Highly Preorganized Calixarene Tweezers for Protein Recognition.

Calixarene scaffolds offer structural robustness and tunable geometry for designing selective supramolecular inhibitors. Here, we developed a focused library of preorganized multivalent calix[4]arene tweezers targeting the cancer-related protease Taspase 1. Seven cone-conformation derivatives were synthesized, varying in linker rigidity, functionalization, and multivalency. Meta-dynamics simulations showed that flexible butynyl linkers enabled conformational adaptability, while rigid benzyl linkers promoted structural preorganization. Different biochemical binding assays showed that rigid constructs, particularly the bivalent c2Tl and upper-rim derivatives uc2T and uc4T, most effectively disrupted the Taspase 1/Importin α-interaction by directly binding to the enzyme's loop region near the active site. All constructs inhibited Taspase 1 activity, with c2Tl and uc4T showing the highest potency (low micromolar K_D values). While polar groups enhanced solubility, they reduced binding affinity; in contrast, increased multivalency and linker rigidity improved inhibition. These results establish rigid, preorganized calix[4]arene ligands as promising scaffolds for targeted enzyme inhibition.