Details of how struggling Biopure Inc. is working to stay afloat emerged Thursday when the company revealed it sold its main manufacturing plant in Pennsylvania for $1.2 million.

According to a sales agreement included in a filing with the federal Securities and Exchange Commission, Biopure inked a deal in February to sell two parcels, including the company’s idled plant in suburban Philadelphia. The buyer, Spear Realty LLC, is a commercial real estate developer that also agreed to lease the facility back to Biopure if production of its artificial blood products ever resumes.

The SEC filing sets up a public sale of BioPure stock, giving two major shareholders the opportunity to cash out their stakes through a public offering. The sellers — heirs of IKON Office Solutions founder Tinkham Veale II and Lebanon-based Blom Bank — intend to offer just over 4.7 million shares of common stock and related warrants acquired through a June 2008 private placement that netted Biopure about $2.3 million.

But that will do nothing to boost the fortunes of Cambridge-based Biopure, which will not receive any proceeds from the stock sale.

The company began the quarter with only $245,000 in cash, after posting a $4.1 million net loss on $347,000 in revenues during the three months ended March 31. The firm in recent months has pared operations to the bone, retaining only four employees while it considers asset sales and other quick-cash efforts.

Earlier this week, the company said it only had enough funds to remain open through July 31.