The deal was announced before the Cardinals played the San Francisco Giants.
The Cardinals also activated outfielder Stephen Piscotty from the 10-day disabled list. Piscotty had been sidelined with a strained right hamstring suffered May 4.
Yepez, 19, signed with the Braves organization as a non-drafted free agent in July 2014, out of Caracas, Venezuela. The right-handed hitting infielder was batting .275 with 13 doubles, one home run and 15 RBIs in 35 games with low-Class A Rome of the South Atlantic League.
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The 6-foot-1, 200-pound Yepez has batted .281 with 34 doubles, six home runs and 54 RBIs in 120 games with three minor-league affiliates since the start of the 2015 season.
Piscotty appeared in three games for Class AAA Memphis during an injury rehabilitation assignment. He is batting .241 with two home runs and 11 RBIs in 25 games with the Cardinals.
Adams has been squeezed out of playing time with Matt Carpenter at first base. Adams has no other position, although he played six games in left field. That was an experiment the Cardinals tested, but did not like the results.
Adams was batting .292 with one homer and seven RBIs in 31 games and 48 at-bats.
The Braves needed a first baseman after Freddie Freeman suffered a broken left wrist Thursday when he was hit by a pitch. Freeman will be sidelined at least 10 weeks.