Fused-ring compounds and use thereof as drugs

Abstract

The present invention provides a fused ring compound of the following formula [I] wherein each symbol is as defined in the specification, a pharmaceutically acceptable salt thereof, and a therapeutic agent for hepatitis C, which contains this compound. The compound of the present invention shows an anti-hapatitis C virus (HCV) action based on the HCV polymerase inhibitory activity, and is useful as a therapeutic agent or prophylactic agent for hepatitis C.

1 . A therapeutic agent for hepatitis C, which comprises a fused ring compound of the following formula [I] or a pharmaceutically acceptable salt thereof as an active ingredient:  
     
       
         
         
             
             
         
       
     
     wherein 
 a broken line is a single bond or a double bond,  
 G 1  is C(—R 1 ) or a nitrogen atom,  
 G 2  is C(—R 2 ) or a nitrogen atom,  
 G 3  is C(—R 3 ) or a nitrogen atom,  
 G 4  is C(—R 1 ) or a nitrogen atom,  
 G 5 , G 6 , G 8  and G 9  are each independently a carbon atom or a nitrogen atom,  
 G 7  is C(—R 7 ), an oxygen atom, a sulfur atom, or a nitrogen atom optionally substituted by R 8 , 
 wherein R 1 , R 2 , R 3  and R 4  are each independently,  
 (1) hydrogen atom,  
 (2) C 1-6  alkanoyl,  
 (3) carboxyl,  
 (4) cyano,  
 (5) nitro,  
 (6) C 1-6  alkyl optionally substituted by 1 to 3 substituent(s) selected from the following group A, 
 group A; halogen atom, hydroxyl group, carboxyl, amino, C 1-6  alkoxy, C 1-6  alkoxy C 1-6  alkoxy, C 1-6  alkoxycarbonyl and C 1-6  alkylamino,  
 
 
 (7) —COOR a1  
 wherein R a1  is optionally substituted C 1-6  alkyl (as defined above), C 6-14  aryl C 1-6  alkyl optionally substituted by 1 to 5 substituent(s) selected from the following group B or glucuronic acid residue,  
 group B; halogen atom, cyano, nitro, C 1-6  alkyl, halogenated C 1-6  alkyl, C 1-6  alkanoyl, —(CH 2 ) r —COOR b1 , —(CH 2 ) r —CONR b1 R b2 , —(CH 2 ) r —NR b1 R b2 , —(CH 2 ) r —NR b1 —COR b2 , —(CH 2 ) r —NHSO 2 R b1 , —(CH 2 ) r —OR b1 , —(CH 2 ) r —SR b1 , —(CH 2 ) r —SO 2 R b1  and —(CH 2 ) r —SO 2 NR b1 R b2  
 wherein R b1  and R b2  are each independently hydrogen atom or C 1-6  alkyl and r is 0 or an integer of 1 to 6,  
 
 
 (8) —CONR a2 R a3  
 wherein R a2  and R a3  are each independently hydrogen atom, C 1-6  alkoxy or optionally substituted C 1-6  alkyl (as defined above),  
 
 (9) —C(═NR a4 )NH 2  
 wherein R a4  is hydrogen atom or hydroxyl group,  
 
 (10) —NHR a5  
 wherein R a5  is hydrogen atom, C 1-6  alkanoyl or C 1-6  alkylsulfonyl,  
 
 (11) —OR a6  
 wherein R a6  is hydrogen atom or optionally substituted C 1-6  alkyl(as defined above),  
 
 (12) —SO 2 R a7  
 wherein R a7  is hydroxyl group, amino, C 1-6  alkyl or C 1-6  alkylamino,  
 
 (13) —P(═O)(OR a31 ) 2  
 wherein R a31  is hydrogen atom, optionally substituted C 1-6  alkyl (as defined above) or C 6-14  aryl C 1-6  alkyl optionally substituted by 1 to 5 substituent(s) selected from the above group B  
 
 or  
 (14) heterocyclic group having 1 to 4 heteroatom(s) selected from an oxygen atom, a nitrogen atom and a sulfur atom, and  
 R 7  and R 8  are each hydrogen atom or optionally substituted C 1-6  alkyl (as defined above),  
 ring Cy is 
 (1) C 3-8  cycloalkyl optionally substituted by 1 to 5 substituent(s) selected from the following group C, 
 group C; hydroxyl group, halogen atom, C 1-6  alkyl and C 1-6  alkoxy,  
 
 
 (2) C 3-8  cycloalkenyl optionally substituted by 1 to 5 substituent(s) selected from the above group C, or  
                     wherein u and v are each independently an integer of 1 to 3,    
 ring A is 
 (1) C 6-14  aryl,  
 (2) C 3-8  cycloalkyl,  
 (3) C 3-8  cycloalkenyl or  
 (4) heterocyclic group having 1 to 4 heteroatom(s) selected from an oxygen atom, a nitrogen atom and a sulfur atom,  
 
 R 5  and R 6  are each independently 
 (1) hydrogen atom,  
 (2) halogen atom,  
 (3) optionally substituted C 1-6  alkyl (as defined above) or  
 (4) —OR a8  
 wherein R a8  is hydrogen atom, C 1-6  alkyl or C 6-14  aryl C 1-6  alkyl, and  
 
 
 X is 
 (1) hydrogen atom,  
 (2) halogen atom,  
 (3) cyano,  
 (4) nitro,  
 (5) amino, C 1-6  alkanoylamino,  
 (6) C 1-6  alkylsulfonyl,  
 (7) optionally substituted C 1-6  alkyl (as defined above),  
 (8) C 2-6  alkenyl optionally substituted by 1 to 3 substituent(s) selected from the above group A,  
 (9) —COOR a9  
 wherein R a9  is hydrogen atom or C 1-6  alkyl,  
 
 
 (10) —CONH—(CH 2 ) l —R a10  
 wherein R a10  is optionally substituted C 1-6  alkyl (as defined above), C 1-6  alkoxycarbonyl or C 1-6  alkanoylamino and l is 0 or an integer of 1 to 6,  
 
 (11) —OR a11  
 wherein R a11  is hydrogen atom or optionally substituted C 1-6  alkyl (as defined above)  
 
 or  
                     wherein    ring B is 
 (1′) C 6-14  aryl,  
 (2′) C 3-8  cycloalkyl or  
 (3′) heterocyclic group (as defined above),  
   each Z is independently 
 (1′) a group selected from the following group D,  
 (2′) C 6-14  aryl optionally substituted by 1 to 5 substituent(s) selected from the following group D,  
 (3′) C 3-8  cycloalkyl optionally substituted by 1 to 5 substituent(s) selected from the following group D,  
 (4′) C 6-14  aryl C 1-6  alkyl optionally substituted by 1 to 5 substituent(s) selected from the following group D,  
 (5′) heterocyclic group optionally substituted by 1 to 5 substituent(s) selected from the following group D,  
 wherein the heterocyclic group has 1 to 4 hetero-atom(s) selected from an oxygen atom, a nitrogen atom and a sulfur atom, or  
 (6′) heterocycle C 1-6  alkyl optionally substituted by 1 to 5 substituent(s) selected from the following group D, 
 wherein the heterocycle C 1-6  alkyl is C 1-6  alkyl substituted by heterocyclic group optionally substituted by 1 to 5 substituent(s) selected from the group D, as defined above,  
 
 group D:  
 (a) hydrogen atom,  
 (b) halogen atom,  
 (c) cyano,  
 (d) nitro,  
 (e) optionally substituted C 1-6  alkyl (as defined above),  
 (f) —(CH 2 ) t —COR a18 ,  
 (hereinafter each t means independently 0 or an integer of 1 to 6), 
 wherein R a18  is  
 (1″) optionally substituted C 1-6  alkyl (as defined above),  
 (2″) C 6-14  aryl optionally substituted by 1 to 5 substituent(s) selected from the above group B or  
 (3″) heterocyclic group optionally substituted by 1 to 5 substituent(s) selected from the above group B  
  wherein the heterocyclic group has 1 to 4 heteroatom(s) selected from an oxygen atom, a nitrogen atom and a sulfur atom,  
 
 (g) —(CH 2 ) t —COOR a19  
 wherein R a19  is hydrogen atom, optionally substituted C 1-6  alkyl (as defined above) or C 6-14  aryl C 1-6  alkyl optionally substituted by 1 to 5 substituent(s) selected from the above group B  
 
 (h) —(CH 2 ) t —CONR a27 R a28  
 wherein R a27  and R a28  are each independently,  
  (1″) hydrogen atom,  
  (2″) optionally substituted C 1-6  alkyl (as defined above),  
  (3″) C 6-14  aryl optionally substituted by 1 to 5 substituent(s) selected from the above group B,  
  (4″) C 6-14  aryl C 1-6  alkyl optionally substituted by 1 to 5 substituent(s) selected from the above group B,  
  (5″) heterocyclic group optionally substituted by 1 to 5 substituent(s) selected from the above group B,  
  (6″) heterocycle C 1-6  alkyl optionally substituted by 1 to 5 substituent(s) selected from the above group B,  
 wherein the heterocycle C 1-6  alkyl is C 1-6  alkyl substituted by heterocyclic group optionally substituted by 1 to 5 substituent(s) selected from the above group B, as defined above,  
  (7″) C 3-8  cycloalkyl optionally substituted by 1 to 5 substituent(s) selected from the above group B,  
  (8″) C 3-8  cycloalkyl C 1-6  alkyl optionally substituted by 1 to 5 substituent(s) selected from the above group B,  
  (9″) hydroxyl group or  
  (10″) C 1-6  alkoxy,  
 
 (i) —(CH 2 ) t —C(═NR a33 )NH 2    
 wherein R a33  is hydrogen atom, C 1-6  alkyl, hydroxyl group or C 1-6  alkoxy,  
 (j) —(CH 2 ) t —OR a20  
 wherein R a20  is  
 (1″) hydrogen atom,  
 (2″) optionally substituted C 1-6  alkyl (as defined above),  
 (3″) optionally substituted C 2-6  alkenyl (as defined above),  
 (4″) C 2-6  alkynyl optionally substituted by 1 to 3 substituent(s) selected from the above group A,  
 (5″) C 6-14  aryl optionally substituted by 1 to 5 substituent(s) selected from the above group B,  
 (6″) C 6-14  aryl C 1-6  alkyl optionally substituted by 1 to 5 substituent(s) selected from the above group B,  
 (7″) heterocyclic group optionally substituted by 1 to 5 substituent(s) selected from the above group B,  
 (8″) heterocycle C 1-6  alkyl optionally substituted by 1 to 5 substituent(s) selected from the above group B,  
 (9″) C 3-8  cycloalkyl optionally substituted by 1 to 5 substituent(s) selected from the above group B, or  
 (10″) C 3-8  cycloalkyl C 1-6  alkyl optionally substituted by 1 to 5 substituent(s) selected from the above group B,  
 
 (k) —(CH 2 ) t —O—(CH 2 ) p —COR a21 ′
 wherein R a21  is amino, C 1-6  alkylamino or heterocyclic group optionally substituted by 1 to 5 substituent(s) selected from the above group B, and p is 0 or an integer of 1 to 6,  
 
 (l) —(CH 2 ) p —NR a22 R a23  
 wherein R a22  and R a23  are each independently  
 (1″) hydrogen atom,  
 (2″) optionally substituted C 1-6  alkyl (as defined above),  
 (3″) C 6-14  aryl optionally substituted by 1 to 5 substituent(s) selected from the above group B,  
 (4″) C 6-14  aryl C 1-6  alkyl optionally substituted by 1 to 5 substituent(s) selected from the above group B,  
 (5″) heterocycle C 1-6  alkyl optionally substituted by 1 to 5 substituent(s) selected from the above group B or  
 (6″) heterocyclic group optionally substituted by 1 to 5 substituent(s) selected from the above group B,  
 
 (m) —(CH 2 ) t —NR a29 CO—R a24  
 wherein R a29  is hydrogen atom, C 1-6  alkyl or C 1-6  alkanoyl, and R a24  is  
 (1″) amino,  
 (2″) C 1-6  alkylamino,  
 (3″) optionally substituted C 1-6  alkyl (as defined above),  
 (4″) C 6-14  aryl optionally substituted by 1 to 5 substituent(s) selected from the above group B,  
 (5″) heterocyclic group optionally substituted by 1 to 5 substituent(s) selected from the above group B or  
 (6″) heterocycle C 1-6  alkyl optionally substituted by 1 to 5 substituent(s) selected from the above group B,  
 
 (n) —(CH 2 ) t —NR a29 SO 2 —R a25  
 wherein R a29  is as defined above, and  
 R a25  is hydrogen atom, optionally substituted C 1-6  alkyl (as defined above),  
 C 6-14  aryl optionally substituted by 1 to 5 substituent(s) selected from the above group B or heterocyclic group optionally substituted by 1 to 5 substituent(s) selected from the above group B,  
 
 (o) —(CH 2 ) t —S(O) q —R a25  
 wherein R a25  is as defined above, and q is 0, 1 or 2,  
 
 (p) —(CH 2 ) t —SO 2 —NHR a26  
 wherein R a26  is hydrogen atom, optionally substituted C 1-6  alkyl (as defined above), C 6-14  aryl optionally substituted by 1 to 5 substituent(s) selected from the above group B or heterocyclic group optionally substituted by 1 to 5 substituent(s) selected from the above group B,  
 
 and  
 (q) heterocyclic group having 1 to 4 heteroatom(s) selected from an oxygen atom, a nitrogen atom and a sulfur atom, and  
   w is an integer of 1 to 3, and    Y is 
 (1′) a single bond,  
 (2′) C 1-6  alkylene,  
 (3′) C 2-6  alkenylene,  
 (4′) —(CH 2 ) m —O—(CH 2 ) n —, 
 (hereinafter m and n are each independently 0 or an integer of 1 to 6),  
 
 (5′) —CO—,  
 (6′) —CO 2 —(CH 2 ) n —,  
 (7′) —CONH—(CH 2 ) n —NH—,  
 (8′) —NHCO 2 —,  
 (9′) —NHCONH—,  
 (10′) —O—(CH 2 ) n —CO—,  
 (11′) —O—(CH 2 ) n —O—,  
 (12′) —SO 2 —,  
 (13′) —(CH 2 ) m —NR a12  (CH 2 ) n , 
 wherein R a12  is  
 (1″) hydrogen atom,  
 (2″) optionally substituted C 1-6  alkyl (as defined above),  
 (3″) C 6-14  aryl C 1-6  alkyl optionally substituted by 1 to 5 substituent(s) selected from the above group B,  
 (4″) C 6-14  aryl optionally substituted by 1 to substituent(s) selected from the above group B,  
 (5″) —COR b5    
  wherein R b5  is hydrogen atom, optionally substituted C 1-6  alkyl (as defined above), C 6-14  aryl optionally substituted by 1 to 5 substituent(s) selected from the above group B or C 6-14  aryl C 1-6  alkyl optionally substituted by 1 to 5 substituent(s) selected from the above group B,  
 (6″) —COOR b5  (R b5  is as defined above) or  
 (7″) —SO 2 R b5  (R b5  is as defined above),  
 
 (14′) —NR a12 CO— (R a12  is as defined above),  
 (15′) —CONR a13 —(CH 2 ) n —
 wherein R a13  is hydrogen atom, optionally substituted C 1-6  alkyl (as defined above) or C 6-14  aryl C 1-6  alkyl optionally substituted by 1 to 5 substituent(s) selected from the above group B,  
 
 (16′) —CONH—CHR a14 —
 wherein R a14  is C 6-14  aryl optionally substituted by 1 to 5 substituent(s) selected from the above group B,  
 
 (17′) —O—(CH 2 ) m —CR a15 R a16 —(CH 2 ) n —
 wherein R a15  and R a16  are each independently  
 (1″) hydrogen atom,  
 (2″) carboxyl,  
 (3″) C 1-6  alkyl,  
 (4″) —OR b6    
 wherein R b6  is C 1-6  alkyl or C 6-14  aryl C 1-6  alkyl,  
 or  
 (5″) —NHR b7    
 wherein R b7  is hydrogen atom, C 1-6  alkyl, C 1-6  alkanoyl or C 6-14  aryl C 1-6  alkyloxycarbonyl, or R a15  is optionally  
                     
  wherein n′, ring B′, Z′ and w′ are the same as the above-mentioned n, ring B, Z and w, respectively, and may be the same as or different from the respective counterparts,  
 
 (18′) —(CH 2 ) n —NR a12 —CHR a15 — (R a12  and R a15  are each as defined above),  
 (19′) —NR a17 SO 2 —
 wherein R a17  is hydrogen atom or C 1-6  alkyl,  
 
 (20′) —S(O) e —(CH 2 ) m —CR a15 R a16 —(CH 2 ) n — (e is 0, 1 or 2, R a15  and R a16  are each as defined above),  
 or  
 (21′) —(CH 2 ) m —CR a15 R a16 —(CH 2 ) n — (R a15  and R a16  are each as defined above).  
   
 
   
   
       2 .- 28 . (canceled)  
   
   
       29 . A fused ring compound of the following formula [II] 
     
       
         
         
             
             
         
       
     
     wherein 
 the moiety  
                     
 is a fused ring selected from  
                     
 wherein R 1 , R 2 , R 3  and R 4  are each independently,  
 (1) hydrogen atom,  
 (2) C 1-6  alkanoyl,  
 (3) carboxyl,  
 (4) cyano,  
 (5) nitro,  
 (6) C 1-6  alkyl optionally substituted by 1 to 3 substituent(s) selected from the following group A, 
 group A; halogen atom, hydroxyl group, carboxyl, amino, C 1-6  alkoxy, C 1-6  alkoxy C 1-6  alkoxy, C 1-6  alkoxycarbonyl and C 1-6  alkylamino,  
 
 (7) —COOR a1  
 wherein R a1  is optionally substituted C 1-6  alkyl (as defined above), C 6-14  aryl C 1-6  alkyl optionally substituted by 1 to 5 substituent(s) selected from the following group B or glucuronic acid residue,  
 group B; halogen atom, cyano, nitro, C 1-6  alkyl, halogenated C 1-6  alkyl, C 1-6  alkanoyl, —(CH 2 ) r —COOR b1 , —(CH 2 ) r —CONR b1 R b2 , —(CH 2 ) r —NR b1 R b2 , —(CH 2 ) r —NR b1 —COR b2 , —(CH 2 ) r —NHSO 2 R b1 , —(CH 2 ) r —OR b1 , —(CH 2 ) r —SR b1 , —(CH 2 ) r —SO 2 R b1  and —(CH 2 ) r —SO 2 NR b1 R b2  
 wherein R b1  and R b2  are each independently hydrogen atom or C 1-6  alkyl and r is 0 or an integer of 1 to 6,  
 
 
 (8) —CONR a2 R a3  
 wherein R a2  and R a3  are each independently hydrogen atom, C 1-6  alkoxy or optionally substituted C 1-6  alkyl (as defined above),  
 
 (9) —C(═NR a4 )NH 2  
 wherein R a4  is hydrogen atom or hydroxyl group,  
 
 (10) —NHR a5  
 wherein R a5  is hydrogen atom, C 1-6  alkanoyl or C 1-6  alkylsulfonyl,  
 
 (11) —OR a6  
 wherein R a6  is hydrogen atom or optionally substituted C 1-6  alkyl (as defined above),  
 
 (12) —SO 2 R a7  
 wherein R a7  is hydroxyl group, amino, C 1-6  alkyl or C 1-6  alkylamino,  
 
 (13) —P(═O)(OR a31 ) 2  
 wherein R a31  is hydrogen atom, optionally substituted C 1-6  alkyl (as defined above) or C 6-14  aryl C 1-6  alkyl optionally substituted by 1 to 5 substituent(s) selected from the above group B,  
 
 or  
 (14) heterocyclic group having 1 to 4 heteroatom(s) selected from an oxygen atom, a nitrogen atom and a sulfur atom, and 
 R 7  is hydrogen atom or optionally substitute C 1-6  alkyl (as defined above),  
 
 ring Cy′ is 
 (1) C 3-8  cycloalkyl optionally substituted by 1 to 5 substituent(s) selected from the following group C, 
 group C; hydroxyl group, halogen atom, C 1-6  alkyl and C 1-6  alkoxy, or  
                     wherein u and v are each independently an integer of 1 to 3,    
 
 
 ring A′ is a group selected from a group consisting of phenyl, pyridyl, pyrazinyl, pyrimidinyl, pyridazinyl, cyclohexyl, cyclohexenyl, furyl and thienyl,  
 R 5′  and R 6′  are each independently 
 (1) hydrogen atom,  
 (2) halogen atom,  
 (3) optionally substituted C 1-6  alkyl (as defined above) or  
 (4) hydroxyl group  
 
 ring B is 
 (1) C 6-14  aryl,  
 (2) C 3-8  cycloalkyl or  
 (3) heterocyclic group having 1 to 4 heteroatom(s) selected from an oxygen atom, a nitrogen atom and a sulfur atom,  
 
 each Z is independently 
 (1) a group selected from the following group D,  
 (2) C 6-14  aryl optionally substituted by 1 to 5 substituent(s) selected from the following group D,  
 (3) C 3-8  cycloalkyl optionally substituted by 1 to 5 substituent(s) selected from the following group D,  
 (4) C 6-14  aryl C 1-6  alkyl optionally substituted by 1 to 5 substituent(s) selected from the following group D,  
 (5) heterocyclic group optionally substituted by 1 to 5 substituent(s) selected from the following group D wherein the heterocyclic group has 1 to 4 heteroatom(s) selected from an oxygen atom, a nitrogen atom and a sulfur atom, or  
 (6) heterocycle C 1-6  alkyl optionally substituted by 1 to 5 substituent(s) selected from the following group D wherein the heterocycle C 1-6  alkyl is C 1-6  alkyl substituted by heterocyclic group optionally substituted by 1 to 5 substituent(s) selected from the group D, as defined above, 
 group D: 
 (a) hydrogen atom,  
 (b) halogen atom,  
 (c) cyano,  
 (d) nitro,  
 (e) optionally substituted C 1-6  alkyl (as defined above),  
 (f) —(CH 2 ) t —COR a18 , 
 (hereinafter each t means independently 0 or an integer of 1 to 6),  
  wherein R a18  is  
  (1′) optionally substituted C 1-6  alkyl (as defined above),  
  (2′) C 6-14  aryl optionally substituted by 1 to 5 substituent(s) selected from the above group B or  
  (3′) heterocyclic group optionally substituted by 1 to 5 substituent(s) selected from the above group B  
  wherein the heterocyclic group has 1 to 4 heteroatom(s) selected from an oxygen atom, a nitrogen atom and a sulfur atom,  
 
 
 (g) —(CH 2 ) t —COOR a19  
 wherein R a19  is hydrogen atom, optionally substituted C 1-6  alkyl (as defined above) or C 6-14  aryl C 1-6  alkyl optionally substituted by 1 to 5 substituent(s) selected from the above group B,  
 
 (h) —(CH 2 ) t —CONR a27 R a28  
 wherein R a27  and R a28  are each independently,  
  (1′) hydrogen atom,  
  (2′) optionally substituted C 1-6  alkyl (as defined above),  
  (3′) C 6-14  aryl optionally substituted by 1 to 5 substituent(s) selected from the above group B,  
  (4′) C 6-14  aryl C 1-6  alkyl optionally substituted by 1 to 5 substituent(s) selected from the above group B,  
  (5′) heterocyclic group optionally substituted by 1 to 5 substituent(s) selected from the above group B,  
  (6′) heterocycle C 1-6  alkyl optionally substituted by 1 to 5 substituent(s) selected from the above group B,  
 wherein the heterocycle C 1-6  alkyl is C 1-6  alkyl substituted by heterocyclic group optionally substituted by 1 to 5 substituent(s) selected from the above group B, as defined above,  
  (7′) C 3-8  cycloalkyl optionally substituted by 1 to 5 substituent(s) selected from the above group B,  
  (8′) C 3-8  cycloalkyl C 1-6  alkyl optionally substituted by 1 to 5 substituent(s) selected from the above group B,  
  (9′) hydroxyl group or  
  (10′) C 1-6  alkoxy,  
 
 (i) —(CH 2 ) t —C(═NR a33 )NH 2  
 wherein R a33  is hydrogen atom, C 1-6  alkyl, hydroxyl group or C 1-6  alkoxy,  
 
 (j) —(CH 2 ) t —OR a20  
 wherein R a20  is  
 (1′) hydrogen atom,  
 (2′) optionally substituted C 1-6  alkyl (as defined above),  
 (3′) optionally substituted C 2-6  alkenyl (as defined above),  
 (4′) C 2-6  alkynyl optionally substituted by 1 to 3 substituent(s) selected from the above group A,  
 (5′) C 6-14  aryl optionally substituted by 1 to 5 substituent(s) selected from the above group B,  
 (6′) C 6-14  aryl C 1-6  alkyl optionally substituted by 1 to 5 substituent(s) selected from the above group B,  
 (7′) heterocyclic group optionally substituted by 1 to 5 substituent(s) selected from the above group B,  
 (8′) heterocycle C 1-6  alkyl optionally substituted by 1 to 5 substituent(s) selected from the above group B,  
 (9′) C 3-8  cycloalkyl optionally substituted by 1 to 5 substituent(s) selected from the above group B, or  
 (10′) C 3-8  cycloalkyl C 1-6  alkyl optionally substituted by 1 to 5 substituent(s) selected from the above group B,  
 
 (k) —(CH 2 ) t —O—(CH 2 ) p —COR a21  
 wherein R a21  is amino, C 1-6  alkylamino or heterocyclic group optionally substituted by 1 to 5 substituent(s) selected from the above group B,  
 and p is 0 or an integer of 1 to 6,  
 
 (l) —(CH 2 ) t —NR a22 R a23  
 wherein R a22  and R a23  are each independently  
 (1′) hydrogen atom,  
 (2′) optionally substituted C 1-6  alkyl (as defined above),  
 (3′) C 6-14  aryl optionally substituted by 1 to 5 substituent(s) selected from the above group B,  
 (4′) C 6-14  aryl C 1-6  alkyl optionally substituted by 1 to 5 substituent(s) selected from the above group B,  
 (5′) heterocycle C 1-6  alkyl optionally substituted by 1 to 5 substituent(s) selected from the above group B or  
 (6′) heterocyclic group optionally substituted by 1 to 5 substituent(s) selected from the above group B,  
 
 (m) —(CH 2 ) t —NR a29 CO—R a24  
 wherein R a29  is hydrogen atom, C 1-6  alkyl or C 1-6  alkanoyl, and  
 R a14  is  
 (1′) amino,  
 (2′) C 1-6  alkylamino,  
 (3′) optionally substituted C 1-6  alkyl (as defined above),  
 (4′) C 6-14  aryl optionally substituted by 1 to 5 substituent(s) selected from the above group B,  
 (5′) heterocyclic group optionally substituted by 1 to 5 substituent(s) selected from the above group B, or  
 (6′) heterocycle C 1-6  alkyl optionally substituted by 1 to 5 substituent(s) selected from the above group B,  
 
 (n) —(CH 2 ) t —NR a29 SO 2 —R a25  
 wherein R a29  is as defined above, and  
 R a25  is hydrogen atom, optionally substituted C 1-6  alkyl (as defined above), C 6-14  aryl optionally substituted by 1 to 5 substituent(s) selected from the above group B or heterocyclic group optionally substituted by 1 to 5 substituent(s) selected from the above group B,  
 
 (o) —(CH 2 ) t —S(O) q —R a25  
 wherein R a25  is as defined above, and q is 0, 1 or 2,  
 
 (p) —(CH 2 ) t —SO 2 —NHR a26  
 wherein R a26  is hydrogen atom, optionally substituted C 1-6  alkyl (as defined above), C 6-14  aryl optionally substituted by 1 to 5 substituent(s) selected from the above group B or heterocyclic group optionally substituted by 1 to 5 substituent(s) selected from the above group B,  
 
 and  
 (q) heterocyclic group having 1 to 4 heteroatom(s) selected from an oxygen atom, a nitrogen atom and a sulfur atom,  
 
 w is an integer of 1 to 3, and  
 Y is 
 (1) a single bond,  
 (2) C 1-6  alkylene,  
 (3) C 2-6  alkenylene,  
 (4) —(CH 2 ) m —O—(CH 2 ) n —, 
 (hereinafter m and n are each independently 0 or an integer of 1 to 6),  
 
 (5) —CO—,  
 (6) —CO 2 —(CH 2 ) n —,  
 (7) —CONH—(CH 2 ) n —NH—,  
 (8) —NHCO 2 —,  
 (9) —NHCONH—,  
 (10) —O—(CH 2 ) n —CO—,  
 (11) —O—(CH 2 ) n —O—,  
 (12) —SO 2 —,  
 (13) —(CH 2 ) m —NR a12 —(CH 2 ) n —
 wherein R a12  is  
 (1′) hydrogen atom,  
 (2′) optionally substituted C 1-6  alkyl (as defined above),  
 (3′) C 6-14  aryl C 1-6  alkyl optionally substituted by 1 to 5 substituent(s) selected from the above group B,  
 (4′) C 6-14  aryl optionally substituted by 1 to 5 substituent(s) selected from the above group B,  
 (5′) —COR b5    
  wherein R b5  is hydrogen atom, optionally substituted C 1-6  alkyl (as defined above),  
  C 6-14  aryl optionally substituted by 1 to 5 substituent(s) selected from the above group B or C 6-14  aryl C 1-6  alkyl optionally substituted by 1 to 5 substituent(s) selected from the above group B,  
 (6′) —COOR b5  (R b5  is as defined above) or  
 (7′) —SO 2 R b5  (R b5  is as defined above),  
 
 (14) —NR a12 CO— (R a12  is as defined above),  
 (15) —CONR a13 —(CH 2 ) n —
 wherein R a13  is hydrogen atom, optionally substituted C 1-6  alkyl (as defined above) or C 6-14  aryl C 1-6  alkyl optionally substituted by 1 to 5 substituent(s) selected from the above group B,  
 
 (16) —CONH—CHR a14  
 wherein R a14  is C 6-14  aryl optionally substituted by 1 to 5 substituent(s) selected from the above group B,  
 
 (17) —O—(CH 2 ) m —CR a15 R a16 —(CH 2 ) n —
 wherein R a15  and R a16  are each independently  
 (1′) hydrogen atom,  
 (2′) carboxyl,  
 (3′) C 1-6  alkyl,  
 (4′) —OR b6    
 wherein R b6  is C 1-6  alkyl or C 6-14  aryl C 1-6  alkyl,  
 or  
 (5′) —NHR b7    
 wherein R b7  is hydrogen atom, C 1-6  alkyl, C 1-6  alkanoyl or C 6-14  aryl C 1-6  alkyloxycarbonyl, or R a15  is optionally  
                     
  wherein n′, ring B′, Z′ and w′ are the same as the above-mentioned n, ring B, Z and w, respectively, and may be the same as or different from the respective counterparts,  
 
 (18) —(CH 2 ) n —NR a12 —CHR a15 —(R a12  and R a15  are each as defined above),  
 (19) —NR a17 SO 2  
 wherein R a17  is hydrogen atom or C 1-6  alkyl,  
 
 (20) —S(O) e —(CH 2 ) m —CR a15 R a16 —(CH 2 ) n — (e is 0, 1 or 2, 
 R a15  and R a16  are each as defined above),  
 
 or  
 (21) —(CH 2 ) m —CR a15 R a16 —(CH 2 ) n —(R a15  and R a16  are each as defined above),  
 or a pharmaceutically acceptable salt thereof.  
 
 
 
   
   
       30 .- 63 . (canceled)  
   
   
       64 . A hepatitis C virus polymerase inhibitor comprising a fused ring compound of  claim 1 , or a pharmaceutically acceptable salt thereof, and a pharmaceutically acceptable carrier.  
   
   
       65 . An anti-hepatitis C virus agent comprising a fused ring compound of  claim 1 , or a pharmaceutically acceptable salt thereof, and a pharmaceutically acceptable carrier.  
   
   
       66 . (canceled)  
   
   
       67 . An anti-hepatitis C virus agent comprising (a) the anti-hepatitis C virus agent of  claim 65  and (b) at least one agent selected from the group consisting of a different antiviral agent, an antiinflammatory agent and an immunostimulant.  
   
   
       68 . An anti-hepatitis C virus agent comprising (a) the anti-hepatitis C virus agent of  claim 65  and (b) interferon.  
   
   
       69 . A therapeutic agent for hepatitis C comprising (a) the hepatitis C virus polymerase inhibitor of  claim 64  and (b) at least one agent selected from the group consisting of a different antiviral agent, an antiinflammatory agent and an immunostimulant.  
   
   
       70 . A therapeutic agent for hepatitis C comprising (a) the hepatitis C virus polymerase inhibitor of  claim 64  and (b) interferon.  
   
   
       71 . A benzimidazole compound of the folllowing formula [III] 
     
       
         
         
             
             
         
       
       wherein R a36  is hydrogen atom or carboxyl-protecting group, R a37  is cyclopentyl or cyclohexyl, and R a38  is hydrogen atom or fluorine atom, or a salt thereof.  
     
   
   
       72 . A thiazole compound selected from the group consisting of 4-(4-fluorophenyl)-5-hydroxymethyl-2-methylthiazole and 4-(4-fluorophenyl)-5-chloromethyl-2-methylthiazole, or a pharmaceutically acceptable salt thereof.  
   
   
       73 . A biphenyl compound selected from the group consisting of 1-(4′-chloro-2-hydroxymethyl-biphenyl-4-yl)-2-pyrrolidinone and 1-(4′-chloro-2-chloromethyl-biphenyl-4-yl)-2-pyrrolidinone, or a pharmaceutically acceptable salt thereof.  
   
   
       74 . A pharmaceutical composition comprising (a) a fused ring compound of the formula [I] of  claim 1  or a pharmaceutically acceptable salt thereof and (b) at least one agent selected from the group consisting of an antiviral agent other than the compound of  claim 1 , an antiinflammatory agent and an immunostimulant.  
   
   
       75 . A pharmaceutical composition comprising (a) a fused ring compound of the formula [I] of  claim 1  or a pharmaceutically acceptable salt thereof and (b) interferon.  
   
   
       76 . A method for treating hepatitis C, which comprises administering an effective amount of a fused ring compound of the formula [I] of  claim 1  or a pharmaceutically acceptable salt thereof.  
   
   
       77 . The method of  claim 76 , further comprising administering an effective amount of at least one agent selected from the group consisting of an antiviral agent other than the compound of  claim 1 , an antiinflammatory agent and an immunostimulant.  
   
   
       78 . The method of  claim 76 , further comprising administering an effective amount of interferon.  
   
   
       79 . A method for inhibiting hepatitis C virus polymerase, which comprises administering an effective amount of a fused ring compound of the formula [I] of  claim 1  or a pharmaceutically acceptable salt thereof.  
   
   
       80 . The method of  claim 79 , further comprising administering an effective amount of at least one agent selected from the group consisting of an antiviral agent other than the compound of  claim 1 , an antiinflammatory agent and an immunostimulant.  
   
   
       81 . The method of  claim 79 , further comprising administering an effective amount of interferon.  
   
   
       82 . 1-Cyclohexyl-2-(3-furanyl)-1H-benzimidazole-5-carboxylic acid.