How to sync iBooks if you have moved your iTunes Library?

My iTunes library was to big so I moved it to an external drive, but now when I want to sync new PDF or Books from the iBook app on my mac, there is only the books from my iPad showing up and I don't have any other selection to sync.

Everything else regarding music is working fine.

I believe sins iBook got separated from iTunes with his own app, iTunes don't see the iBook library.

Please Help, I just need to have my iTunes Library linked with iBook App on my mac, so they can talk to each other.

I have no clues as how to do this.

Thanks, for your help.