The markets opened lower with the Dow slipping a point to 17,543 as concerns about China overshadowed better than expected housing starts in July. Nasdaq lost 14 points to 5,077.

On the upside

Omeros (Nasdaq: OMER) announced additional positive data from a Phase 2 clinical trial of OMS721 to treat thrombotic microangiopathies.

National Penn Bancshares (Nasdaq: NPBC) will be acquired by BB&T in a cash and stock transaction valued at approximately $1.8 billion.
 
SunEdison (NYSE: SUNE) formed a $1 billion warehouse investment vehicle to be managed by Goldman Sachs.
 
On the downside

Stifel Nicolaus downgraded SFX Entertainment (Nasdaq: SFXE) from a Hold rating to a Sell rating.

Second quarter earnings for Wal-Mart (NYSE: WMT) fell more than expected prompting the discount retailer to lower its full year earnings outlook.

Freeport-McMoRan (NYSE: FCX) stopped exporting copper from Indonesia.

In the broad market, declining issues outpaced advancers by a margin of nearly 5 to 2 on the NYSE and by more than 5 to 3 on Nasdaq. The broader S&P 500 slipped 1 point to 2,100. Bitcoin lost $4 to $251.