Complex sentence: In 1944 he was appointed conductor of Riga Opera, then 1947--1952 the Latvian Radio Orchestra, then from 1952 reserve conductor, and tour conductor, of the Leningrad Philharmonic behind Yevgeny Mravinsky and Kurt Sanderling.
Split into simpler sentences: In 1944 he was appointed conductor of Riga Opera, then the Latvian Radio Orchestra (1947--1952). In 1952 he was appointed reserve conductor, and tour conductor, of the Leningrad Philharmonic behind Yevgeny Mravinsky and Kurt Sanderling.