What are you trying to accomplish?
It's been pretty well shown that parental alienation backfires. Look it up, Google is your friend. As your child becomes independent and forms his own opinion, his mother will have less of a hold over him. As others have said, give it time. And I would suggest that you see some counseling so that you are in the best possible place to move forward with a relationship with your son when he is ready. That means not casting blame, or being angry at his mother, who he loves.