Abstract
Phosphoramidate prodrugs stand out for their applications as drug delivery systems. However, information on their activation remains limited to prodrug half-live and metabolite structure, which hinders their development.
Considering the lack of data on phosphoramidate self-immolation, we studied light-triggered self-immolation of phosphoramidate-based linkers bearing various amino acid arms by NMR spectroscopy with in situ irradiation, complemented with mathematical fitting, and by optical methods. By changing the alanine arm, we were able to systematically fine-tune, slow down or speed up the cyclization rate.
The cyclization rate of branched amino acid arms increased with the steric demands of their alpha-substituents according to the Thorpe-Ingold effect. The cyclization of beta-alanine and proline was very slow or did not proceed at all, but lactate may be a good alternative for the alanine arm because lactate exhibits a significantly slower cyclization rate than alanine (ca. 60 times).
Overall, our study demonstrates that phosphoramidate self-immolation strongly depends on the structure of the amino acid arm and on the conditions used (solvent, concentration and temperature), thereby providing a solid foundation for the rational design of new self-immolative phosphoramidate systems with desired properties.