Purchased audiobooks disappeared after syncing with new MacBook Pro

I had my iPhone synced with a Windows laptop which got really slow and decided to replace it with a MacBook Pro. In between the last sync with the laptop and the first sync with the MacBook Pro I had bought a couple of audiobooks through the iTunes Store. After syncing the iPhone with the new Macbook everything was fine except the audiobooks which we gone. Originally I thought it would work as with the apps from the AppStore that I could download them again free of charge by just giving my apple ID and password. However this was not the case. Can someone please help me with this as losing these audiobooks would suppose a more considerable loss of money compared to just apps.

Thank you,

Arne