What Is Peptide Stapling? How a Hydrocarbon Staple Locks a Helix

Published October 2026 · Patriot Labs Research Team · ~22 min read

The short answer

Peptide stapling is a chemical technique that locks a peptide into a fixed three-dimensional shape — almost always an α-helix — by joining two of its side chains with a covalent bridge called a “staple.” The best-known version, the all-hydrocarbon staple, swaps two of the peptide’s amino acids for non-natural residues that carry short carbon tails, then fuses those tails into a single hydrocarbon arch using a reaction called ring-closing metathesis. The result is a small ring, or macrocycle, running along one side of the helix.

The technique exists to solve a specific structural problem. A short stretch of peptide that forms a tidy helix inside a folded protein usually unravels once it is cut out and placed in water, because nothing holds the turns together. An unraveled peptide also presents its backbone to the enzymes that cut peptides apart, so it tends to degrade quickly. A staple pins two turns of the helix in place, which keeps the shape intact and tucks the backbone inside a ring.

This guide covers what a staple is, why the α-helix is the usual target, the all-hydrocarbon chemistry in detail, the geometry that decides where a staple can go, the main alternative stapling chemistries, the difference between single staples, double staples and “stitches,” what the published research reports that stapling changes, the history of the field, and how a laboratory confirms that a staple actually formed. For the related idea of making a whole peptide into a ring, see the companion guide on cyclic peptides.

What a “staple” actually is

A staple is a covalent cross-link between two amino acid side chains in the same peptide, placed so that it braces a secondary structure from the outside. Because the bridge joins two points on one chain, it turns part of the peptide into a ring — a macrocycle — while the backbone itself stays a single, un-cyclized strand.

That is the distinction worth holding onto. A fully cyclic peptide closes its own backbone into a loop, usually head-to-tail or through a disulfide bond between two cysteines. A stapled peptide keeps a linear backbone and adds a separate synthetic brace across it. In the vocabulary of medicinal chemistry, stapled peptides are a type of peptidomimetic — a molecule built to imitate the shape and surface of a natural peptide while behaving more like a small, stable chemical entity.

The word “staple” is a good mental picture: two legs anchored into the peptide at fixed points, and a rigid span bridging them. Change the length of the span or move the legs, and the brace either fits the helix it is meant to stabilize or fights it. Most of the craft of stapling is in getting that fit right.

Why the α-helix is the target

Stapling targets the α-helix because so much of the business of proteins is done by helices, and because a loose helix is exactly the kind of structure a staple is good at rescuing. A very large share of protein–protein interactions are mediated by one partner presenting a short α-helix that docks into a groove on the other. If a researcher wants a peptide that competes for that groove, the obvious starting point is the helix itself.

The problem is that a helix pulled out of its parent protein rarely stays a helix. In the folded protein, the rest of the structure holds it together; alone in solution, a short peptide spends most of its time as a shifting, disordered chain, and only a small fraction of the population is helical at any instant. Folding into a helix carries an entropic cost, because the chain has to give up its freedom to wander. Binding then has to pay that cost all over again, which weakens the interaction.

An α-helix repeats every 3.6 residues, which means that residues roughly three, four or seven positions apart in sequence can end up on the same face of the helix, physically close in space. A staple placed between two such residues does the job the rest of the protein used to do: it holds the turn closed. Because the helix is now pre-formed, the entropic penalty is paid once, during synthesis, rather than every time the peptide binds.

The all-hydrocarbon staple, step by step

The all-hydrocarbon staple is made by building two special amino acids into the peptide and then fusing their side chains together with a single chemical reaction. It is the method introduced by Christian Schafmeister, Julia Po and Gregory Verdine in 2000, and it remains the archetype of the field.

The two special residues are α,α-disubstituted, non-natural amino acids that carry a terminal olefin — a carbon–carbon double bond at the end of a short alkyl chain. The two most common are abbreviated S5, which is (S)-2-(4-pentenyl)alanine, and R8, which is (R)-2-(7-octenyl)alanine; the letter marks the stereochemistry and the number counts the carbons in the tail. The extra methyl group on the α-carbon (the “α,α-disubstituted” part) is not incidental: on its own it biases the local backbone toward a helical turn, so these residues help the helix along even before the staple closes.

The residues are incorporated during solid-phase peptide synthesis, in the ordinary way, at the two positions chosen for the staple. The peptide is then treated, usually while still on the synthesis resin, with a ruthenium catalyst of the kind developed by Robert Grubbs. The catalyst drives ring-closing metathesis: it swaps the ends of the two olefins, joining them into one continuous carbon chain and releasing a small molecule of ethylene gas as the by-product. What was two dangling tails becomes a single hydrocarbon bridge arching across the helix. The peptide is then cleaved from the resin and purified by reversed-phase HPLC like any other synthetic peptide.

Because the bridge is pure hydrocarbon — just carbon and hydrogen, with no polar groups — it is chemically inert and greasy, which is part of why all-hydrocarbon staples are associated in the literature with improved stability and, in some sequences, with better cell entry. The trade-off is that adding a greasy arch can also make a peptide stickier and harder to handle, which is one reason other stapling chemistries exist.

Staple geometry: i,i+4, i,i+7 and i,i+3

A staple only works if its two anchor residues sit on the same face of the helix and its bridge is the right length to span them. Chemists describe the spacing by counting residues: if the first anchor is at position i, the common patterns put the second at i+3, i+4 or i+7.

Because the helix turns once every 3.6 residues, an i,i+4 staple spans a single turn, and an i,i+7 staple spans two turns. The all-hydrocarbon system matches tether length to span: two S5 residues make the shorter bridge for an i,i+4 staple, while an i,i+7 staple pairs one S5 with the longer R8 to reach across the extra turn. An i,i+3 staple is shorter still and is used in some systems, including to stabilize the tighter 3₁₀-helix. Getting the geometry wrong — a bridge too short or anchors on the wrong faces — strains the helix instead of supporting it, and can lower helicity rather than raise it.

Beyond spacing, the position of the staple along the helix matters. A staple is normally placed on the face of the helix that points away from the binding partner, so the bridge braces the structure without blocking the surface that does the recognizing. Choosing that face, and the exact residues to replace, is where most of the design effort goes.

Other ways to staple a peptide

The all-hydrocarbon staple is the most famous, but it is one of several macrocyclization chemistries used to brace a helix. The alternatives differ in what side chains they join, what the bridge is made of, and whether the reaction can be run on a fully unprotected peptide in water.

Lactam staples form an amide bond between the side chains of a lysine and an aspartate or glutamate, giving a polar bridge rather than a greasy one. Disulfide staples join two cysteines and are simple but reversible under reducing conditions. Thioether and “click” triazole staples (the copper-catalyzed azide–alkyne reaction between an azide-bearing and an alkyne-bearing side chain) offer bridges that can be decorated with extra chemistry. A notable cysteine-based approach from the Pentelute group uses perfluoroaryl reagents such as decafluorobiphenyl to arylate two cysteines on an unprotected peptide in a single step. The table below sketches the main families.

No single chemistry is best for every case. A disulfide is quick to install but may not survive a reducing environment; a hydrocarbon bridge is robust but adds greasiness; a lactam keeps the molecule more water-friendly but is harder to place. The choice is made per sequence, against the properties the research calls for.

Single staples, double staples and stitches

A single staple places one bridge across one or two turns of a helix. For longer helices, a single staple may not be enough to hold the whole structure or to protect all of the backbone, and the field has developed two ways to add more bracing.

A double staple is simply two separate staples placed along the same helix. George Bird and colleagues showed in 2010 that double-stapling a long peptide addressed the proteolytic instability that a single staple left behind, because two bridges shield more of the backbone. A stitched peptide goes further: it uses a central amino acid that carries two olefin arms, so that one continuous brace runs through a shared residue and across several turns of the helix in one tandem unit. Stitched peptides are made by a double, or “bis,” ring-closing metathesis, reported by Gerard Hilinski and Gregory Verdine’s group in 2014.

More bracing is not automatically better. Each extra staple is another constraint and another greasy or polar patch added to the molecule, so stitching is a tool for specific long-helix problems rather than a default.

What stapling changes — and what it does not

The published research describes three main things a well-placed staple can change: how helical the peptide is, how well it resists the enzymes that cut peptides, and, in some cases, how readily it enters cells. A fourth, related effect is on binding: a pre-formed helix pays its folding entropy in advance, which can raise affinity for a target. None of these is guaranteed, and all depend on sequence and staple placement.

Helicity is the most direct effect and the easiest to measure. In a 2022 study of hydrocarbon-stapled peptides, circular dichroism showed linear precursors with helical content in the single digits to low twenties of a percent, while stapled analogs rose into the twenties to high forties — a clear structural shift, though the exact numbers are specific to those sequences.

Proteolytic stability tends to rise alongside helicity. The same 2022 work found that linear peptides were cut by α-chymotrypsin with half-lives of roughly eight minutes, while most stapled versions lasted beyond an hour, because the macrocycle hides the backbone from the enzyme’s active site. Earlier work on double-stapling was motivated by exactly this: a single staple on a long peptide was not enough, and a second bridge was needed to protect the rest of the chain.

Cell entry is the most sequence-dependent effect and the most debated. Some all-hydrocarbon stapled peptides cross the cell membrane, and the uptake studied by the Verdine group in 2009 appeared to proceed through active endosomal uptake rather than simple diffusion. But many stapled peptides do not enter cells well, and adding a greasy staple can increase nonspecific stickiness. Reviews of the field are careful to note that potency does not always track helicity or stability, and that a staple that improves one property can worsen another.

A short history of stapling

Stapling grew out of the broader development of olefin metathesis as a synthetic tool. In 1998, Helen Blackwell and Robert Grubbs showed that ring-closing metathesis could covalently cross-link the side chains of a peptide to reinforce a helix, using O-allylserine residues. Two years later, in 2000, Schafmeister, Po and Verdine combined that idea with α,α-disubstituted amino acids and on-resin synthesis to produce the first all-hydrocarbon cross-linking system, reporting improvements in both helicity and metabolic stability.

The approach drew wide attention in 2004, when Loren Walensky and colleagues reported in Science that a hydrocarbon-stapled BH3 helix — a “stabilized alpha-helix of BCL-2 domains,” or SAHB — activated apoptosis in a mouse model of leukemia. Over the following decade, stapled peptides were reported against a series of difficult intracellular targets studied in cell and animal models: the NOTCH transcription-factor complex (Moellering and colleagues, 2009), the apoptosis regulator MCL-1 (Stewart and colleagues, 2010), β-catenin in Wnt signaling (Grossmann and colleagues, 2012), and a potent dual inhibitor of MDM2 and MDMX aimed at the p53 pathway (Chang and colleagues, 2013).

The chemistry also reached the clinic as an industrial matter of record. Aileron Therapeutics, co-founded by Verdine, Walensky and Edward Taylor, ran the first clinical trial of a stapled peptide around 2013 with a growth-hormone-releasing-hormone agonist, and later studied the dual MDM2/MDMX candidate ALRN-6924 (sulanemadlin) in oncology trials. The underlying metathesis chemistry that made all of this practical was itself recognized with the 2005 Nobel Prize in Chemistry, shared by Grubbs. This paragraph is history and regulatory record only; it is not a statement that any stapled peptide is safe or effective for any use.

How a stapled peptide is characterized

Confirming a stapled peptide means confirming two things: that the sequence is right, and that the staple actually closed. The same two instruments used to document any research peptide do most of the work — mass spectrometry for identity and reversed-phase HPLC for purity — backed by circular dichroism for structure.

Mass spectrometry is decisive for the staple itself, because ring-closing metathesis leaves a precise mass signature: fusing the two olefins releases a molecule of ethylene, so the stapled product is lighter than the un-cyclized precursor by that defined amount. An exact-mass measurement that matches the stapled structure, and not the open one, is strong evidence the bridge formed. HPLC then reports purity and typically resolves the stapled species from any unreacted linear peptide, since the two have different shapes and surface chemistry. Circular dichroism spectroscopy quantifies how helical the final peptide is, which is the property the staple was installed to improve, and NMR can resolve the full solution structure when that detail is needed.

HPLC for purity and mass spectrometry for identity are the same two analyses that document the quality of any research vial. At Patriot Labs, for example, every batch is tested by an independent United States laboratory using both techniques, and the certificate of analysis is published on each product page.

What this guide does not establish

This guide explains peptide stapling as a chemistry and structural-biology technique. It does not evaluate, endorse or establish any medical, therapeutic or performance use of a stapled peptide, and nothing here describes how any peptide would be used in or on the body.

The studies cited report what was observed in the specific models used — purified proteins, cultured cells, or laboratory animals — and results in those settings do not establish safety or effectiveness in any other context. Many stapled peptides perform well in one assay and poorly in another, and the field’s own reviews stress that improvements in helicity or stability do not reliably predict potency or cell entry. The clinical and company history above is included as a matter of record, not as evidence that any candidate succeeded. Finally, this guide makes no claim that any product sold here is a stapled peptide; none of the catalog is one, and the guide is offered only to explain a technique readers encounter in the peptide literature.

Frequently asked questions

What is peptide stapling?

Peptide stapling is a chemical technique that locks a peptide into a fixed shape, almost always an α-helix, by joining two of its side chains with a covalent bridge called a staple. The bridge turns part of the peptide into a ring and holds the helix together so it does not unravel in solution.

What is a stapled peptide?

A stapled peptide is a peptide that has had a synthetic cross-link, or staple, added between two of its side chains to brace its structure. The backbone stays linear while the staple forms a macrocycle along one face of the helix, which is what distinguishes a stapled peptide from a fully cyclic one.

How is an all-hydrocarbon peptide staple made?

Two non-natural amino acids carrying short carbon tails with terminal double bonds are built into the peptide during solid-phase synthesis. A ruthenium Grubbs catalyst then performs ring-closing metathesis, fusing the two tails into a single hydrocarbon bridge and releasing ethylene, after which the peptide is cleaved and purified.

What is the difference between an i,i+4 and an i,i+7 staple?

The numbers count how many residues apart the two anchor points are. Because an α-helix turns every 3.6 residues, an i,i+4 staple spans a single turn and an i,i+7 staple spans two turns, so the i,i+7 version uses a longer bridge. In the all-hydrocarbon system, i,i+4 typically uses two S5 residues and i,i+7 uses one S5 with the longer R8.

Are stapled peptides the same as cyclic peptides?

No. A cyclic peptide closes its own backbone into a loop, usually head-to-tail or through a disulfide bond. A stapled peptide keeps a linear backbone and adds a separate synthetic brace across two side chains, forming a ring on the side of the helix rather than in the main chain.

What is a stitched peptide?

A stitched peptide uses a central amino acid with two reactive arms so that a single continuous brace runs through a shared residue and across several turns of a helix. It is made by a double ring-closing metathesis and provides more bracing than one staple, which can help on longer helices.

Why does stapling improve a peptide’s resistance to proteases?

Proteases cut peptides by gripping an extended stretch of the backbone in their active site. A staple holds the peptide in a compact helix and tucks the backbone inside a ring, which hides the bonds the enzyme would otherwise cut, so stapled peptides often last far longer than their linear versions in proteolysis assays.

What are stapled peptides studied for?

In the research literature, stapled peptides are studied mainly as tools to disrupt protein–protein interactions that small molecules struggle to reach, such as helix-in-groove interfaces. Reported laboratory targets include the BCL-2 family, the NOTCH complex, MCL-1, β-catenin and the MDM2/MDMX–p53 axis, all studied in cell and animal models.

References

1. Schafmeister, C. E., Po, J., & Verdine, G. L. (2000). An All-Hydrocarbon Cross-Linking System for Enhancing the Helicity and Metabolic Stability of Peptides. Journal of the American Chemical Society, 122(24), 5891–5892. doi:10.1021/ja000563a
2. Blackwell, H. E., & Grubbs, R. H. (1998). Highly Efficient Synthesis of Covalently Cross-Linked Peptide Helices by Ring-Closing Metathesis. Angewandte Chemie International Edition, 37(23), 3281–3284.
3. Walensky, L. D., Kung, A. L., Escher, I., Malia, T. J., Barbuto, S., Wright, R. D., Wagner, G., Verdine, G. L., & Korsmeyer, S. J. (2004). Activation of Apoptosis in Vivo by a Hydrocarbon-Stapled BH3 Helix. Science, 305(5689), 1466–1470. doi:10.1126/science.1099191
4. Walensky, L. D., & Bird, G. H. (2014). Hydrocarbon-Stapled Peptides: Principles, Practice, and Progress. Journal of Medicinal Chemistry, 57(15), 6275–6288. doi:10.1021/jm4011675
5. Bird, G. H., Madani, N., Perry, A. F., Princiotto, A. M., Supko, J. G., He, X., Gavathiotis, E., Sodroski, J. G., & Walensky, L. D. (2010). Hydrocarbon double-stapling remedies the proteolytic instability of a lengthy peptide therapeutic. Proceedings of the National Academy of Sciences, 107(32), 14093–14098. doi:10.1073/pnas.1002713107
6. Kutchukian, P. S., Yang, J. S., Verdine, G. L., & Shakhnovich, E. I. (2009). All-Atom Model for Stabilization of α-Helical Structure in Peptides by Hydrocarbon Staples. Journal of the American Chemical Society, 131(13), 4622–4627. doi:10.1021/ja805037p
7. Verdine, G. L., & Hilinski, G. J. (2012). Stapled peptides for intracellular drug targets. Methods in Enzymology, 503, 3–33.
8. Hilinski, G. J., Kim, Y.-W., Hu, J., & Verdine, G. L. (2014). Stitched α-Helical Peptides via Bis Ring-Closing Metathesis. Journal of the American Chemical Society, 136(35), 12314–12322.
9. Lau, Y. H., de Andrade, P., Wu, Y., & Spring, D. R. (2015). Peptide stapling techniques based on different macrocyclisation chemistries. Chemical Society Reviews, 44(1), 91–102.
10. Li, X., Chen, S., Zhang, W.-D., & Hu, H.-G. (2020). Stapled Helical Peptides Bearing Different Anchoring Residues. Chemical Reviews, 120(18), 10079–10144.
11. Spokoyny, A. M., Zou, Y., Ling, J. J., Yu, H., Lin, Y.-S., & Pentelute, B. L. (2013). A Perfluoroaryl-Cysteine S_NAr Chemistry Approach to Unprotected Peptide Stapling. Journal of the American Chemical Society, 135(16), 5946–5949.
12. Moellering, R. E., Cornejo, M., Davis, T. N., Del Bianco, C., Aster, J. C., Blacklow, S. C., Kung, A. L., Gilliland, D. G., Verdine, G. L., & Bradner, J. E. (2009). Direct inhibition of the NOTCH transcription factor complex. Nature, 462(7270), 182–188.
13. Stewart, M. L., Fire, E., Keating, A. E., & Walensky, L. D. (2010). The MCL-1 BH3 helix is an exclusive MCL-1 inhibitor and apoptosis sensitizer. Nature Chemical Biology, 6(8), 595–601.
14. Grossmann, T. N., Yeh, J. T.-H., Bowman, B. R., Chu, Q., Moellering, R. E., & Verdine, G. L. (2012). Inhibition of oncogenic Wnt signaling through direct targeting of β-catenin. Proceedings of the National Academy of Sciences, 109(44), 17942–17947.
15. Chang, Y. S., Graves, B., Guerlavais, V., Tovar, C., Packman, K., To, K.-H., et al. (2013). Stapled α-helical peptide drug development: A potent dual inhibitor of MDM2 and MDMX for p53-dependent cancer therapy. Proceedings of the National Academy of Sciences, 110(36), E3445–E3454.
16. Su, H., Liu, Y., Cong, H., He, L., Su, Y., & Hu, Y. (2022). Design, Synthesis, and Antitumor Activity Study of All-Hydrocarbon-Stapled B1-Leu Peptides. Frontiers in Chemistry, 10, 840131. doi:10.3389/fchem.2022.840131
17. Mourtada, R., Herce, H. D., Yin, D. J., Moroco, J. A., Wales, T. E., Engen, J. R., & Walensky, L. D. (2019). Design of stapled antimicrobial peptides that are stable, nontoxic and kill antibiotic-resistant bacteria in mice. Nature Biotechnology, 37(10), 1186–1197. doi:10.1038/s41587-019-0222-z

For more on the chemistry this guide touches, see Cyclic Peptides Explained for backbone macrocycles, What Is a Disulfide Bond? for the simplest side-chain cross-link, Peptide Half-Life Extension for the broader toolkit of making peptides last longer, What Is Solid-Phase Peptide Synthesis? for how the chain is built, and What Are D-Amino Acids? for another way peptides are made protease-resistant.

All Patriot Labs products are sold strictly for in-vitro research and laboratory use only. Not for human or veterinary consumption. This guide is educational and describes peptide stapling chemistry in general terms; it is not medical advice, does not describe how to use any product, and makes no claim that any Patriot Labs product is a stapled peptide.