The Sensex was down sharply in noon trade on jitters over the US financial system, following investment bank Lehman's plans to file for bankruptcy protection. The BSE 30-share index was down 724.24 points. The financial upheaval also involved other US institutions. Bank of America has agreed to acquire Merrill Lynch & Co for $50 billion in an all-stock deal that will give the US bank the world's largest brokerage.