He'd almost made it out, the door was in sight, when someone was suddenly standing in his way. Khan had seen Castiel on the network in passing, but had never spoken directly to him and didn't really know anything about him. He was going to raise his phaser, simply going to shoot him, but when Castiel came at him he didn't even get the chance. He dropped the weapon, tried to dodge the incoming punch, but it nevertheless got him in the jaw.
He stumbled slightly, but only slightly, before he found his footing again, adjusted his expectations. The other was fast, as fast as he was (or faster), this was no mere human. His jaw still stung from the impact of the blow, it was an odd sensation, one he'd not felt in quite some time. Well, not since he got his abilities back months ago.
He turned slightly, so as to limit the amount of him Castiel could swing at, actually managing to dodge the second punch, but only barely. He raised his hands, sending one balled fist toward Castiel's midsection, while the other made a grab for his neck. He knew he likely wouldn't be able to strangle him, but perhaps he could still throw him, or knee him in the gut, or do something that'd knock him down long enough for him to get through the door.