Burlington-based R.J. Kelly Co. has acquired 100 Quannapowitt Parkway in Wakefield for $31 million from Boston-based Digital Realty.

The 169,000-square-foot, multi-tenant building is fully occupied. United HealthGroup is the largest tenant, occupying approximately 60,000 square feet.

R.J. Kelly Co. CEO Brandon Kelly said the property, which was developed in 1999 by Beal Cos., is one of the best-located assets in the Route 128 north market.

"It’s one of those assets that sort of markets itself," Kelly said. "It’s a draw for people who don’t want to deal with Route 128 traffic beyond Wakefield, and historically as space becomes available, it gets absorbed before it hits the market."

R.J. Kelly plans to invest "a significant amount of capital" in upgrades to common areas and parking facilities, Kelly said.

Cambridge Savings Bank provided a $22.8 million mortgage toward the acquisition, according to Middlesex Registry of Deeds records.

JLL’s Capital Markets Group procured the buyer for Boston-based Digital Realty, which has been reducing its office holdings in Greater Boston to focus on data centers. The company owns six data centers in Boston suburban markets.

"This office product was fully leased, so it was time to harvest," said Frank Petz, managing director for JLL.

Digital Realty paid $29.4 million for the property in June 2004.