Living cells reshape dynamic covalent chemical space via selective intracellular disulfide exchange

Dynamic covalent chemistry (DCC) enables adaptive molecular systems, yet whether dynamic covalent networks can operate selectively inside living cells remains largely unknown. Here we show that living cells reshape dynamic covalent chemical space through selective intracellular disulfide exchange. A disulfide-based dynamic combinatorial library (DCL), previously characterized in vitro, undergoes cysteine-directed redistribution in cellular lysates and intact living cells. Fluorescence spectroscopy and live-cell ratiometric imaging reveal functional network reorganization, whereas UPLC–ESI-MS identifies specific species that provide orthogonal consistency with the optical response, including enrichment of a cysteine-containing heterotrimer and a fluorescent homodimer. Notably, this redistribution occurs despite millimolar glutathione and other competing intracellular thiols. These results establish living cells as chemically selective environments capable of biasing dynamic covalent networks, expanding DCC into functional intracellular contexts and providing a framework for target-guided molecular selection in situ.