A compound of formula, formula or formula: or a pharmaceutically acceptable salt thereof, wherein: Rand R 1 are selected from the group consisting of hydrogen, (C 1 -C 6)alkyl, (C 1 -C 4)haloalkyl, (C 1 -C 4)perhaloalkyl, (C 6 -C 10)aryl, (C 1 -C 6)heteroalkyl, (C 5 -C 7)heterocycloalkyl, (5- or 6-membered)heteroaryl, phenylsulfanyl, phenylsulfonyl, phenylsulfinyl and (C 3 -C 6)cycloalkyl; R 2 is selected from the group consisting of hydrogen, (C 1 -C 6)alkyl, -C(=O)R 4, -C(=S)R 4, C(=NR 4)R 5, -C(=NOR 4)R 5, (5- or 6-membered)heteroaryl and (C 6 -C 10)aryl; R 3 is selected from the group consisting of hydrogen, (C 1 -C 6)alkyl, (C 6 -C 10)aryl, and -NR 6 R 7; R 4, R 5, R 6, R 7, and R 8 are each independently selected from the group consisting of hydrogen, (C 1 -C 6)alkyl, phenyl and benzyl; X 1 and X 2 are each independently selected from the group consisting of O, NR 9, S, CR 10, and CR 10 R 11; Y is selected from the group consisting of C(=O), C(=S), C(=NR 9), and CR 10 R 11; Z is selected from the group consisting of O and S; R 9, R 10 and R 11 are each independently selected from the group consisting of hydrogen and (C 1 -C 6)alkyl, wherein said alkyl, aryl, phenyl, benzyl, heteroalkyl, heterocycloalkyl and heteroaryl is unsubstituted or substituted with a substituent selected from halo, (C 1 -C 6)alkyl, (C 1 -C 4)haloalkyl, (C 1 -C 4)perhaloalkyl, (C 1 -C 6)alkoxy, (C 1 -C 4)haloalkoxy, (C 1 -C 4)perhaloalkoxy, -C(=O)OH, -C(=O)O(C 1 -C 6)alkyl, -C(=O)NR 4 R 5, -C(=O)-(C 5 -C 7)heterocycloalkyl, (C 5 -C 7)heterocycloalkyl, (C 1 -C 6)alkylsulfanyl, (C 1 -C 4)haloalkylsulfanyl, (C 1 -C 4)perhaloalkylsulfanyl, (C 1 -C 6)alkylsulfinyl, (C 1 -C 6)alkylsulfonyl, (C 3 -C 6)cycloalkylsulfonyl, (C 1 -C 4)haloalkylsulfinyl, (C 1 -C 4)haloalkylsulfonyl, (C 1 -C 4)perhaloalkylsulfinyl, (C 1 -C 4)perhaloalkylsulfonyl, -S 2 -NH 2, -S 2 -NR 6 R 7, -S 2 -phenyl, -S 2 -(C 5 -C 7)heterocycloalkyl, -S(=O)(=NR 8)(C 1 -C 6)alkyl, -NR 4 R 5, N -(C 1 -C 6)alkylaminosulfonyl, and N, N -di(C 1 -C 6)alkylaminosulfonyl. Rand R 1 are selected from the group consisting of hydrogen, (C 1 -C 6)alkyl, (C 1 -C 4)haloalkyl, (C 1 -C 4)perhaloalkyl, (C 6 -C 10)aryl, (C 1 -C 6)heteroalkyl, (C 5 -C 7)heterocycloalkyl, (5- or 6-membered)heteroaryl, phenylsulfanyl, phenylsulfonyl, phenylsulfinyl and (C 3 -C 6)cycloalkyl; R 2 is selected from the group consisting of hydrogen, (C 1 -C 6)alkyl, -C(=O)R 4, -C(=S)R 4, C(=NR 4)R 5, -C(=NOR 4)R 5, (5- or 6-membered)heteroaryl and (C 6 -C 10)aryl; R 3 is selected from the group consisting of hydrogen, (C 1 -C 6)alkyl, (C 6 -C 10)aryl, and -NR 6 R 7; R 4, R 5, R 6, R 7, and R 8 are each independently selected from the group consisting of hydrogen, (C 1 -C 6)alkyl, phenyl and benzyl; X 1 and X 2 are each independently selected from the group consisting of O, NR 9, S, CR 10, and CR 10 R 11; Y is selected from the group consisting of C(=O), C(=S), C(=NR 9), and CR 10 R 11; Z is selected from the group consisting of O and S; R 9, R 10 and R 11 are each independently selected from the group consisting of hydrogen and (C 1 -C 6)alkyl, wherein said alkyl, aryl, phenyl, benzyl, heteroalkyl, heterocycloalkyl and heteroaryl is unsubstituted or substituted with a substituent selected from halo, (C 1 -C 6)alkyl, (C 1 -C 4)haloalkyl, (C 1 -C 4)perhaloalkyl, (C 1 -C 6)alkoxy, (C 1 -C 4)haloalkoxy, (C 1 -C 4)perhaloalkoxy, -C(=O)OH, -C(=O)O(C 1 -C 6)alkyl, -C(=O)NR 4 R 5, -C(=O)-(C 5 -C 7)heterocycloalkyl, (C 5 -C 7)heterocycloalkyl, (C 1 -C 6)alkylsulfanyl, (C 1 -C 4)haloalkylsulfanyl, (C 1 -C 4)perhaloalkylsulfanyl, (C 1 -C 6)alkylsulfinyl, (C 1 -C 6)alkylsulfonyl, (C 3 -C 6)cycloalkylsulfonyl, (C 1 -C 4)haloalkylsulfinyl, (C 1 -C 4)haloalkylsulfonyl, (C 1 -C 4)perhaloalkylsulfinyl, (C 1 -C 4)perhaloalkylsulfonyl, -S 2 -NH 2, -S 2 -NR 6 R 7, -S 2 -phenyl, -S 2 -(C 5 -C 7)heterocycloalkyl, -S(=O)(=NR 8)(C 1 -C 6)alkyl, -NR 4 R 5, N -(C 1 -C 6)alkylaminosulfonyl, and N, N -di(C 1 -C 6)alkylaminosulfonyl.