Corus Bankshares suffered a preliminary net loss of $487.3 million in the second quarter that made it “critically undercapitalized,” the bank reported. If it founders, it will be on the reef of aggressive condo financing in South Florida. Loans to condo projects such as the Jade Ocean Condominiums in Sunny Isles Beach, Paramount Bay in Miami and the Trump International Hotel and Tower in Fort Lauderdale make up nearly $1 billion of the Chicago-based bank’s loan portfolio. According to federal regulations, Tier 1 capital plummeted to a negative $157 million as of June 30. Federal regulators had required Corus Bank to achieve a Tier 1 capital ratio of at least 9 percent by June 18, which it failed to do, and the bank could be seized by regulators.