A compound having structural Formula I: or a pharmaceutically acceptable salt thereof wherein: n is the integer zero or 1; one of the dashed lines a, b or c represents a -CH 2 - or -CH 2 -CH 2 - bridge, and the other dashed lines are absent; R 1 is -H, -OC 1-3 alkyl or -OH; R 2 is -H or -C 1-3 alkyl; R3 is -H, -F, -C 1-3 alkyl or phenyl; or, when n is zero, R 2 and R 3 are joined together to represent -(CH 2)( q)- and form a 4-6 member ring with the nitrogen and carbon to which each is attached; q is the integer 2, 3 or 4; R 4 and R 5 are each independently -H or -C 1-3 alkyl, or R 4 and R 5 are joined together with the carbon to which they are attached to form C 3-6 cycloalkyl; R 6 is -H, -C 1-3 alkyl, -OH, -OC 1-3 alkyl or -F, or is di-fluoro that replaces two hydrogens on the carbon to which it is attached; R 7 is -H, -C 1-3 alkyl, -OH, -OC 1-3 alkyl or -F, or is di-fluoro that replaces two hydrogens on the carbon to which it is attached; R is -H or -C 1-4 alkyl; R 8 is -H, -F, -Cl, -C 1-6 alkyl, -C 3-6 cycloalkyl or -OC 1-6 alkyl; R 9 is -H, -F, -Cl, -CN, -C 1-6 alkyl, -C 3-6 cycloalkyl or -OC 1-6 alkyl; or when R 10 is -H, then R 9 can be 1 H -tetrazol-1-yl; R 10 is -H, -Cl, -F, -CN, -C 1-6 alkyl, -C 3-6 cycloalkyl or -OC 1-4 alkyl; R 11 is -H, -Cl, -F, -CN, -C 1-4 alkyl, -C 3-6 cycloalkyl or -OC 1-4 alkyl; R 11a is -H, -Cl, -F, -CN, -C 1-4 alkyl, -C 3-6 cycloalkyl or -OC 1-4 alkyl; provided that R 9 and R 10 are not both -H; and provided that one and only one of R 9, R 10 or R 11a is -CN; X 1, X 2, X 3 and X 4 are each independently C(R a) or N, provided that one or two of X 1, X 2, X 3 and X 4 must be N and the others are C(R a); each R a is independently -H or -C 1-3 alkyl; G is -OC 1-3 alkyl, -CN or a 5-membered heteroaryl; R 8a is -H, -F, -Cl, -C 1-6 alkyl, -C 3-6 cycloalkyl or -OC 1-6 alkyl; R 12 is -H, -C 1-3 alkyl, -OC1-3alkyl, -SO 2 C 1-3 alkyl or halo; R 13 is -H, -C 1-3 alkyl, -OC 1-3 alkyl, halo, -NO 2, -CN or a 5-membered heteroaryl; R 14 is -H, -C 1-3 alkyl, -OC 1-3 alkyl, halo, -NO 2, -CN or a 5-membered heteroaryl; provided that only one of R 13 and R 14 is -CN, -NO 2 or the 5-membered heteroaryl and the other is -H, -C 1-3 alkyl, -OC 1-3 alkyl or halo; R 15 is -H, -C 1-3 alkyl, -OC 1-3 alkyl, -SO 2 C 1-3 alkyl or halo; R 15a is -H, -C 1-3 alkyl, -OC 1-3 alkyl, -SO 2 C 1-3 alkyl or halo; or R 2 and R 15 are joined together and represent -CH 2 - to form the bicyclic fused ring system and R 16 is -H, -Cl, -F, -CN, -C 1-4 alkyl, -C 3-6 cycloalkyl or -OC 1-4 alkyl. n is the integer zero or 1; one of the dashed lines a, b or c represents a -CH 2 - or -CH 2 -CH 2 - bridge, and the other dashed lines are absent; R 1 is -H, -OC 1-3 alkyl or -OH; R 2 is -H or -C 1-3 alkyl; R3 is -H, -F, -C 1-3 alkyl or phenyl; or, when n is zero, R 2 and R 3 are joined together to represent -(CH 2)( q)- and form a 4-6 member ring with the nitrogen and carbon to which each is attached; q is the integer 2, 3 or 4; R 4 and R 5 are each independently -H or -C 1-3 alkyl, or R 4 and R 5 are joined together with the carbon to which they are attached to form C 3-6 cycloalkyl; R 6 is -H, -C 1-3 alkyl, -OH, -OC 1-3 alkyl or -F, or is di-fluoro that replaces two hydrogens on the carbon to which it is attached; R 7 is -H, -C 1-3 alkyl, -OH, -OC 1-3 alkyl or -F, or is di-fluoro that replaces two hydrogens on the carbon to which it is attached; R is -H or -C 1-4 alkyl; R 8 is -H, -F, -Cl, -C 1-6 alkyl, -C 3-6 cycloalkyl or -OC 1-6 alkyl; R 9 is -H, -F, -Cl, -CN, -C 1-6 alkyl, -C 3-6 cycloalkyl or -OC 1-6 alkyl; or when R 10 is -H, then R 9 can be 1 H -tetrazol-1-yl; R 10 is -H, -Cl, -F, -CN, -C 1-6 alkyl, -C 3-6 cycloalkyl or -OC 1-4 alkyl; R 11 is -H, -Cl, -F, -CN, -C 1-4 alkyl, -C 3-6 cycloalkyl or -OC 1-4 alkyl; R 11a is -H, -Cl, -F, -CN, -C 1-4 alkyl, -C 3-6 cycloalkyl or -OC 1-4 alkyl; provided that R 9 and R 10 are not both -H; and provided that one and only one of R 9, R 10 or R 11a is -CN; X 1, X 2, X 3 and X 4 are each independently C(R a) or N, provided that one or two of X 1, X 2, X 3 and X 4 must be N and the others are C(R a); each R a is independently -H or -C 1-3 alkyl; G is -OC 1-3 alkyl, -CN or a 5-membered heteroaryl; R 8a is -H, -F, -Cl, -C 1-6 alkyl, -C 3-6 cycloalkyl or -OC 1-6 alkyl; R 12 is -H, -C 1-3 alkyl, -OC1-3alkyl, -SO 2 C 1-3 alkyl or halo; R 13 is -H, -C 1-3 alkyl, -OC 1-3 alkyl, halo, -NO 2, -CN or a 5-membered heteroaryl; R 14 is -H, -C 1-3 alkyl, -OC 1-3 alkyl, halo, -NO 2, -CN or a 5-membered heteroaryl; provided that only one of R 13 and R 14 is -CN, -NO 2 or the 5-membered heteroaryl and the other is -H, -C 1-3 alkyl, -OC 1-3 alkyl or halo; R 15 is -H, -C 1-3 alkyl, -OC 1-3 alkyl, -SO 2 C 1-3 alkyl or halo; R 15a is -H, -C 1-3 alkyl, -OC 1-3 alkyl, -SO 2 C 1-3 alkyl or halo; or R 2 and R 15 are joined together and represent -CH 2 - to form the bicyclic fused ring system and R 16 is -H, -Cl, -F, -CN, -C 1-4 alkyl, -C 3-6 cycloalkyl or -OC 1-4 alkyl.