De Los Santos had his contract selected by the Pirates on Sunday, Jason Mackey of the Pittsburgh Post-Gazette reports.
De Los Santos began the season at Triple-A Indianapolis and posted a 1.72 ERA and 0.64 WHIP in 15.2 innings over 12 relief appearances. The 24-year-old hasn't yet made a major-league appearance but should provide a boost to the Pirates' bullpen. If he remains effective in the big leagues, it's possible that De Los Santos will work his way into high-leverage work at some point.