As mentioned in the comments, regex is not meant for this, since it can't be known how many words there will be. But with your limited example, this works:
^(\w+)\s+(\w+)\s+(\w+)\s+(\w+)\s+(\w+)\s+(\w+)\.$
Replace with
$6 $5 $4 $3 $2 $1.
Try it (press [Java]): http://fiddle.re/67kef