Deuterated EPI-743

A compound of Formula Ia:

• or a pharmaceutically acceptable salt thereof, wherein:
• each of R1, R2, R3, R4, R5, and R6 is independently selected from —CH3 and —CD3;
• each of R7 and R8 is —CD3;
• Y1a and Y1b are the same and are each hydrogen or each deuterium;
• Y2a and Y2b are the same and are each hydrogen or each deuterium;
• Y3a and Y3b are the same and are each hydrogen or each deuterium;
• Y4a and Y4b are the same and are each hydrogen or each deuterium;
• Y6a and Y6b are the same and are each hydrogen or each deuterium;
• Y7a and Y7b are the same and are each hydrogen or each deuterium;
• Y9a and Y9b are the same and are each hydrogen or each deuterium;
• Y10a and Y10b are the same and are each deuterium;
• each of Y5 and Y8 is independently selected from hydrogen and deuterium;
• and
• Y11 is deuterium.