As East San Marco landowner Regency Centers Corp. decides how to proceed after the developer ended the deal for the mixed-use project, Rubin bought another building.Through Atlantic 1639 LLC, Rubin paid $600,000 for the former Family Foundations of Northeast Florida Inc. building.It sits next to his headquarters at 1649 Atlantic Blvd. Rubin, a lawyer and an investor in San Marco and other infill properties, intends to renovate the two-story building for office space upstairs and a restaurant downstairs.