A compound of formula: wherein: X 1 is O or S; R 1 is selected from SR 21, OR 21, and NR 21 R 22; R 3 is selected from hydrogen, alkyl and substituted alkyl; R 4 is selected from hydrogen, alkyl, substituted alkyl, nitro, alkylsulfonyl, substituted alkylsulfonyl, alkylsulfinyl, substituted alkylsulfinyl, cyano, alkylcarbonyl, substituted alkylcarbonyl, C OH, C NH 2, halogen, SO 2 NH 2, alkylaminosulfonyl, substituted alkylaminosulfonyl, alkylsulfonylamino and substituted alkylsulfonylamino, alkanoyl, substituted alkanoyl, alkylaminocarbonyl, substituted alkylaminocarbonyl, alkyloxycarbonyl and substituted alkyloxycarbonyl; R 21 and R 22 are independently selected from hydrogen, alkyl and substituted alkyl; or R 21 and R 22 together with the N atom through which they are connected form a 5- or 6-membered heterocyclic ring, optionally substituted with one or more R 23; Z 2 is selected from -NR 5 R 6, hydrogen, alkyl, substituted alkyl, alkenyl, substituted alkenyl, alkoxy, substituted alkoxy, alkylsulfanyl, substituted alkylsulfanyl, alkynyl, substituted alkynyl, aryl, substituted aryl, heteroaryl, substituted heteroaryl, carbocycle, substituted carbocycle, heterocycle, substituted heterocycle, arylalkoxy, substituted arylalkoxy, aryloxy, substituted aryloxy, aryloxyalkoxy, substituted aryloxyalkoxy, arylsulfanyl, substituted arylsulfanyl, arylsulfanylalkoxy, substituted arylsulfanylalkoxy, cycloalkylalkoxy, substituted cycloalkylalkoxy, cycloalkyloxy, substituted cycloalkyloxy, halogen, carbonyloxy, haloalkoxy, haloalkyl, hydroxy and nitro; Z 3 is selected from heterocycle, substituted heterocycle, -NR 5 R 6, aryl, substituted aryl, heteroaryl, substituted heteroaryl, carbocycle and substituted carbocycle; R 5 and R 6 are independently selected from hydrogen, alkyl and substituted alkyl; R 11 and R 12 are each one or more optional substituents each independently selected from alkyl, substituted alkyl, alkoxy, substituted alkoxy, halogen, cyano, nitro, carboxy, C NH 2, SO 2 NH 2, sulfonate, hydroxyl, alkylsulfonyl, substituted alkylsulfonyl, alkylaminosulfonyl, substituted alkylaminosulfonyl, alkylsulfonylamino, substituted alkylsulfonylamino, alkyloxycarbonyl, substituted alkyloxycarbonyl and -NR 5 R 6; and R 31 is selected from H, R 12 and L 3 -Y 3 wherein L 3 is a linker and Y 3 is selected from aryl, substituted aryl, heteroaryl and substituted heteroaryl. X 1 is O or S; R 1 is selected from SR 21, OR 21, and NR 21 R 22; R 3 is selected from hydrogen, alkyl and substituted alkyl; R 4 is selected from hydrogen, alkyl, substituted alkyl, nitro, alkylsulfonyl, substituted alkylsulfonyl, alkylsulfinyl, substituted alkylsulfinyl, cyano, alkylcarbonyl, substituted alkylcarbonyl, C OH, C NH 2, halogen, SO 2 NH 2, alkylaminosulfonyl, substituted alkylaminosulfonyl, alkylsulfonylamino and substituted alkylsulfonylamino, alkanoyl, substituted alkanoyl, alkylaminocarbonyl, substituted alkylaminocarbonyl, alkyloxycarbonyl and substituted alkyloxycarbonyl; R 21 and R 22 are independently selected from hydrogen, alkyl and substituted alkyl; or R 21 and R 22 together with the N atom through which they are connected form a 5- or 6-membered heterocyclic ring, optionally substituted with one or more R 23; Z 2 is selected from -NR 5 R 6, hydrogen, alkyl, substituted alkyl, alkenyl, substituted alkenyl, alkoxy, substituted alkoxy, alkylsulfanyl, substituted alkylsulfanyl, alkynyl, substituted alkynyl, aryl, substituted aryl, heteroaryl, substituted heteroaryl, carbocycle, substituted carbocycle, heterocycle, substituted heterocycle, arylalkoxy, substituted arylalkoxy, aryloxy, substituted aryloxy, aryloxyalkoxy, substituted aryloxyalkoxy, arylsulfanyl, substituted arylsulfanyl, arylsulfanylalkoxy, substituted arylsulfanylalkoxy, cycloalkylalkoxy, substituted cycloalkylalkoxy, cycloalkyloxy, substituted cycloalkyloxy, halogen, carbonyloxy, haloalkoxy, haloalkyl, hydroxy and nitro; Z 3 is selected from heterocycle, substituted heterocycle, -NR 5 R 6, aryl, substituted aryl, heteroaryl, substituted heteroaryl, carbocycle and substituted carbocycle; R 5 and R 6 are independently selected from hydrogen, alkyl and substituted alkyl; R 11 and R 12 are each one or more optional substituents each independently selected from alkyl, substituted alkyl, alkoxy, substituted alkoxy, halogen, cyano, nitro, carboxy, C NH 2, SO 2 NH 2, sulfonate, hydroxyl, alkylsulfonyl, substituted alkylsulfonyl, alkylaminosulfonyl, substituted alkylaminosulfonyl, alkylsulfonylamino, substituted alkylsulfonylamino, alkyloxycarbonyl, substituted alkyloxycarbonyl and -NR 5 R 6; and R 31 is selected from H, R 12 and L 3 -Y 3 wherein L 3 is a linker and Y 3 is selected from aryl, substituted aryl, heteroaryl and substituted heteroaryl.