Orthogonal functionalisation of α-helix mimetics

Abstract

α-Helix mediated protein-protein interactions are of major therapeutic importance. As such, the design of inhibitors of this class of interaction is of significant interest. We present methodology to modify N-alkylated aromatic oligoamide α-helix mimetics using 'click' chemistry. The effect is shown to modulate the binding properties of a series of selective p53/hDM2 inhibitors.

Fig. 1. Helix mimetics as inhibitors of PPIs: (a) schematic illustrating proteomimetic concept, (b) p53/hDM2 interaction (PDB ID: ; 1YCR), (c) N- and (d) O-alkylated aromatic oligoamides, (e) schematic illustrating concept for orthogonal functionalisation.

Scheme 1. Synthesis of alkyne-functionalised N- and O-alkylated Fmoc monomer, 10.

Scheme 2. Solid-phase synthesis of triazole-functionalised trimers 1–5.

Fig. 2. Overlay of (a) unfunctionalised trimer 1 (RMSD = 0.983 Å), (b) acid functionalised trimers 2 (RMSD = 0.772 Å) and (c) ethylene glycol-functionalised trimer 3 (RMSD = 0.753 Å) with p53. Overlaid residues are shown in CPK format. p53 residues are in dark colours and helix mimetic residues are in light colours (side and top views are given).

Fig. 3. Fluorescence anisotropy binding assays in phosphate buffer pH 7.5, 200 mM NaCl, 0.02 mg ml^–1 BSA. (a) p53/hDM2 competition assay hDM2 is fixed as 154 nM and FITC-p53 is at a concentration of 54.5 nM. (b) Direct binding assay of trimer 5 binding to hDM2 or Mcl-1. Compound 5 is fixed at 50 nM.

Fig. 4. Effects of modification on helix mimicry (a) schematic illustrating potential steric clash of functional handle with helix binding cleft. (b) Dihedral angle analysis showing relative energies at different degrees of rotation about (c) the central N-aryl bond (d) steric clash in the functionalised trimers, between carbonyl and side chain oxygen atoms (shown in CPK format).