Specific modifications at the peptide ends.

• Acetylation, formylation, acylation (typically N-terminus; also side chains possible)
• Amidation (C-terminus)
• Biotinylation
• Introduction of C-terminal alcohol and aldehyde moieties
• Introduction of C-terminal ester and thioester groups

Natural PTM mimics and small-group chemical additions on side chains.

• Phosphorylation and sulfation
• Methylation, alkylation
• Lipidation
• Biotinylation
• Maleimido peptides (maleimide functional handle for thiol conjugation)
• Acylation (when applied to side chains)

Conformational constraints for stability or structure.

• Cyclizations, head to tail and side chain (lactam bridge, thioether)
• Hydrocarbon-stapled peptides
• Multiple disulfide bond formation

Chemistries to build or join Peptides and attach payloads.

• Ligations (e.g., native chemical ligation, oxime, click-assisted ligations)
• Conjugation to small molecules (including imaging agents)
• Conjugation to polymers
• Clickable Peptides (azide/alkyne handles, etc.)
• Maleimido Peptides (e.g. for thiol conjugation)

Fluorescent, chromophoric, and isotopic labels for detection/assays.

• Dye-labelled Peptides
• Biotinylation
• Incorporation of fluorophores or chromophores
• Chromogenic and fluorogenic carboxypeptidase substrates
• Labeling with Tide Fluor™ and Tide Quencher™
• Labeling with stable isotopes

For radiometal labeling, MRI, and metal coordination.

• Incorporation of chelating moieties such as DOTA, DPTA (often DTPA)

Higher-order or non-linear peptide formats.

• Branched Peptides

Approaches to increase half-life, protease resistance, and pharmacokinetics.

• PEGylation
• N-methylated amino acids
• Reduced Peptide bonds
• Lactam/thioether cyclization
• Hydrocarbon-stapled Peptides
• Multiple disulfide bond formation