Barely 15 months after buying a Back Bay apartment building at 313 Commonwealth Ave., Keliher Real Estate has completed the asset's conversion to a condominium structure featuring three high-end units, including the penthouse which traded last week for $3.5 million. The first unit ($1.743 million) closed in mid-February, followed by the second a month later ($2.65 million), with the developer having acquired the building in Dec. 2012 for $2.75 million. Encompassing 2,750 s/f, 313 Commonwealth Ave.'s penthouse unit sits on the top two levels of a four-story brick building that was constructed in 1900. Acquired by Christopher Davis, the prime unit has three bedrooms and 2.5 baths. Accoutrements including three sets of French doors that open to a 280 s/f terrace with south facing views of Commonwealth Ave. and the city, explains the building's marking materials that also touts a wet bar, powder room and two fireplaces. Grassi Design Group handled architectural services for 313 Commonwealth Ave. Developer James Keliher is a 30-year CRE veteran who has purchased, rehabilitated and sold more than 50 buildings in the metropolitan area, having worked on Boston projects such as 195 Beacon St., 125 Charles St. and 249 Newbury St., the latter property situated one door down from Keliher Real Estate's headquarters at 251 Newbury St. The seller's exclusive leasing agents were Patti Donovan and Diane Keliher, herself a 25-year veteran of the local brokerage community. Keliher Real Estate, Inc., a full service locally owned real estate firm formed in 1985, has earned its reputation and integrity through 20 years of successful relationship building with owners and property managers across the city. Our team provides our clients with the most comprehensive real estate experience available - from assistance with attorneys and banks, from investing decisions, to purchasing or renting your dream home.