Walters made his major league debut against the Chicago Cubs on April 17, allowing three runs on six hits and striking out seven in a no-decision.
In six outings, including one start for St. Louis, he is 0-0 with an 8.76 ERA. He was 3-7 with a 4.92 ERA at Memphis, where he started 12 times.
Barden batted .233 with four homers and 10 RBIs in 52 games for the Cardinals.
The moves were made Saturday.