Patent ID: 8883843

Claim:
A compound of Formula I: or a pharmaceutically acceptable salt thereof, wherein: R 1 is selected from CH 3 , CH 2 D, CHD 2 , and CD 3 ; R 2 is CH 3 or CD 3 ; R 3 is CD 3 ; R 4 is an ethyl group substituted with zero to five deuterium, or is a cyclopentyl group substituted with zero to nine deuterium; X is C═O; each of Y 1a , Y 1b , Y 2 , Y 3 , Y 4 , Y 5 , Y 7 and Y 8 is independently selected from H and D; Y 6 is selected from Cl, H, and D; and wherein the isotopic enrichment factor for each designated deuterium atom is at least 3500.