Portugal’s central bank says an offer from U.S. private equity firm Lone Star is the most promising bid to buy Novo Banco , the so-called good bank salvaged by the Portuguese government from the collapse of major lender Banco Espirito Santo. The Bank of Portugal says it has invited the fund, based in Dallas, Texas, to “deepen negotiations” over the possible purchase, though it said rival bidders have expressed a willingness to improve their offers and would not be excluded.