A 600,000-square-foot former Nabisco factory at 85 10th Avenue in Chelsea has been bought by Somerset Partners for $300 million. It’s the first office acquisition by Somerset, which owns more than 3,000 apartments in the southern United States. The former factory was built in 1913 and, since 1999, nearly $200 million in capital improvements have been made to it, according to a release from Somerset. Current tenants include Lehman Brothers, the State of New York, the federal government and Moet Hennessy. The New York Post called the $500-per-square-foot deal, announced today, a record for that area of Chelsea. Somerset is buying the building from a partnership of Angelo Gordon & Company, Belvedere Capital, and Irwin Cohen of ATC Management.