| CPC A61K 31/4045 (2013.01) [A61K 31/166 (2013.01); A61K 31/437 (2013.01); C07C 251/80 (2013.01); C07D 209/10 (2013.01); C07D 471/04 (2013.01)] | 14 Claims | 
| 
               1. A compound of Formula (I): 
              ![]() or a pharmaceutically acceptable salt thereof, wherein: 
              each R1 is fluorine; 
                  R2 is halogen or —NO2; 
                  X1 is C—H; and 
                  X2 is C—H or N. 
                 |