A novel imidazo‐pyramidazine inhibitor of DAPK1 that undergoes class‐specific interactions and extends into the substrate recognition site has been identified. This inhibitor is a good starting point for the development of selective and potent inhibitors of DAPK1, with potential use against stroke and ischemia.
PDZ domains in general, and those of PSD-95 in particular, are emerging as promising drug targets for diseases such as ischemic stroke. We have previously shown that dimeric ligands that simultaneously target PDZ1 and PDZ2 of PSD-95 are highly potent inhibitors of PSD-95. However, PSD-95 and the related MAGUK proteins contain three consecutive PDZ domains, hence we envisioned that targeting all three PDZ domains simultaneously would lead to more potent and potentially more specific interactions with the MAGUK proteins. Here we describe the design, synthesis and characterization of a series of trimeric ligands targeting all three PDZ domains of PSD-95 and the related MAGUK proteins, PSD-93, SAP-97 and SAP-102. Using our dimeric ligands targeting the PDZ1-2 tandem as starting point, we designed novel trimeric ligands by introducing a PDZ3-binding peptide moiety via a cysteine-derivatized NPEG linker. The trimeric ligands generally displayed increased affinities compared to the dimeric ligands in fluorescence polarization binding experiments and optimized trimeric ligands showed low nanomolar inhibition towards the four MAGUK proteins, thus being the most potent inhibitors described. Kinetic experiments using stopped-flow spectrometry showed that the increase in affinity is caused by a decrease in the dissociation rate of the trimeric ligand as compared to the dimeric ligands, likely reflecting the lower probability of simultaneous dissociation of all three PDZ ligands. Thus, we have provided novel inhibitors of the MAGUK proteins with exceptionally high affinity, which can be used to further elucidate the therapeutic potential of these proteins.
An effective procedure for the synthesis of peptide alkyl thioesters by 9‐fluorenylmethoxycarbonyl (Fmoc) solid‐phase peptide synthesis was developed. The free C terminus of a fully protected peptide was coupled in solution with the free amino group of an amino thioester. This furnished the fully protected peptide thioester, which was globally deprotected to afford the desired unprotected peptide thioester. The method is compatible with labile groups such as phosphoryl and glycosyl moieties.
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