? Discovery and Optimization of 5-Hydroxy-Diclofenac toward a New Class of Ligands with Nanomolar Affinity for the CaMKII? Hub Domain

The Ca2+/calmodulin-dependent protein kinase II alpha (CaMKII alpha) is a brain-relevant kinase involved in long-term potentiation and synaptic plasticity. We have recently pinpointed the CaMKII alpha hub domain as the long-sought-after high-affinity target of gamma-hydroxybutyrate ligands substantiated with a high-resolution cocrystal of 5-hydroxydiclofenac (3). Herein, we employed in silico approaches to rationalize and guide the synthesis and pharmacological characterization of a new series of analogues circumventing chemical stability problems associated with 3. The oxygen-bridged analogue 4d showed mid-nanomolar affinity and notable ligandinduced stabilization effects toward the CaMKII alpha hub oligomer. Importantly, 4d displayed superior chemical and metabolic stability over 3 by showing excellent chemical stability in phosphate-buffered saline and high resistance to form reactive intermediates and subsequent sulfur conjugates. Altogether, our study highlights 4d as a new CaMKII alpha hub high-affinity ligand with enhanced pharmacokinetic properties, representing a powerful tool compound for allosteric regulation of kinase activity with subtype specificity.