Patent ID: 8796267

Claim:
A compound of formula I or Ia: or a pharmaceutically acceptable salt thereof, wherein: each of W 1 , W 2 , W 3 , W 4 and W 5 is independently hydrogen or deuterium; each of Y 1 , Y 2 , Y 3 and Y 4 is independently hydrogen or deuterium; each of Z 1 , Z 2 , Z 3 and Z 4 is independently hydrogen, deuterium, or fluorine; and at least one of W 1 , W 2 , W 3 , W 4 , W 5 is deuterium; at least two of Y 1 , Y 2 , Y 3 and Y 4 are deuterium; and at least two of Z 1 , Z 2 , Z 3 and Z 4 are deuterium or fluorine.