The markets opened lower with the Dow tumbling 79 points to 17,896 as the deadline to reach a nuclear deal with Iran loomed. Nasdaq lost 17 points to 4,929.

On the upside

Piper Jaffray upgraded Horizon Pharma (Nasdaq: HZNP) from a Neutral rating to an Overweight rating.

The U.S. Patent and Trademark Office issued a patent to Great Basin Scientific (Nasdaq: GBSN) for the company's method of isothermal helicase-dependent amplification using blocked primers.

Charter Communications (Nasdaq: CHTR) will acquire rival Bright House Networks in a cash and stock deal valued at approximately $10.4 billion.

On the downside

Synta Pharmaceuticals (Nasdaq: SNTA) priced its public offering of 22 million common shares at the discounted price of $1.75.

Teck Resources (NYSE: TCK) denied that it engaged in merger discussions with Antofagasta.

Vaalco Energy (NYSE: EGY) will plug and abandon the post-salt Kindele-1 well offshore Angola.

In the broad market, declining issues outpaced advancers by a margin of nearly 4 to 1 on the NYSE and by more than 3 to 1 on Nasdaq. The broader S&P 500 lost 8 points to 2077. Bitcoin slipped $3 to $242.