Synthesist Summoner 1/Vivisectionist Alchemist 1/Barbarian 1
Biped eidolon; ability increase (str) and improved damage (claws) as evolutions, with improved natural attack as eidolon feat.
Add power attack, and assuming a raging, mutagened full attack, you get two claws at 1d8 + 10 (+1d6 if a sneak attack)
This is off the top of my head, and I'm sure it can be improved.