All four were on the Major League roster briefly this year, before Santana was sent back down. Zeid didn't make the trip to Philadelphia because he's due to have season-ending foot surgery this week, and Cosart was dealt to the Marlins last week.
"I'm excited to play here," Singleton said. "There's a lot of guys that I've played with who are with the organization, so it's going to be cool to see them."
Singleton, who was playing in Class A Clearwater when the trade was made, was subsequently sent to Class A Lancaster and made his Major League debut this year after signing a $10-million contract extension.
Santana, who was the player to be a named later in the deal, was recalled from Triple-A Oklahoma City on Sunday for his second stint with the club. He was 0-for-13 with 11 strikeouts in his first stint in Houston earlier this year.
"I was sad, because I had a pretty good relationship with everybody," Santana said of the trade.
Brian McTaggart is a reporter for MLB.com and writes an MLBlog, Tag's Lines. Follow @brianmctaggart on Twitter. This story was not subject to the approval of Major League Baseball or its clubs.