He is best known for his innovative and pioneering work on d4T (stavudine), 3TC (lamivudine, in collaboration with Dennis C. Liotta), FTC (emtriva, in collaboration with Dr. Woo-Baeg Choi and Dennis C. Liotta), LdT (telbivudine), RCV (racivir) and DAPD (amdoxovir), drugs that are now approved by the FDA (Food and Drug Administration) or at various stages of clinical development.