Review Outlines Synthetic Strategies for Direct Selection of Hybrid Macrocyclic Peptides via Phage Display

Macrocyclic peptides (MPs) are highly sought after in drug discovery, uniquely combining the precise target selectivity characteristic of biologics with the favorable pharmacological properties often seen in small molecules, such as improved bioavailability. However, traditional biological selection platforms, like bacteriophage display, typically identify peptide binders that are genetically encoded and often require substantial post-selection medicinal chemistry. This extensive optimization is frequently necessary to incorporate nonpeptidic scaffolds and synthetic cyclization units, which are critical for enhancing binding affinity, proteolytic stability, membrane permeability, and overall pharmacological performance. The current challenge lies in bridging the gap between high-throughput biological selection and the direct generation of drug-like macrocycles, thereby accelerating the development of next-generation peptide therapeutics.

This comprehensive review critically analyzed various synthetic strategies designed to enable the direct selection of hybrid macrocyclic peptides using bacteriophage display. The authors systematically discussed established cysteine- and lysine-targeting chemistries, which have historically been foundational for peptide cyclization. Furthermore, the review delved into recent advancements in residue-selective and chemoenzymatic cyclization methods, highlighting their precision and efficiency. Emerging approaches were also explored, specifically those that leverage proximity-driven reactivity or exploit the inherent chemical sturdiness of bacteriophages themselves to facilitate cyclization. The review concluded by outlining key design principles for phage-compatible macrocyclization reactions and identifying future opportunities at the intersection of bioconjugation chemistry, enzyme engineering, and machine-learning-guided peptide discovery.

The review found that by integrating advanced synthetic methodologies directly into biological selection platforms, it is possible to simultaneously explore both the peptide sequence and the synthetic chemical space. This integrated approach holds the potential to significantly reduce downstream optimization efforts that are typically required for peptide therapeutics. Key strategies highlighted include established methods utilizing cysteine- and lysine-targeting chemistries for efficient cyclization.

Recent advances in residue-selective and chemoenzymatic cyclization methods offer enhanced control and specificity, allowing for the precise incorporation of nonpeptidic scaffolds.

Emerging techniques, such as those exploiting proximity-driven reactivity or the inherent chemical resilience of bacteriophages, further expand the toolkit for generating diverse hybrid macrocycles. These strategies collectively enable the creation of macrocyclic peptides with improved binding affinity, enhanced proteolytic stability, better membrane permeability, and superior overall pharmacological performance directly from selection, thereby accelerating the drug discovery pipeline.