Once again, a major corporation picked a boutique over a Wall Street mega-bank to advise on its multi-billion dollar deal

Once again, it looks like Wall Street's biggest banks just missed out on one of the biggest deals of 2015.

On one side of the deal, projected to be worth about $40 billion, is Teva Pharmaceuticals, which is aiming to buy its peer Mylan N.V. for $82 per share in a cash-and-stock deal. Teva, according to a statement, is being advised by Greenhill & Co., a boutique bank that went public in 2004.

It isn't yet clear who's advising on the other side of the deal, but Centerview Partners has been an advisor to Mylan N.V. in the past, and as recently as summer 2014.

If that's the case, it's yet another big win for an advisor that has been taking a growing portion of big banks' advisory fees, especially in 2015. And it's part of a pattern of smaller banks displacing boutiques, especially on some big deals.

Representatives for Teva Pharmaceuticals did not immediately comment when contacted by Business Insider; Centerview did not immediately comment.