It sounds like a tough situation. However, I would recommend that you or your friend contact an attorney experienced in federal criminal defense, Its generally difficult if not impossible to give an opinion without the details. But fortunately for your friend you are asking questions. A good starting point may be the Federal Public Defender office from the district where he was sentenced.
That's a very tough situation. Normally, you have a very limited window to file an appeal. It may be that if your friend was sentenced for a crack sentence he may be able to revisit things under the relatively new retroactive crack sentencing guidelines. You should be able to check with the Federal Public Defender's office in the jurisdiction he was sentenced in to find out if that's possible.
Otherwise, you may be able to talk to a lawyer about a possible post-conviction or habeas petition. It would depend a lot on what the facts of the case were, and that may not be possible. Nonetheless, it could be worth exploring.
It sounds as if your friend may have signed a plea agreement in which he waived his right to appeal. Unfortunately, many courts have upheld such waivers.
Your friend should consult with an experienced federal criminal defense attorney to see what options, if any, are available. For example, it could be that his former counsel failed to advise him properly and that an action challenging the conviction could be filed under 18 U.S.C. Section 2255.
Much more information is required to determine whether there is an avenue for relief.