The joint venture paid £47.5m for the 1960s Newcombe House block, which covers a 1 acre site, close to the top end of the famous Portobello Market.
It consist of a 14 storey office block, 13 shops and 55 car parking spaces.
As yet the partners have not decided whether to press ahead with an extensive refurbishment of the site or build an entirely new mixed-use development with luxury apartments.