The present invention in one embodiment provides a compound of Formula I: (I), or a pharmaceutically acceptable salt thereof, wherein Y1, Y2 and Y3 are each independently selected from hydrogen and deuterium R1, R2, and R3 are each methyl and are independently substituted with 0 to 3 deuterium and R4 is t-butyl and is substituted with 0 to 9 deuterium provided that if R1, R2 and R3 are each —CH3, and R4 is —C(CH3)3, then at least one of Y1 and Y2 is deuterium.
