What Are Deletion Sequences in Peptide Synthesis?

A deletion sequence, also called a des-peptide or truncated sequence, is a peptide impurity missing one or more amino acid residues from the intended sequence. During solid-phase peptide synthesis, each coupling step adds one amino acid to the growing chain. If a coupling step fails to go to completion, some chains skip that residue and continue elongating, producing a peptide that is shorter by exactly one residue [1].

Why do they matter?

A 10-residue peptide missing one residue is 9 residues long and may weigh only 100 to 200 Da less than the full-length product. On a standard HPLC chromatogram, the deletion sequence often elutes close to the main peak because its polarity is similar. It may not be resolved as a separate peak, which means the HPLC purity number can overstate the true content of the correct sequence.

How are they detected?

Mass spectrometry is the primary detection method. If the target peptide weighs 1200 Da and a peak appears at 1200 minus the mass of a single residue (for example minus 113 Da for leucine), that signal likely represents a des-Leu sequence. High-resolution or tandem mass spectrometry can confirm which position the deletion occurred at.

Can they be removed?

Purification by preparative HPLC with an optimized gradient can separate most deletion sequences from the main product. The difficulty depends on how similar the two peptides are in polarity. Deletion of a hydrophobic residue changes retention more than deletion of a small polar residue like serine.

Frequently asked questions

Are deletion sequences the same as degradation products?

No. Deletion sequences are synthesis impurities, formed during manufacturing. Degradation products form after synthesis, during storage, from reactions like oxidation or deamidation.

How common are deletion sequences?

They depend on coupling efficiency. A 30-residue peptide with 99 percent coupling efficiency per step still accumulates about 26 percent total deletion sequences across all positions. Longer peptides have more.