Ipamorelin

Four non-standard positions out of five

Aib at position 1 — alanine with a second alpha-carbon methyl, achiral, helix-favouring and a poor aminopeptidase substrate. His at position 2 is the only conventional proteinogenic residue in the sequence. D-2-Nal at position 3 is 2-naphthylalanine in the D configuration — two departures from standard in one position. D-Phe at position 4. Lys-NH₂ at position 5, amidated to remove the terminal negative charge and block carboxypeptidase attack.

Analytical implications

A theoretical mass calculated from a plain five-letter sequence with proteinogenic residue masses will be substantially wrong.

The D substitutions are invisible to mass spectrometry — D-2-Nal and L-2-Nal are isobaric, as are D-Phe and L-Phe. Confirming stereochemistry requires chiral analysis, which is not routine on a research certificate.

Racemization during synthesis is therefore a real impurity class for this peptide: the resulting diastereomers have the correct mass and may or may not resolve chromatographically depending on the method.

Storage is undemanding — no cysteine, methionine, asparagine or glutamine. The two aromatic residues are mildly photosensitive, making dark storage sensible without being critical.