Ambulance operator Rural/Metro Corp., owned by private equity firm Warburg Pincus, filed for chapter 11 protection with the aim of cutting its debts after it missed an interest payment in July, Reuters reported yesterday. The Scottsdale, Arizona-based company also intends to renegotiate unprofitable contracts and free up capital for investments through the bankruptcy process, according to the filings. The provider of private ambulance and fire protection services declared liabilities and assets each worth more than $500 million. Rural/Metro reached an agreement with both its senior secured and unsecured debt holders to reduce its debt and interest payments by nearly 50 percent. Bondholders have also agreed to infuse $135 million in new equity financing once Rural/Metro emerges from chapter 11, according to a filing.