After completing his PhD, he became professor at the
University of Pittsburgh, where he eventually attained the rank of University Professor and taught until 1979. From 1979 to 1993, he was a professor at
Yale University, where he rose to the rank of
Sterling Professor of Chemistry. By 1991 he was sharing his time with Memorial Sloan-Kettering Cancer Center as director of the Laboratory for Cancer Research Bioorganic Chemistry, becoming chair in 1993. He accepted an appointment as professor at Columbia University in 1993, and now splits his time between Columbia and Sloan-Kettering. == Research ==