The Campbell Soup Co. on Monday purchased a landmark building in the impoverished city of Camden, N.J., as part of a plan to redevelop the neighborhood surrounding the corporate headquarters of the Fortune 500 company. The world’s largest soup maker bought a long-vacant former Sears store built in 1927. The move likely ends preservationists’ five-year effort to save and repurpose the building, which was among the first department stores to be built with its own parking lot — an precursor to the shopping malls that popped up decades later. Campbell paid about $3.5 million for the property, company spokesman Anthony Sanzio said. Campbell coveted the land the building sits on as part of the company’s plan to redevelop the neighborhood surrounding its headquarters. The company could soon demolish the landmark building.