Here is a little snippet that I can share with you.
1)Jacob and the Man in Black are connected with Richard Alpert
2)Richard Alpert has met MIB in his Flashback
3)Richard Alpert has met Jacob in his Flashback
4)Jacob and Richard Alpert are involved in a fight which involves a "special" knife
5)This fight occurs in the 1800's
Source: SpoilerTV