Beyond the affinity for protein kinase C: Exploring 2-phenyl-3-hydroxypropyl pivalate analogues as C1 domain-targeting ligands

Over the past fifteen years, we reported the design and synthesis of different series of compounds targeting the C1 domain of protein kinase C (PKC) that were based on various templates. Out of the pivalate template, 2-[4-(benzyloxy)phenyl]-3-hydroxypropyl pivalate (compound 1) emerged as the most potent and promising PKCα ligand, showing a Ki value of 0.7 µM. In the present contribution our efforts are aimed at better understanding which structural modifications of pivalate template are allowed for preserving or increasing its affinity for the C1 domain of PKC. To this aim, thirteen novel analogues of 1 were designed and their interaction with the target evaluated in silico. Designed compounds were then prepared and fully characterized as well as their affinity for the α and δ isoforms of PKC evaluated. Additionally, in order to investigate the role of chirality in the ligand-target interaction, the pure enantiomers of the most interesting PKC ligands were prepared and their affinity for PKC isoforms determined. Results from our study pointed out that: i) the presence of the ester function seems to be essential for the ligand-target interaction; ii) only few structural modifications at the ester group are allowed for preserving the C1 domain affinity; and iii) the [3H]PDBu replacement experiments showed that the C1 domain of PKC does not exhibit enantiopreference for the pure stereoisomers of tested compounds. Altogether our observations provide further insights into the ligand-target interactions of the PKC C1 domain and represent a step-forward in future development of more specific and effective PKC ligands.