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 pKa 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.