Around 20 years ago AA used an MD-80 on their LAX-IAD redeye flight. I'm sure of that because I flew it once. AA.com says that's a distance of 2288 miles.

I remember an empty seat next to me in Y. I don't know, but will speculate that it probably was weight-restricted and only possible when flying eastbound because of prevailing winds but I'm pretty sure that's about as far as anybody would be using a Mad Dog in scheduled service.