Complex sentence: In 1988, he joined the DuPont Pharmaceutical Company, where he worked both as a bench scientist on HIV drug resistance then later designed the clinical trials eventually leading to the FDA approval of Sustiva (efavirenz).
Split into simpler sentences: In 1988, he joined the DuPont Pharmaceutical Company, where he first worked as a bench scientist on HIV drug resistance. He later designed DuPont's clinical trials leading to the FDA approval of Sustiva (efavirenz).