Amazon.com (AMZN.O) shares jumped as much as 20.4 percent to a record of $580.57 after the online retailer posted an unexpected quarterly profit. The jump catapulted Amazon’s market value to about $270 billion, overtaking Wal-Mart (WMT.N). The three major indexes were poised to end the week in the red as Biogen’s (BIIB.O) 19 percent slump weighed the most on the Nasdaq and the S&P 500 and dragged down other health stocks.