If you go to the founders and threaten, they'll probably fire you. They got funding now so you're replaceable with somebody who will accept post-funding equity.
If you go to the founders and beg, they'll probably talk you out of it. They won't increase your compensation unless they see an increase in value.
If you go to the founders and say, "Tell me what I can do to really help the company" and then work like a dog to become an out-and-out performer, they may (repeat, may) appreciate your outperformance of the rest of the team and want to give you a big equity boost. It's hard to hate a total coding monster and you have to be a bad person to want to cheat somebody who will kamikaze himself for your company. Still, you have to do that for several years and really become the guy that they say, "If we only had three more guys exactly like him!" And, in the end, expect it to take years to build up a decent equity position and realize that they don't have to give you anything. And, of course, you've got to be a total coding monster.
I realize this doesn't quite apply to your post, but I'd just like to point out that the "hard to hate a kamikaze" mentality doesn't always apply in a corporate environment. The people you'd be negotiating with may be too preoccupied with political maneuvering to even notice.
Just a warning to anyone who might take that logic and apply it somewhere other than a startup.
I can't help but to think that the founders can be made to act more like needy girls. Make them want you, make them think that they are about to lose because everyone else recognizes how valuable you are. Make them think that they could not go on without you.
More importantly though, working like a dog for years just to impress your for your employer!?! This is not the startup way.
If you go to the founders and threaten, they'll probably fire you. They got funding now so you're replaceable with somebody who will accept post-funding equity.
If you go to the founders and beg, they'll probably talk you out of it. They won't increase your compensation unless they see an increase in value.
If you go to the founders and say, "Tell me what I can do to really help the company" and then work like a dog to become an out-and-out performer, they may (repeat, may) appreciate your outperformance of the rest of the team and want to give you a big equity boost. It's hard to hate a total coding monster and you have to be a bad person to want to cheat somebody who will kamikaze himself for your company. Still, you have to do that for several years and really become the guy that they say, "If we only had three more guys exactly like him!" And, in the end, expect it to take years to build up a decent equity position and realize that they don't have to give you anything. And, of course, you've got to be a total coding monster.