Patent Publication Number: US-11028067-B2

Title: Heteroarylsulfonyl-substituted pyridines and their use in the treatment of cancer

Description:
This application is a 371 of International Application PCT/GB2018/050343, filed Feb. 7, 2018, which claims the benefit of U.S. Provisional Application No. 62/594,799, filed on Dec. 5, 2017, and to U.S. Provisional Application No. 62/455,639, filed on Feb. 7, 2017. The entire contents of these applications are incorporated herein by reference in their entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to novel compounds and compositions, and their use in the treatment of cancer. In particular, the invention relates to novel compounds, compositions and methods for the treatment of cancers through specific and potent inhibition of thioredoxin reductase with minimal inhibition of glutathione reductase. 
     BACKGROUND OF THE INVENTION 
     The listing or discussion of an apparently prior-published document in this specification should not necessarily be taken as an acknowledgement that the document is part of the state of the art or is common general knowledge. 
     Although the increased understanding of the role of oncogenes, and the development of new anticancer treatments and diagnosis, have improved the life expectancy of cancer patients, there is still a high medical need to find more effective and less toxic treatments for cancers, such as breast cancer, head and neck cancer, glioblastoma, melanoma, leukaemia, and colon and lung cancer. 
     It is well known that excessive production of reactive oxygen species is a common feature of cancer cells due to their distorted metabolism and exaggerated replicative drive. Cancer cells are able to survive their unnaturally high production of reactive oxygen species through concomitant upregulation of robust antioxidant defence mechanisms. 
     Radiotherapy and chemotherapy protocols compete against antioxidant defence mechanisms, further increasing reactive oxygen species levels beyond adapted thresholds through targeting of multiple cellular compartments and targets. Thus, sensitization of cancer cells to their endogenous reactive oxygen species production can additionally induce cancer cell death. In contrast, normal cells have reserved capacity to combat oxidative stress. With this in mind, it has been suggested that if reactive oxygen species levels could be further increased, or the cellular defences against reactive oxygen species could be deliberately impaired, these systems may serve to allow for a possible therapeutic mechanism of action for anticancer therapy (Luo, J., et al.,  Cell,  136, 823 (2009); Trachootham, D., et al.,  Nat Rev Drug Discov,  8, 579 (2009)). 
     Increased tolerance to oxidative stress of cancer cells can occur through activation of the two major antioxidant systems in human and other mammals: the glutathione and thioredoxin systems. Concomitant inhibition of the glutathione and thioredoxin systems therefore has been proposed as a mechanism for anticancer activity (Harris, I. S., et al.,  Cancer Cell  27, 211 (2015); Mandal, P. K., et al.,  Cancer Res,  70, 9505-9514 (2010); Fath, M. A., et al.,  Clin Cancer Res.,  17, 6206 (2011)). 
     Cytosolic thioredoxin reductase is a key enzyme for the whole cytosolic thioredoxin system, which in turn is responsible for a cascade of signalling events and antioxidant activities (Arnér, E. S. J.,  Biochim Biophys Acta,  1790, 495-526 (2009)). A high expression level of cytosolic thioredoxin reductase in various cancers correlates to a more severe cancer phenotype, chemotherapeutic drug resistance, and poor prognosis. 
     However, as normal, non-cancerous cells require either the glutathione or the thioredoxin systems for survival (Arnér, E. S. &amp; Holmgren, A.,  Eur J Biochem,  267, 6102 (2000); Lillig, C. H., Berndt, C. &amp; Holmgren, A.,  Biochim Biophys Acta,  1780, 1304 (2008); Prigge, J. R., et al.,  Free Radic Biol Med,  52, 803 (2012)), it is difficult to therapeutically target both of these antioxidant systems without triggering major unwanted toxicities. 
     It has been suggested that several chemotherapeutic protocols for anticancer treatment involve inhibition of cytosolic thioredoxin reductase together with other components of the cell (Becker, K. et al.  Eur. J. Biochem.,  267, 6118 (2000)). For example, motexafin gadolinium, marketed as a radiosensitizing drug and thioredoxin reductase inhibitor, is also a potent ribonucleotide reductase inhibitor (Hashemy, S. I., et al.,  J Biol Chem,  281, 10691 (2006)). Auranofin, a potent thioredoxin reductase inhibitor, concomitantly localizes to and damages the mitochondria (Cox, A. G., et al, M. B.,  Biochem Pharmacol,  76, 1097-1109 (2008); Krishnamurthy, D., et al.,  J Med Chem,  51, 4790 (2008); Rigobello, M. P., et al.,  Free Radic Res,  39, 687 (2005)). 
     The structure and function of thioredoxin reductase, biological effects associated with its inhibition, such as in its potential as a mechanism for cancer treatment, and compounds previously disclosed as potential inhibitors are reviewed in Zhang, B. et al.,  Expert Opinion on Therapeutic Patents  (2016). 
     The present innovation relates to the development and usage of novel compounds specifically and potently targeting cytosolic thioredoxin reductase, without targeting the closely related flavoprotein glutathione reductase that supports the function of the glutathione system, as a means of obtaining a new efficient anticancer treatment that at the same time presents limited toxic side effects. 
     In particular, the inventors have unexpectedly found that novel, pyridinyl sulfone compounds may achieve highly selective inhibition of cytosolic thioredoxin reductase by acting as strongly-binding (and, in some cases, effectively irreversible) inhibitors of the enzyme without causing significant inhibition of glutathione reductase. 
     Specifically, by potently inhibiting thioredoxin reductase selectively over glutathione reductase, the novel pyridinyl sulfones have the potential to be effective against cancer forms having dysfunctional redox status, with minimal general toxic effects to normal cells. Such inhibitors may also be a suitable adjuvant therapy to be used in conjunction with radiotherapies or other chemotherapeutic approaches. Based on these surprising results, the present invention aims to provide new treatments for cancers. 
     Certain heteroarylsulfonyl-nitropyridines have been synthesized or alleged to be commercially available but with no use ascribed to them, as described in: Takahashi, T., et al, Chem Pharm Bull, 6, 369 (1958) and Talik, Z., et al, Prace Naukowe Akademii Ekonomicznej imienia Oskara Langego we Wroclawiu 255, 137 (1984). 
     International patent application WO 2010/138820 refers to the preparation of various N,N′-diarylureas and N,N′-diarylthioureas that are suggested to act to inhibit translation initiation and which are stated to be useful in the treatment of, for example, proliferative disorders. This publication also lists a number of compounds identified in a chemical library. 
     International patent application WO 03/051366 describes certain pyridines as kinase inhibitors and their use in treating cancer. However, none the of exemplified pyridines carry nitro substituents and none are linked via a sulfonyl moiety to an optionally substituted heteroaryl group. 
     International patent application WO 2005/007621 describes certain compounds as ubiquitin ligase inhibitors and their use in treating cell proliferative diseases. However, none of exemplified compounds contain a nitro substituted pyridine that is linked via a sulfonyl moiety to an optionally substituted heteroaryl group. 
     International patent application WO 99/36391 describes two benzenesulfonamides as therapeutic agents. Neither contains a pyridine ring having a nitro substituent. 
     International patent application WO 2005/121121 describes certain compounds as glucose metabolism modulators useful for the treatment of, for example, diabetes and obesity. However, none of the exemplified compounds contain a nitro substituted pyridine linked via a sulfonyl moiety to an optionally substituted heteroaryl group. 
     International patent application WO 2007/124546 describes 3-cyano-4,6-diarylsubstituted pyridines useful for the treatment of viral infections. However, none of the exemplified compounds contain a nitro substituted pyridine linked via a sulfonyl moiety to an optionally substituted heteroaryl group. 
     International patent application WO 95/29897 describes certain (H + /K + )ATPase inhibitors and their use in treating viral infections. However, none of the exemplified compounds contain a nitro substituted pyridine linked via a sulfonyl moiety to an optionally substituted heteroaryl group. 
     International patent application WO 98/54139 describes a process for the preparation of pyridines linked to, for example, an unsubstituted phenyl via a sulfonyl group. However, none of the exemplified compounds contain a nitro substituted pyridine linked via a sulfonyl moiety to an optionally substituted heteroaryl group. 
     International patent applications WO 2013/119931, WO 99/010320, WO 99/18096 and WO 99/017777 describe certain compounds and their use in treating conditions such as cancer. However, none of the exemplified compounds contain a nitro substituted pyridine linked via a sulfonyl moiety to an optionally substituted heteroaryl group. 
     International patent application WO 01/064642 describes certain compounds and their use in treating coagulation disorders. However, none of the exemplified compounds contain a nitro substituted pyridine linked via a sulfonyl moiety to an optionally substituted heteroaryl group. 
     International patent application WO 2011/022440 describes certain compounds and their use for treating proliferative disorders. However, none of the exemplified compounds contain a nitro substituted pyridine linked via a sulfonyl moiety to an optionally substituted heteroaryl group. 
     Chinese patent application CN 102206172 describes certain antiviral compounds. However, none of the exemplified compounds contain a nitro substituted pyridine linked via a sulfonyl moiety to an optionally substituted heteroaryl group. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     It has now been found that certain nitro substituted pyridines linked via a sulfonyl moiety to an optionally substituted heteroaryl group have surprising properties which render such compounds useful in the treatment of cancers. 
     Compounds of the Invention 
     In a first aspect of the invention, there is provided a compound of formula I 
     
       
         
         
             
             
         
       
     
     or a pharmaceutically acceptable salt thereof, wherein: 
     L represents —S(O) n —; 
     n represents 2 or 1; 
     X represents a heteroaryl group, attached to L via a carbon atom, optionally substituted by one or more groups independently selected from Y; 
     R 1 , R 2  and R 3  each independently represent H, halo, R a1 , —CN, -A a1 -C(Q a1 )R b1 , -A b1 -C(Q b1 )N(R c1 )R d1 , —Ac c1 —C(Q c1 )OR e1 , -A d1 -S(O) p R f1 , -A e1 -S(O) p N(R g1 )R h1 , -A f1 -S(O) p OR i1 , —N 3 , —N(R j1 )R k1 , —N(H)CN, —NO 2 , —ONO 2 , —OR l1  or —SR m1 ; 
     each A a1  to A f1  independently represents a single bond, —N(R p1 )— or —O—; 
     each Q a1  to Q c1  independently represents ═O, ═S, ═NR n1  or ═N(OR o1 ); 
     each R a1  and R f1  independently represents C 1-6  alkyl, C 2-6  alkenyl or C 2-6  alkynyl each optionally substituted by one or more groups independently selected from G 1a , heterocyclyl optionally substituted by one or more groups independently selected from G 1b , aryl optionally substituted by one or more groups independently selected from G 1c , or heteroaryl optionally substituted by one or more groups independently selected from G 1d ; 
     each R b1 , R c1 , R d1 , R e1 , R g1 , R h1 , R i1 , R j1 , R k1 , R l1 , R m1 , R n1 , R o1  and R p1  independently represents H, C 1-6  alkyl, C 2-6  alkenyl or C 2-6  alkynyl each optionally substituted by one or more groups independently selected from G 1a , heterocyclyl optionally substituted by one or more groups independently selected from G 1b , aryl optionally substituted by one or more groups independently selected from G 1c , or heteroaryl optionally substituted by one or more groups independently selected from G 1d ; 
     any of R c1  and R d1 , R g1  and R h1  and/or R j1  and R k1  are linked together to form, together with the nitrogen atom to which they are attached, a 3- to 6-membered ring, which ring optionally contains one further heteroatom and which ring optionally is substituted by one or more groups independently selected from halo, and C 1-3  alkyl, C 2-3  alkenyl or C 2-3  alkynyl each optionally substituted by one or more halo, and ═O; 
     each G 1a  and G 1b  independently represents halo, —CN, —N(R a2 )R b2 , —OR c2 , —SR d2  or ═O; 
     each G 1c  and G 1d  independently represents halo, —CN, —N(R a2 )R b2 , —OR c2  or —SR d2 ; 
     each R a2 , R b2 , R c2  and R d2  independently represents H or C 1-6  alkyl, C 2-6  alkenyl or C 2-6  alkynyl each optionally substituted by one or more fluoro; or 
     R a2  and R b2  are linked together to form, along with the nitrogen atom to which they are attached, a 3- to 6-membered ring, which ring optionally contains one further heteroatom and which ring optionally is substituted by one or more groups independently selected from fluoro, C 1-3  alkyl, C 2-3  alkenyl or C 2-3  alkynyl each optionally substituted by one or more fluoro; 
     each Y independently represents halo, R a3 , —CN, -A a2 -C(Q a2 )R b3 , -A b2 C(Q b2 )N(R c3 )R d3 , -A c2 -C(Q c2 )OR e3 , -A d2 -S(O) q R f3 , -A e2 -S(O) q N(R g3 )R h3 , -A f2 -S(O) q OR i3 , —N 3 , —N(R j3 )R k3 , —N(H)CN, —NO 2 , —ONO 2 , —OR l3  or —SR m3 ; 
     each Q a2  to Q c2  independently represents ═O, ═S, ═NR n3  or ═N(OR o3 ); 
     each A a2  to A f2  independently represents a single bond, —N(R p3 )— or —O—; 
     each R a3  and R f3  independently represents C 1-6  alkyl, C 2-6  alkenyl or C 2-6  alkynyl each optionally substituted by one or more groups independently selected from G 2a , heterocyclyl optionally substituted by one or more groups independently selected from G 2b , aryl optionally substituted by one or more groups independently selected from G 2c , or heteroaryl optionally substituted by one or more groups independently selected from G 2d ; 
     each R b3 , R c3 , R d3 , R e3 , R g3 , R h3 , R i3 , R j3 , R k3 , R l3 , R m3 , R n3 , R o3  and R p3  independently represents H, C 1-6  alkyl, C 2-6  alkenyl or C 2-6  alkynyl each optionally substituted by one or more groups independently selected from G 2a , heterocyclyl optionally substituted by one or more groups independently selected from G 2b , aryl optionally substituted by one or more groups independently selected from G 2c , or heteroaryl optionally substituted by one or more groups independently selected from G 2d ; or 
     any two R c3  and R d3 , R g3  and R h3  and/or R j3  and R k3  are linked together to form, along with the nitrogen atom to which they are attached, a 3- to 6-membered ring, which ring optionally contains one further heteroatom and which ring optionally is substituted by one or more groups independently selected from heterocyclyl optionally substituted by one or more groups independently selected from G 2b , aryl optionally substituted by one or more groups independently selected from G 2c , or heteroaryl optionally substituted by one or more groups independently selected from G 2d , and ═O; 
     each G 2a  independently represents halo, —CN, —N(R j4 )R k4 , —OR l4 , —SR m4  or ═O; 
     each G 2b  independently represents halo, R a4 , —CN, —N(R j4 )R k4 , —OR l4 , —SR m4  or ═O; 
     each G 2c  and G 2d  independently represents halo, R a4 , —CN, -A a3 -C(Q a4 )R b4 , -A b3 -C(Q b3 )N(R c4 )R d4 , -A c3 -C(Q c3 )OR e4 , -A d3 -S(O) q R f4 , -A e3 -S(O) q N(R g4 )R h4 , -A f3 -S(O) q OR i4 , —N 3 , —N(R j4 )R k4 , —N(H)CN, —NO 2 , —ONO 2 , —OR l4  or —SR m4 ; 
     each Q a3  to Q c3  independently represents ═O, ═S, ═NR n4  or ═N(OR o4 ); 
     each A a3  to A f3  independently represents a single bond, —N(R p4 )— or —O—; 
     each R a4  and R f4  independently represents C 1-6  alkyl, C 2-6  alkenyl or C 2-6  alkynyl each optionally substituted by one or more groups independently selected from G 3a , heterocyclyl optionally substituted by one or more groups independently selected from G 3b , aryl optionally substituted by one or more groups independently selected from G 3c , or heteroaryl optionally substituted by one or more groups independently selected from G 3d ; 
     each R b4 , R c4 , R d4 , R e4 , R g4 , R h4 , R i4 , R j4 , R k4 , R l4 , R m4 , R n4 , R o4  and R p4  independently represents H, C 1-6  alkyl, C 2-6  alkenyl or C 2-6  alkynyl each optionally substituted by one or more groups independently selected from G 3a  or heterocyclyl optionally substituted by one or more groups independently selected from G 3b , aryl optionally substituted by one or more groups independently selected from G 3c , or heteroaryl optionally substituted by one or more groups independently selected from G 3d ; or 
     any of R c4  and R d4 , R g4  and R h4  and/or R j4  and R k4  are linked together to form, together with the nitrogen atom to which they are attached, a 3- to 6-membered ring, which ring optionally contains one further heteroatom and which ring optionally is substituted by one or more groups independently selected G 3b ; 
     each G 3a  and G 3b  independently represents halo, R a5 , —CN, —N(R b5 )R c5 , —OR d5 , —SR e5  or ═O; 
     each R a5  independently represents C 1-6  alkyl, C 2-6  alkenyl or C 2-6  alkynyl each optionally substituted by one or more groups independently selected from G 4 ; 
     each R b5 , R c5 , R d5  and R e5  independently represents H, or C 1-6  alkyl, C 2-6  alkenyl or C 2-6  alkynyl each optionally substituted by one or more groups independently selected from G 4 ; or 
     each R b5  and R c5  are linked together to form, together with the nitrogen atom to which they are attached, a 3- to 6-membered ring, which ring optionally contains one further heteroatom and which ring optionally is substituted by one or more groups independently selected from G 4 ; 
     each G 4  independently represents halo, R a6 , —CN, —N(R b6 )R c6 , —OR d6  or ═O; 
     each R a6  independently represents C 1-6  alkyl, C 2-6  alkenyl or C 2-6  alkynyl each optionally substituted by one or more fluoro; 
     each R b6 , R c6  and R d6  independently represents H, or C 1-6  alkyl, C 2-6  alkenyl or C 2-6  alkynyl each optionally substituted by one or more fluoro; and 
     each p and q independently represents 1 or 2, 
     which compounds and pharmaceutically acceptable salts thereof may be referred to as compounds of the invention, 
     but with the provisos that the compound of formula I does not represent: 
     (A)
     3-nitro-2-(pyridin-2-ylsulfonyl)pyridine,   2-((3-nitropyridin-2-yl)sulfonyl)pyrimidine, or   N-(6-chloro-2-((5-chloro-3-nitropyridin-2-yl)sulfonyl)pyridin-3-yl)acetamide;   

     or 
     (B)
     3-nitro-2-[(3-nitro-2-thienyl)sulfinyl]-pyridine.   

     For the avoidance of doubt, compounds of formula I and pharmaceutically acceptable salts thereof, not including the provisos, may be referred to herein as compounds of the invention. Similarly, references to compounds of the first aspect of the invention will refer to compounds of formula I as defined in the first aspect of the invention, including the provisos, and pharmaceutically acceptable salts thereof. As such, compounds of the first aspect of the invention represent a particular embodiment of compounds of the invention. 
     The skilled person will understand that references herein to compounds of the invention (e.g. compounds of the first aspect of the invention) will include references to all embodiments and particular forms thereof. 
     Unless indicated otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. 
     Pharmaceutically-acceptable salts include acid addition salts and base addition salts. Such salts may be formed by conventional means, for example by reaction of a free acid or a free base form of a compound of the invention with one or more equivalents of an appropriate acid or base, optionally in a solvent, or in a medium in which the salt is insoluble, followed by removal of said solvent, or said medium, using standard techniques (e.g. in vacuo, by freeze-drying or by filtration). Salts may also be prepared by exchanging a counter-ion of a compound of the invention in the form of a salt with another counter-ion, for example using a suitable ion exchange resin. 
     Particular acid addition salts that may be mentioned include carboxylate salts (e.g. formate, acetate, trifluoroacetate, propionate, isobutyrate, heptanoate, decanoate, caprate, caprylate, stearate, acrylate, caproate, propiolate, ascorbate, citrate, glucuronate, glutamate, glycolate, α-hydroxybutyrate, lactate, tartrate, phenylacetate, mandelate, phenylpropionate, phenylbutyrate, benzoate, chlorobenzoate, methylbenzoate, hydroxybenzoate, methoxybenzoate, dinitrobenzoate, o-acetoxybenzoate, salicylate, nicotinate, isonicotinate, cinnamate, oxalate, malonate, succinate, suberate, sebacate, fumarate, malate, maleate, hydroxymaleate, hippurate, phthalate or terephthalate salts), halide salts (e.g. chloride, bromide or iodide salts), sulfonate salts (e.g. benzenesulfonate, methyl-, bromo- or chloro-benzenesulfonate, xylenesulfonate, methanesulfonate, ethanesulfonate, propanesulfonate, hydroxyethanesulfonate, 1- or 2-naphthalene-sulfonate or 1,5-naphthalenedisulfonate salts) or sulfate, pyrosulfate, bisulfate, sulfite, bisulfite, phosphate, monohydrogenphosphate, dihydrogenphosphate, metaphosphate, pyrophosphate or nitrate salts, and the like. 
     Particular base addition salts that may be mentioned include salts formed with alkali metals (such as Na and K salts), alkaline earth metals (such as Mg and Ca salts), organic bases (such as ethanolamine, diethanolamine, triethanolamine, tromethamine and lysine) and inorganic bases (such as ammonia and aluminium hydroxide). More particularly, base addition salts that may be mentioned include Mg, Ca and, most particularly, K and Na salts. 
     For the avoidance of doubt, compounds of the invention may exist as solids, and thus the scope of the invention includes all amorphous, crystalline and part crystalline forms thereof, and may also exist as oils. Where compounds of the invention exist in crystalline and part crystalline forms, such forms may include solvates, which are included in the scope of the invention. Compounds of the invention may also exist in solution. 
     Compounds of the invention may contain double bonds and may thus exist as E (entgegen) and Z (zusammen) geometric isomers about each individual double bond. All such isomers and mixtures thereof are included within the scope of the invention. 
     Compounds of the invention may also exhibit tautomerism. All tautomeric forms and mixtures thereof are included within the scope of the invention. 
     Compounds of the invention may also contain one or more asymmetric carbon atoms and may therefore exhibit optical and/or diastereoisomerism. Diastereoisomers may be separated using conventional techniques, e.g. chromatography or fractional crystallisation. The various stereoisomers may be isolated by separation of a racemic or other mixture of the compounds using conventional, e.g. fractional crystallisation or HPLC, techniques. Alternatively the desired optical isomers may be made by reaction of the appropriate optically active starting materials under conditions which will not cause racemisation or epimerisation (i.e. a ‘chiral pool’ method), by reaction of the appropriate starting material with a ‘chiral auxiliary’ which can subsequently be removed at a suitable stage, by derivatisation (i.e. a resolution, including a dynamic resolution); for example, with a homochiral acid followed by separation of the diastereomeric derivatives by conventional means such as chromatography, or by reaction with an appropriate chiral reagent or chiral catalyst all under conditions known to the skilled person. All stereoisomers and mixtures thereof are included within the scope of the invention. 
     As used herein, references to halo and/or halogen will independently refer to fluoro, chloro, bromo and iodo (for example, fluoro and chloro). 
     Unless otherwise specified, C 1-z  alkyl groups (where z is the upper limit of the range) defined herein may be straight-chain or, when there is a sufficient number (i.e. a minimum of two or three, as appropriate) of carbon atoms, be branched-chain, and/or cyclic (so forming a C 3-z  cycloalkyl group). When there is a sufficient number (i.e. a minimum of four) of carbon atoms, such groups may also be part cyclic (so forming a C 3-z  partial cycloalkyl group). Part cyclic alkyl groups that may be mentioned include cyclopropylmethyl and cyclohexylethyl. When there is a sufficient number of carbon atoms, such groups may also be multicyclic (e.g. bicyclic or tricyclic) or spirocyclic. 
     Unless otherwise specified, C 2-z  alkenyl groups (where z is the upper limit of the range) defined herein may be straight-chain or, when there is a sufficient number (i.e. a minimum of three) of carbon atoms, be branched-chain, and/or cyclic (so forming a C 4-z  cycloalkenyl group). When there is a sufficient number (i.e. a minimum of five) of carbon atoms, such groups may also be part cyclic. Part cyclic alkenyl groups that may be mentioned include cyclopentenylmethyl and cyclohexenylmethyl. When there is a sufficient number of carbon atoms, such groups may also be multicyclic (e.g. bicyclic or tricyclic) or spirocyclic. 
     Unless otherwise specified, C 2-z  alkynyl groups (where z is the upper limit of the range) defined herein may be straight-chain or, when there is a sufficient number (i.e. a minimum of four) of carbon atoms, be branched-chain. 
     For the avoidance of doubt, the skilled person will understand that the term alkyl will refer to saturated hydrocarbon moieties, whereas the term alkenyl will refer to unsaturated hydrocarbon moieties containing at least one carbon-carbon double bond and the term alkynyl will refer to unsaturated hydrocarbon moieties containing at least one carbon-carbon triple bond, which alkyl, alkenyl and alkynyl groups may be referred to collectively as hydrocarbyl groups. Further, such unsaturated hydrocarbon moieties will be referred to by reference to the highest degree of unsaturation comprised therein (e.g. a hydrocarbon moiety comprising at least one carbon-carbon double bond and at least one carbon-carbon triple bond will be referred to as alkynyl, although such moieties may also be referred to using terms such as “alkenyl alkynyl” and the like). 
     As used herein, the term heterocyclyl may refer to non-aromatic monocyclic and bicyclic heterocyclyl groups (which groups may further be bridged) in which at least one (e.g. one to four) of the atoms in the ring system is other than carbon (i.e. a heteroatom), and in which the total number of atoms in the ring system is between three and twelve (e.g. between five and ten and, most preferably, between three and eight, e.g. a 5- or 6-membered heterocyclyl group). Further, such heterocyclyl groups may be saturated, forming a heterocycloalkyl, or unsaturated containing one or more carbon-carbon or, where possible, carbon-heteroatom or heteroatom-heteroatom double and/or triple bonds, forming for example a C 2-z  (e.g. C 4-z ) heterocycloalkenyl (where z is the upper limit of the range) or a C 7-z  heterocycloalkynyl group. C 2-z  heterocyclyl groups that may be mentioned include 7-azabicyclo-[2.2.1]heptanyl, 6-azabicyclo[3.1.1]heptanyl, 6-azabicyclo[3.2.1]-octanyl, 8-azabicyclo[3.2.1]octanyl, aziridinyl, azetidinyl, 2,3-dihydroisothiazolyl, dihydropyranyl, dihydropyridinyl, dihydropyrrolyl (including 2,5-dihydropyrrolyl), dioxolanyl (including 1,3-dioxolanyl), dioxanyl (including 1,3-dioxanyl and 1,4-dioxanyl), dithianyl (including 1,4-dithianyl), dithiolanyl (including 1,3-dithiolanyl), imidazolidinyl, imidazolinyl, isothiazolidinyl, morpholinyl, 7-oxabicyclo[2.2.1]heptanyl, 6-oxabicyclo[3.2.1]-octanyl, oxetanyl, oxiranyl, piperazinyl, piperidinyl, pyranyl, pyrazolidinyl, pyrrolidinonyl, pyrrolidinyl, pyrrolinyl, quinuclidinyl, sulfolanyl, 3-sulfolenyl, tetrahydropyranyl, tetrahydrofuryl, tetrahydropyridinyl (such as 1,2,3,4-tetrahydropyridinyl and 1,2,3,6-tetrahydropyridinyl), thietanyl, thiiranyl, thiolanyl, tetrahydrothiopyranyl, thiomorpholinyl, trithianyl (including 1,3,5-trithianyl), tropanyl and the like. Substituents on heterocyclyl groups may, where appropriate, be located on any atom in the ring system including a heteroatom. Further, in the case where the substituent is another cyclic compound, then the cyclic compound may be attached through a single atom on the heterocyclyl group, forming a so-called “spiro”-compound. The point of attachment of heterocyclyl groups may be via any atom in the ring system including (where appropriate) a further heteroatom (such as a nitrogen atom), or an atom on any fused carbocyclic ring that may be present as part of the ring system. Heterocyclyl groups may also be in the N- or S-oxidised form. 
     At each occurrence when mentioned herein, particular heterocyclyl groups that may be mentioned include 3- to 8-membered heterocyclyl groups (e.g. a 4- to 6-membered heterocyclyl group). 
     As may be used herein, the term aryl includes references to C 6-14  (e.g. C 6-10 ) aromatic groups. Such groups may be monocyclic or bicyclic and, when bicyclic, be either wholly or partly aromatic. C 6-10  aryl groups that may be mentioned include phenyl, naphthyl, 1,2,3,4-tetrahydronaphthyl, indanyl, and the like (e.g. phenyl, naphthyl and the like, such as phenyl). For the avoidance of doubt, the point of attachment of substituents on aryl groups may be via any carbon atom of the ring system. 
     As may be used herein, the term heteroaryl (or heteroaromatic) includes references to 5- to 14- (e.g. 5- to 10-, such as 5- or 6-) membered heteroaromatic groups (as may be specified) containing one or more heteroatoms selected from oxygen, nitrogen and/or sulfur. Where possible, such heteroaryl groups may comprise one, two, or three rings, of which at least one is aromatic. Substituents on heteroaryl/heteroaromatic groups may, where appropriate, be located on any atom in the ring system including a heteroatom. Unless otherwise specified, the point of attachment of heteroaryl/heteroaromatic groups may be via any atom in the ring system including (where appropriate) a heteroatom. Bicyclic heteroaryl/heteroaromatic groups may comprise a benzene ring fused to one or more further aromatic or non-aromatic heterocyclic rings, in which instances, the point of attachment of the polycyclic heteroaryl/heteroaromatic group may be via any ring including the benzene ring or the heteroaryl/heteroaromatic or heterocyclyl ring. Examples of heteroaryl/heteroaromatic groups that may be mentioned include pyridinyl, pyrrolyl, furanyl, thiophenyl, oxadiazolyl, thiadiazolyl, thiazolyl, oxazolyl, pyrazolyl, triazolyl, tetrazolyl, isoxazolyl, isothiazolyl, imidazolyl, imidazopyrimidinyl, imidazothiazolyl, thienothiophenyl, pyrimidinyl, furopyridinyl, indolyl, azaindolyl, pyrazinyl, pyrazolopyrimidinyl, indazolyl, pyrimidinyl, quinolinyl, isoquinolinyl, quinazolinyl, benzofuranyl, benzothiophenyl, benzoimidazolyl, benzoxazolyl, benzothiazolyl, benzotriazolyl and purinyl. The oxides of heteroaryl/heteroaromatic groups are also embraced within the scope of the invention (e.g. the N-oxide). As stated above, heteroaryl includes polycyclic (e.g. bicyclic) groups in which one ring is aromatic (and the other may or may not be aromatic). Hence, other heteroaryl groups that may be mentioned include e.g. benzo[1,3]dioxolyl, benzo[1,4]dioxinyl, dihydrobenzo[d]isothiazole, 3,4-dihydrobenz[1,4]oxazinyl, dihydrobenzothiophenyl, indolinyl, 5H,6H, 7H-pyrrolo[1,2-b]pyrimidinyl, 1,2,3,4-tetrahydroquinolinyl, thiochromanyl and the like. 
     For the avoidance of doubt, as used herein, references to heteroatoms will take their normal meaning as understood by one skilled in the art. Particular heteroatoms that may be mentioned include phosphorus, selenium, tellurium, silicon, boron, oxygen, nitrogen and sulfur (e.g. oxygen, nitrogen and sulfur). 
     For the avoidance of doubt, references to polycyclic (e.g. bicyclic) groups (e.g. when employed in the context of heterocyclyl groups) will refer to ring systems wherein more than two scissions would be required to convert such rings into a straight chain, with the minimum number of such scissions corresponding to the number of rings defined (e.g. the term bicyclic may indicate that a minimum of two scissions would be required to convert the rings into a straight chain). For the avoidance of doubt, the term bicyclic (e.g. when employed in the context of heterocyclyl groups) may refer to groups in which the second ring of a two-ring system is formed between two adjacent atoms of the first ring, and may also refer to groups in which two non-adjacent atoms are linked by either an alkylene or heteroalkylene chain (as appropriate), which later groups may be referred to as bridged. 
     For the avoidance of doubt, when an aryl or an heteroaryl group is substituted with a group via a double bond, such as ═O, it is understood that the aryl or heteroaryl group is partly aromatic, i.e. the aryl or heteroaryl group consists of at least two rings where at least one ring is not aromatic. 
     The present invention also embraces isotopically-labelled compounds of the present invention which are identical to those recited herein, but for the fact that one or more atoms are replaced by an atom having an atomic mass or mass number different from the atomic mass or mass number usually found in nature (or the most abundant one found in nature). 
     All isotopes of any particular atom or element as specified herein are contemplated within the scope of the compounds of the invention. Hence, the compounds of the invention also include deuterated compounds, i.e. in which one or more hydrogen atoms are replaced by the hydrogen isotope deuterium. 
     For the avoidance of doubt, in cases in which the identity of two or more substituents in a compound of the invention may be the same, the actual identities of the respective substituents are not in any way interdependent. For example, in the situation in which two or more Y groups are present, those Y groups may be the same or different. Similarly, where two or more Y groups are present and each represent R a2 , the R 2a  groups in question may be the same or different. Likewise, when more than one R a1  is present and each independently represents C 1-6  alkyl substituted by one or more G 1a  group, the identities of each G 1a  are in no way interdependent. 
     For the avoidance of doubt, when a term such as “A a1  to A f1 ” is employed herein, this will be understood by the skilled person to mean A a1 , A b1 , A c1 , A d1 , A e1  and A f1  inclusively. Unless otherwise stated, the same reasoning will apply to other such terms used herein. 
     The skilled person will appreciate that compounds of the invention that are the subject of this invention include those that are stable. That is, compounds of the invention include those that are sufficiently robust to survive isolation, e.g. from a reaction mixture, to a useful degree of purity. 
     All embodiments of the invention and particular features mentioned herein may be taken in isolation or in combination with any other embodiments and/or particular features mentioned herein (hence describing more particular embodiments and particular features as disclosed herein) without departing from the disclosure of the invention. 
     For the avoidance of doubt, the compounds listed in the provisos provided in the first aspect of the invention (and therefore excluded as compounds of formula I in the first aspect of the invention) may be represented structurally as follows: 
     
       
         
         
             
             
         
       
     
     In particular embodiments of compounds of the invention (including compounds of the first aspect of the invention), the heteroaryl group representing X is a 5- to 6-membered heteroaryl group. Thus, in such embodiments, X represents a 5- to 6-heteroaryl group, attached to L via a carbon atom, optionally substituted by one or more groups independently selected from Y. 
     For the avoidance of doubt, the skilled person will understand that 5- to 6-membered heteroaryl groups will be necessarily monocyclic. 
     Particular compounds of the invention that may be mentioned include those in which n represents 2. 
     Further compounds of the invention that may be mentioned include those in which n represents 1. 
     Particular compounds of the invention that may be mentioned (e.g. in relation to the first aspect of the invention) include those in which X is unsubstituted or substituted with one or two Y groups. 
     For example, particular compounds of the invention that may be mentioned include those in which X is unsubstituted. 
     Further compounds of the invention that may be mentioned include those in which X is substituted with one Y. 
     More particular compounds of the invention that may be mentioned include those in which each Y independently represents halo (such as fluoro or chloro), R a3 , —N(R j3 )R k3  or —OR l3 . 
     More particular compounds of the invention that may be mentioned include those in which: 
     each R a3  independently represents C 1-6  alkyl (e.g. methyl) optionally substituted by one or more fluoro; and/or (e.g. and) 
     each R j3 , R k3  and R l3  independently represents H, or C 1-6  alkyl, C 2-6  alkenyl or C 2-6  alkynyl (e.g. C 1-6  alkyl) each optionally substituted by one or more fluoro. 
     More particular compounds of the invention that may be mentioned include those in which: 
     X is unsubstituted or substituted with one Y; 
     each Y (i.e. where present) independently represents halo (such as fluoro or chloro), —N(R j3 )R k3 , —OR l3 , or R a3 ; 
     each R a3  independently represents C 1-6  alkyl, C 2-6  alkenyl or C 2-6  alkynyl (e.g. C 1-6  alkyl, such as methyl) each optionally substituted by one or more fluoro; and/or (e.g. and) 
     each R j3 , R k3  and R l3  independently represents H, or C 1-6  alkyl, C 2-6  alkenyl or C 2-6  alkynyl (e.g. C 1-6  alkyl) each optionally substituted by one or more fluoro. 
     More particular compounds of the invention that may be mentioned include those in which: 
     X is unsubstituted or substituted with one Y; and/or (e.g. and) 
     Y represents halo (e.g. fluoro or chloro) —OC 1-6  alkyl, —OC 2-6  alkenyl or —OC 2-6  alkynyl (e.g. —OC 1-6  alkyl) each optionally substituted by one or more fluoro (e.g. —OCH 3 ), or C 1-6  alkyl, C 2-6  alkenyl or C 2-6  alkynyl (e.g. C 1-6  alkyl) each optionally substituted by one or more fluoro (e.g. —CH 3 ). 
     Yet more particular compounds of formula I that may be mentioned include those in which: 
     X is unsubstituted or substituted with one Y; and/or (e.g. and) 
     Y represents fluoro, chloro, or C 1-6  alkyl optionally substituted by one or more fluoro (e.g. —CH 3 ). 
     In certain embodiments of compounds of formula I, each Y (where present) represents methyl optionally substituted with one or more fluoro (e.g. —CH 3 ). 
     Thus, examples of more particular compounds that may be mentioned include those in which: 
     X is unsubstituted or substituted with one Y; and/or (e.g. and) 
     Y represents methyl optionally substituted with one or more fluoro (e.g. —CH 3 ). 
     In a particular embodiment (i.e. of compounds of the invention, e.g. compounds of the first aspect of the invention), the compound of formula I is a compound of formula Ia 
                         
wherein:
 
     L, R 1 , R 2  and R 3  and are defined for compounds of the invention (including all particular features and embodiments thereof); 
     each of Z 1  to Z 5  represents CR 4  to CR 8 , respectively, with the exception that one or two of Z 1  to Z 5  instead represents a heteroatom, which where possible may be substituted with R 9 , and optionally one of Z 1  to Z 5  may instead represent a direct bond; and 
     each of R 4  to R 9  represents H or Y as defined herein for compounds of the invention (including all particular features and embodiments thereof). 
     For the avoidance of doubt, where the compound of formula I (i.e. the compound of the invention) is a compound of formula Ia, compounds of the invention (e.g. compounds of the first aspect of the invention) include pharmaceutically acceptable salts of compounds of formula Ia. 
     For the avoidance of doubt, in compounds of formula Ia, the ring containing Z 1  to Z 5  is aromatic (as indicated by the presence of the circle inside that ring as depicted hereinabove). 
     For the avoidance of doubt, in relation to all compounds having such as group defined herein, the group X may be defined as a moiety of structural formula: 
                         
wherein the bond dissected by the dashed line is the bond forming the attachment to the required sulfonyl moiety, and wherein Z 1  to Z 5  are as defined herein for compounds of formula Ia (including all embodiments and features thereof).
 
     In a particular embodiment of compounds of formula Ia, where Z 1  to Z 5  represents a heteroatom, which where possible may be substituted with R 9 , that group may represent O, S, N or NR 9 . 
     In a particular embodiment of compounds of formula Ia, each of Z 1  to Z 5  represents CR 4  to CR 8 , respectively, with the exception that one or two of Z 1  and Z 3  to Z 5  instead represents a heteroatom, which where possible may be substituted with R 9 , and optionally Z 3  may instead represent a direct bond. 
     In a particular embodiment of compounds of formula Ia, R 9  (where present) represents H. 
     Thus, in a particular embodiment of compounds of formula Ia, where Z 1  to Z 5  represents a heteroatom, which where possible may be substituted with R 9 , that group may represent O, S, N or NH. 
     In a particular embodiment, each of R 4  to R 9  represents H with the exception that one or two (e.g. one) of R 4  to R 9  (e.g. one or two of R 4  to R 8 ) may optionally instead represent Y as defined herein for compounds of formula I (including all particular features and embodiments thereof). 
     In a more particular embodiment, each of R 4 , R 5 , R 7 , R 8  and R 9  (where present) represents H and R 6  (where present) represents H or Y as defined for compounds of formula I (including all particular features and embodiments thereof). 
     In a yet more particular embodiment, each of R 4 , R 5 , R 7 , R 8  and R 9  (where present) represents H and R 6  (where present) represents H or Y, wherein Y represents halo (e.g. fluoro or chloro), C 1-6  alkyl, C 2-6  alkenyl or C 2-6  alkynyl (e.g. C 1-6  alkyl) each optionally substituted by one or more fluoro (e.g. —CH 3 , —CHF 2  or —CF 3 ), or —OC 1-6  alkyl, —OC 2-6  alkenyl or —OC 2-6  alkynyl (e.g. —OC 1-6  alkyl) optionally substituted by one or more fluoro (e.g. —OCH 3 , —OCHF 2  or —OCF 3 ). 
     In a yet more particular embodiment, each of R 4 , R 5 , R 7 , R 8  and R 9  (where present) represents H and R 6  (where present) represents H or Y, wherein Y represents C 1-6  alkyl, C 2-6  alkenyl or C 2-6  alkynyl (e.g. C 1-6  alkyl) each optionally substituted by one or more fluoro (e.g. —CH 3 , —CHF 2  or —CF 3 ). 
     In a yet more particular embodiment, each of R 4 , R 5 , R 7 , R 8  and R 9  (where present) represents H and R 6  (where present) represents H or Y, wherein Y represents methyl optionally substituted by one or more fluoro. 
     For example, particular compounds of formula I that may be mentioned include those in which X represents pyridinyl (e.g. 2-pyridinyl or 4-pyridinyl, such as 2-pyridinyl), pyrimidinyl (e.g. 2-pyrimidinyl or 4-pyrimidinyl, such as 2-pyrimidinyl), imidazolyl (e.g. 2-imidazolyl) and thiazolyl (e.g. 2-thiazolyl), each optionally substituted with one or more (e.g. one) Y group. 
     Thus, yet more particular compounds of formula I that may be mentioned include those in which X represents pyridinyl (e.g. 2-pyridinyl or 4-pyridinyl, such as 2-pyridinyl), pyrimidinyl (e.g. 2-pyrimidinyl), imidazolyl (e.g. 2-imidazolyl) and methyl thiazolyl (e.g. 4-methyl-2-thiazolyl). 
     For example, in particular embodiments, when X represents pyridinyl optionally substituted with one or more Y group, that pyridinyl is a 2-pyridinyl, particularly unsubstituted 2-pyridinyl. 
     Particular compounds of the invention (e.g. compounds of the first aspect of the invention, including formula I and Ia, and all particular features and embodiments thereof) that may be mentioned include those in which R 1 , R 2  and R 3  each independently represents H, halo, R a1 , —N(R j1 )R k1  or —OR l1 . 
     More particular compounds of the invention that may be mentioned include those in which: 
     each R a1  and R f1  independently represents C 1-6  alkyl, C 2-6  alkenyl or C 2-6  alkynyl each optionally substituted by one or more groups independently selected from G 1a , or heterocyclyl optionally substituted by one or more groups independently selected from G 1b ; and 
     each R b1 , R c1 , R d1 , R e1 , R g1 , R h1 , R i1 , R j1 , R k1 , R l1 , R m1 , R n1 , R o1  and R p1  independently represents H, C 1-6  alkyl, C 2-6  alkenyl or C 2-6  alkynyl each optionally substituted by one or more groups independently selected from G 1a  or heterocyclyl optionally substituted by one or more groups independently selected from G 1b ; or 
     any of R c1  and R d1 , R g1  and R h1  and/or R j1  and R k1  are linked together to form, together with the nitrogen atom to which they are attached, a 3- to 6-membered ring, which ring optionally contains one further heteroatom and which ring optionally is substituted by one or more groups independently selected from halo, and C 1-3  alkyl, C 2-3  alkenyl or C 2-3  alkynyl each optionally substituted by one or more halo, and ═O. 
     More particular compounds of the invention that may be mentioned include those in which: 
     each R 1 , R 2  and R 3  each independently represent H, halo, R a1 , —N(R j1 )R k1 , —OR l1  or —SR m1  (e.g. H, halo, R a1 , —N(R j1 )R k1  or —OR l1 ); and/or (e.g. and) 
     each of R a1 , R j1 , R k1 , R l1  and R m1  independently represents C 1-6  alkyl (e.g. methyl) optionally substituted by one or more fluoro. 
     In certain embodiments that may be mentioned, only R c1  and R d1 , and/or R g1  and R h1  may alternatively be linked together in the manner described herein. 
     In more particular embodiments that may be mentioned, G 1a  groups (i.e. where present as a substituent on R 1a , which in such instances may be alternatively referred to as G 1ax  groups) may represent halo (e.g. fluoro). 
     In particular embodiments, R 1 , R 2  and R 3  each independently represent H, halo (e.g. fluoro or chloro, such as chloro), —N(R j1 )R k1  or —OR l1 . 
     For example, particular compounds of the invention (e.g. compounds of the first aspect of the invention, including formula I and Ia, and all particular features and embodiments thereof) that may be mentioned include those in which: 
     each R 1 , R 2  and R 3  each independently represent H, halo, —N(R j1 )R k1  or —OR l1 ; and 
     each R j1 , R k1  and R l1  independently represents C 1-6  alkyl, C 2-6  alkenyl or C 2-6  alkynyl (e.g. C 1-6  alkyl, such as C 1-3  alkyl) each optionally substituted by one or more fluoro. 
     More particular compounds of the invention (e.g. compounds of the first aspect of the invention, including formula I and Ia, and all particular features and embodiments thereof) that may be mentioned include those in which: 
     each R 1 , R 2  and R 3  each independently represent H, halo (e.g. fluoro or chloro, such as chloro), —N(R j1 )R k1  or —OR l1 ; and 
     each R j1 , R k1  and R l1  represents methyl optionally substituted by one or more fluoro. 
     Particular compounds of the invention (e.g. compounds of the first aspect of the invention, including formula I and Ia, and all particular features and embodiments thereof) that may be mentioned include those in which R 2  and R 3  each represent H or fluoro. 
     More particular compounds of the invention (e.g. compounds of the first aspect of the invention, including formula I and Ia, and all particular features and embodiments thereof) that may be mentioned include those in which R 2  and R 3  each represent H. 
     Particular compounds of the invention (e.g. compounds of the first aspect of the invention, including formula I and Ia, and all particular features and embodiments thereof) that may be mentioned include those in which R 1  represents other than H. 
     Thus, in particular embodiments, compounds of the invention (e.g. compounds of the first aspect of the invention, including formula I and Ia, and all particular features and embodiments thereof) that may be mentioned include those in which: 
     R 2  and R 3  each represent H; and 
     R 1  represents H or, particularly, halo (e.g. fluoro or chloro, such as chloro), —N(R j1 )R k1  or —OR l1 , more particularly wherein each R j1 , R k1  and R l1  represents C 1-6  alkyl, C 2-6  alkenyl or C 2-6  alkynyl (e.g. C 1-6  alkyl or, particularly, C 1-3  alkyl, such as methyl) each optionally substituted by one or more fluoro. 
     In more particular embodiments, compounds of the invention (e.g. compounds of the first aspect of the invention, including formula I and Ia, and all particular features and embodiments thereof) that may be mentioned include those in which: 
     R 2  and R 3  each represent H; 
     R 1  represents halo (e.g. fluoro or chloro, such as chloro), —N(R j1 )R k1  or —OR l1 ; and 
     each R j1 , R k1  and R l1  represents methyl optionally substituted by one or more fluoro. 
     In certain embodiments, compounds of the invention (e.g. compounds of the first aspect of the invention, including formula I and Ia, and all particular features and embodiments thereof) that may be mentioned include those in which R 1  represents —OC 1-3  alkyl optionally substituted with one or more fluoro. 
     In further embodiments, compounds of the invention (e.g. compounds of the first aspect of the invention, including formula I and Ia, and all particular features and embodiments thereof) that may be mentioned include those in which R 1  represents —OCH 3 . 
     Thus, in particular embodiments, compounds of the invention (e.g. compounds of the first aspect of the invention, including formula I and Ia, and all particular features and embodiments thereof) that may be mentioned include those in which: 
     R 2  and R 3  each represent H; and 
     R 1  represents —OCH 3 . 
     As indicated herein above, particular features and embodiments as described herein may be combined without departing from the teaching of the invention. 
     For example, in a particular embodiments of compounds of the invention (e.g. compounds of the first aspect of the invention, including formula I and Ia, and all particular features and embodiments thereof): 
     X represents a 5- to 6-membered heteroaryl group, attached to L via a carbon atom, optionally substituted by one or more (particularly, one or two) groups independently selected from Y; 
     each Y independently represents halo (such as fluoro or chloro, e.g. chloro), R a3 , —N(R j3 )R k3  or —OR l3 ; and 
     each R 1 , R 2  and R 3  each independently represents H, halo, R a1 , —N(R j1 )R k1  or —OR l1 . 
     In further such embodiments of compounds of the invention (e.g. compounds of the first aspect of the invention, including formula I and Ia, and all particular features and embodiments thereof): 
     X represents a 5- to 6-membered heteroaryl group, attached to L via a carbon atom, optionally substituted by one Y group; 
     Y represents methyl optionally substituted with one or more fluoro (e.g. —CH 3 ); 
     R 2  and R 3  each represent H; 
     R 1  represents H or, particularly, halo (e.g. fluoro or chloro, such as chloro), —N(R j1 )R k1  or —OR l1 ; and 
     each R j1 , R k1  and R l1  represents C 1-6  alkyl, C 2-6  alkenyl or C 2-6  alkynyl (e.g. C 1-3  alkyl, such as methyl) each optionally substituted by one or more fluoro. 
     For the avoidance of doubt, the skilled person will understand that each G 3c  and G 3d  may be construed relative to G 3a  and G 3b  in the same manner as the corresponding G 2c  and G 2d  groups are construed relative to construed relative to G 2a  and G 2b , i.e. such that: 
     G 3c  and G 3d  independently representing halo, R a5 , —CN, -A a4 -C(Q a4 )R b5 , -A b4 -C(Q b4 )N(R c5 )R d5 , -A c4 C(Q c4 )OR e5 , -A d5 -S(O) q R f5 , -A e4 -S(O) q N(R g5 )R h5 , -A f4 -S(O) q OR i5 , —N 3 , —N(R j5 )R k5 , —N(H)CN, —NO 2 , —ONO 2 , —OR l5  or —SR m5 , 
     each Q a4  to Q c4  independently represents ═O, ═S, ═NR n5  or ═N(OR o5 ); 
     each A a4  to A f4  independently represents a single bond, —N(R p5 )— or —O—; 
     with each R f5  to R p5  independently representing H, or C 1-6  alkyl, C 2-6  alkenyl or C 2-6  alkynyl each optionally substituted by one or more groups independently selected from G 4 , or with each R g5  and R h5 , and R j5  and R k5  being linked together to form, together with the nitrogen atom to which they are attached, a 3- to 6-membered ring, which ring optionally contains one further heteroatom and which ring optionally is substituted by one or more groups independently selected from G 4 . 
     Particular compounds of the invention (including compounds of formula I and Ia, and all embodiments and particular forms thereof) that may be mentioned include the compounds of the examples as provided herein, or a pharmaceutically acceptable salt thereof. 
     Where an example compound is indicated to have been obtained in a particular salt form, the skilled person will understand that particular compounds of the invention that may be mentioned include the free base or free acid (as appropriate) of that compound, and vice versa. Further, where an example compound is indicated to have been obtained in a particular salt form, particular compounds of the invention that may be mentioned include other (i.e. different) pharmaceutically acceptable salts of that compound. 
     Thus, for the avoidance of doubt, particular compounds of the invention that may be mentioned include:
     6-methoxy-3-nitro-2-(pyridin-2-ylsulfonyl)pyridine;   6-chloro-3-nitro-2-(pyridin-2-ylsulfonyl)pyridine;   6-dimethylamino-3-nitro-2-(pyridin-2-ylsulfonyl)pyridine;   6-methoxy-3-nitro-2-(pyridin-4-ylsulfonyl)pyridine;   2-((6-methoxy-3-nitropyridin-2-yl)sulfonyl)pyrimidine;   2-((1H-imidazol-2-yl)sulfonyl)-6-methoxy-3-nitropyridine; and   2-((6-methoxy-3-nitropyridin-2-yl)sulfonyl)-4-methylthiazole,
 
and pharmaceutically acceptable salts thereof.
   

     Compositions and Medical Uses 
     As discussed hereinbefore, compounds of the invention, and therefore compositions and kits comprising the same, are useful as pharmaceuticals. 
     According to a second aspect of the invention there is provided a compound of the invention, as hereinbefore defined (i.e. in the first aspect of the invention, including all embodiments and particular features therein, but without the provisos), for use as a pharmaceutical. Further, there is provided a compound of the invention, as hereinbefore defined, for use in medicine. 
     In a particular embodiment of the second aspect of the invention, the compound of the invention is a compound of the first aspect of the invention (i.e. including the provisos). 
     As indicated herein, compounds of the invention may be of particular use in treating cancers. 
     Thus, in a third aspect of the invention, there is provided a compound of the invention, as hereinbefore defined (i.e. in the first aspect of the invention, including all embodiments and particular features therein, but without the provisos), for use in the treatment of cancer. 
     In an alternative third aspect of the invention, there is provided the use of a compound of the invention, as hereinbefore defined, in the manufacture of a medicament for the treatment of cancer. 
     In a further alternative third aspect of the invention, there is provided a method of treating cancer comprising administering to a patient in need thereof a therapeutically effective amount of a compound of the invention. 
     In a particular embodiment of the third aspect of the invention, the compound of the invention is a compound of the first aspect of the invention (i.e. including the provisos). 
     The skilled person will understand that references to the treatment of a particular condition (or, similarly, to treating that condition) take their normal meanings in the field of medicine. In particular, the terms may refer to achieving a reduction in the severity of one or more clinical symptom associated with the condition. For example, in the case of a cancer, the term may refer to achieving a reduction of the amount of cancerous cells present (e.g. in the case of a cancer forming a solid tumour, indicated by a reduction in tumour volume). 
     As used herein, references to patients will refer to a living subject being treated, including mammalian (e.g. human) patients. 
     As used herein, the term effective amount will refer to an amount of a compound that confers a therapeutic effect on the treated patient. The effect may be objective (i.e. measurable by some test or marker) or subjective (i.e. the subject gives an indication of and/or feels an effect). 
     Although compounds of the invention may possess pharmacological activity as such, certain pharmaceutically-acceptable (e.g. “protected”) derivatives of compounds of the invention may exist or be prepared which may not possess such activity, but may be administered parenterally or orally and thereafter be metabolised in the body to form compounds of the invention. Such compounds (which may possess some pharmacological activity, provided that such activity is appreciably lower than that of the active compounds to which they are metabolised) may therefore be described as “prodrugs” of compounds of the invention. 
     As used herein, references to prodrugs will include compounds that form a compound of the invention, in an experimentally-detectable amount, within a predetermined time, following enteral or parenteral administration (e.g. oral or parenteral administration). All prodrugs of the compounds of the invention are included within the scope of the invention. 
     Furthermore, certain compounds of the invention may possess no or minimal pharmacological activity as such, but may be administered parenterally or orally, and thereafter be metabolised in the body to form compounds of the invention that possess pharmacological activity as such. Such compounds (which also includes compounds that may possess some pharmacological activity, but that activity is appreciably lower than that of the active compounds of the invention to which they are metabolised), may also be described as “prodrugs”. 
     Thus, the compounds of the invention are useful because they possess pharmacological activity, and/or are metabolised in the body following oral or parenteral administration to form compounds that possess pharmacological activity. 
     Without wishing to be bound by theory, it is believed that compounds of the invention wherein n represents 1 may be metabolised in vivo to form corresponding compounds of the invention wherein n represents 2. 
     As indicated herein, the compounds of the invention may be useful in the treatment of cancer (i.e. particular cancers). 
     Particular cancers that may be mentioned include those selected from the group comprising: 
     soft tissue cancers, such as sarcoma (e.g. angiosarcoma, fibrosarcoma, rhabdomyosarcoma, liposarcoma), myxoma, rhabdomyoma, fibroma, lipoma and teratoma; 
     lung cancers, such as bronchogenic carcinoma (e.g. squamous cell, undifferentiated small cell, undifferentiated large cell, adenocarcinoma), alveolar (or bronchiolar) carcinoma, bronchial adenoma, sarcoma, lymphoma, chondromatous hamartoma, mesothelioma, including non-small cell lung cancer; 
     gastrointestinal cancers: such as esophageal cancers (e.g. squamous cell carcinoma, adenocarcinoma, leiomyosarcoma, lymphoma), stomach cancers (e.g. carcinoma, lymphoma, leiomyosarcoma), pancreatic cancers (e.g. ductal adenocarcinoma, insulinoma, glucagonoma, gastrinoma, carcinoid tumors, vipoma), small bowel cancers (e.g. adenocarcinoma, lymphoma, carcinoid tumors, Kaposi&#39;s sarcoma, leiomyoma, hemangioma, lipoma, neurofibroma, fibroma), large bowel cancers (e.g. adenocarcinoma, tubular adenoma, villous adenoma, hamartoma, leiomyoma); 
     genitourinary tract cancers, such as cancer of the kidney (e.g. adenocarcinoma, Wilm&#39;s tumor (nephroblastoma), lymphoma, leukemia), bladder and urethra (e.g. squamous cell carcinoma, transitional cell carcinoma, adenocarcinoma), prostate (e.g. adenocarcinoma, sarcoma), testis (e.g. seminoma, teratoma, embryonal carcinoma, teratocarcinoma, choriocarcinoma, sarcoma, interstitial cell carcinoma, fibroma, fibroadenoma, adenomatoid tumors, lipoma); 
     liver cancers, such as hepatoma (e.g. hepatocellular carcinoma), cholangiocarcinoma, hepatoblastoma, angiosarcoma, hepatocellular adenoma, hemangioma; 
     bone cancers, such as osteogenic sarcoma (e.g. osteosarcoma), fibrosarcoma, malignant fibrous histiocytoma, chondrosarcoma, Ewing&#39;s sarcoma, malignant lymphoma (e.g. reticulum cell sarcoma), multiple myeloma, malignant giant cell tumor chordoma, osteochronfroma (e.g osteocartilaginous exostoses), benign chondroma, chondroblastoma, chondromyxofibroma, osteoid osteoma and giant cell tumors; 
     cancers of the head and/or nervous system, such as cancer of the skull (e.g. osteoma, hemangioma, granuloma, xanthoma, osteitis deformans), meninges (e.g. meningioma, meningiosarcoma, gliomatosis), brain (e.g. astrocytoma, medulloblastoma, glioma, ependymoma, germinoma (pinealoma), glioblastoma multiform, oligodendroglioma, schwannoma, retinoblastoma, congenital tumors), spinal cord (e.g. neurofibroma, meningioma, glioma, sarcoma); 
     gynecological cancers, such as cancers of the uterus (e.g. endometrial carcinoma), cervix (cervical carcinoma, pre-tumor cervical dysplasia), ovaries (e.g. ovarian carcinoma (serous cystadenocarcinoma, mucinous cystadenocarcinoma, unclassified carcinoma), granulosa-thecal cell tumors, Sertoli-Leydig cell tumors, dysgerminoma, malignant teratoma), cancers of the vulva (e.g. squamous cell carcinoma, intraepithelial carcinoma, adenocarcinoma, fibrosarcoma, melanoma), vagina (e.g. clear cell carcinoma, squamous cell carcinoma, botryoid sarcoma (embryonal rhabdomyosarcoma)), fallopian tubes (e.g. carcinoma); 
     haematologic cancers, such as cancers of the blood and bone marrow (e.g. myeloid leukemia (acute and chronic), acute lymphoblastic leukemia, chronic lymphocytic leukemia, myeloproliferative diseases, multiple myeloma, myelodysplastic syndrome), Hodgkin&#39;s disease, non-Hodgkin&#39;s lymphoma (malignant lymphoma); 
     skin cancers, such as malignant melanoma, basal cell carcinoma, squamous cell carcinoma, Kaposi&#39;s sarcoma, moles dysplastic nevi, lipoma, angioma, dermatofibroma, keloids; neurofibromatosis and Adrenal glands; and 
     neuroblastomas. 
     As used herein, references to cancerous cells and the like will include references to a cell afflicted by any one of the above identified conditions. 
     More particular cancers that may be mentioned include those corresponding to the cell lines used in the examples provided herein. 
     For example, particular cancers that may be mentioned include breast cancer (such as mammary adenocarcinoma, e.g. metastatic mammary adenocarcinoma) and/or glioblastoma (such as glioblastoma multiform). 
     More particular cancers that may be mentioned include: 
     head and neck cancer (such as throat cancer, e.g. pharyngeal squamous cell carcinoma); 
     colon cancer (such as colorectal carcinoma); 
     skin cancer (such as epidermoid (skin) carcinoma); 
     gastrointestinal cancers (such as pancreatic cancer, e.g. pancreatic ductal carcinoma); 
     breast cancer (such as mammary adenocarcinoma, e.g. metastatic mammary adenocarcinoma); 
     lung cancer (such as carcinoma); and 
     haematologic cancers (such as leukemia, e.g. acute monocytic leukemia). 
     In particular embodiments, the cancer is a solid tumor cancer. 
     In more particular embodiments, the cancer is selected from pancreatic cancer, ovarian cancer and colorectal cancer. 
     For example, in certain embodiments, the cancer is selected from colorectal cancer (including those processing Ras mutations), small cell lung cancer, non-small cell lung cancer (NSCLC), and glioma. 
     In other embodiments, the cancer is selected from non-small cell lung cancer, ovarian cancer, metastatic breast cancer, pancreatic cancer, hepatobiliary cancer (including hepatocellular cancer, bile duct cancer and cholangiocarcinoma), and gastric cancer. 
     In further embodiments, the cancer is selected from colorectal cancer (including Ras mutations), small cell lung cancer, non-small cell lung cancer, ovarian cancer, hepatobiliary cancer (including hepatocellular cancer, bile duct cancer and cholangiocarcinoma), gastric cancer, testicular cancer, and head and neck squamous cell carcinoma. 
     In certain embodiments of the present invention, the cancer is selected from leukemia (including acute myeloid leukemia, acute lymphoblastic leukemia, chronic myeloid leukemia, and chronic lymphoid leukemia), lymphoma (including mantle cell lymphoma, Hodgkin&#39;s lymphoma and non-Hodgkin&#39;s lymphoma), and prostate cancer 
     The skilled person will understand that treatment with compounds of the invention may further comprise (i.e. be combined with) further treatment(s) for the same condition. In particular, treatment with compounds of the invention may be combined with means for the treatment of cancer, such as treatment with one or more other therapeutic agent that is useful in the in the treatment of cancer and/or one or more physical method used in the treatment of cancer (such as treatment through surgery), as known to those skilled in the art. 
     In particular, treatment with compounds of the invention may be performed in patients who are being or have been (i.e. as part or of a treatment for the same condition, such as within a month of treatment with compounds of the invention, such as within two weeks, e.g. within a week or, particularly, on the same day) treated with a therapeutic agent or physical method that is capable of causing (e.g. can be demonstrated to cause) an increase in reactive oxygen species. 
     For the avoidance of doubt, the skilled person will understand that therapeutic agents or physical methods capable of causing (e.g. can be demonstrated to cause) an increase in reactive oxygen species may not necessarily be effective treatments per se, but will become effective when used in combination with compounds of the invention. 
     For the avoidance of doubt, the skilled person will understand that compounds of the invention may also be used in combination with one or more other therapeutic agent that is useful in the in the treatment of cancer and/or one or more physical method used in the treatment of cancer (such as treatment through surgery) wherein such methods do not cause an increase in reactive oxygen species. 
     In particular, treatment with compounds of the invention may be performed in patients who are being or have been treated with radiotherapy. 
     Thus, there is also provided: 
     a method of treating cancer in a patient in need thereof wherein the patient is administered a therapeutically effective amount of a compound of the invention in combination with treatment by radiotherapy (i.e. concomitantly or sequentially); and 
     a compound of the invention for use in treating cancer in a patient who is also being treated with radiotherapy. 
     Compounds of the invention will normally be administered orally, intravenously, subcutaneously, buccally, rectally, dermally, nasally, tracheally, bronchially, sublingually, intranasally, topically, by any other parenteral route or via inhalation, in a pharmaceutically acceptable dosage form. 
     Compounds of the invention may be administered alone or may be administered by way of known pharmaceutical compositions/formulations, including tablets, capsules or elixirs for oral administration, suppositories for rectal administration, sterile solutions or suspensions for parenteral or intramuscular administration, and the like. 
     According to a fourth aspect of the invention there is thus provided a pharmaceutical composition/formulation comprising a compound of the invention as hereinbefore defined (i.e. in the first aspect of the invention, including all embodiments and particular features therein, but without the provisos), and optionally (e.g. in admixture with) one or more pharmaceutically acceptable adjuvant, diluent and/or carrier. 
     In a particular embodiment of the fourth aspect of the invention, the compound of the invention is a compound of the first aspect of the invention (i.e. including the provisos). 
     The skilled person will understand that references herein to compounds of the invention being for particular uses (and, similarly, to uses and methods of use relating to compounds of the invention) may also apply to pharmaceutical compositions comprising compounds of the invention as described herein. 
     Compounds of the invention may be administered in the form of tablets or capsules, e.g. time-release capsules that are taken orally. Alternatively, the compounds of the invention may be in a liquid form and may be taken orally or by injection. The compounds of the invention may also be in the form of suppositories, or, creams, gels, and foams e.g. that can be applied to the skin. In addition, they may be in the form of an inhalant that is applied nasally or via the lungs. 
     The skilled person will understand that compounds of the invention may act systemically and/or locally (i.e. at a particular site). 
     Compounds of the invention may be administered orally, intravenously, subcutaneously, buccally, rectally, dermally, nasally, tracheally, bronchially, by any other parenteral route or via inhalation, in a pharmaceutically acceptable dosage form. Alternatively, particularly where compounds of the invention are intended to act locally, compounds of the invention may be administered topically. 
     Thus, in a particular embodiment, the pharmaceutical formulation is provided in a pharmaceutically acceptable dosage form, including tablets or capsules, liquid forms to be taken orally or by injection, suppositories, creams, gels, foams, or inhalants (e.g. to be applied intranasally). For the avoidance of doubt, in such embodiments, compounds of the invention may be present as a solid (e.g. a solid dispersion), liquid (e.g. in solution) or in other forms, such as in the form of micelles. 
     In more particular embodiments, the pharmaceutical formulation is provided the form of a tablets or capsules, liquid forms to be taken orally or by injection (e.g. a form suitable for intravenous injection). In particular, injection may take place using conventional means, and may include the use of microneedles. 
     Depending on e.g. potency and physical characteristics of the compound of the invention (i.e. active ingredient), pharmaceutical formulations that may be mentioned include those in which the active ingredient is present in at least 1% (or at least 10%, at least 30% or at least 50%) by weight. That is, the ratio of active ingredient to the other components (i.e. the addition of adjuvant, diluent and carrier) of the pharmaceutical composition is at least 1:99 (or at least 10:90, at least 30:70 or at least 50:50) by weight. 
     As described herein, compounds of the invention may also be combined with one or more other (i.e. different, e.g. agents other than compounds of formula I) therapeutic agents that are useful in the treatment of cancer. Such combination products that provide for the administration of a compound of the invention in conjunction with one or more other therapeutic agent may be presented either as separate formulations, wherein at least one of those formulations comprises a compound of the invention, and at least one comprises the other therapeutic agent, or may be presented (i.e. formulated) as a combined preparation (i.e. presented as a single formulation including a compound of the invention and the one or more other therapeutic agent). 
     Thus, according to a fifth aspect of the invention, there is provided a combination product comprising: 
     (A) a compound of the invention as hereinbefore defined (i.e. in the first aspect of the invention, including all embodiments and particular features therein, but without the provisos); and 
     (B) one or more other therapeutic agent that is useful in the treatment of cancer, wherein each of components (A) and (B) is formulated in admixture, optionally with one or more a pharmaceutically-acceptable adjuvant, diluent or carrier. 
     In a sixth aspect of the invention there is provided a kit-of-parts comprising: 
     (a) a pharmaceutical formulation as hereinbefore defined (i.e. in the fourth aspect of the invention); and 
     (b) one or more other therapeutic agent that is useful in the treatment of cancer, optionally in admixture with one or more pharmaceutically-acceptable adjuvant, diluent or carrier, 
     which components (a) and (b) are each provided in a form that is suitable for administration in conjunction (i.e. concomitantly or sequentially) with the other. 
     In particular embodiments of the fourth and fifth aspects of the invention, the compound of the invention is a compound of the first aspect of the invention (i.e. including the provisos). 
     The skilled person will understand that compounds of the invention, and pharmaceutically-acceptable salts thereof, may be administered (for example, as formulations as described hereinabove) at varying doses, with suitable doses being readily determined by one of skill in the art. Oral, pulmonary and topical dosages (and subcutaneous dosages, although these dosages may be relatively lower) may range from between about 0.01 μg/kg of body weight per day (μg/kg/day) to about 200 μg/kg/day, preferably about 0.01 to about 10 μg/kg/day, and more preferably about 0.1 to about 5.0 μg/kg/day. For example, when administered orally, treatment with such compounds may comprise administration of a formulations typically containing between about 0.01 μg to about 2000 mg, for example between about 0.1 μg to about 500 mg, or between 1 μg to about 100 mg (e.g. about 20 μg to about 80 mg), of the active ingredient(s). When administered intravenously, the most preferred doses will range from about 0.001 to about 10 μg/kg/hour during constant rate infusion. Advantageously, treatment may comprise administration of such compounds and compositions in a single daily dose, or the total daily dosage may be administered in divided doses of two, three or four times daily (e.g. twice daily with reference to the doses described herein, such as a dose of 10 mg, 20 mg, 30 mg or 40 mg twice daily). 
     In any event, the physician, or the skilled person, will be able to determine the actual dosage which will be most suitable for an individual patient, which is likely to vary with the route of administration, the type and severity of the condition that is to be treated, as well as the species, age, weight, sex, renal function, hepatic function and response of the particular patient to be treated. The above-mentioned dosages are exemplary of the average case; there can, of course, be individual instances where higher or lower dosage ranges are merited, and such are within the scope of this invention. 
     Preparation of Compounds/Compositions 
     Pharmaceutical compositions/formulations, combination products and kits as described herein may be prepared in accordance with standard and/or accepted pharmaceutical practice. 
     Thus, in a further aspect of the invention there is provided a process for the preparation of a pharmaceutical composition/formulation, as hereinbefore defined, which process comprises bringing into association a compound of the invention, as hereinbefore defined, with one or more pharmaceutically-acceptable adjuvant, diluent or carrier. 
     In further aspects of the invention, there is provided a process for the preparation of a combination product or kit-of-parts as hereinbefore defined, which process comprises bringing into association a compound of the invention, as hereinbefore defined, or a pharmaceutically acceptable salt thereof with the other therapeutic agent that is useful in the treatment of cancer, and at least one pharmaceutically-acceptable adjuvant, diluent or carrier. 
     As used herein, references to bringing into association will mean that the two components are rendered suitable for administration in conjunction with each other. 
     Thus, in relation to the process for the preparation of a kit of parts as hereinbefore defined, by bringing the two components “into association with” each other, we include that the two components of the kit of parts may be: 
     (i) provided as separate formulations (i.e. independently of one another), which are subsequently brought together for use in conjunction with each other in combination therapy; or 
     (ii) packaged and presented together as separate components of a “combination pack” for use in conjunction with each other in combination therapy. 
     Compounds of the invention as described herein may be prepared in accordance with techniques that are well known to those skilled in the art, such as those described in the examples provided hereinafter. 
     According to a seventh aspect of the invention there is provided a process for the preparation of a compound of the first aspect of the invention as hereinbefore defined (i.e. a compound of the invention but including the provisos), which process comprises: 
     (i) where n represents 2, reaction of a compound of formula IIA 
                         
wherein R 1 , R 2  and R 3  are as defined herein (i.e. for compounds of the invention, or any particular feature or embodiment thereof) and LG 1  represents a suitable leaving group (such as halo, e.g. chloro), with a compound of formula IIIA
 
                         
wherein X is as defined herein (i.e. for compounds of the invention, or any particular feature or embodiments thereof) and M represents an alkali metal ion (such as a Na ion), in the presence of a suitable acid (such as a concentrated acid, e.g. a concentrated mineral acid, for example concentrated HCl, e.g. concentrated aqueous HCl) and in the presence of a suitable solvent (such as a polar organic solvent, e.g. N,N′-dimethylacetamide, N,N′-dimethylformamide or tetrahydrofuran), and optionally in the presence of a suitable phase transfer catalyst (such as a quaternary ammonium salt, e.g. tetra-butyl ammonium chloride);
 
     (ii) where n represents 2, particularly where at least one Y is present and represents an electron-withdrawing group (such as —NO 2 ), reaction of a compound of formula IIB 
                         
wherein R 1 , R 2  and R 3  are as defined herein (i.e. for compounds of the invention, or any particular feature or embodiments thereof) and M represents an alkali metal ion (such as a Na ion), with a compound of formula IIIB
 
                         
wherein X is as defined herein in formula I (i.e. for compounds of the invention, or any particular feature or embodiments thereof) and LG 2  represents a suitable leaving group (such as halo, e.g. chloro), in the presence of a suitable acid (such as a concentrated acid, e.g. a concentrated mineral acid, for example concentrated HCl, e.g. concentrated aqueous HCl) and in the presence of a suitable solvent (such as a polar organic solvent, e.g. N,N′-dimethylacetamide, N,N′-dimethylformamide or tetrahydrofuran), and optionally in the presence of a suitable phase transfer catalyst (such as a quaternary ammonium salt, e.g. tetra-butyl ammonium chloride);
 
     (iii) where n represents 2, reaction of a compound of formula IIA as hereinbefore defined with a compound of formula IIIA as hereinbefore defined, in the presence of a suitable metal halide (such as a suitable metal iodide, e.g. CuI, or a suitable metal bromide, e.g. CuBr; which metal halide may be present in excess, such as in amount corresponding to at least 2 molar equivalents of the compound of formula IIA and/or the compound of formula IIIA) and in the presence of a suitable solvent (such as a polar organic solvent, e.g. N,N′-dimethylacetamide, N,N′-dimethylformamide, tetrahydrofuran or 3-dimethyl-2-imidazolidinone), under conditions known to those skilled in the art; 
     (iv) where n represents 2, reaction of a compound of formula IIB as hereinbefore defined (particularly where at least one R 4  is present and represents an electron-withdrawing group, such as —NO 2 ) with a compound of formula IIIB as hereinbefore defined, in the presence of a suitable metal halide (such as a suitable metal iodide, e.g. CuI, or a suitable metal bromide, e.g. CuBr; which metal halide may be present in excess, such as in amount corresponding to at least 2 molar equivalents of the compound of formula IIB and/or the compound of formula IIIB) and in the presence of a suitable solvent (such as a polar organic solvent, e.g. N,N′-dimethylacetamide, N,N′-dimethylformamide, tetra-hydrofuran or 3-dimethyl-2-imidazolidinone), under conditions known to those skilled in the art; 
     (v) reaction of a compound of formula IV 
                         
wherein R 1  to R 3  and X are as defined herein (i.e. for compounds of the invention, or any particular feature or embodiments thereof), with a suitable oxidising agent (i.e. an oxidising agent chosen and used in a manner as required to achieved the desired degree of oxidation; such as a hypochlorite salt, e.g. sodium hypochlorite, a peroxymonosulfate salt, e.g. potassium peroxymonosulfate (Oxone), a percarboxylic acid, e.g. meta-chloroperoxybenzoic add (mCPBA), or potassium permanganate) in the presence of a suitable solvent (such as a polar organic solvent, e.g. N,N′-dimethylacetamide, N,N′-dimethylformamide or terahydrofuran), and optionally in the presence of water, under conditions known to those skilled in the art;
 
     (vi) where n represents 2, particularly where one or more Y is present and represents an electron donating group (such as an alkyl group), reaction of a compound of formula V 
                         
wherein R 1 , R 2  and R 3  are as defined herein (i.e. for compounds of the invention, or any particular feature or embodiments thereof) and LG 3  represents a suitable leaving group (such as halo, e.g. chloro) with a compound of formula VI
 
                         
wherein X is as defined (i.e. for compounds of the invention, or any particular feature or embodiments thereof), in the presence of a suitable Lewis acid (such as AlCl 3 ) and in the presence of a suitable solvent (such as an organic solvent, e.g. dichloromethane or dichloroethane);
 
     (vii) where n represents 2, reaction of a compound of formula V as defined herein with a compound of formula VI as defined herein (for example, where one or more Y group is present in the alpha position relative to the point of attachment to the sulfonyl group and represents a suitable directing group), in the presence of a suitable catalyst (such as palladium(II) acetate) and a suitable base (such as a alkali metal carbonate, e.g. potassium carbonate), and in the presence of a suitable solvent (such as an organic solvent, e.g. dichloromethane); 
     (viii) where n represents 2, reaction of a compound of formula V as defined herein with a compound of formula VII 
                         
wherein X is as defined herein (i.e. for compounds of the invention, or any particular feature or embodiments thereof) and LG 4  represents a suitable leaving group (such as a boronic acid), in the presence of a suitable catalyst (such as a suitable metal halide, e.g. CuBr, or phenanthroline) and in the presence of a suitable solvent (such as an organic solvent, e.g. dichloromethane or dichloroethane); or
 
     (ix) where n represents 2, reaction of a compound of formula IIB as defined herein with (a) a compound of formula VI as defined herein having at least one Y group, or (b) a compound of formula VI as defined herein but having a group that may be converted to a Y group, wherein the Y group or group that may be converted to a Y group is present in the alpha position relative to the essential H substituent and represents a suitable directing group (such as a suitable amide, e.g. —C(O)N(H)C(CH 3 ) 2 -2-pyridinyl), in the presence of a suitable catalyst and/or oxidant (such as copper(II) acetate and/or silver carbonate), and in the presence of a suitable solvent (such as an organic solvent, e.g. dichloroethane), which step may further comprise conversion of the group that may be converted to a Y group to the required Y group, under conditions known to those skilled in the art. 
     Compounds of formulae IIA, IIB, IIIA, IIIB, IV, V, VI and VII are either commercially available, are known in the literature, or may be obtained either by analogy with the processes described herein, or by conventional synthetic procedures, in accordance with standard techniques, from available starting materials using appropriate reagents and reaction conditions. In this respect, the skilled person may refer to inter alia “ Comprehensive Organic Synthesis ” by B. M. Trost and I. Fleming, Pergamon Press, 1991. Further references that may be employed include “ Heterocyclic Chemistry ” by J. A. Joule, K. Mills and G. F. Smith, 3 rd  edition, published by Chapman &amp; Hall, “ Comprehensive Heterocyclic Chemistry II ” by A. R. Katritzky, C. W. Rees and E. F. V. Scriven, Pergamon Press, 1996 and “ Science of Synthesis ”, Volumes 9-17 (Hetarenes and Related Ring Systems), Georg Thieme Verlag, 2006. 
     In particular, compounds of formula IV may be prepared by reaction of a compound of formula VIII 
                         
wherein X is as defined herein (i.e. for compounds of the invention, or any particular feature or embodiments thereof), with a compound of formula IIA as herein before defined, under conditions known to those skilled in the art, such as in the presence of a suitable base (such as a metal carbonate, e.g. potassium carbonate, a metal hydroxide, e.g. sodium hydroxide, or an amine base, e.g. triethyl amine), and in the presence of a suitable solvent (such as a polar organic solvent, e.g. N,N′-dimethylacetamide, N,N′-dimethylformamide or tetrahydrofuran, or a mixture of a polar organic solvent and water), under conditions known to those skilled in the art.
 
     Similarly, compounds of formula IV (particularly where at least one Y is present and represents an electron-withdrawing group, such as —NO 2 ) may be prepared by reaction of a compound of formula IX 
                         
wherein R 1 , R 2  and R 3  are as defined herein (i.e. for compounds of the invention, or any particular feature or embodiments thereof), with a compound of formula IIIB as described herein, under conditions known to those skilled in the art (for example, where the R 4  groups present in the compound of formula IIIB are not sufficiently electron withdrawing, the reaction may be performed in the presence of a suitable catalyst, such as palladium(II) acetate or copper oxide, in which case the suitable base may be an alkali metal tert-butoxide, such as Kt-OBu).
 
     Similarly, compounds of formulae VIII and IX are either commercially available, are known in the literature, or may be obtained either by analogy with the processes described herein, or by conventional synthetic procedures, in accordance with standard techniques, from available starting materials using appropriate reagents and reaction conditions. 
     The substituents R 1  to R 3  and Y (or, when the compound of formula I is defined as a compound of formula Ia, the substituents R 1  to R 9 ), as hereinbefore defined, may be modified one or more times, after or during the processes described above for preparation of compounds of formula I (including compounds of formula Ia) by way of methods that are well known to those skilled in the art. Examples of such methods include substitutions, reductions, oxidations, dehydrogenations, alkylations, dealkylations, acylations, hydrolyses, esterifications, etherifications, halogenations and nitrations. The precursor groups can be changed to a different such group, or to the groups defined in formula I, at any time during the reaction sequence. The skilled person may also refer to “ Comprehensive Organic Functional Group Transformations ” by A. R. Katritzky, O. Meth-Cohn and C. W. Rees, Pergamon Press, 1995 and/or “ Comprehensive Organic Transformations ” by R. C. Larock, Wiley-VCH, 1999. 
     Compounds of the invention may be isolated from their reaction mixtures and, if necessary, purified using conventional techniques as known to those skilled in the art. Thus, processes for preparation of compounds of the invention as described herein may include, as a final step, isolation and optionally purification of the compound of the invention. 
     It will be appreciated by those skilled in the art that, in the processes described above and hereinafter, the functional groups of intermediate compounds may need to be protected by protecting groups. The protection and deprotection of functional groups may take place before or after a reaction in the above-mentioned schemes. 
     Protecting groups may be applied and removed in accordance with techniques that are well known to those skilled in the art and as described hereinafter. For example, protected compounds/intermediates described herein may be converted chemically to unprotected compounds using standard deprotection techniques. The type of chemistry involved will dictate the need, and type, of protecting groups as well as the sequence for accomplishing the synthesis. The use of protecting groups is fully described in “ Protective Groups in Organic Synthesis”,  3rd edition, T. W. Greene &amp; P. G. M. Wutz, Wiley-Interscience (1999). 
     In a further aspect of the invention, there is provided a compound of formula IV as defined herein (i.e. wherein R 1 , R 2 , R 3  and X are as defined herein, including all particular features and embodiments thereof), or a pharmaceutically acceptable salt thereof. 
     Particular compounds of formula IV that may be mentioned include those prepared in the examples provided herein, and pharmaceutically acceptable salts thereof. 
     Compounds of the invention may have the advantage that they may be more efficacious than, be less toxic than, be longer acting than, be more potent than, produce fewer side effects than, be more easily absorbed than, and/or have a better pharmacokinetic profile (e.g. higher oral bioavailability and/or lower clearance) than, and/or have other useful pharmacological, physical, or chemical properties over, compounds known in the prior art, whether for use in the above-stated indications or otherwise. In particular, compounds of the invention may have the advantage that they are more efficacious and/or exhibit advantageous properties in vivo. 
     Without wishing to be bound by theory, it is thought that inhibition of thioredoxin reductase is obtained by the utilization of strong electrophilicity of small molecule inhibitors in combination with a pronounced inherent nucleophilicity of NADPH-reduced, but not oxidized, thioredoxin reductase, resulting in selective and potent inhibition of said enzyme without major targeting of other cellular pathways or enzymes. 
     Moreover, it is thought that normal non-cancerous cells may survive without a functional cytosolic thioredoxin reductase enzyme because of maintained function of the glutathione system, while cancer cells cannot survive upon specific inhibition of cytosolic thioredoxin reductase. 
     EXAMPLES 
     The invention is illustrated by way of the following examples, in which the following abbreviations may be employed.
     aq aqueous   BSA bovine serum albumin   conc concentrated   DMA N,N′-dimethylacetamide   DMF N,N′-dimethylformamide   DMSO dimethyl sulfoxide   DTNB 5,5′-dithio-bis-(2-nitrobenzoic acid)   EDTA ethylenediaminetetraacetic add   GSSG glutathione disulfide   HPLC high performance liquid chromatography   HRMS high resolution mass spectrometry   mCPBA meta-chloroperbenzoic acid   NADPH nicotinamide adenine dinucleotide phosphate   NMR nuclear magnetic resonance   PBS phosphate buffered saline   rt room temperature   

     Starting materials and chemical reagents specified in the syntheses described below are commercially available from a number of suppliers, such as Sigma Aldrich. 
     In the event that there is a discrepancy between nomenclature and the structure of compounds as depicted graphically, it is the latter that presides (unless contradicted by any experimental details that may be given and/or unless it is clear from the context). The names of the final compounds may be translated to the structures e.g. using ChemBioDraw Ultra 14. 
     Example 1: 6-Methoxy-3-nitro-2-(pyridin-2-ylsulfonyl)pyridine 
     
       
         
         
             
             
         
       
     
     (a) 6-Methoxy-3-nitro-2-(pyridin-2-ylthio)pyridine 
     A mixture of 2-chloro-6-methoxy-3-nitropyridine (0.25 g, 1.33 mmol), 2-mercaptopyridine (0.16 g, 1.46 mmol), K 2 CO 3  (0.22 g, 1.62 mmol) and DMF (1 mL) was stirred at rt for 0.5 h. The mixture was poured into water and filtered to give the sub-title compound (0.34 g, 98%). 
     (b) 6-Methoxy-3-nitro-2-(pyridin-2-ylsulfonyl)pyridine 
     NaOCl (aq, 10%, 1.71 mL, 2.86 mmol) was added dropwise to a stirred mixture of 6-methoxy-3-nitro-2-(pyridin-2-ylthio)pyridine (0.34 g, 1.30 mmol), glacial acetic acid (0.10 mL, 1.67 mmol) and DMF (1 mL) at rt. The mixture was stirred at rt for 4 h and poured into water. The pH was adjusted to ˜9 with aq NaOH (20% (w/v)). After stirring for 30 seconds the precipitate was collected and washed with water. The solid was recrystallized from H 2 O/EtOH (4:1) to give the title compound (0.12 g, 31%). 
       1 H NMR (400 MHz, CDCl 3 ) δ8.74-8.67 (1H, m), 8.31-8.24 (2H, m), 8.08-8.00 (1H, m), 7.61-7.54 (1H, m), 7.01-6.96 (1H, m), 3.65 (3H, s); 
       13 C-NMR (100 MHz, CDCl 3 ) δ164.2, 157.4, 150.3, 150.2, 138.1, 136.9, 127.5, 124.0, 115.3, 55.2; 
     ESI-MS: 296 [M+H] + . 
     Example 2: 6-Chloro-3-nitro-2-(pyridin-2-ylsulfonyl)pyridine 
     
       
         
         
             
             
         
       
     
     (a) 6-Chloro-5-nitropyridin-2-amine 
     
       
         
         
             
             
         
       
     
     Conc. HNO 3  (2.39 mL, 35.00 mmol) was added dropwise to a mixture of conc H 2 SO 4  (56 mL, 1050 mmol) and 6-chloropyridin-2-amine (3.00 g, 23.34 mmol) at 0° C. The mixture was stirred at 0° C. for 4 h and poured into ice-water. The mixture was extracted with EtOAc (3×100 mL). The combined organic layers were dried over anhydrous Na 2 SO 4  and concentrated. The residue was purified by chromatography to give the sub-title compound (1.38 g, 34%). 
     (b) 5-Nitro-6-(pyridin-2-ylthio)pyridin-2-amine 
     
       
         
         
             
             
         
       
     
     A mixture of 6-chloro-5-nitropyridin-2-amine (0.26 g, 1.50 mmol), 2-mercaptopyridine (0.18 g, 1.65 mmol), K 2 CO 3  (0.25 g, 1.83 mmol) and DMF (2.1 mL) was stirred at 80° C. for 3.5 h. The mixture was poured into water and extracted with CH 2 Cl 2  (3×15 mL). The combined organic layers were dried over anhydrous Na 2 SO 4  and concentrated. The residue was dissolved in CH 2 Cl 2 , and the product was precipitated by addition of hexane to give the sub-title compound (0.27 g, 73%). 
     (c) 6-Chloro-3-nitro-2-(pyridin-2-ylthio)pyridine 
     
       
         
         
             
             
         
       
     
     Isoamylnitrite (0.26 mL, 1.93 mmol) was added to a stirred mixture of 5-nitro-6-(pyridin-2-ylthio)pyridin-2-amine (0.24 g, 0.97 mmol), CuCl 2  (0.26 g, 1.93 mmol) and MeCN (5 mL) at rt. The mixture was stirred at 60° C. for 14 h, poured into acidic water (1N HCl, 4 mL) and extracted with EtOAc (3×15 mL). The combined organic layers were washed with saturated aq NaHCO 3  (10 mL), brine (10 mL) and dried over anhydrous Na 2 SO 4  and concentrated. The residue was purified by chromatography to give the sub-title compound (0.08 g, 32%). 
     (d) 6-Chloro-3-nitro-2-(pyridin-2-ylsulfonyl)pyridine 
     mCPBA (0.17 g, 0.67 mmol) was added in portions to a stirred mixture of 6-chloro-3-nitro-2-(pyridin-2-ylthio)pyridine (0.08 g, 0.31 mmol) and CH 2 Cl 2  (8 mL) at 0° C. The mixture was stirred at rt for 14 h and poured into saturated aq Na 2 S 2 O 3  (3 mL) at 0° C. The phases were separated and the organic layer extracted with saturated aq NaHCO 3  (2×5 mL) and brine (5 mL). The organic phase was dried over anhydrous Na 2 SO 4  and concentrated. The crude mixture was purified by chromatography to give the title compound (0.03 g, 29%). 
       1 H NMR (400 MHz, CDCl 3 ) δ8.67 (ddd, J=4.7, 1.7, 0.9 Hz, 1H), 8.27 (dt, J=7.9, 1.0 Hz, 1H), 8.24 (d, J=8.4 Hz, 1H), 8.06 (td, J=7.8, 1.7 Hz, 1H), 7.70 (d, J=8.4 Hz, 1H), 7.59 (ddd, J=7.7, 4.7, 1.1 Hz, 1H); 
       13 C-NMR (100 MHz, CDCl 3 ) δ 156.7, 153.7, 150.6, 150.3, 144.5, 138.3, 136.1, 129.2, 128.0, 123.8; 
     ESI-MS: 300 [M+H] + . 
     Example 3: 6-Dimethylamino-3-nitro-2-(pyridin-2-ylsulfonyl)pyridine 
     
       
         
         
             
             
         
       
     
     (a) 6-Chloro-N,N-dimethylpyridin-2-amine 
     
       
         
         
             
             
         
       
     
     A mixture of 2,6-dichloropyridine (2.20 g, 14.9 mmol) and DMF (11.5 mL, 148.7 mmol) was heated under microwave irradiation at 180° C. for 1 h. The mixture was poured into water and extracted with EtOAc (3×30 mL). The combined organic phases were dried over anhydrous Na 2 SO 4  and concentrated. The residue was purified by chromatography to give the sub-title compound (2.12 g, 91%). 
     (b) 6-Chloro-N,N-dimethyl-5-nitropyridin-2-amine 
     
       
         
         
             
             
         
       
     
     Conc HNO 3  (0.9 mL, 13.52 mmol) was added dropwise to a mixture of conc H 2 SO 4  (32.4 mL, 608.6 mmol) and 6-chloro-N,N-dimethylpyridin-2-amine (2.12 g, 13.5 mmol) at 0° C. The mixture was stirred at 0° C. for 1.5 h and poured into ice-water. The mixture was extracted with CH 2 Cl 2  (3×100 mL). The combined organic layers were washed with saturated aq Na 2 CO 3 , dried over anhydrous Na 2 SO 4  and concentrated. The residue was purified by chromatography to give the sub-title compound (0.89 g, 33%). 
     (c) N,N-Dimethyl-5-nitro-6-(pyridin-2-ylthio)pyridin-2-amine 
     
       
         
         
             
             
         
       
     
     A mixture of 6-chloro-N,N-dimethyl-5-nitropyridin-2-amine (0.11 g, 0.55 mmol), 2-mercaptopyridine (0.07 mg, 0.61 mmol), K 2 CO 3  (0.09 g, 0.67 mmol) and DMF (1 mL) was stirred at 80° C. for 1 h. The mixture was poured into water (150 mL), the precipitate was collected, washed with water and dried to give the sub-title compound (0.12 g, 76%). 
     (d) 6-Dimethylamino-3-nitro-2-(pyridin-2-ylsulfonyl)pyridine 
     mCPBA (0.22 g, 0.92 mmol) was added in portions to a stirred mixture of N,N-dimethyl-5-nitro-6-(pyridin-2-ylthio)pyridin-2-amine (0.12 g, 0.42 mmol) and CH 2 Cl 2  (8 mL) at 0° C. The mixture was stirred at rt for 5 h and poured into saturated aq K 2 CO 3  (5 mL). The phases were separated and the aq layer extracted with CH 2 Cl 2 . The combined organic phases were washed with saturated aq Na 2 S 2 O 5  and NaHSO 3  mixture, dried over anhydrous Na 2 SO 4  and concentrated. The residue was recrystallized from H 2 O/EtOH (1:9) and additionally purified by chromatography to give the title compound (0.06 g, 44%). 
       1 H NMR (400 MHz, CDCl 3 ) δ8.74-8.68 (1H, m), 8.27-8.23 (1H, m), 8.21 (1H, d, J=9.4 Hz), 8.03-7.96 (1H, m), 7.55-7.49 (1H, m), 6.54 (1H, d, J=9.4 Hz), 2.90 (6H, br s); 
       13 C-NMR (100 MHz, CDCl 3 ) δ 158.2, 157.9, 152.4, 149.9, 137.8, 136.0, 126.9, 124.0, 107.2, 38.2; 
     ESI-MS: 309 [M+H] + . 
     The following example compounds where prepared from 2-chloro-6-methoxy-3-nitropyridine and the appropriate heteroarylthiol in accordance with the procedure in Example 1, Step a, and Example 2, Step d. 
     
       
         
           
               
               
               
            
               
                   
               
               
                   
                 Chemical structure 
                 MS [m/z (M + H) + ]  
               
            
           
           
               
               
            
               
                   
                 Name 
               
               
                   
                   1 H-NMR [solvent, δ] 
               
               
                 Ex. 
                   13 C-NMR [solvent, δ] 
               
               
                   
               
            
           
           
               
               
               
            
               
                 4 
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 MS [m/z (M + H) +  =  (Calculated for C 11 H 9 N 3 O 5 S + H: 296.04) found: 296.1] 
               
               
                   
               
            
           
           
               
               
            
               
                   
                 6-methoxy-3-nitro-2-(pyridin-4-ylsulfonyl)pyridine 
               
               
                   
                   1 H-NMR [DMSO-d 6 , δ 8.51 (d, J = 8 Hz, 1H), 8.29 (d, J = 7 
               
               
                   
                 Hz, 2H), 7.82 (d, J = 7 Hz, 2H), 7.16 (d, J = 8 Hz, 1H), 4.09  
               
               
                   
                 (s, 3H)] 
               
               
                   
               
            
           
           
               
               
               
            
               
                 5 
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 MS [m/z (M + H) +  =  (Calculated for C 10 H 8 N 4 O 5 S + H: 297.03) found: 297.1] 
               
               
                   
               
            
           
           
               
               
            
               
                   
                 2-((6-methoxy-3-nitropyridin-2-yl)sulfonyl)pyrimidine 
               
               
                   
                   1 H-NMR [CDCl 3 , δ 8.93 (d, J = 5 Hz, 2H), 8.38 (d, J = 9 Hz,  
               
               
                   
                 1H), 7.55 (t, J = 5 Hz, 1H), 7.06 (d, J = 9 Hz, 1H), 3.87 (s, 3H)] 
               
               
                   
               
            
           
           
               
               
               
            
               
                 6 
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 MS [m/z (M + H) +  =  (Calculated for C 9 H 8 N 4 O 5 S + H: 285.03) found: 385.1] 
               
               
                   
               
            
           
           
               
               
            
               
                   
                 2-((1H-imidazol-2-yl)sulfonyl)-6-methoxy-3-nitropyridine 
               
               
                   
                   1 H-NMR [DMSO-d 6 , δ 14.09 (s, 1H), 8.54 (d, J = 9 Hz, 1H),  
               
               
                   
                 7.63-7.28 (m, 3H), 3.55 (s, 3H)] 
               
               
                   
               
            
           
           
               
               
               
            
               
                 7 
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 MS [m/z (M + H) +  =  (Calculated for C 10 H 9 N 3 O 5 S 2  + H: 316.01) found: 315.8] 
               
               
                   
               
            
           
           
               
               
            
               
                   
                 2-((6-methoxy-3-nitropyridin-2-yl)sulfonyl)-4-methylthiazole 
               
               
                   
                   1 H-NMR [CDCl 3 , δ 8.30 (d, J = 9 Hz, 1H), 7.41 (s, 1H), 6.98  
               
               
                   
                 (d, J = 9 Hz, 1H), 3.60 (s, 3H), 2.55 (s, 3H)] 
               
               
                   
               
            
           
         
       
     
     Example 8: 6-Methoxy-3-nitro-2-(pyridin-2-ylsufinyl)-pyridine 
     
       
         
         
             
             
         
       
     
     (a) 6-Methoxy-3-nitro-2-(pyridin-2-ylsulfanyl)-pyridine 
     
       
         
         
             
             
         
       
     
     To a solution of 6-methoxy-2-chloro-3-nitro pyridine (5 g, 26.59 mmol) in dimethylformamide (50 mL) was added potassium carbonate (4.40 g, 31.91 mmol) and 2-mercapto pyridine (3.62 g, 29.25 mmol) at room temperature. The reaction mixture was stirred overnight at room temperature. Progress of reaction was monitored by LCMS. The reaction mixture was quenched with ice cold water (10 mL) and was extracted with ethyl acetate (100 mL). The organic layer was washed with water (3×20 mL) followed by brine (1×30 mL). The organic layer was dried over anhydrous sodium sulphate and was evaporated under reduced pressure to give the crude product which was purified by column chromatography eluting with 5% ethyl acetate in hexane affording the sub-title compound as yellow solid (3 g, 42.85%). 
       1 H NMR (CDCl 3 , 400 MHz) δ 8.72 (d, J=3.4 Hz, 1H), 8.39 (d, J=8.9 Hz, 1H), 7.79-7.75 (m, 1H), 7.68 (d, J=7.7 Hz, 1H), 7.35-7.33 (m, 1H), 6.49 (d, J=9.0 Hz, 1H), 3.32 (s, 3H); LCMS [m/z (M+H) + ] 264 (MW calc=263), R t =1.83 
     (b) 6-methoxy-3-nitro-2-(pyridin-2-ylsufinyl)-pyridine 
     To a solution of 6-methoxy-3-nitro-2-(pyridin-2-ylsulfanyl)-pyridine (1.5 g, 57.03 mmol) in dichloromethane (30 mL) was added m-chloroperbenzoic acid (1.47 g, 85.55 mmol) at room temperature. The reaction mixture was stirred at room temperature overnight. Progress of reaction was monitored by LCMS. The reaction mixture was diluted with dichloromethane (20 mL) and washed with saturated sodium sulphite solution (2×20 mL) followed by brine (1×20 mL). The organic layer was dried over anhydrous sodium sulphate and was evaporated under reduced pressure to give the crude product which was purified by column chromatography eluting with 20% ethyl acetate in hexane affording the title compound as yellow solid (1.59 g, 37.67%). 
       1 H NMR (DMSO-d 6 , 400 MHz) δ 8.59-8.51 (m, 2H), 8.06 (d, J=7.5 Hz, 1H), 7.97 (d, J=7.7 Hz, 1H), 7.52 (d, J=6.0 Hz, 1H), 7.18 (d, J=8.9 Hz, 1H), 3.97 (s, 3H); LCMS [m/z (M+H) + ] 280 (MW calc=279); R t =1.56; HPLC purity at λ=210 nm: 99.05%. 
     BIOLOGICAL EXAMPLES 
     Biological Example 1: Inhibition of Recombinant TrxR1 and GR 
     Small molecule inhibition of recombinant thioredoxin reductase 1 (TrxR1) and gluthathione reductase (GR) was examined in 96-well plate format. 30 nM TrxR1 was incubated in the presence of 250 μM NADPH, 0.1 mg/ml BSA, and various concentrations of the compounds (1% DMSO final) in 50 mM Tris (pH 7.5) and 2 mM EDTA buffer for 15 minutes. Following the incubation period, 2 mM DTNB was added to each well and the change in O.D. at 412 nm was followed. Percent activity was determined using DMSO vehicle and no TrxR1 (blank) controls. 2 nM GR was incubated in the presence of 250 μM NADPH, 0.1 mg/ml BSA, and various concentrations of compounds (1% DMSO final) in 50 mM Tris (pH 7.5) and 2 mM EDTA buffer for 15 minutes. Following the incubation period, 1 mM GSSG was added to each well and the change in O.D. at 340 nm was followed. Percent activity was determined using DMSO vehicle and no GR (blank) controls. 
     Using the assays described in Biological Example 1, the following IC 50  values were obtained. The results obtained are provided in Table 1 below. 
     
       
         
           
               
               
               
               
             
               
                   
                   
               
               
                   
                   
                 TrxR 
                 GR 
               
               
                   
                   
                 inhibition 
                 inhibition 
               
               
                   
                 Example 
                 (nM) 
                 (μM) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 1 
                 26.8 
                 64.19 
               
               
                   
                 2 
                 56.9 
                 9.89 
               
               
                   
                 3 
                 558 
                 &gt;100 μM 
               
               
                   
                 4 
                 0.854 
                 11.17 
               
               
                   
                 5 
                 10.8 
                 &gt;100 μM 
               
               
                   
                 6 
                 3.99 
                 &gt;100 μM 
               
               
                   
                 7 
                 6.90 
                 &gt;100 μM 
               
               
                   
                 8 
                 5.50 
                 — 
               
               
                   
                   
               
            
           
         
       
     
     Biological Example 2: Head and Neck Cancer Cell Viability Assay 
     FaDu cells were plated 2000 cells/well in 96-well black optical plates in the presence of 10% FBS media containing 25 nM selenite. The following day cells were treated with various concentrations of the compound of Example 1 (0.1% DMSO final) and incubated for 72 hrs. After the incubation Cell-Quanti Blue reagent was added to each well and incubated for additional 3 hrs. Fluorescence was read ex: 530 nm/em: 590 nm, and percent of viability was determined using DMSO vehicle and no cell (blank) controls. 
     Using the assays described in Biological Example 2, the following IC 50  values were obtained. The results obtained are provided in Table 2 below. 
     
       
         
           
               
               
               
             
               
                   
                   
               
               
                   
                   
                 FaDu 
               
               
                   
                   
                 Cell IC50 
               
               
                   
                 Example 
                 (μM) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 1 
                 1.61 
               
               
                   
                 2 
                 0.61 
               
               
                   
                 3 
                 2.89 
               
               
                   
                 7 
                 45.71 
               
               
                   
                   
               
            
           
         
       
     
     Bioloical Example 3: Breast Cancer Cell Viability Assay 
     MDA-MB-231 cells were plated 2000 cells/well in 96-well black optical plates in the presence of 10% FBS media containing 25 nM selenite. The following day cells were treated with various concentrations of compounds (0.1% DMSO final) and incubated for 72 hrs. After the incubation Alamar Blue reagent was added to each well and incubated for additional 3 hrs. Fluorescence was read ex: 530 nm/em: 590 nm, and percent of viability was determined using DMSO vehicle and no cell (blank) controls. 
     Using the assays described in Biological Example 3, the following IC 50  values were obtained. The results obtained are provided in Table 3 below. 
     
       
         
           
               
               
               
             
               
                   
                   
               
               
                   
                   
                 MDA-MB-231  
               
               
                   
                   
                 Cell viability  
               
               
                   
                   
                 IC50 
               
               
                   
                 Example 
                 (μM) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 1 
                 3.61 
               
               
                   
                 4 
                 &gt;100 μM 
               
               
                   
                 5 
                 4.54 
               
               
                   
                 6 
                 10.85 
               
               
                   
                 7 
                 3.09 
               
               
                   
                   
               
            
           
         
       
     
     Biological Example 4: Cancer Cell Viability Assay 
     Breast cancer and glioblastoma cell lines were plated 4000 cells/well in 96-well plates in the presence of 10% FBS media. The following day cells were treated with various concentrations of example compounds (0.1% DMSO final) and incubated for 72 hrs. After the incubation An MTT assay was performed to access cell viability. Percent of viability was determined using DMSO vehicle and no cell (blank) controls. 
     Using the assays described in Biological Example 4, the following IC 50  values were obtained. The results obtained are provided in Table 4 below. 
     
       
         
           
               
               
               
               
             
               
                   
               
               
                   
                 U-87  
                 MDA-MB-231  
                 MDA-MB-468  
               
               
                   
                 MG IC50 
                 IC50 
                 IC50 
               
               
                 Example 
                 (μM) 
                 (μM) 
                 (μM) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 1 
                 8.2 
                 2.97 
                 4.34 
               
               
                 8 
                 2.53 
                 1.02 
                 0.96