Ipamorelin

Ipamorelin is a synthetic pentapeptide of the growth hormone secretagogue class. It is frequently grouped with the GHRH analogues elsewhere in this library, and that grouping is misleading: ipamorelin acts at a different receptor family entirely and shares no sequence relationship with any of them.

Identity and classification

Ipamorelin is catalogued as an agonist at the growth hormone secretagogue receptor GHS-R1a — the ghrelin receptor. Sermorelin, CJC-1295 and tesamorelin all act at the GHRH receptor, a class B GPCR. GHS-R1a is a class A GPCR. These are different receptor families with different architecture and different endogenous ligands.

The practical point for a reagent user: ipamorelin is not a GHRH analogue, is not derived from the GHRH sequence, and is not interchangeable with one in any experimental design.

Structure

Five residues, of which three are not standard proteinogenic amino acids — an unusually high proportion, and the reason this small peptide is more synthetically demanding than its length suggests:

• Aib (α-aminoisobutyric acid) at position 1. A doubly methylated alanine with no chiral centre. Also present in retatrutide, where it serves the same purpose of conformational restriction and protease resistance.
• His at position 2. The only standard residue in the sequence.
• D-2-Nal at position 3. D-2-naphthylalanine — a bulky bicyclic aromatic side chain, in the D configuration.
• D-Phe at position 4. A second D-residue.
• Lys-NH₂ at position 5. C-terminal lysine as a primary carboxamide.

The molecule is linear — no cyclisation, no disulfide. The two D-residues and the Aib together make it highly resistant to proteolysis without any need for the backbone substitutions used in the GHRH analogues.

Specification and characterisation

• RP-HPLC purity at 214 nm. The naphthylalanine gives strong absorbance around 280 nm, and the D-2-Nal:backbone ratio is a useful compositional check — this residue is expensive and its absence is a meaningful adulteration route.
• Mass confirmation against 711.9. At this size a singly-charged ion is straightforward and high-resolution work is undemanding.
• Stereochemical purity. This is the specification point that matters most for ipamorelin and the one least often reported. Two of five residues are D-amino acids. Epimerisation at either during synthesis produces a diastereomer of identical mass — mass spectrometry cannot detect it. Detection requires chiral analysis, or chromatography with sufficient resolution to separate diastereomers. A certificate reporting only mass and RP-HPLC area percent has not addressed stereochemistry.
• Amidation completeness. The free acid differs by +1 Da.
• Counter-ion and net peptide content. Commonly supplied as the acetate.

Handling and stability

Store sealed at 2–8 °C, dry, protected from light. Equilibrate in a desiccator before opening.

There is no cysteine and no methionine, so neither disulfide scrambling nor sulfoxide formation applies. Combined with the Aib and the two D-residues, this makes ipamorelin one of the more chemically robust peptides in this catalogue as a dry solid. Its liabilities are synthetic rather than degradative — what can go wrong is more likely to have gone wrong before the vial was filled.

Related compounds in this library

No close structural relative here. Retatrutide shares the Aib residue as a design element. The GHRH-family peptides are the compounds ipamorelin is most often grouped with and most clearly distinct from.

References

Chemical, specification and analytical sources. This list is deliberately limited to chemistry and analytical references.

• Cayman Chemical, ipamorelin record — formula, molecular weight, sequence
• MedChemExpress, ipamorelin — target classification and specification
• ChemicalBook, CAS 170851-70-4 — registry and formula confirmation
• Bachem, Handling and Storage Guidelines for Peptides — lyophilised solid handling

Cosmic Aminos supplies this material as a laboratory reagent for in-vitro research use only. It is not a drug, food, cosmetic or dietary supplement, is not approved by the Food and Drug Administration for any use, and is not for human or veterinary consumption. No dosing, administration or preparation guidance is provided.