the invention will now be described with reference to the following examples which illustrate some preferred aspects of the present invention . however , it is to be understood that the particularity of the following description of the invention is not to supersede the generality of the preceding description of the invention . ( a ) preparation of 2 - mercapto - 6 - hydroxybenzoxazole ( see also j . org . chem ., 19 , 758 ) a mixture of aminoresorcinol hydrochloride ( 1 . 1 g ), potassium ethyl xanthate ( 1 . 2 g ) and potassium carbonate ( 1 . 0 g ) was dissolved in ethanol / water ( 1 : 1 , 20 ml ) and ( under an argon balloon ) heated under reflux for 3 hours . the pale yellow solution was cooled to rt and then acetic acid ( 2 ml ) was added to make the solution slightly acidic ( gas evolution ). a cream precipitate soon formed and the sealed flask was kept in the fridge overnight . the cream solid was collected by filtration and the damp product ( 0 . 9 g ) was used immediately in the next step . a mixture of 6 - hydroxy - 2 - mercaptobenzoxazole ( 165 mg ), sodium bicarbonate ( 84 mg ) and dimethyl sulfate ( 94 μl ) was dissolved in water ( 2 ml ) with stirring and under an argon atmosphere . the reaction mixture was stirred at rt overnight and hplc showed that all starting material was gone . the reaction mixture was evaporated to dryness to give a dark brown solid ( one can also extract the reaction mixture with chloroform to give the crude product ). chromatography on silica gel using 10 % ethyl acetate / hexane gave the pure product as a near - white crystalline solid ( 45 mg , 25 %). a mixture of 6 - hydroxy - 2 - methylthiobenzoxazole ( 100 mg ), 3 -[ 4 -( 2 - chloroethyl )- 1 - piperidinyl ]- 6 - methylpyridazine ( 130 mg ) and potassium carbonate ( 100 mg ) was heated and stirred in dmf ( 3 ml ) at 90 - 100 ° under argon for 20 hr . tlc showed that the reaction was virtually complete and the dmf was removed under reduced pressure and the residue was partitioned between water and chloroform . the chloroform extracts were evaporated and the residue was chromatographed on silica / chloroform to give the product as a pale cream solid ( 110 mg , 50 %). the 1 h nmr spectrum is summarized in table 6 below . sodium metal ( 100 mg ) was dissolved in ethanol ( 5 ml ) and the solution was added to a solution of the methylthiobenzoxazole ( compound no . 4 ) ( 74 mg ) in thf ( 2 ml ). the resultant solution was stirred at rt for 24 hr when hplc indicated that all starting material had disappeared . the reaction mixture was evaporated to dryness and the residue was partitioned between water and dichloromethane . the crude organic product was purified by chromatography on silica / ch 2 cl 2 to give compound no . 5 as a pale cream solid ( 46 mg ). the 1 h nmr and ms data are recorded in table 6 below . compounds no 1 , 2 , 3 , 6 , 7 , 8 , 9 , 17 , 19 , 22 , 25 , 26 , 27 were prepared by reacting the appropriate het - a - alk - cl or het - a - alk - oh with the required 2 - substituted 5 - or 6 - hydroxybenz - azole ( benzoxazole , benzothiazole or benzimidazole ) following similar conditions to those described in example 1 part ( c ). the 1 h nmr and / or ms data are recorded in table 6 below . the 2 - alkoxybenz - azole derivatives , compounds no 10 , 11 , 12 , 13 , 14 , 15 , 18 , 20 , 21 , 23 were prepared from the corresponding 2 - methylthio or 2 - ethylthiobenzoxazole or benzothiazole by reaction with the appropriate sodium alkoxide following essentially the same conditions as described in example 2 . the 1 h nmr and / or ms data are recorded in table 6 below . methylation of 2 - ethylthio - 5 - hydroxybenzimidazole gave an approximately 1 : 1 mixture of 2 - ethylthio - 3 - methyl - 5 - hydroxybenzimidazole and 2 - ethylthio - 3 - methyl - 6 - hydroxybenzimidazole which could not be easily separated . reaction of this mixture of hydroxy compounds with 3 -[ 4 -( 2 - chloroethyl )- 1 - piperidinyl ]- 6 - methylpyridazine , following the method described in example 1 , gave a 1 : 1 mixture of isomeric products ( compound no 16 ). ( a ) preparation of 2 - hydroxy - 4 - methoxybenzohydroxamic acid according to literature procedure chem . ber . 100 , 954 - 960 ( 1967 ) an hydroxylamine solution was prepared by addition of aqueous sodium hydroxide ( 393 mg , 9 . 82 mmol )/ water ( 1 . 6 ml ) to a stirred solution of hydroxylamine hydrochloride ( 292 mg , 4 . 21 mmol ) in water ( 3 . 5 ml ). immediately slowly added a solution of methyl 2 - hydroxy - 4 - methoxybenzoate ( 511 mg , 2 . 81 mmol ) in 1 , 4 - dioxane ( 1 . 5 ml ). the resulting reaction mixture was stirred at room temperature for 18 hours , under an argon atmosphere . the reaction mixture was concentrated on a rotary evaporator to half the original volume , and the product precipitated by addition of concentrated hydrochloric acid , keeping flask cool in an ice bath . filtered the suspension to give 2 - hydroxy - 4 - methoxybenzohydroxamic acid ( 476 mg , 92 %) as a pale brown solid . 1 h nmr spectrum ( cdcl 3 ) δ ( ppm ): 3 . 72 ( s , 3h ); 6 . 36 ( m , 2h ); 7 . 41 ( d , 1h ). a solution of carbonyl diimidazole ( 1 . 07 g , 6 . 57 mmol ) in anhydrous thf ( 8 ml ) was added to a stirred boiling solution of the hydroxamic acid ( 602 mg , 3 . 29 mmol ) in thf ( 6 ml ). the resulting solution was heated at reflux for approx . 8 - 10 hours , then allowed to cool to room temperature and stirred overnight under an argon atmosphere . thin layer chromatography ( tlc ) ( silica ; 1 : 1 hexane / ethyl acetate ) showed minimal starting material and new non polar material . the solution was evaporated on a rotary evaporator to give an orange colored oil . water ( 6 ml ) was added , and contents cooled ( ice bath ) and acidified to ph 2 with concentrated hydrochloric acid . the crude , damp 3 - hydroxy - 6 - methoxy - 1 , 2 - benzisoxazole precipitated as a cream orange solid ( 645 mg ). 1 h nmr spectrum ( cdcl 3 ) δ ( ppm ): 3 . 82 ( s , 3h ); 6 . 73 ( fd , 1h ); 6 . 80 ( dd , 1h ); 7 . 52 ( d , 1h ). benzisoxazole from part ( b ) ( 193 mg , 1 . 17 mmol ), ethanol ( 75 μl , 1 . 29 mmol ) and triphenylphosphine ( 460 mg , 1 . 75 mmol ) were dissolved in anhydrous thf ( 4 ml ) and cooled ( 0 °). diisopropylazodicarboxylate ( 345 μl , 1 . 75 mmol ) was added slowly and after 10 - 15 min the reaction flask was removed from the ice bath and the reaction mixture was stirred at room temperature overnight under an argon atmosphere . the solution was evaporated to dryness and the residue pre - absorbed onto silica , and chromatographed on silica ( 19 g ); eluent : hexane ( 300 ml ), 10 - 30 % ethyl acetate / hexane to give 3 - ethoxy - 6 - methoxy - 1 , 2 - benzisoxazole ( 101 mg , 44 %) as white crystals . 1 h nmr spectrum ( cdcl 3 ) δ ( ppm ): 1 . 50 ( t , 3h ); 3 . 87 ( s , 3h ); 4 . 47 ( q , 2h ); 6 . 86 ( m , 2h ), 7 . 47 ( d , 1h ). boron tribromide ( 1 . 0m solution in dichloromethane ; 1 . 39 ml , 1 . 39 mmol ) was added to a stirred , − 78 ° cooled solution of benzisoxazole from part ( c ) ( 179 mg , 928 μmol ) in dichloromethane ( 4 ml ) under an argon atmosphere . the reaction mixture was gradually warmed to room temperature over approx . 2 hours , and stirred overnight . tlc ( silica , 2 : 1 hexane / ethyl acetate ) showed new polar material as well as unreacted starting material . the reaction was worked up by adding water ( 5 ml ) and ice . the aqueous phase was neutralized by addition of saturated nahco 3 solution , and saturated with nacl . the aqueous phase was extracted into dichloromethane ( 3 × 60 ml ), then the organic extracts combined and washed with brine ( 10 ml ) and dried ( naso 4 ). the product was purified by chromatography on silica ( 18 g ; eluent 2 . 5 %, 5 %, then 15 % ethyl acetate / hexane ). the first compound to elute was unreacted 3 - ethoxy - 6 - methoxy - 1 , 2 - benzisoxazole , ( 46 mg ), followed by 3 - ethoxy - 6 - hydroxy - 1 , 2 - benzisoxazole 108 mg ( 65 %). 1 h nmr spectrum ( cdcl 3 ) δ ( ppm ): 1 . 45 ( t , 3h ); 4 . 40 ( q , 2h ); 6 . 74 ( m , 2h ); 7 . 38 ( m , 1h ). a mixture of 2 -[- 1 -( 6 - methyl - 3 - pyridazinyl )- 4 - piperidinyl ] ethanol ( 42 mg , 188 μmol ), benzisoxazole from part ( d ) ( 28 mg , 156 μmol ) and polymer - supported triphenylphosphine ( 145 mg , 234 μmol ) in anhydrous thf ( 3 ml ) was cooled ( 0 °) and stirred under an argon atmosphere . neat diisopropylazodicarboxylate ( 46 μml , 234 μmol ) was added slowly and the reaction mixture was allowed to warm to room temperature and stir overnight . the reaction mixture was filtered , then pre - adsorbed onto silica and chromatographed on silica ( approx . 5 g ); using firstly 2 : 1 hexane / ethyl acetate as eluent , then gradually increased to 70 % ethyl acetate / hexane to afford compound 35 ( 44 mg ; 73 %) as a white powder . the 1 h nmr and ms data are recorded in table 6 below . compounds no 36 , 37 , 38 , 39 , 40 , 41 , 42 , 49 , 50 , 56 and 57 were prepared by reacting the appropriate het - a - alk - cl or het - a - alk - oh with the required 3 - substituted 6 - hydroxy - 1 , 2 - benzisoxazole ( or 1 , 2 - benzisothiazole ) following similar conditions to those described in example 6 . the 1 h nmr and / or ms data are recorded in table 6 below . the n - propylaminobenzothiazole derivative , compound no 24 , was prepared from the corresponding 2 - methoxy - benzothiazole ( compound 14 ) by heating with excess n - propylamine . the 1 h nmr and / or ms data are recorded in table 6 below . a mixture of equivalent amounts of 4 - aminoresorcinol hydrochloride and anhydrous sodium acetate in anhydrous ethanol was stirred for 16 hours at room temperature with a slight excess of tetraethyl orthocarbonate to give 2 - ethoxy - 6 - hydroxybenzoxazole in 60 % yield . ( b ) reaction of 2 - ethoxy - 6 - hydroxybenzoxazole with 2 -[- 1 -( 5 , 6 - dimethyl - 3 - pyridazinyl )- 4 - piperidinyl ] ethanol was carried out using a mitsunobu coupling and similar conditions to those described in example 6 part ( e ). the 1 h nmr and / or ms data for compound 28 are recorded in table 6 below . compounds no 29 , 30 , 31 , 32 , 33 , 34 , 47 and 48 were prepared by reacting the appropriate het - a - alk - cl or het - a - alk - oh with 2 - ethoxy - 6 - hydroxybenzoxazole following similar conditions to those described in example 1 , part ( c ) or example 6 part ( e ). the 1 h nmr and / or ms data are recorded in table 6 below . 6 - methoxy - 4 - hydroxycinnoline ( osborn , a . r . and schofield , k . j . chem . soc ., 1955 , 2100 ) was prepared from 2 - amino - 5 - methoxyacetophenone by diazotisation . phosphorous oxychloride ( 5 ml ) was added to a mix of dimethylaniline ( 157 mg , 1 . 3 mmol ) and 6 - methoxy - 4 - hydroxycinnoline ( 208 mg , 1 . 2 mmol ). the reaction was heated at reflux for 15 min , then cooled and concentrated under vacuum . the residue was partitioned between chloroform ( 100 ml ) and water ( 30 ml ), then the organic layer was washed with brine and dried ( na 2 so 4 ). chromatography of the residue adsorbed onto silica gel ( 3 g ) on silica gel ( 15 g ) eluent ch 2 cl 2 to 10 % ethylacetate / ch 2 cl 2 gave 6 - methoxy - 4 - chlorocinnoline ( 135 mg , 0 . 7 mmol ) in 59 % yield as white yellow solid . δ h ( cdcl 3 )= 4 . 03 ( s , 3h ); 7 . 28 ( d , 1h ); 7 . 51 ( dd , 1h ); 8 . 41 ( d , 1h ) and 9 . 22 ( br s , 1h ). ms ( esi ) ( m + h ) + 195 . a solution of 6 - methoxy - 4 - chlorocinnoline ( 135 mg , 0 . 7 mmol ) in toluene ( 7 ml ) was added to a stirred suspension of aluminium trichloride ( 231 mg , 1 . 73 mmol ) in toluene ( 7 ml ) and the red brown suspension was refluxed for 1 hr . the solvent was removed under vacuum and the residue was partitioned between water ( 20 ml ) and 10 % ethanol / chloroform ( 2 × 100 ml ). the organic layer was washed with brine and dried ( na 2 so 4 ). removal of the solvent under vacuum gave 6 - hydroxy - 4 - chlorocinnoline ( 154 mg ) as a single component by tlc ( 1 : 1 ethylacetate / hexanes ). δ h ( cd 3 od )= 7 . 33 ( d , 1h ); 7 . 56 ( dd , 1h ); 8 . 32 ( d , 1h ) and 9 . 15 ( br s 1h ). ms ( esi ) ( m + h ) + 181 . a solution of diad ( 42 mg , 0 . 21 mmol ) in thf ( 0 . 4 ml ) was added slowly to a suspension containing 6 - hydroxy - 4 - chlorocinnoline ( 30 mg , 0 . 17 mmol ), triphenylphosphine ( 65 mg , 0 . 25 mmol ) and 1 -( 6 - methyl - 3 - pyridazinyl )- 4 -( 2 - hydroxyethyl )- piperidine ( 40 mg , 0 . 18 mmol ) in thf ( 5 ml ) and the suspension cleared . the reaction was left to stir overnight , then the reaction was adsorbed onto silica ( 1 . 5 g ) and chromatography on silica gel ( 8 g ) eluent ethylacetate gave the product ( 50 mg , 0 . 13 mmol ) in 72 % yield . 1 h nmr δ h ( cd 3 od )= 1 . 35 ( m , 2h ); 1 . 9 ( m , 5h ); 2 . 46 ( s , 3h ); 2 . 95 ( m , 2h ); 4 . 34 ( m , 4h ); 7 . 19 ( d , 1h ); 7 . 26 ( d , 1h ); 7 . 42 ( d , 1h ); 7 . 64 ( dd , 1h ); 8 . 34 ( d 1h ) and 9 . 24 ( br s 1h ). a solution of sodium ethoxide ( 0 . 3 mmol ) in ethanol ( 0 . 15 ml ) was added dropwise to a solution of the above ( part c ) 4 - chlorocinnoline ( 23 mg , 60 μmol ) in dry ethanol ( 3 ml ) and the reaction was allowed to stir for 2 hr . the reaction was quenched with saturated ammonium chloride / brine ( 1 ml ) and solvents removed under vacuum . the residue was partitioned between brine ( 5 ml ) and 5 % ethanol / ethylacetate ( 2 × 30 ml ), dried ( na 2 so 4 ) and adsorbed onto silica ( 1 g ) under vacuum . chromatography on silica gel ( 8 g ) eluent 5 % methanol / ethylacetate gave compound no 53 ( 15 mg , 38 mol ) in 63 % yield . 4 - hydroxy - 7 - methoxy - cinnoline ( osborn , a . r . and schofield , k . j . chem . soc . ( 1955 ) 2100 ) was prepared following a similar method to that described in example 11 for the 6 - isomer . this compound was converted to compound 52 in a similar manner to that described in example 11 for the 6 - isomer . the 1 h nmr and ms data are recorded in table 6 below a mixture of 4 - nitroanthranilic acid ( 2 . 17 g , 11 . 91 mmol ) and formamide ( 1 . 5 ml , 38 . 43 mmol ) was heated at 165 ° c . for 4 hours . the warm reaction mixture was poured into ice / water ( 30 ml ) and the resulting precipitate was collected via filtration , to give an orange solid ( 2 . 16 g , 95 % yield ) which was dried over p 2 o 5 . this was used without further purification . 1 h nmr ; 8 . 24 ( d , 1h ), 8 . 32 ( s , 1h ), 8 . 34 ( s , 1h ), 8 . 35 ( d , 1h ). pd / c ( 100 mg ) was added as a single portion to a degassed and flushed ( 3 × ar ) suspension of 7 - nitroquinazolin - 4 - one ( 1 . 15 g , 6 . 02 mmol ) in methanol ( 150 ml ). the resulting black mixture was degassed , flushed with hydrogen and allowed to stir for 4 hours . the mixture was filtered through celite , washed well with methanol , and the filtrate concentrated to give a tanned solid . this was purified by column chromatography ( silica ) using 10 % methanol / ethyl acetate as the eluent . combined fractions gave a beige solid ( 949 mg , 98 % yield ). 1 h nmr ; 6 . 68 ( s , 1h ), 6 . 87 ( d , 1h ), 7 . 73 ( d , 1h ), 7 . 83 ( s , 1h ), 11 . 40 ( bs , 1h ). a solution of sodium nitrite ( 1 . 40 g , 20 . 32 mmol ) in water ( 17 ml ) was added dropwise to a cooled suspension of 7 - aminoquinazolin - 4 - one ( 712 mg , 4 . 42 mmol ) in sulfuric acid / water ( 4 . 4 ml , 18 ml ), keeping the temperature at approx . 0 ° c . the mixture was stirred at room temperature for 2 hours , diluted with water ( 15 ml ) and heated at reflux for 15 minutes . the cooled mixture was neutralized and the precipitate was collected via filtration , and purified by column chromatography ( silica ) using 10 % methanol / ethyl acetate as the eluent . the combined fractions gave an orange solid ( 541 mg , 76 %). 1 h nmr ; 6 . 85 - 6 . 91 ( m , 2h ), 7 . 87 ( s , 1h ), 7 . 92 ( s , 1h ). a mixture of 7 - hydroxyquinazolin - 4 - one ( 105 mg , 648 μmol ), phosphorous oxychloride ( 2 ml ), and dimethylaniline ( 85 μl , 671 μmol ) was heated at reflux for 15 minutes in an argon atmosphere . the cooled mixture was concentrated under vacuum , and kept in an argon atmosphere to avoid hydrolysis . this residue was dissolved in ethanol ( anhydrous , 3 ml ), and a solution of sodium ( 283 mg , 12 . 34 mmol ) in ethanol ( 3 ml ) was added dropwise . the resulting yellow mixture was stirred at room temperature under argon for 2 hours , acidified to ph 6 using nah 2 po 4 and extracted with ethyl acetate ( 3 × 50 ml ). the combined extracts were dried ( mgso 4 ), filtered and concentrated . the white solid ( 156 mg ) was used without further purification . 1 h nmr ; 1 . 49 ( t , 3h ), 4 . 78 ( q , 2h ), 7 . 26 ( d , 1h ), 7 . 43 ( s , 1h ), 8 . 11 ( d , 1h ), 8 . 83 ( s , 1h ). a mixture of 3 -[ 4 -( 2 - chloroethyl )- 1 - piperidinyl ]- 6 - methylpyridazine ( 76 mg , 318 μmol ), 7 - hydroxy - 4 - ethoxyquinazoline ( 100 mg , 526 μmol ), potassium carbonate ( 109 mg , 789 μmol ) and potassium iodide ( 53 mg , 319 μmol ) in dmf ( 5 ml ) was heated at 90 ° c . overnight in an argon atmosphere . the mixture was concentrated , and the residue partitioned between ethyl acetate ( 100 ml ), and water ( 20 ml ). the organic phase was dried ( mgso 4 ), filtered , concentrated and purified by column chromatography ( silica ), using gradient elution ( ethyl acetate - methanol / ea ). the combined fractions gave a white solid ( 22 mg , 18 %). the 1 h nmr data are recorded in table 6 below . compounds no 54 and 55 were prepared by reacting 3 -[ 4 -( 2 - chloroethyl )- 1 - piperidinyl ]- 6 - methylpyridazine with the appropriate 6 - hydroxyquinazoline following similar conditions to those described in example 13 , part ( e ). the 1 h nmr and / or ms data are recorded in table 6 below . aluminium trichloride ( 85 mg , 638 μmol ) was added as a single portion to a stirred mixture of 2 - chloro - 6 - methoxyquinoxaline ( 73 mg , 375 μmol ) and anhydrous toluene ( 3 ml ) under an argon atmosphere . the reaction mixture was heated at reflux for approx . 1 hr , then allowed to stir overnight at room temperature . tlc ( silica ; 2 : 1 hexane / ethyl acetate ) showed no remaining starting material and new polar material . water ( 1 ml ) and ice were added and the mixture stirred . the contents were partitioned between water ( 5 ml ) and ethyl acetate ( 100 ml ). the aqueous phase was extracted into ethyl acetate ( 50 ml ), then the organic extracts combined and washed with water ( 10 ml ), followed by brine ( 10 ml ) and dried ( na 2 so 4 ). concentration gave a brown solid , which was pre - adsorbed onto silica , then chromatographed on silica ( 9 g ); eluent : 20 % ethyl acetate in hexane then 25 % ethyl acetate in hexane to give 2 - chloro - 6 - hydroxyquinoxaline 54 mg ( 79 %). a mixture of 2 - chloro - 6 - hydroxyquinoxaline ( 52 mg , 288 μmol ), 3 -[- 4 -( 2 - chloroethyl )- 1 - piperidinyl ]- 6 - methylpyridazine ( 76 mg , 317 μmol ), potassium iodide ( 53 mg , 317 μmol ) and potassium carbonate ( 199 mg , 1 . 44 mmol ) in anhydrous dimethylformamide ( 2 ml ) was heated at 90 ° under an argon atmosphere for 2 days . tlc ( silica ; ethyl acetate ) showed new polar material . removal of the solvent under high vacuum and then chromatography on silica ( 5 g ; eluent : 30 % hexane in ethyl acetate ) gave the product as a white solid 68 mg ( 61 %). sodium ( 78 mg , 3 . 39 mmol ) was added portionwise to anhydrous ethanol ( 2 ml ). the resulting sodium ethoxide solution was added to a stirred solution of the chloroquinoxaline from part ( b ) ( 65 mg , 169 μmol ) in anhydrous tetrahydrofuran ( 2 ml ) under an argon atmosphere . the reaction mixture was heated at reflux for several hours then allowed to stir at room temperature overnight . the reaction mixture was quenched with saturated ammonium chloride solution ( 1 ml ), then the contents partitioned between water ( 3 ml ) and dichloromethane ( 50 ml ). the aqueous phase was extracted into dichloromethane ( 50 ml ), the organic extracts combined and washed with brine then dried ( na 2 so 4 ). the crude product was pre - adsorbed onto silica then chromatographed on silica ( 11 g ; eluent 2 : 1 ethyl acetate / hexane ) to give compound 43 as a white solid ( 57 mg 86 %). compounds no 44 , 45 and 46 were prepared by reacting 3 -[ 4 -( 2 - chloroethyl )- 1 - piperidinyl ]- 6 - methylpyridazine or 2 -[- 1 -( 6 - methyl - 3 - pyridazinyl )- 4 - piperidinyl ] ethanol with the appropriate 6 - hydroxyquinoxaline following similar conditions to those described in earlier examples . the 1 h nmr and / or ms data are recorded in table 6 below . the compounds of the invention which are listed in tables 1 to 5 were generally purified by chromatography on silica gel and were isolated as solids and characterised by 1 h nmr and mass spectroscopy . for convenience , the nmr and ms data are recorded in table 6 below . the ability of compounds to suppress virus replication and thereby protect cells from hrv - induced cpe was measured using human embryo lung ( mrc - 5cells infected with hrv type 1a . cells grown in 96 well tissue culture plates using conventional mammalian tissue culture medium ( such as minimum essential medium ) supplemented with fetal calf serum were used in an assay essentially similar to that described by sidwell and huffman ( applied microbiology , 22 , 797 - 801 ( 1971 )). test compounds were dissolved in 100 % anhydrous dimethyl sulfoxide and serially diluted in tissue culture medium . the antiviral potency of the test compounds was assessed by exposing replicate tissue culture wells to a selected dilution series of between 6 and 7 compound concentrations in the presence of sufficient test virus to invoke significant cpe over the course of the assay . control cells were also exposed to identical concentrations of compounds in the absence of virus or were infected with virus under the same conditions but in the absence of compounds . compounds of established anti - hrv efficacy ( enviroxime , ribavirin and pirodavir ) were assayed by identical procedures in parallel to the test compounds . tissue culture media were identically supplemented to maintain cell viability and support viral growth while suppressing bacterial growth over the period of the assay ( supplements : 2 % fetal calf serum , 0 . 01 % sodium bicarbonate , 50 μg / ml gentamicin , 5 μm magnesium chloride , 10 mm of zinc chloride ). the assays were incubated at 37 ° c . in a 5 % co 2 atmosphere until significant cpe was observed by microscopic examination of the untreated , hrv infected control cells ( generally between 5 and 8 days ). at this time all infected cultures were examined by eye using a light microscope and cpe scored on a scale of 0 ( no cpe ) to 4 ( maximum cpe ). uninfected treated cultures were similarly scored for cytotoxic effects ( e . g ., cell enlargement , granularity , rounding , detachment ). these scores were used to generate ec 50 ( concentration of compound yielding 50 % antiviral efficacy ) and cc 50 ( concentration of compound yielding 50 % cytotoxicity ) values by line regression analysis from plots of compound concentration versus % cpe or % cytotoxicity , respectively . as an alternative to a cc 50 value , cytoxicity in some cases was expressed as the minimum toxic concentration ( mtc ). the mtc corresponds to the lowest compound concentration at which cytotoxic effects were observed . in some cases the visual scoring system described above was validated by vital dye staining to measure cell viability . the vital dye technique used was a modification of the method described by mcmanus ( appl . environment . microbiol ., 31 , 35 - 38 , 1976 ). after the assay had been scored by eye with the aid of a microscope , 100 μl of neutral red ( nr ) solution ( 0 . 34 % nr in phosphate buffered saline ( pbs )) was added to each well and mixed gently . the assays were returned to the 37 ° c . incubator for 2 hours to facilitate uptake of the nr by viable cells . the medium / nr mixture was then aspirated from the surface of the cells , which were washed twice with pbs . 0 . 25 ml of absolute ethanol containing sorensen &# 39 ; s citrate buffer i , was added with gentle mixing and the assays incubated at room temperature in the dark for 30 minutes to dissolve the nr . nr staining of viable cells was then quantified spectrophotometrically by measuring the color density of the nr solution using a biotek el - 309 microplate reader at dual wavelengths of 540 and 405 nm . the differences in the two readings were automatically determined to eliminate background errors . ec 50 and cc 50 values were determined by regression analysis matching compound concentration to nr staining . the results are shown in the tables 7 and 8 below . selectivity indices ( si ) are the cc 50 or mtc divided by the ec 50 . tables 7 and 8 also show ic 50 data for the testing of the compounds of the invention against hrv strains 2 and 14 . these results were obtained using a similar cpe method to that described above for hrv1a . throughout this specification and the claims that follow , unless the context requires otherwise , the word “ comprise ”, and variations such as “ comprises ” and “ comprising ”, will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps . those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described . it is to be understood that the invention includes all such variations and modifications . the invention also includes all of the steps , features , compositions and compounds referred to or indicated in this specification , individually or collectively , and any and all combinations of any two or more of said steps or features . all of the above u . s . patents , u . s . patent application publications , u . s . patent applications , foreign patents , foreign patent applications and non - patent publications referred to in this specification and / or listed in the application data sheet , are incorporated herein by reference , in their entirety .
this invention relates to compounds of formula i their salts , and pharmaceutically acceptable derivatives thereof , pharmaceutical compositions comprising these compounds and their use in the treatment of picornavirus infections in mammals , as well as novel intermediates useful in the preparation of the compounds of formula i .