Design, synthesis and evaluation of clickable photoaffinity probes for nuclear lamins

Nuclear lamins are type V intermediate filament proteins to support the mechanical stability of mammalian cell nucleus. They also participate in various signaling activities in the cells. We recently discovered substituted pyrroloquinazoline LBL1 as the first small molecule to directly target nuclear lamins despite their poor druggability. Based on LBL1, a clickable photoaffinity probe LBL1-PCF was designed to identify lamin-interactors in native cells. In this work, we designed and synthesized a series of clickable photoaffinity probes to evaluate the structure-activity relationships for lamin labeling. Appending an azidopropyl group to the pyrroloquinazoline core at N-7 was well-tolerated without affecting the labeling EC₅₀. Substitution at N-1 significantly reduced its efficiency for lamin labeling. On the other hand, shifting the azidopropyl group to the benzamide at N-3 of pyrroloquinazoline core abolished its capability for lamin labeling. Our results demonstrate that strategic placement of the clickable group at the pyrroloquinazoline core is of paramount importance for target identification studies.