Rapid Arene Triazene Chemistry for Macrocyclization.

Here, we report a novel rapid arene triazene strategy for the macrocyclization of peptides that generates an inbuilt chromophoric triazene moiety at the site of cyclization within a minute. The rapid arene triazene chemistry is chemoselective for secondary amines and -amino phenylalanine. Importantly, the resulting triazene cyclic peptide is highly stable at neutral pH and under harsh conditions but rapidly responds to various external stimuli such as UV radiations and acidic conditions, resulting in the ring opening to generate the linear peptides in an unchanged form, which further cyclizes under neutral pH conditions. This method works with completely unprotected peptides and has been applied for the synthesis of 18- to 66-membered monocycles and bicycles with various amino acid compositions in one pot under neutral pH conditions. Due to the high stability of triazene cyclic peptides, the postcyclization modification was carried out with various functional groups. This rapid, macrocyclization strategy featuring a triazene scaffold, amenable to late-stage diversification and responsive to external stimuli, should find application in various fields of chemical biology, selective drug delivery, and identification of cyclic peptide hits after library screening.