Poly-Dha Sequences as Pro-polypeptides: An Original Mechanistic Postulate Leads to the Discovery of a Long-Acting Vasodilator KU04212

The construction of polypeptides was revolutionized by Merrifield’s solid-phase synthesis more than half a century ago. Herein, we explore a completely different approach to making peptides. We test an original mechanistic postulate wherein a single peptide made entirely of dehydroalanine (Dha) residues can give rise to regio- and stereodefined peptides by iterative conjugate addition of one- or two-electron nucleophiles. Each nucleophile appends a unique amino acid side chain to the peptide backbone. We show that side chain addition is not random. Side chains are added in one of two ways, in an electrophilicity-gated fashion (most cases) or in a substrate-directed manner, depending on the first nucleophile used in the synthesis. One peptide made in this series, KU04212, a first-in-class polyazole peptide, was found to reduce vascular length density (−17%; p < 0.05) and increase vessel diameter (124%; p < 0.001) in healthy day 6 chick embryos at 24 h post-single dose. It also rescued 75% of the embryos administered a 32-fold lethal dose of ischemia-inducing CoCl₂ after 12 h and 12.5% of the embryos after 24 h. In comparison to three mechanistically distinct vasodilators, e.g., isosorbide mononitrate, amlodipine besylate, and prazosin, only KU04212 showed long-acting effects in vivo, making it an enticing lead for the treatment of ischemic disorders.