D.C. United acquire Kamara, Galaxy's Boateng
Boateng came from the LA Galaxy for $250,000 in targeted allocation money.
D.C. United paid Chinese team Shenzhen F.C. a $2.5 million transfer fee.
Boateng, a 25-year-old Ghana native, had one goal and one assist in 21 games this season and tallied nine goals and 13 assists in 108 appearances for the Galaxy since 2016.
"Adding Emmanuel gives us another dynamic option from wide areas," said D.C. United general manager Dave Kasper. "His ability to stretch the field and get behind the opponent's defensive line will give us an additional attacking threat as we enter the final stages of the regular season."
Boateng's best season in Los Angeles came in 2018 when he tallied four goals and two assists in 34 games.
Boateng could make his Black-and-Red debut on Sunday night when his former Galaxy teammates visit Audi Field in Washington, D.C.
Kamara is another former Galaxy player. He left Los Angeles before the MLS season started, appearing in six matches for Shenzhen F.C.
Kamara, 29, has scored 48 goals in 90 MLS games, playing for the Columbus Crew in 2016 and 2017 before moving on last season to the Galaxy, where he scored 14 goals.
"We are extremely excited to acquire a dynamic attacking talent in Ola Kamara," Kasper said. "He has been one of the most prolific goal scorers in MLS during his three years with the Crew and Galaxy and he will be a key offensive piece for us as we look towards the 2019 MLS Cup Playoffs and beyond."
D.C. United (9-7-9, 36 points) sit fourth in the MLS Eastern Conference, but have won just one of their past seven matches.