I doubt there is a formula cause if I understood it correctly you have to define which dupe to remove and it's going to be specific for each particular case.
If you don't care which of the dupes to remove then I have a solution for sentences consisting of up to 8 words.
First of all do what Adraco said, separate each word in a separate cell.
Then here's your formula:
IF((AND(A1<>B1,A1<>C1,A1<>D1 and etc up to 8 conditions)),A1,"blahblah")
Make sure that the 1st output cell is in 8+ columns from the last cell in the initial input
When done copy the output, go to a separate list and do special paste, select paste values. Then run search and replace for the "blahblah), empty the cells with the blahblah.
Then copy the output and paste in notepad, select the space between two words (it will be the Tab sign) run search and replace. replace it with a space. This function can create double spaces, you can remove them later.
Hope this helps to solve at least a part of your problem
