Complex sentence: He published a number of books while writing his memoirs about the Gulag, but waited until Gorbachev became General Secretary of the CPSU before beginning in 1987 to publish excerpts from his memoirs in a variety of Soviet literary magazines.
Split into simpler sentences: He published a number of books while writing his memoirs about the Gulag. Instead, Razgon waited until Gorbachev became General Secretary of the CPSU before beginning in 1987 to publish excerpts from his memoirs in a variety of Soviet literary magazines.