Triazole compounds that modulate hsp90 activity

Abstract

The present invention relates to substituted triazole compounds and compositions comprising substituted triazole compounds. The invention further relates to methods of inhibiting the activity of Hsp90 in a subject in need thereof and methods for preventing or treating hyperproliferative disorders, such as cancer, in a subject in need thereof comprising administering to the subject a substituted triazole compound of the invention, or a composition comprising such a compound.

What is claimed is: 
     
         1 . A compound represented by the following structural formula: 
       
         
           
           
               
               
           
         
         or a tautomer, pharmaceutically acceptable salt, or prodrug thereof, wherein:
 X 42  is CR 44  or N; 
 R 41  is —H, —OH, —SH, an optionally substituted alkyl, an optionally substituted alkenyl, an optionally substituted alkynyl, an optionally substituted cycloalkyl, an optionally substituted cycloalkenyl, an optionally substituted heterocyclyl, an optionally substituted aryl, an optionally substituted heteroaryl, an optionally substituted aralkyl, an optionally substituted heteraralkyl, halo, cyano, nitro, guanadino, a haloalkyl, a heteroalkyl, an alkoxy or cycloalkoxy, a haloalkoxy, —NR 10 R 11 , —OR 7 , —C(O)R 7 , —C(O)OR 7 , —C(S)R 7 , —C(O)SR 7 , —C(S)SR 7 , —C(S)OR 7 , —C(S)NR 10 R 11 , —C(NR 8 )OR 7 , —C(NR 8 )R 7 , —C(NR 8 )NR 10 R 11 , —C(NR 8 )SR 7 , —OC(O)R 7 , —OC(O)OR 7 , —OC(S)OR 7 , —OC(NR 8 )OR 7 , —SC(O)R 7 , —SC(O)OR 7 , —SC(NR 8 )OR 7 , —OC(S)R 7 , —SC(S)R 7 , —SC(S)OR 7 , —OC(O)NR 10 R 11 , —OC(S)NR 10 R 11 , —OC(NR 8 )NR 10 R 11 , —SC(O)NR 10 R 11 , —SC(NR 8 )NR 10 R 11 , —SC(S)NR 10 R 11 , —OC(NR 8 )R 7 , —SC(NR 8 )R 7 , —C(O)NR 10 R 11 , —NR 8 C(O)R 7 , —NR 7 C(S)R 7 , —NR 7 C(S)OR 7 , —NR 7 C(NR 8 )R 7 , —NR 7 C(O)OR 7 , —NR 7 C(NR 8 )OR 7 , —NR 7 C(O)NR 10 R 11 , —NR 7 C(S)NR 10 R 11 , —NR 7 C(NR 8 )NR 10 R 11 , —SR 7 , —S(O) p R 7 , —OS(O) p R 7 , —OS(O) p OR 7 , —OS(O) p NR 10 R 11 , —S(O) p OR 7 , —NR 8 S(O) p R 7 , —NR 7 S(O) p NR 10 R 11 , —NR 7 S(O) p OR 7 , —S(O) p NR 10 R 11 , —SS(O) p R 7 , —SS(O) p OR 7 , —SS(O) p NR 10 R 11 , —OP(O)(OR 7 ) 2 , or —SP(O)(OR 7 ) 2 ; 
 R 42  is —H, an optionally substituted alkyl, an optionally substituted alkenyl, an optionally substituted alkynyl, an optionally substituted cycloalkyl, an optionally substituted cycloalkenyl, an optionally substituted heterocyclyl, an optionally substituted aryl, an optionally substituted heteroaryl, an optionally substituted aralkyl, an optionally substituted heteraralkyl, hydroxyalkyl, alkoxyalkyl, a haloalkyl, a heteroalkyl, —C(O)R 7 , —(CH 2 ) m C(O)OR 7 , —C(O)OR 7 , —OC(O)R 7 , —C(O)NR 10 R 11 , —S(O) p R 7 , —S(O) p OR 7 , or —S(O) p NR 10 R 11 ; 
 R 43  and R 44  are, independently, —H, —OH, an optionally substituted alkyl, an optionally substituted alkenyl, an optionally substituted alkynyl, an optionally substituted cycloalkyl, an optionally substituted cycloalkenyl, an optionally substituted heterocyclyl, an optionally substituted aryl, an optionally substituted heteroaryl, an optionally substituted aralkyl, an optionally substituted heteraralkyl, hydroxyalkyl, alkoxyalkyl, halo, cyano, nitro, guanadino, a haloalkyl, a heteroalkyl, —C(O)R 7 , —C(O)OR 7 , —OC(O)R 7 , —C(O)NR 10 R 11 , —NR 8 C(O)R 7 , —SR 7 , —S(O) p R 7 , —OS(O) p R 7 , —S(O) p OR 7 , —NR 8 S(O) p R 7 , —S(O) p NR 10 R 11 , or R 43  and R 44  taken together with the carbon atoms to which they are attached form an optionally substituted cycloalkenyl, an optionally substituted aryl, an optionally substituted heterocyclyl, or an optionally substituted heteroaryl; 
 R 45  is —H, —OH, —SH, —NR 7 H, —OR 26 , —SR 26 , —NHR 26 , —O(CH 2 ) m OH, —O(CH 2 ) m SH, —O(CH 2 ) m NR 7 H, —S(CH 2 ) m OH, —S(CH 2 ) m SH, —S(CH 2 ) m NR 7 H, —OC(O)NR 10 R 11 , —SC(O)NR 10 R 11 , —NR 7 C(O)NR 10 R 11 , —OC(O)R 7 , —SC(O)R 7 , —NR 7 C(O)R 7 , —OC(O)OR 7 , —SC(O)OR 7 , —NR 7 C(O)OR 7 , —OCH 2 C(O)R 7 , —SCH 2 C(O)R 7 , —NR 7 CH 2 C(O)R 7 , —OCH 2 C(O)OR 7 , —SCH 2 C(O)OR 7 , —NR 7 CH 2 C(O)OR 7 , —OCH 2 C(O)NR 10 R 11 , —SCH 2 C(O)NR 10 R 11 , —NR 7 CH 2 C(O)NR 10 R 11 , —OS(O) p R 7 , —SS(O) p R 7 , —NR 7 S(O) p R 7 , —OS(O) p NR 10 R 11 ; —SS(O) p NR 10 R 11 , —NR 7 S(O) p NR 10 R 11 , —OS(O) p OR 7 , —SS(O) p OR 7 , —NR 7 S(O) p OR 7 , —OC(S)R 7 , —SC(S)R 7 , —NR 7 C(S)R 7 , —OC(S)OR 7 , —SC(S)OR 7 , —NR 7 C(S)OR 7 , —OC(S)NR 10 R 11 , —SC(S)NR 10 R 11 , —NR 7 C(S)NR 10 R 11 , —OC(NR 8 )R 7 , —SC(NR 8 )R 7 , —NR 7 C(NR 8 )R 7 , —OC(NR 8 )OR 7 , —SC(NR 8 )OR 7 , —NR 7 C(NR 8 )OR 7 , —OC(NR 8 )NR 10 R 11 , —SC(NR 8 )NR 10 R 11 , or —NR 7 C(NR 8 )NR 10 R 11 ; and 
 R 7  and R 8 , for each occurrence, is independently, —H, an optionally substituted alkyl, an optionally substituted alkenyl, an optionally substituted alkynyl, an optionally substituted cycloalkyl, an optionally substituted cycloalkenyl, an optionally substituted heterocyclyl, an optionally substituted aryl, an optionally substituted heteroaryl, an optionally substituted aralkyl, or an optionally substituted heteraralkyl; 
 R 10  and R 11 , for each occurrence, is independently —H, an optionally substituted alkyl, an optionally substituted alkenyl, an optionally substituted alkynyl, an optionally substituted cycloalkyl, an optionally substituted cycloalkenyl, an optionally substituted heterocyclyl, an optionally substituted aryl, an optionally substituted heteroaryl, an optionally substituted aralkyl, or an optionally substituted heteraralkyl; or R 10  and R 11 , taken together with the nitrogen to which they are attached, form an optionally substituted heterocyclyl or an optionally substituted heteroaryl; 
 R 26  is a lower alkyl; 
 R 35  and R 36 , for each occurrence, is independently —H, an optionally substituted alkyl, an optionally substituted alkenyl, an optionally substituted alkynyl, an optionally substituted cycloalkyl, an optionally substituted cycloalkenyl, an optionally substituted heterocyclyl, an optionally substituted aryl, an optionally substituted heteroaryl, an optionally substituted aralkyl, or an optionally substituted heteraralkyl, or R 35  and R 36 , together with N to which they are attached form a 5 to 7 membered heterocyclic ring; 
 m, for each occurrence, is independently, 1, 2, 3, or 4; 
 p, for each occurrence, is independently, 1 or 2. 
 
       
     
     
         2 . The compound of  claim 1 , wherein X 42  is CR 44 , R 43  and R 44  are, independently, selected from the group consisting of —H, methyl, ethyl, propyl, isopropyl, and cyclopropyl, and one of R 35  or R 36  is —H. 
     
     
         3 . The compound of  claim 1 , wherein R 43  and R 44 , taken together with the carbon atoms to which they are attached, form a C 5 -C 8  cycloalkenyl or a C 5 -C 8  aryl, and one of R 35  or R 36  is —H. 
     
     
         4 . The compound of  claim 1 , wherein the compound is represented by the following structural formula: 
       
         
           
           
               
               
           
         
         or a tautomer, pharmaceutically acceptable salt, or prodrug thereof, wherein: 
         X 45  is CR 54  or N; 
         R 56  is selected from the group consisting of —H, methyl, ethyl, isopropyl, and cyclopropyl; 
         R 52  is selected from the group consisting of —H, methyl, ethyl, n-propyl, isopropyl, n-butyl, n-pentyl, n-hexyl, —(CH 2 ) 2 OCH 3 , —CH 2 C(O)OH, and —C(O)N(CH 3 ) 2 ; 
         R 53  and R 54  are each, independently, —H, methyl, ethyl, or isopropyl; or 
         R 53  and R 54  taken together with the carbon atoms to which they are attached form a phenyl, cyclohexenyl, or cyclooctenyl ring; and 
         R 55  is selected from the group consisting of —H, —OH, —OCH 3 , and OCH 2 CH 3 . 
       
     
     
         5 . The compound of  claim 4 , wherein one of R 35  or R 36  is —H. 
     
     
         6 . A compound represented by the following structural formula: 
       
         
           
           
               
               
           
         
         or a tautomer, pharmaceutically acceptable salt, or a prodrug thereof, wherein: 
         Y is —O— or —S—; 
         R 1  is an optionally substituted alkyl, an optionally substituted aryl, an optionally substituted heteroaryl, an optionally substituted alkenyl, an optionally substituted alkynyl, an optionally substituted cycloalkyl, an optionally substituted cycloalkenyl, an optionally substituted heterocyclyl, optionally substituted aralkyl, an optionally substituted heteraralkyl, or 
       
       —C(O)N(R 13 ) 2 ;
 R′ 3  is —OH, —SH, —OR 26 , —SR 26 , —O(CH 2 ) m OH, —O(CH 2 ) m SH, —O(CH 2 ) m NR 7 H, —S(CH 2 ) m OH, —S(CH 2 ) m SH, —S(CH 2 ) m NR 7 H, —OC(O)NR 10 R 11 , —SC(O)NR 10 R 11 , —OC(O)R 7 , —SC(O)R 7 , —OC(O)OR 7 , —SC(O)OR 7 , —OCH 2 C(O)R 7 , —SCH 2 C(O)R 7 , —OCH 2 C(O)OR 7 , —SCH 2 C(O)OR 7 , —OCH 2 C(O)NR 10 R 11 , —SCH 2 C(O)NR 10 R 11 , —OS(O) p R 7 , —SS(O) p R 7 , —S(O) p OR 7 , —OS(O) p NR 10 R 11 , —SS(O) p NR 10 R 11 , —OS(O) p OR 7 , —SS(O) p OR 7 , —OC(S)R 7 , —SC(S)R 7 , —OC(S)OR 7 , —SC(S)OR 7 , —OC(S)NR 10 R 11 , —SC(S)NR 10 R 11 , —OC(NR 8 )R 7 , —SC(NR 8 )R 7 , —OC(NR 8 )OR 7 , —SC(NR 8 )OR 7 , —OC(NR 8 )NR 10 R 11 , —SC(NR 8 )NR 10 R 11 , —OP(O)(OR 7 ) 2 , or —SP(O)(OR 7 ) 2 ; 
 R′ 5  is —X 20 R 50 , an optionally substituted alkyl, an optionally substituted alkenyl, an optionally substituted alkynyl, an optionally substituted cycloalkyl, an optionally substituted cycloalkenyl, an optionally substituted heterocyclyl, an optionally substituted aryl, an optionally substituted heteroaryl, an optionally substituted aralkyl, or an optionally substituted heteraralkyl; 
 R 6  is an optionally substituted alkyl, an optionally substituted alkenyl, an optionally substituted alkynyl, an optionally substituted cycloalkyl, an optionally substituted cycloalkenyl, an optionally substituted heterocyclyl, an optionally substituted aryl, an optionally substituted heteroaryl, an optionally substituted aralkyl, an optionally substituted heteroaralkyl, halo, cyano, nitro, guanadino, a haloalkyl, a heteroalkyl, alkoxy, haloalkoxy, —NR 10 R 11 , —OR 7 , —C(O)R 7 , —C(O)OR 7 , —C(S)R 7 , —C(O)SR 7 , —C(S)SR 7 , —C(S)OR 7 , —C(S)NR 10 R 11 , —C(NR 8 )OR 7 , —C(NR 8 )R 7 , —C(NR 8 )NR 10 R 11 , —C(NR 8 )SR 7 , —OC(O)R 7 , —OC(O)OR 7 , —OC(S)OR 7 , —OC(NR 8 )OR 7 , —SC(O)R 7 , —SC(O)OR 7 , —SC(NR 8 )OR 7 , —OC(S)R 7 , —SC(S)R 7 , —SC(S)OR 7 , —OC(O)NR 10 R 11 , —OC(S)NR 10 R 11 , —OC(NR 8 )NR 10 R 11 , —SC(O)NR 10 R 11 , —SC(NR 8 )NR 10 R 11 , —SC(S)NR 10 R 11 , —OC(NR 8 )R 7 , —SC(NR 8 )R 7 , —C(O)NR 10 R 11 , —NR 8 C(O)R 7 , —NR 7 C(S)R 7 , —NR 7 C(S)OR 7 , —NR 7 C(NR 8 )R 7 , —NR 7 C(O)OR 7 , —NR 7 C(NR 8 )OR 7 , —NR 7 C(O)NR 10 R 11 , —NR 7 C(S)NR 10 R 11 , —NR 7 C(NR 8 )NR 10 R 11 , —SR 7 , —S(O) p R 7 , —OS(O) p R 7 , —OS(O) p OR 7 , —OS(O) p NR 10 R 11 , —S(O) p OR 7 , —NR 8 S(O) p R 7 , —NR 7 S(O) p NR 10 R 11 , —NR 7 S(O) p OR 7 , —S(O) p NR 10 R 11 , —SS(O) p R 7 , —SS(O) p OR 7 , —SS(O) p NR 10 R 11 , —OP(O)(OR 7 ) 2 , or —SP(O)(OR 7 ) 2 ; 
 R 7  and R 8 , for each occurrence, is independently, —H, an optionally substituted alkyl, an optionally substituted alkenyl, an optionally substituted alkynyl, an optionally substituted cycloalkyl, an optionally substituted cycloalkenyl, an optionally substituted heterocyclyl, an optionally substituted aryl, an optionally substituted heteroaryl, an optionally substituted aralkyl, or an optionally substituted heteraralkyl; 
 R 10  and R 11 , for each occurrence, is independently —H, an optionally substituted alkyl, an optionally substituted alkenyl, an optionally substituted alkynyl, an optionally substituted cycloalkyl, an optionally substituted cycloalkenyl, an optionally substituted heterocyclyl, an optionally substituted aryl, an optionally substituted heteroaryl, an optionally substituted aralkyl, or an optionally substituted heteraralkyl; or R 10  and R 11 , taken together with the nitrogen to which they are attached, form an optionally substituted heterocyclyl or an optionally substituted heteroaryl; 
 each R 13  is independently —H, an optionally substituted alkyl, an optionally substituted alkenyl, an optionally substituted alkynyl, an optionally substituted cycloalkyl, an optionally substituted cycloalkenyl, an optionally substituted heterocyclyl, an optionally substituted aryl, an optionally substituted heteroaryl, an optionally substituted aralkyl, or an optionally substituted heteraralkyl; 
 R 26  is a lower alkyl; 
 R 50  is an optionally substituted aryl or an optionally substituted heteroaryl; 
 X 20  is a C1-C4 alkyl, NR 7 , C(O), C(S), C(NR 8 ), or S(O) p ; 
 Z, for each occurrence, is independently an optionally substituted alkyl, an optionally substituted alkenyl, an optionally substituted alkynyl, an optionally substituted cycloalkyl, an optionally substituted cycloalkenyl, an optionally substituted heterocyclyl, an optionally substituted aryl, an optionally substituted heteroaryl, an optionally substituted aralkyl, an optionally substituted heteroaralkyl, halo, cyano, nitro, guanadino, a haloalkyl, a heteroalkyl, alkoxy, haloalkoxy, —NR 10 R 11 , —OR 7 , —C(O)R 7 , —C(O)OR 7 , —C(S)R 7 , —C(O)SR 7 , —C(S)SR 7 , —C(S)OR 7 , —C(S)NR 10 R 11 , —C(NR 8 )OR 7 , —C(NR 8 )R 7 , —C(NR 8 )NR 10 R 11 , —C(NR 8 )SR 7 , —OC(O)R 7 , —OC(O)OR 7 , —OC(S)OR 7 , —OC(NR 8 )OR 7 , —SC(O)R 7 , —SC(O)OR 7 , —SC(NR 8 )OR 7 , —OC(S)R 7 , —SC(S)R 7 , —SC(S)OR 7 , —OC(O)NR 10 R 11 , —OC(S)NR 10 R 11 , —OC(NR 8 )NR 10 R 11 , —SC(O)NR 10 R 11 , —SC(NR 8 )NR 10 R 11 , —SC(S)NR 10 R 11 , —OC(NR 8 )R 7 , —SC(NR 8 )R 7 , —C(O)NR 10 R 11 , —NR 8 C(O)R 7 , —NR 7 C(S)R 7 , —NR 7 C(S)OR 7 , —NR 7 C(NR 8 )R 7 , —NR 7 C(O)OR 7 , —NR 7 C(NR 8 )OR 7 , —NR 7 C(O)NR 10 R 11 , —NR 7 C(S)NR 10 R 11 , —NR 7 C(NR 8 )NR 10 R 11 , —SR 7 , —S(O) p R 7 , —OS(O) p R 7 , —OS(O) p OR 7 , —OS(O) p NR 10 R 11 , —S(O) p OR 7 , —NR 8 S(O) p R 7 , —NR 7 S(O) p NR 10 R 11 , —NR 7 S(O) p OR 7 , —S(O) p NR 10 R 11 , —SS(O) p R 7 , —SS(O) p OR 7 , —SS(O) p NR 10 R 11 , —OP(O)(OR 7 ) 2 , or —SP(O)(OR 7 ) 2 ; 
 m for each occurrence is independently 1, 2, 3, or 4; 
 p, for each occurrence, is independently, 1 or 2; 
 n is 0, 1, 2, or 3; and 
 provided that when Y is —S— and R 1  is an optionally substituted C1-C3 alkyl, then R′ 3  is not —OCH 2 OMe; 
 provided that when Y is —S—, R 1  is Me and R′ 5  is lower alkyl, then R 6  is not halo. 
 
     
     
         7 . The compound of  claim 6 , wherein n is 0 or 1. 
     
     
         8 . The compound of  claim 6 , wherein R 1  is an optionally substituted lower alkyl; R′ 3  is C1-C6 alkoxy or —OH; and R 6  is a C1-C6 alkyl, a C1-C6 haloalkyl, a C1-C6 alkoxy, a C1-C6 haloalkoxy, a C1-C6 alkyl sulfanyl or a C3-C6 cycloalkyl. 
     
     
         9 . The compound of  claim 6 , wherein R′ 5  is represented by the following formula: 
       
         
           
           
               
               
           
         
         wherein: 
         R 33  is a halo, lower alkyl, a lower alkoxy, a lower haloalkyl, a lower haloalkoxy, and lower alkyl sulfanyl; 
         R 34  is H, a lower alkyl, or a lower alkylcarbonyl; and 
         Ring B and Ring C are optionally substituted with one or more substituents. 
       
     
     
         10 . The compound of  claim 6 , wherein R′ 5  is an optionally substituted indolyl, an optionally substituted benzoimidazolyl, an optionally substituted indazolyl, an optionally substituted 3H-indazolyl, an optionally substituted indolizinyl, an optionally substituted quinolinyl, an optionally substituted isoquinolinyl, an optionally substituted benzoxazolyl, an optionally substituted benzo[1,3]dioxolyl, an optionally substituted benzofuryl, an optionally substituted benzothiazolyl, an optionally substituted benzo[d]isoxazolyl, an optionally substituted benzo[d]isothiazolyl, an optionally substituted thiazolo[4,5-c]pyridinyl, an optionally substituted thiazolo[5,4-c]pyridinyl, an optionally substituted thiazolo[4,5-b]pyridinyl, an optionally substituted thiazolo[5,4-b]pyridinyl, an optionally substituted oxazolo[4,5-c]pyridinyl, an optionally substituted oxazolo[5,4-c]pyridinyl, an optionally substituted oxazolo[4,5-b]pyridinyl, an optionally substituted oxazolo[5,4-b]pyridinyl, an optionally substituted imidazopyridinyl, an optionally substituted benzothiadiazolyl, benzoxadiazolyl, an optionally substituted benzotriazolyl, an optionally substituted tetrahydroindolyl, an optionally substituted azaindolyl, an optionally substituted quinazolinyl, an optionally substituted purinyl, an optionally substituted imidazo[4,5-a]pyridinyl, an optionally substituted imidazo[1,2-a]pyridinyl, an optionally substituted 3H-imidazo[4,5-b]pyridinyl, an optionally substituted 1H-imidazo[4,5-b]pyridinyl, an optionally substituted 1H-imidazo[4,5-c]pyridinyl, an optionally substituted 3H-imidazo[4,5-c]pyridinyl, an optionally substituted pyridopyrdazinyl, and optionally substituted pyridopyrimidinyl, an optionally substituted pyrrolo[2,3]pyrimidyl, an optionally substituted pyrazolo[3,4]pyrimidyl an optionally substituted cyclopentaimidazolyl, an optionally substituted cyclopentatriazolyl, an optionally substituted pyrrolopyrazolyl, an optionally substituted pyrroloimidazolyl, an optionally substituted pyrrolotriazolyl, or an optionally substituted benzo[b]thienyl. 
     
     
         11 . The compound of  claim 6 , wherein R′ 5  is selected from the group consisting of: 
       
         
           
           
               
               
           
         
         wherein: 
         X 11 , for each occurrence, is independently CH, CR 9 , N, N(O), or N + (R 17 ); 
         X 12 , for each occurrence, is independently CH, CR 9 , N, N(O), N + (R 17 ), 
         provided that at least one X 12  group is independently selected from CH and CR 9 ; 
         X 13 , for each occurrence, is independently O, S, S(O)p, NR 7 , or NR 17 ; 
         R 9 , for each occurrence, is independently a substituent selected from the group consisting of an optionally substituted alkyl, an optionally substituted alkenyl, an optionally substituted alkynyl, an optionally substituted cycloalkyl, an optionally substituted cycloalkenyl, an optionally substituted heterocyclyl, an optionally substituted aryl, an optionally substituted heteroaryl, an optionally substituted aralkyl, an optionally substituted heteraralkyl, halo, cyano, nitro, guanadino, a hydroxyalkyl, alkoxyalkyl, haloalkyl, a heteroalkyl, —NR 10 R 11 , —OR 7 , —C(O)R 7 , —C(O)OR 7 , —OC(O)R 7 , —C(O)NR 10 R 11 , —NR 8 C(O)R 7 , —SR 7 , —S(O) p R 7 , —OS(O) p R 7 , —S(O) p OR 7 , —NR 8 S(O) p R 7 , or —S(O) p NR 10 R 11 , —S(O) p OR 7 , —OP(O)(OR 7 ) 2 , or —SP(O)(OR 7 ) 2 , —S(O) p OR 7 , —OP(O)(OR 7 ) 2 , or —SP(O)(OR 7 ) 2 ; 
         or two R 9  groups taken together with the carbon atoms to which they are attached form a fused ring; and 
         R 17 , for each occurrence, is independently an alkyl or an aralkyl. 
       
     
     
         12 . The compound of  claim 6 , wherein R′ 5  is X 20 R 50 ; X 20  is a C1-C4 alkyl and R 50  is an optionally substituted phenyl.