Turning the Sulfur Dial: Strategic Oxidation-State Manipulation in Modern Drug Discovery.
Sulfur occupies a distinct niche in the toolkit of a medicinal chemist. Unlike oxygen, sulfur rationalized by ionic-resonance, negative hyperconjugation into low-lying σ* orbitals, and high polarizability of its 3p valence shell, accommodates the oxidation states from -2 to +6, adopting a diverse range of molecular geometries. Such properties position sulfur as a tunable element that contributes to drug molecules beyond passive lipophilic bulk. The proportion of sulfur-containing motifs among newly FDA-approved small-molecule drugs has increased from approximately 11% in 2020 to about 20% in 2024. Here, we argue that oxidation state switching at a single sulfur atom should be treated as a first-line lead optimization strategy. We map how different oxidation states impact geometry, polarity, and stability and how their interconversion enables rapid tuning of both target engagement and ADMET properties. We analyze synthetic innovations like SuFEx click chemistry, DABSO-mediated sulfonylation, etc., which make these motifs experimentally accessible. We propose a decision-making framework positioning sulfur oxidation state as a dynamic design variable in medicinal chemistry.