MedSolutions, an 1,100-person health care company based in Franklin and one of the region's largest private employers, is selling to South Carolina-based CareCore National. Earlier this month, Moody's Investors Services affirmed ratings for the companies following MedSolutions' definitive agreement to be bought by CareCore National LLC, which is backed by General Atlantic LLC. Sources familiar with the deal have estimated its value at between $800 million and $1 billion.