Alan Moore and Dave Gibbons originally kicked around the idea for a small prequel project featuring the Minutemen, but it did not come to pass. Moore quickly moved onto other things.

I believe some of the material for that proposed story ended up in a Watchmen role-playing game in the late 1980s, which a buddy of mine owned at the time. It was fun, as far as that goes. More biographical information and all that. I didn't weep for the loss of the prequel, though.