Douglas Marr, senior vice president of the commercial division for Keliher Real Estate, Inc. has sold 31 Gloucester St. in Back Bay for $2.1 million. This 5 story, 5,600 s/f brick residential apartment building is located between Newbury St. and Commonwealth Avenue. The seller was Lawless Family Trust and the buyer is Rubin LLC. The property consists of 8 apartments and 2 parking spaces.