A compound having the structure of Formula: or a pharmaceutically acceptable salt thereof, wherein: R 1 is hydrogen, halogen, C 5 -C 18 aryl or C 2 -C 17 heteroaryl; R 2 is C 1 -C 5 alkyl, C 3 -C 10 cycloalkyl, C 5 -C 18 aryl, C 3 -C 10 cycloalkyl(C 1 -C 5 alkylene), C 5 -C 18 ar(C 1 -C 5 alkylene), C 2 -C 12 heterocyclyl, C 2 -C 12 heterocyclyl(C 1 -C 5 -alkylene) or C 2 -C 17 heteroaryl(C 1 -C 5 alkylene); R 3 is hydrogen; R 4 is -CO 2 H, -CO 2 R 6, -C N CN, -C N OH, or tetrazolyl; each R 5 is independently hydrogen, C 1 -C 5 alkyl, fluoroalkyl, C 3 -C 10 cycloalkyl, C 5 -C 18 aryl, C 3 -C 10 cycloalkyl(C 1 -C 5 alkylene) or C 5 -C 18 ar(C 1 -C 5 alkylene); and R 6 is C 1 -C 5 alkyl; wherein C 5 -C 18 aryl is optionally substituted with one or more groups selected from halogen, -OR 5, -N(R 5) 2, cyano, -CON(R 5) 2, C 1 -C 5 alkyl, C 2 -C 8 alkynyl, fluoroalkyl, C 3 -C 10 cycloalkyl, C 5 -C 18 aryl, C 3 -C 10 cycloalkyl(C 1 -C 5 alkylene) and C 5 -C 18 ar(C 1 -C 5 alkylene), C2-C12 heterocyclyl, C 2 -C 17 heteroaryl; wherein tetrazolyl is optionally substituted with one or more groups selected from C 1 -C 5 alkyl; wherein C 1 -C 5 alkyl is optionally substituted with one more more groups selected from halogen, -OR 5, -N(R 5) 2, -CON(R 5) 2, (C 1 -C 5 alkyl)-O-, (C 1 -C 5 alkyl) 2 N-, (C 5 -C 18 aryl)(C 1 -C 5 alkyl)N-, (C 3 -C 10 cycloalkyl)(C 1 -C 5 alkyl)N-, [C 5 -C 18 ar(C 1 -C 5 alkylene)](C 1 -C 5 alkyl)N-, [C 3 -C 10 cycloalkyl(C 1 -C 5 alkylene)](C 1 -C 5 alkyl)N-; wherein C 2 -C 12 heterocyclyl is optionally substituted with one or more groups selected from halogen, oxo, OR 5, -N(R 5) 2, -CON(R 5) 2, cyano, C 1 -C 5 alkyl, C 2 -C 8 alkynyl, fluoroalkyl, C 3 -C 10 cycloalkyl, C 5 -C 18 aryl, C 3 -C 10 cycloalkyl(C 1 -C 5 alkylene) and C 5 -C 18 ar(C 1 -C 5 alkylene); wherein C 3 -C 10 cycloalkyl is optionally substituted with one or more groups selected from halogen, oxo, OR 5, -N(R 5) 2, -CON(R 5) 2, cyano, C 1 -C 5 alkyl, C 2 -C 8 alkynyl, fluoroalkyl, C 3 -C 10 cycloalkyl, C 5 -C 18 aryl, C 3 -C 10 cycloalkyl(C 1 -C 5 alkylene) and C 5 -C 18 ar(C 1 -C 5 alkylene); wherein C 2 -C 17 heteroaryl is optionally substituted with one or more groups selected from halogen, oxo, OR 5, -N(R 5) 2, cyano, -CON(R 5) 2, C 1 -C 5 alkyl, C 2 -C 8 alkynyl, fluoroalkyl, C 3 -C 10 cycloalkyl, C 5 -C 18 aryl, C 3 -C 10 cycloalkyl(C 1 -C 5 alkylene) and C 5 -C 18 ar(C 1 -C 5 alkylene); and wherein a C 2 -C 17 heteroaryl group is a 3 to 18-membered aromatic ring comprising 2 to 17 carbon atoms and from 1 to 6 heteroatoms selected from nitrogen, oxygen and sulfur; and a C 2 -C 12 heterocyclyl group is a 3 to 18-membered non-aromatic ring comprising 2 to 12 carbon atoms and from 1 to 6 heteroatoms selected from nitrogen, oxygen and sulfur. R 1 is hydrogen, halogen, C 5 -C 18 aryl or C 2 -C 17 heteroaryl; R 2 is C 1 -C 5 alkyl, C 3 -C 10 cycloalkyl, C 5 -C 18 aryl, C 3 -C 10 cycloalkyl(C 1 -C 5 alkylene), C 5 -C 18 ar(C 1 -C 5 alkylene), C 2 -C 12 heterocyclyl, C 2 -C 12 heterocyclyl(C 1 -C 5 -alkylene) or C 2 -C 17 heteroaryl(C 1 -C 5 alkylene); R 3 is hydrogen; R 4 is -CO 2 H, -CO 2 R 6, -C N CN, -C N OH, or tetrazolyl; each R 5 is independently hydrogen, C 1 -C 5 alkyl, fluoroalkyl, C 3 -C 10 cycloalkyl, C 5 -C 18 aryl, C 3 -C 10 cycloalkyl(C 1 -C 5 alkylene) or C 5 -C 18 ar(C 1 -C 5 alkylene); and R 6 is C 1 -C 5 alkyl; wherein C 5 -C 18 aryl is optionally substituted with one or more groups selected from halogen, -OR 5, -N(R 5) 2, cyano, -CON(R 5) 2, C 1 -C 5 alkyl, C 2 -C 8 alkynyl, fluoroalkyl, C 3 -C 10 cycloalkyl, C 5 -C 18 aryl, C 3 -C 10 cycloalkyl(C 1 -C 5 alkylene) and C 5 -C 18 ar(C 1 -C 5 alkylene), C2-C12 heterocyclyl, C 2 -C 17 heteroaryl; wherein tetrazolyl is optionally substituted with one or more groups selected from C 1 -C 5 alkyl; wherein C 1 -C 5 alkyl is optionally substituted with one more more groups selected from halogen, -OR 5, -N(R 5) 2, -CON(R 5) 2, (C 1 -C 5 alkyl)-O-, (C 1 -C 5 alkyl) 2 N-, (C 5 -C 18 aryl)(C 1 -C 5 alkyl)N-, (C 3 -C 10 cycloalkyl)(C 1 -C 5 alkyl)N-, [C 5 -C 18 ar(C 1 -C 5 alkylene)](C 1 -C 5 alkyl)N-, [C 3 -C 10 cycloalkyl(C 1 -C 5 alkylene)](C 1 -C 5 alkyl)N-; wherein C 2 -C 12 heterocyclyl is optionally substituted with one or more groups selected from halogen, oxo, OR 5, -N(R 5) 2, -CON(R 5) 2, cyano, C 1 -C 5 alkyl, C 2 -C 8 alkynyl, fluoroalkyl, C 3 -C 10 cycloalkyl, C 5 -C 18 aryl, C 3 -C 10 cycloalkyl(C 1 -C 5 alkylene) and C 5 -C 18 ar(C 1 -C 5 alkylene); wherein C 3 -C 10 cycloalkyl is optionally substituted with one or more groups selected from halogen, oxo, OR 5, -N(R 5) 2, -CON(R 5) 2, cyano, C 1 -C 5 alkyl, C 2 -C 8 alkynyl, fluoroalkyl, C 3 -C 10 cycloalkyl, C 5 -C 18 aryl, C 3 -C 10 cycloalkyl(C 1 -C 5 alkylene) and C 5 -C 18 ar(C 1 -C 5 alkylene); wherein C 2 -C 17 heteroaryl is optionally substituted with one or more groups selected from halogen, oxo, OR 5, -N(R 5) 2, cyano, -CON(R 5) 2, C 1 -C 5 alkyl, C 2 -C 8 alkynyl, fluoroalkyl, C 3 -C 10 cycloalkyl, C 5 -C 18 aryl, C 3 -C 10 cycloalkyl(C 1 -C 5 alkylene) and C 5 -C 18 ar(C 1 -C 5 alkylene); and wherein a C 2 -C 17 heteroaryl group is a 3 to 18-membered aromatic ring comprising 2 to 17 carbon atoms and from 1 to 6 heteroatoms selected from nitrogen, oxygen and sulfur; and a C 2 -C 12 heterocyclyl group is a 3 to 18-membered non-aromatic ring comprising 2 to 12 carbon atoms and from 1 to 6 heteroatoms selected from nitrogen, oxygen and sulfur.