I'm guessing you don't have an owner's manual? Unfortunately, Volkswagen is one of the few manufacturers left in the US that don't let you download an owner's manual online. If synthetic is required, Mobile One makes one specifically for higher mileage engines.
I have around 150,000 miles on my Nissan and I use whatever regular oil is on sale (5W30 iirc). But mine's not a turbo, so that may make a difference.
If no owners reply in here, check out the forums link above for a Passat discussion.