Peptidrings

Peptidrings are a class of macrocyclic peptides whose defining feature is a covalently closed ring formed by a sequence of amino acid residues. The term is used in chemical biology and medicinal chemistry to describe cyclic peptide scaffolds that are typically constrained by the ring, sometimes incorporating noncanonical amino acids or chemical cross-links to enhance rigidity and tailor function. Peptidrings can be found in natural biosynthetic pathways or produced synthetically.

Structurally, peptidrings range from relatively small rings of about 6 to 12 residues to larger macrocycles. Closure can occur through head-to-tail cyclization or via side-chain to side-chain or side-chain to backbone linkages, including disulfide bonds, lactam bridges, or other chemoselective connections. The rigidity imparted by cyclization often reduces conformational entropy in binding interactions and can improve receptor affinity and selectivity. The inclusion of nonstandard amino acids or cross-links further modulates properties such as stability, permeability, and solubility.

Synthesis strategies for peptidrings include solid-phase peptide synthesis followed by cyclization, native chemical ligation, and various chemoselective ligation techniques. Enzymatic approaches using cyclases or engineered biosynthetic routes also contribute to access, especially for larger or more complex rings. Challenges remain, notably achieving cell permeability for larger rings and controlling stereochemistry during cyclization.

Applications of peptidrings span drug discovery, enzyme inhibition, and protein–protein interaction modulation. Their tunable rigidity, stability, and binding profiles make them valuable as therapeutic leads and molecular probes. Ongoing research explores expanding chemical diversity, improving delivery, and elucidating structure–activity relationships.