Advancing Blue‐Light Photoactivatable TAM Kinase Inhibitors for Cancer Treatment: Challenges in Using π ‐Extended Coumarins as Photocleavable Protecting Groups

We developed a series of photocleavable TAM kinase inhibitors that incorporate various π ‐extended coumarins as photoremovable groups, enabling blue‐light activation. This study emphasizes the critical role of π ‐extended coumarins, particularly how their electronic properties (electron‐withdrawing and donating groups) affect the photorelease efficiency and the biological recovery of UNC2025 . Among all candidates, the N,O‐dicaged inhibitors showed the strongest restoration of kinase inhibition. Specifically, the one bearing an electron‐donating substituent at position 3 emerged as the optimal design. Indeed, it combines high photosensitivity with rapid blue‐light uncaging (<2 min) , loss of UNC2025 ’s kinase inhibitory and cytotoxic activities prior to irradiation, and full recovery of UNC2025 potency in enzymatic and cellular assays upon illumination. In contrast, compounds bearing π ‐extended coumarins functionalized with electron‐withdrawing groups showed inconsistent uncaging behavior and incomplete biological recovery, highlighting the decisive influence of coumarin electronics on photorelease efficiency. Ultimately, the use of π ‐extended coumarins enabled preliminary two‐photon absorption measurements, suggesting that designing inhibitors with enhanced two‐photon sensitivity may be key to achieving therapeutically relevant photoactivation windows.