A former gang member, now an undercover cop, travels through a dangerous inner-city labyrinth to kill a notorious gang leader. Boyz n the Hood meets Apocalypse Now.

Yes, I agree with Anonymous. The comparison to other movies (with the goal of describing what genre(s) it fits and its marketability) belong in your pitch or treatment, not the logline. If you can give us a quick clue as to why your protagonist wants/needs to kill this person that would help, too. Sounds interesting, though!

I've always heard that naming other movies is the mark of a hack or amateur. I would take that out if I were you.

Apocalypse Now is, I believe, losely based on the novel Heart of Darkness by Joseph Conrad.