BOSTON — L3 Capital and LaSalle Investment Management have purchased a vacant commercial building located at 399 Washington St. in Boston’s Downtown Crossing for an $63.2 million. The buyers will renovate and rebrand the 74,500-square-foot building as DTX 399. The building will offer six levels of retail and creative office space. Evan Papanastasiou of Eastern Consolidated represented the seller, Robert Posner, while Adelaide Polsinelli, also of Eastern, procured the buyer in the deal. The owners have retained Colliers International to market the property for lease.