Dopirak hit 39 home runs and knocked in 120 runs en route to being named MVP of the Midwest League in 2004, then regressed the following year at Class High-A Daytona before his season was cut short due to a foot injury at Double-A in 2006.
A season ago, he played in 115 games between Class High-A Daytona and Double-A Tennessee, batting .266 with 18 home runs and 68 RBIs.
"Brian was a real difficult release," said Cubs Vice President of Player Personnel Oneri Fleita. "He had been with this organization for a very long time."
Dopirak was named the top prospect in the Cubs' farm system by Baseball America entering 2005. He finished his career with the Cubs a .265 hitter with 89 home runs and 340 RBIs over six minor league seasons.
Rick, 24, was drafted two rounds behind Dopirak in 2002. He batted .236 with 33 home runs in six seasons. Rick asked the Cubs for his release, he said.
"They said if I ever wanted to coach, they'd give me full support," Rick said. "But I told them I could still play ... There wasn't really a roster spot for me."
Koerber, 25, was signed by Chicago as a non-drafted free agent in 2004 following a four-year collegiate career at Michigan State, where he was primarily an infielder.
As a pitcher, Koerber logged 200-plus innnings over four minor league seasons.
Other minor league players that have been released this spring include: OFs Chris Walker and Brian Leclerc; LHPs Tim Layden and Taylor Parker; RHPs Miguel Cuevas-Novas, Simon Lee and Yuri Higgins; and catcher Matt Canepa.
"It's hard to tell someone goodbye and that they're no longer part of the organization," said Fleita. "It's probably the worst two weeks of the year from my position."