STAPLED HELIX SERIES

(16) A critically important consequence of α-helical stabilization by all-hydrocarbon stapling was the observed protease resistance, (11) a direct result of sequestering the amide bonds in the interior of the helix core and thus rendering them poor substrates for enzymatic hydrolysis. The resultant constructs were later dubbed stapled peptides, (13) based on the prior use of the term “staple” to reflect the organization conferred by covalent linkage of two previously independent entities, such as in stapled molecules (14) and disulfide bridge stapling, (15) and as elegantly depicted on a Blackwell and Grubbs journal cover. (12) Importantly, Verdine and colleagues combined the principles of RCM with α,α-disubstitution of the amino acid chiral carbon and on-resin peptide synthesis to ultimately achieve the goal of structural stabilization (11) (Figure 1). (11) This work was an extension of the pioneering studies of Blackwell and Grubbs, who created a cross-link between O-allylserine residues on a peptide template to form a covalent bond using the Grubbs catalyst.

STAPLED HELIX SERIES

The all-hydrocarbon cross-link for peptide α-helix stabilization was first published in 2000 by Verdine and colleagues, who sampled a large series of α,α-disubstituted non-natural amino acids bearing olefin tethers to determine optimal length and stereochemistry for ruthenium-catalyzed ring-closing metathesis (RCM) across one or two α-helical turns. The purpose of this review is to describe our practical experience to date with inserting all-hydrocarbon cross-links into bioactive peptide motifs and how this chemical intervention created a new class of structured peptides for biological discovery and clinical translation. With proof-of-concept for chemical stabilization of peptide helices in hand, a critical next step was to transform structured peptides into reagents that could withstand the in vivo proteolytic environment, target and penetrate intact cells, and ultimately achieve clinically relevant biological activity. Covalent approaches based on installing disulfide (7) and lactam (8-10) bridges into the peptide architecture have provided even further enhancements. (1, 2) For example, designs that include helical caps between terminal side chains and the peptide backbone, (3) hydrogen bonding or electrostatic interactions between side chains at select positions, (4) and introduction of α,α-disubstituted amino acids, (5, 6) such as aminoisobutyric acid, have yielded peptides with improved α-helical structure in solution.

A diversity of clever approaches to reinforcing α-helical structure, spanning noncovalent and covalent strategies, have been advanced over the past several decades. Here, we describe our more than decade-long experience in developing stapled peptides as biomedical research tools and prototype therapeutics, highlighting lessons learned, pitfalls to avoid, and keys to success.Ĭhemists and biologists have long sought to recapitulate the shape and bioactivity of the peptide α-helix for basic science and therapeutic applications. The all-hydrocarbon staple has emerged as one such solution, conferring α-helical structure, protease resistance, cellular penetrance, and biological activity upon successful incorporation of a series of design and application principles. Because peptides can lose their shape when taken out of context, developing chemical interventions to stabilize their bioactive structure remains an active area of research. The peptide α-helix represents a common structural motif that mediates communication between signaling proteins. Although small molecules represent the lion’s share of agents that target proteins for therapeutic benefit, there remains no substitute for the natural properties of proteins and their peptide subunits in the majority of biological contexts. Protein structure underlies essential biological processes and provides a blueprint for molecular mimicry that drives drug discovery.

Stapled helix