Ipamorelin — reading a COA for unnatural residues
Ipamorelin contains Aib, two D-amino acids and a C-terminal amide. Each one changes what standard peptide analysis reports, and how a COA should be read.
Ipamorelin is a synthetic pentapeptide, CAS 170851-70-4, molecular weight 711.85 g/mol. Four of its five positions are not standard L-amino acids: it contains Aib, two D-configuration residues and a C-terminal amide. Each of those changes what routine peptide analysis reports, which is what makes its COA worth reading carefully.
By the Bench Grade Research Team ·
Ipamorelin identity data
| Property | Value |
|---|---|
| CAS Registry Number | 170851-70-4 |
| Molecular formula | C38H49N9O5 |
| Molecular weight | 711.85 g/mol |
| Sequence | Aib-His-D-2-Nal-D-Phe-Lys-NH2 |
| Length | 5 residues |
| C-terminus | Amide, not free acid |
| Common vial sizes | 5 mg, 10 mg |
What each unusual feature does to the analysis
Aib is alpha-aminoisobutyric acid, a non-proteinogenic residue. It is not one of the twenty amino acids that standard amino acid analysis quantifies, so an AAA report for this peptide either uses a modified method or simply omits that position.
The two D-configuration residues are mirror images of the standard L forms. They have identical masses, so mass spectrometry cannot distinguish a correctly synthesised peptide from one where a residue has racemised. That distinction requires chiral analysis, which most routine COAs do not include.
The C-terminal amide is a mass check that is easy to apply. An amide is one dalton lighter than the corresponding free acid. A COA reporting a mass 1 Da above the expected figure is describing the free-acid form, which is a different compound from the one the literature used.
Why a short peptide is not automatically a simple one
At five residues this looks like it should be the easiest compound on a supplier's list to make correctly. The opposite is closer to true: four of five positions require non-standard building blocks, each of which is more expensive and more prone to incomplete coupling than a routine L-amino acid.
The practical consequence is that impurity profiles for this peptide are worth looking at rather than skipping. Deletion sequences missing one of the unnatural residues are the failure mode to look for, and they show as distinct peaks with predictable mass differences.
A different receptor from the GHRH analogs it is paired with
Ipamorelin is described in the literature as a growth hormone secretagogue acting at the ghrelin receptor, GHS-R1a. That is a different receptor from the one CJC-1295 and sermorelin act at, which is the stated rationale for pairing an analog of each — two receptors rather than two molecules at one.
It is also why the original characterisation paper called it selective. Earlier secretagogues in the same class were described as producing effects beyond growth hormone release; this compound was reported as more confined in that respect, and selectivity rather than potency is what the naming refers to.
Why the unnatural residues are the design
Four of five positions are non-standard, and each choice does specific work. The D-configuration residues resist proteases, which read the L-form backbone and cleave it. Aib is a constrained residue that restricts the backbone conformations available, holding the molecule closer to the shape that engages the receptor. The 2-naphthylalanine provides a large aromatic side chain in a position where bulk appears to matter.
This is a designed molecule rather than a natural sequence or a fragment of one, and every unusual feature in it is there to solve a stability or binding problem. That is the opposite of most compounds in this catalog, which are sequences borrowed from biology and used as found.
The analytical cost of that design
Non-standard residues are more expensive to source and more prone to incomplete coupling during synthesis, so the impurity profile for this peptide is worth reading rather than skipping. Deletion sequences missing one of the unnatural residues are the failure mode, and they appear as distinct peaks at predictable mass differences.
The D-residues carry a second cost: mass spectrometry cannot see them. A racemised peptide reports the correct mass and a correct-looking chromatogram while presenting a different three-dimensional shape to a receptor that selects on shape.
Reconstitution arithmetic for ipamorelin
A 5 mg vial in 2 mL gives 2.5 mg/mL nominal. At 711.85 g/mol that is about 3.51 mM — a considerably higher molar concentration than the same mass and volume of a larger peptide, which is the general rule for short sequences and the reason molarity rather than mass per volume is the unit to compare against published work.
What the ipamorelin literature examined
The published work indexed in the research library includes the original characterisation of this peptide as a selective growth hormone secretagogue and subsequent animal studies. Those describe research findings; no human clinical approval exists for this compound.
References
Primary literature for the compounds discussed above. Links open the record on PubMed.
- Ipamorelin, a new growth-hormone-releasing peptide, induces longitudinal bone growth in rats Svensson J, et al. Growth Horm IGF Res. 1999. PMID 10373343 → · summary
- Ipamorelin, the first selective growth hormone secretagogue Raun K, et al. Eur J Endocrinol. 1998. PMID 9849822 → · summary
Primary sources
Frequently asked questions
- What is the molecular weight of ipamorelin?
- 711.85 g/mol, formula C38H49N9O5, CAS 170851-70-4. It is a pentapeptide with the sequence Aib-His-D-2-Nal-D-Phe-Lys-NH2, ending in a C-terminal amide rather than a free acid.
- Why does the C-terminal amide matter on an ipamorelin COA?
- Because it is a one-dalton mass check. An amide is 1 Da lighter than the corresponding free acid, so a COA reporting a mass 1 Da high is describing the free-acid form — a different compound from the one used in the published work.
- Can mass spectrometry confirm ipamorelin is correctly synthesised?
- Only partly. Two of its residues are D-configuration, and D and L forms have identical masses, so mass spec cannot detect racemisation at those positions. That requires chiral analysis, which routine COAs generally do not include.
Compounds discussed in this guide
More on identification
- Sermorelin — GHRH (1-29) and the peptide family built on itSermorelin is the unmodified first 29 residues of growth hormone releasing hormone. Every GHRH analog in this market is a modification of it.
- Semax — an ACTH fragment with a Pro-Gly-Pro tailSemax is ACTH (4-7) with a proline-glycine-proline tail attached. That tail is a design decision shared with Selank, and it explains both compounds.
- Selank — a tuftsin analog, and the tail it shares with SemaxSelank is tuftsin with the same Pro-Gly-Pro tail Semax carries. Two compounds, one structural idea, and no methionine to worry about.
All products discussed in this guide are supplied by Bench Grade Peptides for laboratory research use only. Not for human or veterinary use.