Theoretically, uninteresting would corresponds to «неинтересно». :D However, I'm not sure this distinction makes any sense.
The distinction makes sense. Мне не интересно, а скучно. Это неинтересно.
Yeah, I know that rule. But does this rule reflect the inherent difference in the language, or is it just an orthographic rule? I personally don't know.
Since интересно is a predicate adjective, I read it as "(It is) not interesting" The issue remains unanswered as to whom it is not interesting: me, them, anyone, everyone. Or if it's stating an opinion that I don't think it's interesting to anyone.