Stocks ended lower as the latest Federal Reserve meeting minutes showed a central bank committed to monetary tightening. Benchmark indexes fell into the red in the final hour. The central bank committed to reducing its balance sheet, possibly later this year. Reducing the balance sheet and phasing out reinvestments could have the same tightening impact as a rate hike. Plug Power(PLUG) - Get Report exploded after securing a supply agreement with Amazon(AMZN) - Get Report . The e-commerce company has the right to purchase up to 23% of Plug Power and will also use its fuel cells in Amazon warehouses. Walgreens(WBA) - Get Report declined after falling short of earnings and revenue estimates over its second quarter. The pharmacy chain missed profit consensus by a penny, while revenue fell short by nearly $1 billion.