Complex sentence: In June 1990, Marcus was transferred to New York's Memorial Sloan-Kettering Cancer Center to undergo an autologous bone barrow transplant, but the treatment was unsuccessful and Marcus died on September 20 1990.
Split into simpler sentences: In June 1990, Marcus was transferred to New York's Memorial Sloan-Kettering Cancer Center to undergo an autologous bone barrow transplant. Unfortunately, the treatment was unsuccessful and Marcus passed away on September 20 1990.