The one developer building new office in Washington, D.C., is going for a triple.  BXP is nearing its third deal in two years to build a trophy office project in the city, executives disclosed on the company’s second-quarter earnings call Wednesday. They said the REIT is working with an institutional owner to put together a joint venture and hopes to have a lease commitment by the end of the year. “We’re working on what we hope will be a third in the series here of opportunities in downtown D.C. with inbound clients,” BXP Executive Vice President Pete Otteni said on the call.