Ipamorelin

Ipamorelin is a pentapeptide growth hormone secretagogue acting at the GHS-R1a receptor. Its defining property in the literature is selectivity: earlier secretagogues in the same class also produced measurable ACTH, cortisol and prolactin responses, which made it difficult to attribute an observed effect to growth hormone rather than to the accompanying hormonal noise. Ipamorelin largely does not, which is why it became the default tool compound for isolating growth hormone signalling.

As a five-residue peptide with two D-amino acids and a C-terminal amide, its synthesis is short but the stereochemistry is where lots go wrong. D-to-L epimerisation at the D-2-Nal or D-Phe positions produces a same-mass diastereomer that mass spectrometry cannot distinguish. We resolve it chromatographically against a qualified reference standard, which is the only way to catch it.