"This is a unique property," Mike Girard, associate at Apartment Realty Advisors, tells GlobeSt.com. "There aren't many complexes that combine retail access on the first floor, this comprehensive of an amenities package, and underground parking in such close proximity to the Mass Pike."

Apartments are currently listed on Forest Properties website at $1,800 to $2,300 for a one-bedroom, $2,200 to $2,800 for a two-bedroom and $3,600 for a penthouse. Karlton plans to offer the condominiums for sale "in the next few months," according to Phil Restifo, president of JS Karlton. Following renovations to the apartments and the building, they will be listed for sale "in the $250,000 to $450,000 range."

This is the second Boston acquisition for Karlton, which also owns Strada 234, a six-floor luxury condominium complex that sits on top of the Causeway, a mixed-use office/residential/retail property near the Fleet Center. They purchased the residential portion in August 2003 for $40.5 million from Intercontinental Real Estate Corp.

The sale of Union Square was brokered by the Apartment Realty Advisors team of Girard, Terrence Scott, Jonathan Close and Richard Robinson. ARA exclusively represented Forest Properties and procured the buyer. This was the third sale in the month of December for ARA, totaling $90 million. The multifamily sales firm has sold $587 million in properties since 2003.