Noncovalent Peptide Stapling Using Alpha-Methyl-l-Phenylalanine for -Helical Peptidomimetics

Peptides and peptidomimetics are attractive drug candidatesbecauseof their high target specificity and low-toxicity profiles. Developingpeptidomimetics using hydrocarbon (HC)-stapling or other staplingstrategies has gained momentum because of their high stability andresistance to proteases; however, they have limitations. Here, wetake advantage of the & alpha;-methyl group and an aromatic phenylring in a unique unnatural amino acid, & alpha;-methyl-l-phenylalanine(& alpha;F), and propose a novel, noncovalent stapling strategy tostabilize peptides. We utilized this strategy to create an & alpha;-helicalB-chain mimetic of a complex insulin-like peptide, human relaxin-3(H3 relaxin). Our comprehensive data set (in vitro, ex vivo, and in vivo) confirmedthat the new high-yielding B-chain mimetic, H3B10-27(13/17 & alpha;F),is remarkably stable in serum and fully mimics the biological functionof H3 relaxin. H3B10-27(13/17 & alpha;F) is an excellent scaffold forfurther development as a drug lead and an important tool to decipherthe physiological functions of the neuropeptide G protein-coupledreceptor, RXFP3.