Scientists developed a versatile new method for making ring-shaped peptides, using it to create a library of potent melanocortin receptor agonists with selective activity at different receptor subtypes.
Subtype-selective libraryThe SNAr macrocyclization method generated a diverse library of cyclic melanocortin peptides that can selectively activate different receptor subtypes
What the researchers found
Researchers developed a new and efficient method for creating cyclic peptides — ring-shaped peptide molecules that are generally more stable and drug-like than their linear counterparts. Using nucleophilic aromatic substitution (SNAr), they created thioether macrocycles that can be built in solution on unprotected peptides or on resin-bound peptides with side-chain protection in place.
The method's key advantage is that it is "doubly orthogonal" — the chemical reactions used for cyclization don't interfere with standard peptide synthesis chemistry, and the resulting products contain electron-withdrawing groups that can be used for further modifications like adding labels or drug conjugates. Applied to melanocortin receptor targets, the approach generated a library of potent melanocortin agonists with distinct subtype selectivity — meaning different cyclic peptides could preferentially activate specific melanocortin receptor subtypes.
Why it matters
Melanocortin receptors control critical functions including appetite, sexual function, skin pigmentation, and inflammation. Drugs like bremelanotide (Vyleesi) and setmelanotide already target this system. But creating selective melanocortin agonists — ones that activate specific receptor subtypes without triggering unwanted effects — has been a major challenge. This new cyclization method allows rapid generation of diverse cyclic peptide libraries, accelerating the discovery of more selective and potent melanocortin drugs.
The numbers in context
SNAr macrocyclization method · Thioether-linked cyclic peptides · Library of potent melanocortin agonists generated · Distinct subtype selectivity achieved · Published in J. Med. Chem.
How the study worked
The researchers developed and validated a macrocyclization method using nucleophilic aromatic substitution (SNAr) to form thioether bridges in peptides. They tested the approach both in solution with unprotected peptidomimetics and on solid-phase resin with protected peptides. The resulting cyclic peptides were evaluated for binding and activation at melanocortin receptors, generating a library with varying subtype selectivity profiles.
Who was studied
Not applicable (medicinal chemistry study with in vitro receptor assays)
What this study cannot tell us
This is a chemistry/drug design study — no animal or human testing. The potency and selectivity were assessed in receptor binding assays only, not in vivo. Whether these cyclic peptides would be bioavailable, stable in the body, or therapeutically useful requires further preclinical and clinical testing. The library approach generates many candidates but doesn't guarantee any will become drugs.
How to read the evidence
Published in the Journal of Medicinal Chemistry, the top-tier journal for drug design research. This is a well-executed chemistry study demonstrating a novel method, but the biological evaluation is limited to in vitro receptor assays with no in vivo data.
When this study was published
Published in 2023 in the Journal of Medicinal Chemistry. Represents a current approach in cyclic peptide drug design with potential applications still being explored.
The bigger picture
Cyclic peptides are one of the most promising drug formats in pharmaceutical development — more stable than linear peptides, more selective than small molecules, and cheaper to make than antibodies. This macrocyclization method adds a new tool to the medicinal chemist's toolkit that could accelerate discovery across many peptide drug programs, not just melanocortin. The melanocortin application is particularly timely given the growing interest in this receptor family for obesity, sexual dysfunction, and rare genetic conditions.
Questions still open
- Will any of the cyclic melanocortin agonists from this library advance to animal testing and show favorable pharmacokinetics?
- Can the SNAr macrocyclization method be applied to other therapeutic peptide targets beyond melanocortin receptors?
- Could this approach produce more selective MC4R agonists than existing drugs, reducing side effects like nausea and skin darkening?
Common questions
Why are cyclic peptides better than regular (linear) peptides as drugs?
What are melanocortin receptors and why do they matter for drug development?
Read the original research
Targeting Melanocortin Receptors Using SNAr-Type Macrocyclization: A Doubly Orthogonal Route to Cyclic Peptide Conjugates.
Journal of medicinal chemistry, 66(5), 3273-3283
Citation
Yue, Wenxiao K; Zhang, Tianxia; Shandre Mugan, Rekha; Barlow, Nicholas; Chalmers, David K; Pouton, Colin W; Thompson, Philip E. (2023). Targeting Melanocortin Receptors Using SNAr-Type Macrocyclization: A Doubly Orthogonal Route to Cyclic Peptide Conjugates.. Journal of medicinal chemistry, 66(5), 3273-3283. https://doi.org/10.1021/acs.jmedchem.2c01587