A series of rational modifications to the structure of known S-(N-aryl-N-hydroxycarbamoyl)glutathione-based glyoxalase I inhibitors culminated in the discovery of the first single-digit nanomolar inhibitor. This study makes available key information about possible means to address the issues of metabolic instability, low potency, and synthetic complexicity that have plagued the area of glyoxalase I inhibition. Knowledge garnered from this study has implications in the design of inhibitors with higher conformational definition and lower peptidic character.