tumours. The role of Akt3 in EMT makes it an attractive target for the development of targeted cancer therapies. While pan-Akt inhibitors are known, they do not show very potent activity against Akt3 and have associated toxicity problems. For example, the inhibition of Akt2 is associated with glucose homeostasis defects. Akt1 is the most widely expressed isoform in the body and, being involved in overall growth, has the most serious knockout phenotype. Furthermore, simultaneous inhibition of Akt1 and Akt2 has been found to lead to feedback amplification of Akt signalling, which may lead to resistance of the cancer against the treatment. There is thus a need to develop inhibitors which have specificity for Akt3, reducing or eliminating the undesirable effects described above that are associated with inhibition of Akt1 and Akt2. This invention is directed to pyridine, pyridazine and triazine derivatives which are useful in the treatment of cancer. According to a first aspect of the invention, there is provided a compound of formula (I): wherein either (a) one of Q1 and Q2 represents a nitrogen atom and the other represents CH, or both Q1 and Q2 represent nitrogen atoms, and Q3 represents CH; or (b) Q1, Q2 and Q3 all represent nitrogen atoms; A represents an optionally substituted five- or six-membered aromatic ring; R1 represents an aliphatic carbocyclic or heterocyclic ring, optionally substituted by —(C═O)xNRaRb, —ORc, —SO2R or optionally substituted alkyl, in which x is 0 or 1; Ra and Rb independently represent (a) H, (b) optionally substituted alkyl, (c) optionally substituted cycloalkyl, (d) optionally substituted heterocycloalkyl, (e) —(C═O)Rd, or (f) —SO2Re, wherein Rd and Re independently represent (i) optionally substituted alkyl, (ii) optionally substituted alkoxy, or (iii) optionally substituted cycloalkyl; or Ra and Rb together with the nitrogen atom to which they are attached form an optionally substituted aromatic or aliphatic heterocyclic ring; Rc represents optionally substituted alkyl; and Rg represents optionally substituted cycloalkyl; R2 represents H, optionally substituted alkyl or halo; R3 represents an optionally substituted aryl or heteroaryl ring; R5 and R6 independently represent H or optionally substituted alkyl; or R5 and R6 together with the carbon atom to which they are attached form an optionally substituted cycloalkyl ring, optionally containing a heteroatom; and the corresponding N-oxides, and their prodrugs; and pharmaceutically acceptable salts and solvates (e.g. hydrates) of such compounds and their N-oxides and prodrugs. As used in the specification and appended claims, unless specified to the contrary, the following terms have the meaning indicated: “Oxo” refers to an ═O radical. “Alkyl” refers to a straight or branched saturated hydrocarbon chain radical consisting solely of carbon and hydrogen atoms, having from one to twelve carbon atoms, preferably one to eight carbon atoms or one to six carbon atoms, and which is attached to the rest of the molecule by a single bond, for example, methyl, ethyl, n-propyl, 1-methylethyl, 1,1-dimethylethyl, 2,2-dimethylpropyl, t-butyl and the like. “C1-6 alkyl” refers to an alkyl as described above, having from one to six carbon atoms. “Alkoxy” refers to a radical of the formula —OR8 where R8 is an alkyl radical as defined above containing from one to twelve carbon atoms. C1-6 alkoxy refers to an alkoxy as previously defined, wherein R8 is an alkyl radical containing from one to six carbon atoms. “Aryl” refers to an aromatic hydrocarbon ring system radical comprising hydrogen and from five to ten carbon atoms. An aryl radical is commonly, but not necessarily, attached to the compound via an aromatic ring of the aryl radical. Aryl radicals include, but are not limited to, aryl radicals derived from benzene. “Cycloalkyl” or “carbocycle” refers to a stable non-aromatic monocyclic hydrocarbon radical consisting solely of carbon and hydrogen atoms, having from three to ten carbon atoms, preferably having from three to six carbon atoms, and which is unsaturated and attached to the rest of the molecule by a single bond. Cycloalkyl radicals include, for example, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl and cyclooctyl. C3-6 cycloalkyl refers to cycloalkyl groups containing from three to six carbon atoms, e.g. cyclopropyl, cyclobutyl, cyclopentyl and cyclohexyl. “Halo” refers to a halogen radical, i.e. F, Cl, Br or I. “Heterocycloalkyl” or “heterocycle” refers to a stable 3- to 10-membered aliphatic mono or bicyclic ring radical which comprises one to nine carbon atoms and from one to four heteroatoms selected from the group consisting of nitrogen, oxygen and sulfur. Unless stated otherwise, the nitrogen, carbon or sulfur atoms in the heterocycloalkyl radical may be optionally oxidized; the nitrogen atom may be optionally quaternized; and the heterocycloalkyl radical may be partially or fully saturated. Examples of such heterocycloalkyl radicals include, but are not limited to morpholinyl, oxazolidinyl, oxetanyl, piperidyl, pyrrolidinyl and octahydro-2(1H)-quinolinonyl. “Heteroaryl” refers to a 5- to 10-membered ring system radical comprising hydrogen atoms, one to nine carbon atoms, one to four heteroatoms selected from the group consisting of nitrogen, oxygen and sulfur, and at least one aromatic ring, the aromatic ring comprising at least one of the heteroatoms. A heteroaryl radical is commonly, but not necessarily, attached to the compound via an aromatic ring of the heteroaryl radical. For purposes of this invention, the heteroaryl radical may be a monocyclic, bicyclic or tricyclic ring system, but is preferably monocyclic. The nitrogen, carbon or sulfur atoms in the heteroaryl radical may be optionally oxidized, and the nitrogen atom may be optionally quaternized. Examples of heteroaryl radicals include, but are not limited to, piperazinyl, pyridyl, thienyl and triazinyl. Certain chemical groups named herein may be preceded by a shorthand notation indicating the total number of carbon atoms that are to be found in the indicated chemical group. For example, C1-6 alkyl describes an alkyl group, as defined above, having a total of from 1 to 6 carbon atoms, and C3-6 cycloalkyl describes a cycloalkyl group, as defined above, having a total of from 3 to 6 carbon atoms. The total number of carbons in the shorthand notation does not include carbons that may exist in substituents of the group described. “Optional” or “optionally” means that the subsequently described condition may or may not occur. For example, “optionally substituted aryl” means that the aryl radical may carry one or more substituents or may be unsubstituted. Unless indicated otherwise, “optionally substituted” means that one or more substituents may be present, and where there is more than one substituent, those substituents may be the same or different. In general, but without limitation and unless otherwise indicated: a) an “optionally substituted alkyl” group may carry one or more substituents selected from alkoxy (e.g. C1-6 alkoxy), cycloalkyl (e.g. C1-3 cycloalkyl) and halo. b) an “optionally substituted cycloalkyl” group may carry one or more substituents selected from alkyl (e.g. C1-6 alkyl), alkoxy (e.g. C1-6 alkoxy), OH and halo. c) an “optionally substituted heterocycloalkyl” group may carry one or more substituents selected from alkyl (e.g. C1-6 alkyl), alkoxy (e.g. C1-6 alkoxy), OH and halo. d) an “optionally substituted alkoxy” group may carry one or more substituents selected from alkyl (e.g. C1-6 alkyl), cycloalkyl (e.g. C1-3 cycloalkyl) and halo. e) an “optionally substituted aromatic or aliphatic heterocyclic” group may carry one or more substituents selected from alkyl (e.g. C1-6 alkyl), alkoxy (e.g. C1-6 alkoxy), oxo and halo. f) an “optionally substituted aryl” group may carry one or more substituents selected from alkyl (e.g. C1-6 alkyl), alkoxy (e.g. C1-6 alkoxy), OH and halo. g) an “optionally substituted heteroaryl” group may carry one or more substituents selected from alkyl (e.g. C1-6 alkyl), alkoxy (e.g. C1-6 alkoxy), OH and halo h) an “optionally substituted five- or six-membered aromatic ring” may carry one or more substituents selected from alkyl (e.g. C1-6 alkyl), alkoxy (e.g. C1-6 alkoxy), OH and halo. “Pharmaceutically acceptable excipient” includes without limitation any adjuvant, carrier, excipient, glidant, sweetening agent, diluent, preservative, dye/colourant, flavour enhancer, surfactant, wetting agent, dispersing agent, suspending agent, stabilizer, isotonic agent, solvent, or emulsifier which is suitable for use in humans or domestic animals. “Pharmaceutically acceptable salt” includes both acid and base addition salts. “Prodrug” means a compound which is convertible in vivo by metabolic means (e.g. by hydrolysis) to a compound of formula (I), including N-oxides thereof. For example, an ester of a compound of formula (I) containing a hydroxy group may be convertible by hydrolysis in vivo to the compound of formula (I). “Therapeutically effective amount” refers to that amount of a compound of the invention which, when administered to a subject, preferably a mammal, and more particularly a human, is sufficient to effect treatment, as defined below, of a disease or condition of interest in the subject, preferably a human. The amount of a compound of the invention which constitutes a “therapeutically effective amount” will vary depending on the compound, the disease or condition and its severity, and the age of the subject to be treated, but can be determined routinely by one of ordinary skill in the art having regard to his own knowledge and to this disclosure. “Treating” or “treatment” as used herein covers the treatment of the disease or condition of interest in a subject, preferably a mammal, and more particularly a human, having the disease or condition of interest, and includes: (i) preventing the disease or condition from occurring in a subject, in particular, when such subject is predisposed to the condition but has not yet been diagnosed as having it; (ii) inhibiting the disease or condition, i.e., arresting its development; (iii) relieving the disease or condition, i.e., causing regression of the disease or condition; or (iv) stabilizing the disease or condition. The compounds of the invention, or their pharmaceutically acceptable salts, may contain one or more asymmetric centres and may thus give rise to enantiomers, diastereomers, and other stereoisomeric forms that may be defined, in terms of absolute stereochemistry, as (R)- or (S)- or as (D)- or (L)- for amino acids. The present invention includes all such possible isomers, as well as their racemic and optically pure forms. Optically active (+) and (−), (R)- and (S)-, or (D)- and (L)- isomers may be prepared using chiral synthons or chiral reagents, or resolved using conventional techniques, such as HPLC using a chiral column. When the compounds described herein contain olefinic double bonds or other centres of geometric asymmetry, and unless specified otherwise, it is intended that the compounds include both E and Z geometric isomers. Likewise, all tautomeric forms are also intended to be included. A “stereoisomer” refers to a compound made up of the same atoms bonded by the same bonds but having different three-dimensional structures, which are not interchangeable. The present invention contemplates various stereoisomers and mixtures thereof and includes “enantiomers”, which refers to two stereoisomers whose molecules are nonsuperimposeable mirror images of one another. A “tautomer” refers to a proton shift from one atom of a molecule to another atom of the same molecule. The present invention includes tautomers of any said compounds. “Atropisomers” are stereoisomers resulting from hindered rotation about single bonds where the barrier to rotation is high enough to allow for the isolation of the conformers (Eliel, E. L.; Wilen, S. H. Stereochemistry of Organic Compounds; Wiley & Sons: New York, 1994; Chapter 14). Atropisomerism is significant because it introduces an element of chirality in the absence of stereogenic atoms. The invention is meant to encompass atropisomers, for example in cases of limited rotation around the single bonds emanating from the core triazole structure, atropisomers are also possible and are also specifically included in the compounds of the invention. Particular embodiments of the compounds of formula (I) described in the first aspect of the invention are set out below. It is to be understood that this invention covers all appropriate combinations of the substituents referred to herein, and that, where alternatives are provided for any one substituent, the invention covers all lists which may be formed by combinations of these alternatives. In the compounds of formula (I), unless otherwise stated, any or all alkyl groups may independently be C1-6 alkyl groups, any or all alkoxy groups may independently be C1-6 alkoxy groups, and/or any or all cycloalkyl groups may independently be C3-6 cycloalkyl groups. One of Q1 and Q2 may represent a nitrogen atom while the other represents CH, i.e. Q1 represents a nitrogen atom and Q2 represents CH, or Q1 represents CH and Q2 represents a nitrogen atom. When one of Q1 or Q2 represents CH, Q3 represents CH. Alternatively, Q1 and Q2 may both represent nitrogen atoms, and Q3 may represent CH. Alternatively, Q1, Q2 and Q3 may all represent nitrogen atoms. A may represent an optionally substituted five- or six-membered aromatic ring, and may be carbocyclic or heterocyclic. A may represent an optionally substituted five- or six-membered heterocyclic ring. The heterocyclic ring may contain one, two or three heteroatoms, which may be the same or different, and may be selected from N, O and/or S. For example, A may represent optionally substituted pyridyl, pyrimidinyl, thienyl, oxadiazolyl or pyridazinyl. A may represent optionally substituted phenyl. A may be optionally substituted by halo, e.g. F, or by C1-6 alkoxy, e.g. —OCH3. R1 may represent a six-membered aliphatic carbocyclic or heterocyclic ring, optionally substituted by —(C═O)xNRaRb, —ORc, —SO2R or optionally substituted alkyl. R1 may represent an aliphatic carbocyclic ring optionally substituted by —(C═O)xNRaRb, —ORc, —SO2R or optionally substituted alkyl. R1 may represent a six-membered aliphatic carbocyclic ring, optionally substituted by —(C═O)xNRaRb, —ORc, —SO2R or optionally substituted alkyl. R1 may represent a six-membered aliphatic carbocyclic ring, optionally substituted by —(C═O)xNRaRb or —ORc. R1 may represent a six-membered aliphatic carbocyclic ring, optionally substituted by —(C═O)xNRaRb. R1 may represent a six-membered aliphatic carbocyclic ring, optionally substituted by —ORc. R1 may represent a six-membered aliphatic heterocyclic ring, optionally substituted by —(C═O)xNRaRb, —ORc, —SO2R or optionally substituted alkyl. R1 may represent a six-membered aliphatic heterocyclic ring, optionally substituted by —SO2R or optionally substituted alkyl. R1 may represent a six-membered aliphatic heterocyclic ring, optionally substituted by —SO2Rg. R1 may represent a six-membered aliphatic heterocyclic ring, optionally substituted by optionally substituted alkyl. R1 may represent a six-membered aliphatic heterocyclic ring, optionally substituted by alkyl. x may be 0, or x may be 1. Ra and/or Rb may represent H. Ra and/or Rb may represent optionally substituted alkyl, optionally substituted cycloalkyl or optionally substituted heterocycloalkyl. Ra and/or Rb may represent alkyl optionally substituted by alkoxy, cycloalkyl or a heterocycloalkyl ring, any of which is optionally substituted by alkyl. Ra and/or Rb may represent alkyl optionally substituted by alkoxy, for example —OCH3. Ra and/or Rb may represent cycloalkyl optionally substituted by alkyl. For instance, Ra and/or Rb may represent cyclopropyl or cyclobutyl, any of which is optionally substituted by alkyl. Ra and/or Rb may represent a heterocycloalkyl ring optionally substituted by alkyl. For instance, Ra and/or Rb may represent a 3- to 6-membered heterocycloalkyl ring, optionally substituted by alkyl. Ra and/or Rb may represent a 4-membered heterocycloalkyl ring, optionally substituted by alkyl. Ra and/or Rb may represent oxetanyl, optionally substituted by alkyl. Ra and/or Rb may represent —(C═O)Rd, or Ra and/or Rb may represent —SO2Re. Ra and Rb may, together with the nitrogen atom to which they are attached, form an optionally substituted aromatic or aliphatic heterocyclic ring, for example an optionally substituted 5- or 6-membered aromatic or aliphatic heterocyclic ring. The ring may be optionally substituted by oxo or alkyl. In particular, Ra and Rb may, together with the nitrogen atom to which they are attached, form a 5- or 6-membered aromatic or aliphatic heterocyclic ring selected from triazinyl, oxazolidinyl, pyrrolidinyl, piperidinyl and morpholinyl, any of which may be optionally substituted by oxo or alkyl. Ra and Rb may, together with the nitrogen atom to which they are attached, form triazinyl, morpholinonyl, oxazolidinonyl, pyrrolidonyl or piperidonyl, any of which may be optionally substituted by alkyl. One of Ra and Rb may represent H or optionally substituted alkyl, while the other of Ra and Rb represents (i) optionally substituted alkyl, (ii) optionally substituted cycloalkyl, (iii) optionally substituted heterocycloalkyl, (v) —(C═O)Rd, or (vi) —SO2Re. One of Ra and Rb may represent H or alkyl, while the other of Ra and Rb represents (i) alkyl optionally substituted by alkoxy, (ii) cycloalkyl optionally substituted by alkyl, (iii) a 3- to 6-membered heterocycloalkyl ring optionally substituted by alkyl, (iv) —(C═O)Rd, or (v) —SO2Re. Rd and/or Re may represent optionally substituted alkyl, for instance alkyl optionally substituted by cycloalkyl, halo, e.g. F, or alkoxy, e.g. —OCH3. Rd and/or Re may represent —CH3, —CHF2, —C(CH3)2CF3, —C(CH3)3, —CH2C(CH3)3, —CH(CH3)2, —CH2CH3 or —CH2CH2CH3. Rd and/or Re may represent alkyl optionally substituted by cyclopropyl or cyclobutyl, for example —CH2-cyclopropyl. Rd and/or Re may represent alkoxy, for example —OCH3 or —OCH2CH3. Rd and/or Re may represent optionally substituted cycloalkyl, for example cycloalkyl optionally substituted by alkyl. In particular, Rd and/or Re may represent cyclopropyl or cyclobutyl optionally substituted by alkyl, for example methyl. Rc may represent alkyl, for example methyl. Rg may represent cycloalkyl, for example cyclopropyl. R2 may be H. R2 may be optionally substituted alkyl, or R2 may be alkyl, for example methyl. R2 may be halo, for example F. R3 may be an optionally substituted 5- or 6-membered aryl or heteroaryl ring, for example optionally substituted by alkyl or halo, for instance F. In particular, R3 may be phenyl, optionally substituted by alkyl, e.g. methyl, or halo, e.g. F. R3 may be phenyl. R3 may be thienyl optionally substituted by alkyl, e.g. methyl, or halo, e.g. F. R3 may be thienyl. R3 may be pyridyl optionally substituted by alkyl, e.g. methyl, or halo, e.g. F. R3 may be pyridyl. R5 and/or R6 may represent H. R5 and/or R6 may represent alkyl, e.g. methyl, optionally substituted by halo, e.g. F. R5 and/or R6 may represent methyl optionally substituted by F. R5 and/or R6 may represent —CHF2. R5 and/or R6 may represent alkyl, for example methyl. R5 and R6 may represent methyl. R5 and R6 may, together with the carbon atom to which they are attached, form an optionally substituted cycloalkyl ring, optionally containing a heteroatom. The ring may be an optionally substituted 3- or 4-membered cycloalkyl ring, optionally containing a heteroatom. Optional substituents include OH, alkyl and/or halo. Thus, R5 and R6 may, together with the carbon atom to which they are attached, form a 3- or 4-membered cycloalkyl ring, optionally containing a heteroatom and optionally substituted by —OH, alkyl and/or F. In particular, R5 and R6 may, together with the carbon atom to which they are attached, form a cyclopropyl or cyclobutyl ring, optionally substituted by —OH, alkyl and/or F. R5 and R6 may, together with the carbon atom to which they are attached, form a cyclopropyl ring. R5 and R6 may, together with the carbon atom to which they are attached, form a cyclobutyl ring, optionally substituted by —OH, alkyl and/or F. R5 and R6 may, together with the carbon atom to which they are attached, form 2,2-difloro-cyclobutyl or 2-methyl-2-hydroxy-cyclobutyl. R5 and R6 may, together with the carbon atom to which they are attached, form a 3- or 4-membered cycloalkyl ring, containing a heteroatom selected from N, O and S, and optionally substituted by —OH, alkyl and/or halo. R5 and R6 may, together with the carbon atom to which they are attached, form a 3- or 4-membered cycloalkyl ring, containing an oxygen heteroatom and optionally substituted by —OH, alkyl and/or halo. R5 and R6 may, together with the carbon atom to which they are attached, form an oxetanyl ring, optionally substituted by —OH, alkyl and/or halo. R5 and R6 may, together with the carbon atom to which they are attached, form an oxetanyl ring. A preferred embodiment of the compound of formula (I), as described above, is where the compound of formula (I) is a compound of formula (Ia): wherein one of Q1 and Q2 represents a nitrogen atom and the other represents CH, or both Q1 and Q2 represent nitrogen atoms; A represents an optionally substituted five- or six-membered aromatic ring; R1 represents an aliphatic carbocyclic or heterocyclic ring, optionally substituted by —(C═O)xNRaRb, —ORc, —SO2R or optionally substituted alkyl, in which x is 0 or 1; Ra and Rb independently represent (a) H, (b) optionally substituted alkyl, (c) optionally substituted cycloalkyl, (d) optionally substituted heterocycloalkyl, (e) —(C═O)Rd, or (f) —SO2Re, wherein Rd and Re independently represent (i) optionally substituted alkyl, (ii) optionally substituted alkoxy, or (iii) optionally substituted cycloalkyl; or Ra and Rb together with the nitrogen atom to which they are attached form an optionally substituted aromatic or aliphatic heterocyclic ring; Rc represents optionally substituted alkyl; and Rg represents optionally substituted cycloalkyl; R2 represents H, optionally substituted alkyl or halo; R3 represents an optionally substituted aryl or heteroaryl ring; R5 and R6 independently represent H or optionally substituted alkyl; or R5 and R6 together with the carbon atom to which they are attached form an optionally substituted cycloalkyl ring, optionally containing a heteroatom; and the corresponding N-oxides, and their prodrugs; and pharmaceutically acceptable salts and solvates (e.g. hydrates) of such compounds and their N-oxides and prodrugs. Particular embodiments of the compounds of formula (Ia) described above are set out below. It is to be understood that this invention covers all appropriate combinations of the substituents referred to herein, and that, where alternatives are provided for any one substituent, the invention covers all lists which may be formed by combinations of these alternatives. In the compounds of formula (Ia), unless otherwise stated, any or all alkyl groups may independently be C1-6 alkyl groups, any or all alkoxy groups may independently be C1-6 alkoxy groups, and/or any or all cycloalkyl groups may independently be C3-6 cycloalkyl groups. One of Q1 and Q2 may represent a nitrogen atom while the other represents CH, i.e. Q1 represents a nitrogen atom and Q2 represents CH, or Q1 represents CH and Q2 represents a nitrogen atom. Alternatively, Q1 and Q2 may both represent nitrogen atoms. A may represent an optionally substituted five- or six-membered aromatic ring, and may be carbocyclic or heterocyclic. A may represent an optionally substituted five- or six-membered heterocyclic ring. The heterocyclic ring may contain one, two or three heteroatoms, which may be the same or different, and may be selected from N, O and/or S. For example, A may represent optionally substituted pyridyl, pyrimidinyl, thienyl, oxadiazolyl or pyridazinyl. A may represent optionally substituted phenyl. A may be optionally substituted by halo, e.g. F, or by C1-6 alkoxy, e.g. —OCH3. R1 may represent a six-membered aliphatic carbocyclic or heterocyclic ring, optionally substituted by —(C═O)xNRaRb, —ORc, —SO2R or optionally substituted alkyl. R1 may represent an aliphatic carbocyclic ring optionally substituted by —(C═O)xNRaRb, —ORc, —SO2R or optionally substituted alkyl. R1 may represent a six-membered aliphatic carbocyclic ring, optionally substituted by —(C═O)xNRaRb, —ORc, —SO2R or optionally substituted alkyl. R1 may represent a six-membered aliphatic carbocyclic ring, optionally substituted by —(C═O)xNRaRb or —ORc. R1 may represent a six-membered aliphatic carbocyclic ring, optionally substituted by —(C═O)xNRaRb. R1 may represent a six-membered aliphatic carbocyclic ring, optionally substituted by —ORc. R1 may represent a six-membered aliphatic heterocyclic ring, optionally substituted by —(C═O)xNRaRb, —OR, —SO2R or optionally substituted alkyl. R1 may represent a six-membered aliphatic heterocyclic ring, optionally substituted by —SO2R or optionally substituted alkyl. R1 may represent a six-membered aliphatic heterocyclic ring, optionally substituted by —SO2R. R1 may represent a six-membered aliphatic heterocyclic ring, optionally substituted by optionally substituted alkyl. R1 may represent a six-membered aliphatic heterocyclic ring, optionally substituted by alkyl. x may be 0, or x may be 1. Ra and/or Rb may represent H. Ra and/or Rb may represent optionally substituted alkyl, optionally substituted cycloalkyl or optionally substituted heterocycloalkyl. Ra and/or Rb may represent alkyl optionally substituted by alkoxy, cycloalkyl or a heterocycloalkyl ring, any of which is optionally substituted by alkyl. Ra and/or Rb may represent alkyl optionally substituted by alkoxy, for example —OCH3. Ra and/or Rb may represent cycloalkyl optionally substituted by alkyl. For instance, Ra and/or Rb may represent cyclopropyl or cyclobutyl, any of which is optionally substituted by alkyl. Ra and/or Rb may represent a heterocycloalkyl ring optionally substituted by alkyl. For instance, Ra and/or Rb may represent a 3- to 6-membered heterocycloalkyl ring, optionally substituted by alkyl. Ra and/or Rb may represent a 4-membered heterocycloalkyl ring, optionally substituted by alkyl. Ra and/or Rb may represent oxetanyl, optionally substituted by alkyl. Ra and/or Rb may represent —(C═O)Rd, or Ra and/or Rb may represent —SO2Re. Ra and Rb may, together with the nitrogen atom to which they are attached, form an optionally substituted aromatic or aliphatic heterocyclic ring, for example an optionally substituted 5- or 6-membered aromatic or aliphatic heterocyclic ring. The ring may be optionally substituted by oxo or alkyl. In particular, Ra and Rb may, together with the nitrogen atom to which they are attached, form a 5- or 6-membered aromatic or aliphatic heterocyclic ring selected from triazinyl, oxazolidinyl, pyrrolidinyl, piperidinyl and morpholinyl, any of which may be optionally substituted by oxo or alkyl. Ra and Rb may, together with the nitrogen atom to which they are attached, form triazinyl, morpholinonyl, oxazolidinonyl, pyrrolidonyl or piperidonyl, any of which may be optionally substituted by alkyl. One of Ra and Rb may represent H or optionally substituted alkyl, while the other of Ra and Rb represents (i) optionally substituted alkyl, (ii) optionally substituted cycloalkyl, (iii) optionally substituted heterocycloalkyl, (v) —(C═O)Rd, or (vi) —SO2Re. One of Ra and Rb may represent H or alkyl, while the other of Ra and Rb represents (i) alkyl optionally substituted by alkoxy, (ii) cycloalkyl optionally substituted by alkyl, (iii) a 3- to 6-membered heterocycloalkyl ring optionally substituted by alkyl, (iv) —(C═O)Rd, or (v) —SO2Re. Rd and/or Re may represent optionally substituted alkyl, for instance alkyl optionally substituted by cycloalkyl, halo, e.g. F, or alkoxy, e.g. —OCH3. Rd and/or Re may represent —CH3, —CHF2, —C(CH3)2CF3, —C(CH3)3, —CH2C(CH3)3, —CH(CH3)2 or —CH2CH2CH3. Rd and/or Re may represent alkyl optionally substituted by cyclopropyl or cyclobutyl, for example —CH2-cyclopropyl. Rd and/or Re may represent alkoxy, for example —OCH3 or —OCH2CH3. Rd and/or Re may represent optionally substituted cycloalkyl, for example cycloalkyl optionally substituted by alkyl. In particular, Rd and/or Re may represent cyclopropyl or cyclobutyl optionally substituted by alkyl, for example methyl. Rc may represent alkyl, for example methyl. Rg may represent cycloalkyl, for example cyclopropyl. R2 may be H. R2 may be optionally substituted alkyl, or R2 may be alkyl, for example methyl. R2 may be halo, for example F. R3 may be an optionally substituted 5- or 6-membered aryl or heteroaryl ring, for example optionally substituted by alkyl or halo, for instance F. In particular, R3 may be phenyl, optionally substituted by alkyl, e.g. methyl, or halo, e.g. F. R3 may be phenyl. R3 may be thienyl optionally substituted by alkyl, e.g. methyl, or halo, e.g. F. R3 may be thienyl. R3 may be pyridyl optionally substituted by alkyl, e.g. methyl, or halo, e.g. F. R3 may be pyridyl. R5 and/or R6 may represent H. R5 and/or R6 may represent alkyl, e.g. methyl, optionally substituted by halo, e.g. F. R5 and/or R6 may represent methyl optionally substituted by F. R5 and/or R6 may represent —CHF2. R5 and/or R6 may represent alkyl, for example methyl. R5 and R6 may represent methyl. R5 and R6 may, together with the carbon atom to which they are attached, form an optionally substituted cycloalkyl ring, optionally containing a heteroatom. The ring may be an optionally substituted 3- or 4-membered cycloalkyl ring, optionally containing a heteroatom. Optional substituents include OH, alkyl and/or halo. Thus, R5 and R6 may, together with the carbon atom to which they are attached, form a 3- or 4-membered cycloalkyl ring, optionally containing a heteroatom and optionally substituted by —OH, alkyl and/or F. In particular, R5 and R6 may, together with the carbon atom to which they are attached, form a cyclopropyl or cyclobutyl ring, optionally substituted by —OH, alkyl and/or F. R5 and R6 may, together with the carbon atom to which they are attached, form a cyclopropyl ring. R5 and R6 may, together with the carbon atom to which they are attached, form a cyclobutyl ring, optionally substituted by —OH, alkyl and/or F. R5 and R6 may, together with the carbon atom to which they are attached, form 2,2-difloro-cyclobutyl or 2-methyl-2-hydroxy-cyclobutyl. R5 and R6 may, together with the carbon atom to which they are attached, form a 3- or 4-membered cycloalkyl ring, containing a heteroatom selected from N, O and S, and optionally substituted by —OH, alkyl and/or halo. R5 and R6 may, together with the carbon atom to which they are attached, form a 3- or 4-membered cycloalkyl ring, containing an oxygen heteroatom and optionally substituted by —OH, alkyl and/or halo. R5 and R6 may, together with the carbon atom to which they are attached, form an oxetanyl ring, optionally substituted by —OH, alkyl and/or halo. R5 and R6 may, together with the carbon atom to which they are attached, form an oxetanyl ring. A preferred embodiment of the compound of formula (I), as described above, is where the compound of formula (I) is a compound of formula (Ib): wherein one of Q1 and Q2 represents a nitrogen atom and the other represents CH, or both Q1 and Q2 represent nitrogen atoms; Q4 represents CH or a nitrogen atom; R1 represents an aliphatic carbocyclic or heterocyclic ring, optionally substituted by —(C═O)xNRaRb, —ORc, —SO2R or optionally substituted alkyl, in which x is 0 or 1; Ra and Rb independently represent (a) H, (b) optionally substituted alkyl, (c) optionally substituted cycloalkyl, (d) optionally substituted heterocycloalkyl, (e) —(C═O)Rd, or (f) —SO2Re, wherein Rd and Re independently represent (i) optionally substituted alkyl, (ii) optionally substituted alkoxy, or (iii) optionally substituted cycloalkyl; or Ra and Rb together with the nitrogen atom to which they are attached form an optionally substituted aromatic or aliphatic heterocyclic ring; Rc represents optionally substituted alkyl; and Rg represents optionally substituted cycloalkyl; R2 represents H, optionally substituted alkyl or halo; R3 represents an optionally substituted aryl or heteroaryl ring; R4 represents H, halo or —ORf, where Rf is optionally substituted alkyl; R5 and R6 independently represent H or optionally substituted alkyl; or R5 and R6 together with the carbon atom to which they are attached form an optionally substituted cycloalkyl ring, optionally containing a heteroatom; and the corresponding N-oxides, and their prodrugs; and pharmaceutically acceptable salts and solvates (e.g. hydrates) of such compounds and their N-oxides and prodrugs. Particular embodiments of the compounds of formula (Ib) described above are set out below. It is to be understood that this invention covers all appropriate combinations of the substituents referred to herein, and that, where alternatives are provided for any one substituent, the invention covers all lists which may be formed by combinations of these alternatives. In the compounds of formula (Ib), unless otherwise stated, any or all alkyl groups may independently be C1-6 alkyl groups, any or all alkoxy groups may independently be C1-6 alkoxy groups, and/or any or all cycloalkyl groups may independently be C3-6 cycloalkyl groups. One of Q1 and Q2 may represent a nitrogen atom while the other represents CH, i.e. Q1 represents a nitrogen atom and Q2 represents CH, or Q1 represents CH and Q2 represents a nitrogen atom. Alternatively, Q1 and Q2 may both represent nitrogen atoms. Q4 may represent CH, or Q4 may represent a nitrogen atom. R1 may represent a six-membered aliphatic carbocyclic or heterocyclic ring, optionally substituted by —(C═O)xNRaRb, —ORc, —SO2R or optionally substituted alkyl. R1 may represent an aliphatic carbocyclic ring optionally substituted by —(C═O)xNRaRb, —ORc, —SO2R or optionally substituted alkyl. R1 may represent a six-membered aliphatic carbocyclic ring, optionally substituted by —(C═O)xNRaRb, —ORc, —SO2R or optionally substituted alkyl. R1 may represent a six-membered aliphatic carbocyclic ring, optionally substituted by —(C═O)xNRaRb or —ORc. R1 may represent a six-membered aliphatic carbocyclic ring, optionally substituted by —(C═O)xNRaRb. R1 may represent a six-membered aliphatic carbocyclic ring, optionally substituted by —ORc. R1 may represent a six-membered aliphatic heterocyclic ring, optionally substituted by —(C═O)xNRaRb, —OR, —SO2R or optionally substituted alkyl. R1 may represent a six-membered aliphatic heterocyclic ring, optionally substituted by —SO2R or optionally substituted alkyl. R1 may represent a six-membered aliphatic heterocyclic ring, optionally substituted by —SO2Rg. R1 may represent a six-membered aliphatic heterocyclic ring, optionally substituted by optionally substituted alkyl. R1 may represent a six-membered aliphatic heterocyclic ring, optionally substituted by alkyl. x may be 0, or x may be 1. Ra and/or Rb may represent H. Ra and/or Rb may represent optionally substituted alkyl, optionally substituted cycloalkyl or optionally substituted heterocycloalkyl. Ra and/or Rb may represent alkyl optionally substituted by alkoxy, cycloalkyl or a heterocycloalkyl ring, any of which is optionally substituted by alkyl. Ra and/or Rb may represent alkyl optionally substituted by alkoxy, for example —OCH3. Ra and/or Rb may represent cycloalkyl optionally substituted by alkyl. For instance, Ra and/or Rb may represent cyclopropyl or cyclobutyl, any of which is optionally substituted by alkyl. Ra and/or Rb may represent a heterocycloalkyl ring optionally substituted by alkyl. For instance, Ra and/or Rb may represent a 3- to 6-membered heterocycloalkyl ring, optionally substituted by alkyl. Ra and/or Rb may represent a 4-membered heterocycloalkyl ring, optionally substituted by alkyl. Ra and/or Rb may represent oxetanyl, optionally substituted by alkyl. Ra and/or Rb may represent —(C═O)Rd, or Ra and/or Rb may represent —SO2Re. Ra and Rb may, together with the nitrogen atom to which they are attached, form an optionally substituted aromatic or aliphatic heterocyclic ring, for example an optionally substituted 5- or 6-membered aromatic or aliphatic heterocyclic ring. The ring may be optionally substituted by oxo or alkyl. In particular, Ra and Rb may, together with the nitrogen atom to which they are attached, form a 5- or 6-membered aromatic or aliphatic heterocyclic ring selected from triazinyl, oxazolidinyl, pyrrolidinyl, piperidinyl and morpholinyl, any of which may be optionally substituted by oxo or alkyl. Ra and Rb may, together with the nitrogen atom to which they are attached, form triazinyl, morpholinonyl, oxazolidinonyl, pyrrolidonyl or piperidonyl, any of which may be optionally substituted by alkyl. One of Ra and Rb may represent H or optionally substituted alkyl, while the other of Ra and Rb represents (i) optionally substituted alkyl, (ii) optionally substituted cycloalkyl, (iii) optionally substituted heterocycloalkyl, (v) —(C═O)Rd, or (vi) —SO2Re. One of Ra and Rb may represent H or alkyl, while the other of Ra and Rb represents (i) alkyl optionally substituted by alkoxy, (ii) cycloalkyl optionally substituted by alkyl, (iii) a 3- to 6-membered heterocycloalkyl ring optionally substituted by alkyl, (iv) —(C═O)Rd, or (v) —SO2Re. Rd and/or Re may represent optionally substituted alkyl, for instance alkyl optionally substituted by cycloalkyl, halo, e.g. F, or alkoxy, e.g. —OCH3. Rd and/or Re may represent —CH3, —CHF2, —C(CH3)2CF3, —C(CH3)3, —CH2C(CH3)3, —CH(CH3)2, —CH2CH3 or —CH2CH2CH3. Rd and/or Re may represent alkyl optionally substituted by cyclopropyl or cyclobutyl, for example —CH2-cyclopropyl. Rd and/or Re may represent alkoxy, for example —OCH3 or —OCH2CH3. Rd and/or Re may represent optionally substituted cycloalkyl, for example cycloalkyl optionally substituted by alkyl. In particular, Rd and/or Re may represent cyclopropyl or cyclobutyl optionally substituted by alkyl, for example methyl. Rc may represent alkyl, for example methyl. Rg may represent cycloalkyl, for example cyclopropyl. R2 may be H. R2 may be optionally substituted alkyl, or R2 may be alkyl, for example methyl. R2 may be halo, for example F. R3 may be an optionally substituted 5- or 6-membered aryl or heteroaryl ring, for example optionally substituted by alkyl or halo, for instance F. In particular, R3 may be phenyl, optionally substituted by alkyl, e.g. methyl, or halo, e.g. F. R3 may be phenyl. R3 may be thienyl optionally substituted by alkyl, e.g. methyl, or halo, e.g. F. R3 may be thienyl. R3 may be pyridyl optionally substituted by alkyl, e.g. methyl, or halo, e.g. F. R3 may be pyridyl. R4 may represent H. R4 may represent halo, for example F. R4 may represent —ORf. Rf may represent optionally substituted alkyl. Rf may represent alkyl, for example methyl. R5 and/or R6 may represent H. R5 and/or R6 may represent alkyl, e.g. methyl, optionally substituted by halo, e.g. F. R5 and/or R6 may represent methyl optionally substituted by F. R5 and/or R6 may represent —CHF2. R5 and/or R6 may represent alkyl, for example methyl. R5 and R6 may represent methyl. R5 and R6 may, together with the carbon atom to which they are attached, form an optionally substituted cycloalkyl ring, optionally containing a heteroatom. The ring may be an optionally substituted 3- or 4-membered cycloalkyl ring, optionally containing a heteroatom. Optional substituents include OH, alkyl and/or halo. Thus, R5 and R6 may, together with the carbon atom to which they are attached, form a 3- or 4-membered cycloalkyl ring, optionally containing a heteroatom and optionally substituted by —OH, alkyl and/or F. In particular, R5 and R6 may, together with the carbon atom to which they are attached, form a cyclopropyl or cyclobutyl ring, optionally substituted by —OH, alkyl and/or F. R5 and R6 may, together with the carbon atom to which they are attached, form a cyclopropyl ring. R5 and R6 may, together with the carbon atom to which they are attached, form a cyclobutyl ring, optionally substituted by —OH, alkyl and/or F. R5 and R6 may, together with the carbon atom to which they are attached, form 2,2-difloro-cyclobutyl or 2-methyl-2-hydroxy-cyclobutyl. R5 and R6 may, together with the carbon atom to which they are attached, form a 3- or 4-membered cycloalkyl ring, containing a heteroatom selected from N, O and S, and optionally substituted by —OH, alkyl and/or halo. R5 and R6 may, together with the carbon atom to which they are attached, form a 3- or 4-membered cycloalkyl ring, containing an oxygen heteroatom and optionally substituted by —OH, alkyl and/or halo. R5 and R6 may, together with the carbon atom to which they are attached, form an oxetanyl ring, optionally substituted by —OH, alkyl and/or halo. R5 and R6 may, together with the carbon atom to which they are attached, form an oxetanyl ring. A preferred embodiment of the compound of formula (I), as described above, is where the compound of formula (I) is a compound of formula (Ic): one of Q1 and Q2 represents a nitrogen atom and the other represents CH, or both Q1 and Q2 represent nitrogen atoms; Q4 represents CH or a nitrogen atom; R1 represents a six-membered aliphatic carbocyclic or heterocyclic ring, optionally substituted by —(C═O)xNRaRb, —ORc, —SO2R or C1-6 alkyl, in which x is 0 or 1; Ra and Rb independently represent (a) H, (b) C1-6 alkyl optionally substituted by C1-6 alkoxy, (c) C3-6 cycloalkyl optionally substituted by C1-6 alkyl, (d) a 3- to 6-membered heterocycloalkyl ring optionally substituted by C1-6 alkyl, (ie) —(C═O)Rd, or (f) —SO2Re, wherein Rd and Re independently represent (i) C1-6 alkyl optionally substituted by cycloalkyl or halo, (ii) C1-6 alkoxy, or (iii) C3-6 cycloalkyl optionally substituted by C1-6 alkyl; or Ra and Rb together with the nitrogen atom to which they are attached form a 5- or 6-membered aromatic or aliphatic heterocyclic ring optionally substituted by oxo or C1-6 alkyl; Rc represents C1-6 alkyl; and Rg represents C3-6 cycloalkyl; R2 represents H, C1-6 alkyl or halo; R3 represents a 5- or 6-membered aryl or heteroaryl ring, optionally substituted by C1-6 alkyl or halo; R4 represents H, halo or —ORf, where Rf is C1-6 alkyl; R5 and R6 independently represent H or C1-6 alkyl optionally substituted by halo; or R5 and R6 together with the carbon atom to which they are attached form a 3- or 4-membered cycloalkyl ring, optionally containing a heteroatom and optionally substituted by —OH, C1-6 alkyl or halo; and the corresponding N-oxides, and their prodrugs; and pharmaceutically acceptable salts and solvates (e.g. hydrates) of such compounds and their N-oxides and prodrugs. Particular embodiments of the compounds of formula (Ic) described above are set out below. It is to be understood that this invention covers all appropriate combinations of the substituents referred to herein, and that, where alternatives are provided for any one substituent, the invention covers all lists which may be
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