Rotamer-Controlled Self-Immolative Linkers Enable Tunable Release of Neurosteroid Oxime Prodrugs

In this work we present a modular prodrug strategy for the controlled release of neurosteroid oximes, exemplified through new synthetic routes for both progesterone and allopregnanolone derivatives. By systematically modifying the self-immolative linker with steric, electronic, heterocyclic, and angle-strained elements, we achieved control over syn/anti-rotamer populations and self-immolation kinetics. In vitro studies across different pH values, temperatures, and biological media revealed a broad range of release rates, while in silico modeling corroborated that syn/anti-conformer energy differences and pK _a values are key predictors of reactivity. Notably, heterocyclic and electronic designs maintained consistent behavior in both PBS and human plasma, whereas sterically hindered derivatives showed plasma-specific stabilization of the anti-conformer. Comparative studies in mouse and rat plasma revealed minimal interspecies differences. These findings clarify critical factors governing self-immolative prodrug behavior in complex environments and offer a framework for the rational design of next generation neurosteroid prodrugs.