the term “ alkyl ” is intended to include both straight - and branched - chain alkyl groups . the same terminology applies to the non - aromatic moiety of an aralkyl radical . examples of alkyl groups include : methyl group , ethyl group , n - propyl group , iso - propyl group , n - butyl group , iso - butyl group , sec - butyl group , t - butyl group , n - pentyl group , 1 , 1 - dimethylpropyl group , 1 , 2 - dimethylpropyl group , 2 , 2 - dimethylpropyl group , 1 - ethylpropyl group , 2 - ethylpropyl group , n - hexyl group and 1 - methyl - 2 - ethylpropyl group . the term “ aryl ” means an aromatic radical having 4 to 18 carbon atoms and includes heteroaromatic radicals . examples include monocyclic groups , as well as fused groups such as bicyclic groups and tricyclic groups . some examples include phenyl group , indenyl group , 1 - naphthyl group , 2 - naphthyl group , azulenyl group , heptalenyl group , biphenyl group , indacenyl group , acenaphthyl group , fluorenyl group , phenalenyl group , phenanthrenyl group , anthracenyl group , cyclopentacyclooctenyl group , and benzocyclooctenyl group , pyridyl group , pyrrolyl group , pyridazinyl group , pyrimidinyl group , pyrazinyl group , triazolyl group , tetrazolyl group , benzotriazolyl group , pyrazolyl group , imidazolyl group , benzimidazolyl group , indolyl group , isoindolyl group , indolizinyl group , purinyl group , indazolyl group , furyl group , pyranyl group , benzofuryl group , isobenzofuryl group , thienyl group , thiazolyl group , isothiazolyl group , benzothiazolyl group , oxazolyl group , and isoxazolyl group . the term “ optionally substituted ” means , in reference to the optionally substituted group , that that group may carry one or more substituent chosen from amongst an alkyl group , an alkoxy group ( wherein the alkyl group is as defined above ), a halogen atom , an amino group , carboxylic acid group , an carboxylate alkyl ester group , or an alkylthio group . the term “ prodrug ” as used herein means a pharmacologically acceptable derivative of the compound of formula ( i ), such that an in vivo biotransformation of the derivative gives the compound as defined in formula ( i ). prodrugs of compounds of formula ( i ) may be prepared by modifying functional groups present in the compounds in such a way that the modifications are cleaved in vivo to give the parent compound . the term “ pharmaceutically acceptable salts ” is intended to apply to non - toxic salts derived from inorganic or organic acids , including , for example , the following acid salts : acetate , adipate , alginate , aspartate , benzoate , benzenesulfonate , bisulfate , butyrate , citrate , camphorate , camphorsulfonate , cyclopentanepropionate , digluconate , dodecylsulfate , ethanesulfonate , formate , fumarate , glucoheptanoate , glycerophosphate , glycolate , hemisulfate , heptanoate , hexanoate , hydrochloride , hydrobromide , hydroiodide , 2 - hydroxyethanesulfonate , lactate , maleate , malonate , methanesulfonate , 2 - naphthalenesulfonate , nicotinate , nitrate , oxalate , palmoate , pectinate , persulfate , 3 - phenylpropionate , phosphate , picrate , pivalate , propionate , p - toluenesulfonate , salicylate , succinate , sulfate , tartrate , thiocyanate , and undecanoate . the ethylene - linked compounds of the invention are surprisingly potent inhibitors of pnp . a class of pnp inhibitor compounds containing methylene linkages is described in the applicants &# 39 ; pct application pct / nz03 / 00186 . the methylene - linked compounds were designed to match the fully dissociated transition states of human pnp and plasmodium falciparum pnp . the applicants have carried out detailed investigations of this methylene - linked class . based on their particular knowledge of the pnp enzyme , and the activities of the methylene - linked compounds , the applicants would not have predicted that ethylene - linked compounds would be potent pnp inhibitors , or would even exhibit pnp inhibitory activity at all . it was previously considered that the presence of the extra carbon atom in the linkage would have rendered the ethylene class inactive . it was thought that the inclusion of an extra carbon atom in the linkage would elongate the distance between the ribose mimic ( the amine moiety ) and the base moiety beyond the length that had been found to be optimum for inhibition of the pnp enzyme . the prior art and the applicants &# 39 ; previous special knowledge of the pnp enzyme actually taught away from synthesising and investigating the activities of the ethylene - linked compounds . however , despite the linkage being outside of the predicted optimal length , the compounds of the invention prove to be surprisingly potent inhibitors of human pnp . indeed , one compound of the invention ( compound 1 ) has a k i * for human pnp of 0 . 46 ± 0 . 05 nm , a potency sufficient to have therapeutic potential . the compounds may be prepared by any method . however , preferably they are prepared by independently synthesising the amine moiety and the base part , and then linking the base part to the nitrogen atom in the ring of the amine moiety . in one preferred embodiment , the ethylene linkage is constructed on the base part in the form of a 2 - substituted acetaldehyde moiety , and then linked to the amine moiety by way of a reductive amination reaction . the compounds of the invention are useful in both free base form and in the form of salts . it will be appreciated that the representation of a compound of formula ( i ), where b and / or d is a hydroxy group , is of the enol - type tautomeric form of a corresponding amide , and this will largely exist in the amide form . the use of the enol - type tautomeric representation is simply to allow fewer structural formulae to represent the compounds of the invention . the active compounds may be administered to a patient by a variety of routes , including orally , parenterally , by inhalation spray , topically , rectally , nasally , buccally or via an implanted reservoir . the amount of compound to be administered will vary widely according to the nature of the patient and the nature and extent of the disorder to be treated . typically the dosage for an adult human will be in the range less than 1 to 1000 milligrams , preferably 0 . 1 to 100 milligrams . the specific dosage required for any particular patient will depend upon a variety of factors , including the patient &# 39 ; s age , body weight , general health , sex , etc . for oral administration the compounds can be formulated into solid or liquid preparations , for example tablets , capsules , powders , solutions , suspensions and dispersions . such preparations are well known in the art as are other oral dosage regimes not listed here . in the tablet form the compounds may be tableted with conventional tablet bases such as lactose , sucrose and corn starch , together with a binder , a disintegration agent and a lubricant . the binder may be , for example , corn starch or gelatin , the disintegrating agent may be potato starch or alginic acid , and the lubricant may be magnesium stearate . for oral administration in the form of capsules , diluents such as lactose and dried cornstarch may be employed . other components such as colourings , sweeteners or flavourings may be added . when aqueous suspensions are required for oral use , the active ingredient may be combined with carriers such as water and ethanol , and emulsifying agents , suspending agents and / or surfactants may be used . colourings , sweeteners or flavourings may also be added . the compounds may also be administered by injection in a physiologically acceptable diluent such as water or saline . the diluent may comprise one or more other ingredients such as ethanol , propylene glycol , an oil or a pharmaceutically acceptable surfactant . the compounds may also be administered topically . carriers for topical administration of the compounds of include mineral oil , liquid petrolatum , white petrolatum , propylene glycol , polyoxyethylene , polyoxypropylene compound , emulsifying wax and water . the compounds may be present as ingredients in lotions or creams , for topical administration to skin or mucous membranes . such creams may contain the active compounds suspended or dissolved in one or more pharmaceutically acceptable carriers . suitable carriers include mineral oil , sorbitan monostearate , polysorbate 60 , cetyl ester wax , cetearyl alcohol , 2 - octyldodecanol , benzyl alcohol and water . the compounds may further be administered by means of sustained release systems . for example , they may be incorporated into a slowly dissolving tablet or capsule . the following examples further illustrate the invention . it is to be appreciated that the invention is not limited to the examples . n - butyllithium ( 5 . 30 ml of a 1 . 3 m solution in hexanes , 6 . 90 mmol ) was added to a solution of bromide 1a ( 2 . 00 g , 5 . 75 mmol ) in diethyl ether ( 40 ml ) and anisole ( 16 ml ) under argon at − 78 ° c . thin - layer chromatography confirmed that no starting material remained . dimethylformamide ( 4 . 4 ml , 57 . 5 mmol ) was added and the mixture stirred at − 78 ° c . for 30 minutes then the mixture was allowed to warm to room temperature . dichloromethane ( 200 ml ) was added and the solution was washed with water ( 100 ml ), dried and the solvent was removed . the residue was chromatographed on silica gel to give compound 1b ( 1 . 20 g , 70 %) as a white solid . methyltriphenylphosphonium bromide ( 1 . 20 g , 3 . 37 mmol ) was suspended in tetrahydrofuran ( 25 ml ) and cooled to − 78 ° c . under an atmosphere of argon . n - butyllithium ( 1 . 94 ml of a 1 . 3 m solution in hexanes , 2 . 52 mmol ) was added to give a yellow solution , which was stirred for 15 minutes . aldehyde 1b ( 0 . 500 g , 1 . 68 mmol ) was added as a solid and the solution was allowed to warm to room temperature then stirred for 2 hours . the solvent was removed and the residue was chromatographed on silica gel to give compound 1c ( 0 . 450 g , 91 %) as a pale yellow solid . borane dimethyl sulfide ( 3 . 12 ml , 32 . 9 mmol ) was added to a solution of alkene 1c ( 0 . 970 g , 3 . 29 mmol ) in tetrahydrofuran ( 11 ml ) under an atmosphere of argon and the solution was stirred for 18 hours at room temperature . sodium hydroxide ( 1 . 97 g , 49 . 3 mmol ) was dissolved in water ( 4 ml ) then diethyl ether ( 2 ml ) was added slowly to the solution at 0 ° c . 30 % aqueous hydrogen peroxide ( 30 % w / w , 8 ml ) was added slowly and the mixture was stirred at room temperature for 3 hours . dichloromethane ( 100 ml ) was added and the mixture was washed with water ( 100 ml ), dried and the solvent was removed . chromatography of the residue on silica gel gave compound 1d ( 0 . 670 g , 65 %) as a white solid . dess - martin periodinane ( 176 mg , 0 . 415 mmol ) was added to a solution of alcohol 1d ( 100 mg , 0 . 319 mmol ) in dichloromethane ( 2 ml ) at room temperature giving a yellow precipitate . the mixture was stirred for 10 minutes then chromatographed on silica gel to give compound 1e ( 41 mg , 41 %). this reaction was repeated with 460 mg of alcohol 1d , but was left for only 2 minutes with the oxidant and purification was carried out quickly . the yield of compound 1e increased to 71 %, although this material was shown to be not as pure by nmr spectroscopy . aldehyde 1e ( 110 mg , 0 . 354 mmol ) was added to a solution of amine 1f ( 60 mg , 0 . 389 mmol ; reference 1 ) in methanol ( 1 ml ) at room temperature and the solution stirred for 15 minutes . sodium cyanoborohydride ( 29 mg , 0 . 460 mmol ) was then added to the solution , which was stirred for an additional 30 minutes . the mixture was adsorbed onto silica and chromatographed on silica gel giving compound 1g ( 20 mg , 14 %) as a tan gum . 10 % palladium on carbon ( 20 mg ) was added to a solution of 1g ( 13 mg , 0 . 0315 mmol ) in ethanol ( 1 ml ) and methanol saturated with ammonia ( 0 . 5 ml ) and the mixture was stirred under an atmosphere of hydrogen at room temperature for 18 hours . the mixture was filtered and the solvent removed . the residue was chromatographed on silica gel to give compound 1h ( 5 mg , 54 %) as a tan gum . compound 1h ( 4 mg , 0 . 137 mmol ) was heated to reflux in concentrated hydrochloric acid ( 1 ml ) for 2 hours . the solvent was removed to give compound 1 ( dad - et - immucillin - h ) hydrochloride salt ( 3 mg , 73 %) as a white solid . a mixture of bromobutyronitrile ( 2a ) ( 7 . 45 g , 50 . 3 mmol ), sodium benzoate ( 14 . 5 g , 101 mmol ), tetrabutylammonium hydrogen sulfate ( 34 . 2 g , 101 mmol ) and molecular sieves ( 1 g ) in dry acetone ( 100 ml ) was heated under reflux for 4 hrs . the reaction mixture was cooled to rt and filtered through the celite pad and concentrated to dryness . dichloromethane was added and the mixture was washed with sat . nahco 3 followed by water , dried and concentrated . chromatography ( etoac : petroleum ether , 1 : 4 ) afforded 9 . 5 g ( 100 %) of ( 2a ) as clear syrup . 1 h nmr ( cdcl 3 ) δ 8 . 02 - 8 . 12 ( m , 2h ), 7 . 41 - 7 . 59 ( m , 3h ), 4 . 42 ( t , 2h ), 2 . 52 ( t , 2h ), 2 . 13 ( m , 2h ); 13 c nmr δ 171 . 5 ( c ), 166 . 7 ( c ), 134 . 0 ( ch ), 133 . 6 ( ch ), 130 . 5 ( ch ), 130 . 1 ( ch ), 130 . 0 ( ch ), 128 . 9 ( ch ), 119 . 3 ( c ), 63 . 1 ( ch 2 ), 25 . 4 ( ch 2 ), 14 . 8 ( ch 2 ). to a mixture of benzoate ( 2b ) ( 9 . 5 g , 50 . 2 mmol ) in methanol ( 80 ml ) was added water ( 20 ml ) and 2m naoh ( 10 ml ). after stirring for 1 hr at room temperature the reaction mixture was treated with 2m hcl ( 10 ml ), stirred for 15 min and then was concentrated to dryness and dried in vacuo to afford a white solid which was used in the next step without further purification . the crude material in dry pyridine was treated with trityl chloride ( 10 . 49 g , 37 . 6 mmol ), and the mixture was stirred at room temperature for 17 hrs and concentrated to dryness . ethyl acetate was added and the mixture was washed twice with water , dried and concentrated . chromatography ( etoac : petroleum ether , 1 : 9 ) gave trityl derivative ( 2c ), 15 g ( 91 %) as a white solid . 1 h nmr ( cdcl 3 ) δ 7 . 20 - 7 . 42 ( m , 15h ), 3 . 21 ( t , 2h ), 2 . 44 ( t , 2h ), 1 . 85 - 1 . 9 ( m , 2h ); 13 c nmr δ 147 . 3 ( c ), 144 . 3 ( c ), 128 . 9 ( ch ), 128 . 3 ( ch ), 127 . 6 ( ch ), 127 . 5 ( ch ), 119 . 9 ( c ), 87 . 2 ( c ), 61 . 7 ( ch 2 ), 26 . 7 ( ch 2 ), 14 . 8 ( ch 2 ). trityl derivative ( 2c ) ( 1 g , 3 . 05 mmol ) was dissolved in dry dmf ( 15 ml ). bredereck &# 39 ; s reagent ( 0 . 84 g , 4 . 84 mmol ) was added and the reaction mixture was stirred at 130 ° c . in a flask with a stopper for 1 hr . bredereck &# 39 ; s reagent ( 0 . 84 g , 4 . 84 mmol ) was added once more and the mixture was stirred at 130 ° c . for 2 hrs and concentrated to dryness . chromatography ( etoac : petroleum ether , 1 : 4 ) gave dimethylamino derivative ( 2d ), 0 . 73 g ( 62 . 5 %) as a clear syrup . 1 h nmr ( cdcl 3 ) δ 7 . 21 - 7 . 45 ( m , 15h ), 6 . 25 ( s , 1h ), 3 . 17 ( t , 2h ), 3 . 00 ( s , 6h ), 2 . 26 ( t , 2h ); 13 c nmr δ 151 . 2 ( ch ), 144 . 7 ( c ), 129 . 1 ( ch ), 128 . 2 ( ch ), 127 . 3 ( ch ), 122 . 9 ( c ), 87 . 0 ( c ), 69 . 7 ( c ), 63 . 9 ( ch 2 ), 34 . 5 ( ch 3 ), 28 . 4 ( ch 2 ). compound ( 2d ) ( 0 . 722 g , 1 . 888 mmol ) was dissolved in dry methanol ( 50 ml ). sodium acetate ( 1 . 239 g , 15 . 10 mmol ) and aminoacetonitrile bisulfate ( 1 . 164 g , 7 . 55 mmol ) were added and the reaction mixture was stirred under reflux for 5 hrs . the mixture was concentrated to dryness . chloroform was added , and the reaction mixture was then washed twice with water , dried and concentrated . chromatography ( etoac : petroleum ether , 1 : 2 ) gave a mixture of cis - trans isomers ( 2e ), 0 . 74 g ( 100 %) as a pale yellow foam . 1 h nmr ( cdcl 3 ) δ 7 . 22 - 7 . 44 ( m , 30h ), 6 . 61 ( d , j = 12 . 0 hz , 1h ), 6 . 43 ( d , j = 12 . 6 hz , 1h ), 5 . 86 - 5 . 94 ( m , 1h ), 4 . 79 - 4 . 85 ( m , 1h ), 3 . 89 ( d , j = 6 . 1 hz , 2h ), 3 . 66 ( d , j = 6 . 1 hz , 2h ), 3 . 35 ( t , 2h ), 3 . 18 ( t , 2h ), 2 . 26 - 2 . 32 ( m , 4h ); 13 c nmr δ 146 . 7 ( ch ), 146 . 6 ( ch ), 143 . 0 ( c ), 142 . 2 ( c ), 127 . 6 ( ch ), 127 . 1 ( ch ), 126 . 9 ( ch ), 126 . 5 ( ch ), 126 . 1 ( ch ), 121 . 0 ( c ), 114 . 9 ( c ), 114 . 8 ( c ), 87 . 0 ( c ), 85 . 8 ( c ), 81 . 3 ( c ), 79 . 3 ( c ), 62 . 7 ( ch 2 ), 61 . 5 ( ch 2 ), 34 . 2 ( ch 2 ), 33 . 9 ( ch 2 ), 30 . 1 ( ch 2 ), 27 . 7 ( ch 2 ). dbu ( 1 . 7 ml , 11 . 28 mmol ) was added to a stirred solution of nitrile ( 2e ) ( 0 . 74 g , 1 . 88 mmol ) in dry dichloromethane at room temperature . methyl chloroformate ( 0 . 44 ml , 5 . 64 mmol ) was added drop wise and the reaction mixture was stirred at rt for 17 hrs . methanol ( 4 ml ) was then added and after 1 hr the resulting solution was diluted with dichloromethane ( 150 ml ), washed with 2m hcl ( 20 ml ), followed by aq . sodium bicarbonate ( 30 ml ), dried ( mgso 4 ), and concentrated in vacuo to afford a syrup . chromatography ( ethyl acetate : petroleum ether , 1 : 2 ) gave pyrrole ( 2f ), 0 . 508 g ( 68 . 6 %) as a clear syrup . 1 h nmr ( cdcl 3 ) δ 7 . 86 ( s , 1h ), 7 . 13 - 7 . 31 ( m , 15h ), 6 . 35 ( d , j = 3 . 1 hz , 1h ), 3 . 18 ( t , 2h ); 2 . 49 ( t , 2h ); 13 c nmr δ 142 . 9 ( c ), 141 . 8 ( c ), 127 . 7 ( ch ), 126 . 8 ( ch ), 126 . 1 ( ch ), 121 . 3 ( ch ), 114 . 2 ( c ), 110 . 3 ( c ), 86 . 2 ( c ), 63 . 4 ( ch 2 ), 23 . 9 ( ch 2 ). pyrrole ( 2f ) ( 0 . 480 g , 1 . 220 mmol ) was dissolved in abs etoh ( 15 ml ). formamidine acetate ( 0 . 635 g , 6 . 10 mmol ) was added and the reaction mixture was heated under reflux for 4 hrs . the solution was concentrated to dryness . chromatography ( ethyl acetate ) gave ( 2g ), 0 . 42 g ( 82 %) as a solidified syrup . 1 h nmr ( meoh - d 4 ) δ 8 . 47 ( s , 1h ), 7 . 54 ( s , 1h ), 7 . 12 - 7 . 41 ( m , 15h ), 3 . 30 - 3 . 35 ( m , 2h ); 3 . 0 ( t , 2h ); 13 c nmr δ 152 . 8 ( c ), 149 . 6 ( ch ), 146 . 0 ( c ), 144 . 6 ( c ), 130 . 2 ( ch ), 130 . 0 ( ch ), 129 . 0 ( ch ), 128 . 3 ( ch ), 115 . 3 ( c ), 114 . 0 ( c ), 88 . 2 ( c ), 65 . 1 ( ch 2 ), 25 . 8 ( ch 2 ). pyrrolo - pyrimidine ( 2f ) ( 0 . 4 g , 0 . 951 mmol ) was dissolved in dry pyridine ( 15 ml ) and cooled to 0 ° c . benzoyl chloride ( 2 ml , 17 . 22 mmol ) was added and the reaction mixture was stirred at rt for 17 hrs . the resulting solution was diluted with dichloromethane , washed with water , followed by aq . sodium bicarbonate , dried ( mgso 4 ), and concentrated in vacuo to afford a syrup . chromatography ( ethyl acetate : petroleum ether , 1 : 4 ) gave over - n - benzoylated material as a syrup . this was dissolved in dry meoh ( 20 ml ) and treated with triethylamine ( 1 ml ). the solution was stirred at rt for 17 hrs and concentrated to dryness . chromatography ( ethyl acetate : petroleum ether , 1 : 2 ) gave ( 2h ), 0 . 53 g ( 89 %) as a white foam . 1 h nmr ( cdcl 3 ) δ 8 . 4 ( s , 1h ), 8 . 1 ( m , 1h ), 7 . 8 - 8 . 0 ( m , 4h ), 7 . 13 - 7 . 49 ( m , 21h ), 3 . 4 ( t , 2h ); 3 . 1 ( t , 2h ); 13 c nmr d 171 . 5 ( c ), 167 . 5 ( c ), 151 . 7 ( c ), 148 . 8 ( ch ), 144 . 8 ( c ), 142 . 8 ( c ), 133 . 8 ( ch ), 132 . 2 ( ch ), 131 . 3 ( ch ), 130 . 4 ( ch ), 130 . 2 ( ch ), 129 . 1 ( ch ), 128 . 7 ( ch ), 128 . 5 ( ch ), 128 . 1 ( ch ), 127 . 3 ( ch ), 116 . 3 ( c ), 114 . 4 ( c ), 87 . 0 ( c ), 63 . 9 ( ch 2 ), 24 . 9 ( ch 2 ). n - benzoyl derivative ( 2h ) ( 0 . 2 g , 0 . 318 mmol ) was dissolved in aq . acetic acid ( 80 %, 5 ml ) and stirred at 60 ° c . for 4 hrs . the resulting solution was concentrated in vacuo to afford a syrup . chromatography ( ethyl acetate : pethroleum ether , 1 : 1 ) gave ( 9 ), 111 mg ( 90 %) as a clear syrup . alcohol ( 21 ) ( 78 mg , 202 μmol ) was dissolved in dry dichloromethane ( 5 ml ) and treated with dess - martin periodinane ( 1 . 5 eq ., 128 mg ). the reaction mixture was stirred at rt for 1 hr . the resulting solution was diluted with ether and treated with 1m naoh . after 15 min the organic layer was washed with water , dried ( mgso 4 ) and concentrated in vacuo to afford a syrup . chromatography ( ethyl acetate : petroleum ether , 1 : 1 ) gave ( 2j ), 71 mg ( 92 %) as a clear syrup . acetaldehdo - derivative ( 2j ) can be coupled with the ( 3s , 4r )- 3 - hydroxy - 4 - methylthiomethylpyrrolidine ( 2k ) by reductive amination using sodium cyanoborohydride in methanol at room temperature , following methodology reported in evans et al , j . med . chem ., 48 ( 2005 ) 4679 - 4689 , ( see scheme 1 ), and the n - benzoyl protecting groups can then be removed by treatment of the product with methanolic ammonia , to yield the title compound ( 2 ). initial ( k i ) and equilibrium ( k i *) dissociation constants of dad - et - immucillin - h were determined for human pnp . inhibitor dissociation constants for the phosphorolysis of inosine were based on initial and equilibrium reaction rate measurements with varied inhibitor concentrations ( miles , r . w ., tyler , p . c ., furneaux , r . h ., bagdassarian , c . k . and schramm , v . l . ( 1998 ) one - third - the - sites transition state inhibitors for purine nucleoside phosphorylase , biochemistry 37 , 8615 - 8621 ; morrison , j . f . and walsh , c . t . ( 1988 ) the behaviour and significance of slow - binding enzyme inhibitors , adv . enzymol . relat . areas mol . biol . 61 , 201 - 301 ). reactions were started by adding hupnp ( 1 . 4 nm ) to reaction mixtures ( 25 ° c .) containing 1 mm inosine in 50 mm khpo 4 ph 7 . 4 with xanthine oxidase at 60 mu / ml . hypoxanthine formed by phosphorolysis of inosine was oxidized to uric acid and monitored spectrophotometrically at 293 nm ( extinction coefficient for uric acid ε 293 = 12 . 9 mm − 1 cm − 1 ). enzyme concentration was adjusted to give absorbance changes not exceeding 1 . 0 during the time required to characterize initial and final slow - onset inhibition equilibria . the large excess of substrate and continuous product depletion provided extended initial rate conditions . in most cases the concentration of the inhibitor compound was & gt ; 10 - fold greater than the enzyme concentration as required for simple analysis of two - state slow - onset tight - binding inhibition ( morrison , j . f . and walsh , c . t . ( 1988 ) the behavior and significance of slow - binding enzyme inhibitors , adv . enzymol . relat . areas mol . biol . 61 , 201 - 301 ). the inhibition constant k i ; describes the reversible equilibrium between enzyme and inhibitor ( compound 1 ) for the initial inhibitor binding step . k i was determined by fitting the initial rates at different inhibitor concentration to the equation for competitive inhibition : ν i =( k cat × s )/( k m ( 1 + i / k i )+ s ), where μ i is initial reaction rate , k cat is the catalytic turnover number , k m is the michaelis constant , k i is the dissociation constant of enzyme - inhibitor complex ( ei ), i is inhibitor concentration and s is substrate concentration . the dissociation constant for the complex formed after slow onset equilibrium ( k i *) was determined by ν =( k cat × s )/( k m ( 1 + i / k i *)+ s ), where ν is the steady state reaction rate and the other variables are the same as above . initial ( k i ) and equilibrium ( k i *) dissociation constants of compound 1 for hupnp were found to be 1 . 6 ± 0 . 3 nm and 0 . 46 ± 0 . 05 nm , respectively . although the invention has been described by way of example , it should be appreciated the variations or modifications may be made without departing from the scope of the invention . furthermore , when known equivalents exist to specific features , such equivalents are incorporated as if specifically referred to in the specification . the present invention relates to compounds that are inhibitors of pnp , pprt , mtap , mtan and / or nh . the compounds are therefore expected to be useful in the treatment of diseases in which the inhibition of pnp , pprt , mtap , mtan and / or nh is desirable . such diseases include cancer , and bacterial infection , protozoal infection or t - cell mediated diseases .