A General Synthesis Approach to Double-Guanidinium Stapled Peptides and Foldamers.

In the broader context of peptide macrocyclization, methods enabling the formation of specific crosslinks between orthogonally protected, amino-functionalized side chains (e.g., Lys-Lys crosslinks) are of potential interest for expanding molecular diversity and stabilizing peptide secondary structures. We recently introduced a solid-phase synthesis approach for the rapid generation of guanidinium stapled helical peptides and have shown their utility for inhibition of protein-protein interactions. Whereas our previous work concentrated on the formation of mono-guanidinium crosslinks, we show here that we can expand this approach to prepare bis-guanidinium stapled peptides and foldamers on-resin. The methodology similarly uses two orthogonally protected amino-functionalized side chains and features the use of a diamino connector. The two guanidinium groups are introduced sequentially, the first one intermolecularly and the second intramolecularly. The method is compatible with the i,i + 4 and i,i + 7 cyclization schemes and tolerates a diversity of diamino linkers. We applied the strategy to the synthesis of macrocyclic inhibitors of hDM2 and hDMX and identified several high affinity binders for the two proteins.