What Is Ipamorelin? Pentapeptide GH Secretagogue Specs

Key takeaways

• Ipamorelin is a synthetic pentapeptide: a single chain of five amino-acid residues, three of which are non-proteinogenic, capped with a C-terminal amide.
• Its sequence is commonly written Aib-His-D-2-Nal-D-Phe-Lys-NH2, where Aib is aminoisobutyric acid, D-2-Nal is D-2-naphthylalanine, and D-Phe is the D-isomer of phenylalanine.
• It is classed as a growth-hormone secretagogue and is described in the literature as a selective agonist at the ghrelin receptor (the growth-hormone-secretagogue receptor, GHS-R1a).
• The free-base molecular formula is commonly given as C38H49N9O5 with an average molecular weight near 711.9 g/mol; it is frequently supplied as an acetate salt, which raises the as-weighed mass per vial.
• Ascend Bio Labs supplies Ipamorelin with a public, per-batch COA keyed to the batch ID on each vial, with independent third-party HPLC for purity and LC-MS for identity, all US-domestic.

Ipamorelin is widely catalogued among research peptides in the growth-hormone-secretagogue group, and like most compounds in that group it is most useful to describe by its chemistry rather than by anything it is claimed to do. This guide stays strictly structural: it covers what kind of molecule Ipamorelin is, the five-residue sequence that defines it (including its three unusual, non-proteinogenic amino acids), the C-terminal amide, how its molecular formula and weight are calculated, the salt form you are likely to receive, and the mechanics of reconstituting and storing a lyophilized research vial. Nothing here addresses effects in any organism it is written for laboratory handling and characterization only.

Understanding the structure is also what lets you read a certificate of analysis for the material. The sequence and the C-terminal amide fix the theoretical mass that LC-MS should confirm; the salt form changes the net peptide content per vial; and the lyophilized presentation dictates how reconstitution math works. Each section below ties a structural fact to the practical handling consequence that follows from it.

Peptide class: a synthetic pentapeptide growth-hormone secretagogue

Ipamorelin belongs to the peptide class by the plain definition of the term: it is a short chain of amino acids joined by peptide bonds, far below the length at which a chain is conventionally called a protein. Specifically it is a pentapeptide a chain of just five residues. That makes it one of the shorter peptides in a typical research catalogue, and the small size is part of why it is a well-defined, easily characterized synthetic target rather than a recombinant product.

In catalogue terms it is grouped with the growth-hormone secretagogues a family of small molecules and peptides described in the literature as acting at the growth-hormone-secretagogue receptor (GHS-R1a), the same receptor that the endogenous peptide ghrelin binds. Ipamorelin is characterized in published work as a selective agonist at that receptor, which is the structural-pharmacology classification that distinguishes it from growth-hormone-releasing-hormone (GHRH) analogs, which act on a different receptor entirely. That receptor-class distinction is the key conceptual difference between Ipamorelin and the GHRH-analog peptides covered in What Is CJC-1295? GHRH Analog Structure, With and Without DAC and What Is Tesamorelin? GHRH Analog Sequence and Molecular Weight.

Structurally it is a linear, single-chain peptide. It carries no cysteine residues, so there are no disulfide bridges, and it has no glycosylation or other post-translational modifications the only modification is the C-terminal amide described below. As a research-catalogue label, treat 'Ipamorelin' as a name for the defined five-residue sequence rather than as a description of any biological role.

• Class: peptide, specifically a pentapeptide (5 residues).
• Catalogue group: growth-hormone secretagogue (ghrelin-receptor class).
• Described in the literature as a selective GHS-R1a agonist.
• Topology: linear single chain, no disulfide bonds, C-terminally amidated.

The sequence: five residues, three of them non-proteinogenic

The defining feature of any peptide is its primary sequence the ordered list of amino acids. For Ipamorelin the sequence is commonly written, N-terminus to C-terminus, as Aib-His-D-2-Nal-D-Phe-Lys-NH2. Reading it left to right gives the order in which the residues are assembled and the order a synthesis log or a mass-spec readout will reference. Only two of the five residues histidine and lysine are standard proteinogenic L-amino acids; the other three are not, which is the most distinctive thing about this peptide's primary structure.

The three unusual residues are worth naming explicitly. 'Aib' is alpha-aminoisobutyric acid, a non-proteinogenic residue with two methyl groups on the alpha carbon that constrains the backbone and resists enzymatic cleavage. 'D-2-Nal' is D-2-naphthylalanine, a bulky aromatic residue built on a naphthalene ring and in the D (rather than L) configuration. 'D-Phe' is the D-isomer of phenylalanine. The deliberate use of D-amino acids and the Aib residue is a classic peptide-design pattern for increasing stability against proteolysis, and it is also why this short sequence cannot be produced by ordinary ribosomal translation it is a solid-phase synthetic construct.

The sequence is what a mass-spectrometry identity check is really validating. When an LC-MS report states an observed mass consistent with the theoretical mass, it is asserting that the assembled chain matches this exact residue order and composition including the unusual residues and the C-terminal amide. A clean purity peak with the wrong mass would indicate a pure but incorrect molecule, which is why identity and purity are reported as two separate measurements on a complete certificate.

• Sequence (N→C): Aib-His-D-2-Nal-D-Phe-Lys-NH2.
• Aib = alpha-aminoisobutyric acid (non-proteinogenic, backbone-constraining).
• D-2-Nal = D-2-naphthylalanine; D-Phe = D-phenylalanine (both D-isomers).
• Only His and Lys are standard L-amino acids; the rest are non-proteinogenic.

The C-terminal amide and what it changes

Ipamorelin is C-terminally amidated, written as the '-NH2' at the end of the sequence. In an ordinary peptide the C-terminus is a free carboxylic acid (-COOH); amidation replaces that terminal hydroxyl with an amino group, so the chain ends in a carboxamide instead. This is a small change in atom count but a meaningful structural feature, and it is the single covalent modification on the molecule.

The amide matters for two practical reasons. First, it changes the molecular formula and exact mass relative to the free-acid form, so it must be accounted for when calculating the theoretical mass an LC-MS report should confirm an amidated peptide is roughly one mass unit lighter than the corresponding free acid because -OH is replaced by -NH2. Second, C-terminal amidation removes a negative charge that a free carboxylate would carry, which subtly alters the peptide's overall charge profile and is a common design choice for receptor-targeted peptides.

For characterization purposes, the takeaway is simply that the amide is part of the molecule's definition. A correct identity check is confirming the amidated structure, not the free acid, and any reference mass you compare against should be the amidated value.

• The terminal residue (Lys) is capped as a carboxamide (-NH2), not a free acid.
• Amidation slightly lowers the exact mass versus the free-acid form.
• It removes the C-terminal negative charge, altering the charge profile.
• Reference masses for identity checks must use the amidated value.

Molecular formula and weight, and why the salt form matters

Summing the residues of the free-base (non-salt), C-terminally amidated peptide gives a molecular formula commonly cited as C38H49N9O5. The corresponding average molecular weight is approximately 711.9 g/mol, with the monoisotopic mass slightly lower; you will see small rounding differences between sources depending on whether average or monoisotopic mass is quoted and exactly how the termini are counted. For research characterization, the figure that matters is that the observed mass on an LC-MS readout should land on the theoretical mass for this formula within instrument tolerance.

The salt form is the most common source of confusion about how much peptide is actually in the vial. Ipamorelin is frequently supplied as an acetate salt, because the acetate (or, depending on the purification, trifluoroacetate) counterions used in synthesis and lyophilization remain associated with the basic residues here the histidine and lysine side chains and the N-terminus. An acetate salt weighs more than the free base for the same number of peptide molecules, so a vial labeled by gross fill weight contains slightly less net peptide than the free-base molecular weight alone would suggest. A rigorous COA may report net peptide content (active weight) separately from gross fill, which is why some certificates emphasize 'active weight content.'

For reconstitution math (next section) this matters only if you are working from net peptide content; if you simply use the labeled peptide mass printed for the vial, the salt is already accounted for. The structural takeaway is that the molecular weight you calculate from the sequence describes the free base, while the powder you weigh out is typically a salt.

• Free-base molecular formula: commonly C38H49N9O5.
• Average molecular weight: approximately 711.9 g/mol (monoisotopic slightly lower).
• Often supplied as an acetate salt, raising as-weighed mass per vial.
• Net peptide content (active weight) can differ from gross fill weight.

Reconstitution: turning labeled mass into a known concentration

Ipamorelin ships as a lyophilized (freeze-dried) powder or thin cake in a sealed vial, typically under an inert headspace, and reconstitution is the step that converts that dry vial into a solution of known concentration for laboratory work. The diluent is typically bacteriostatic water (sterile water with a small amount of benzyl alcohol as a preservative) or plain sterile water; bacteriostatic water is common when a reconstituted vial will be drawn from more than once. The diluent is added slowly down the inner wall of the vial rather than directly onto the cake, and the vial is swirled, not shaken vigorously, until the powder fully dissolves.

The concentration that results is pure arithmetic: it is the labeled peptide mass divided by the volume of diluent you add. Adding 2 mL of water to a 5 mg vial yields 5 mg / 2 mL = 2.5 mg/mL; adding 1 mL to the same vial yields 5 mg/mL. The vial's peptide mass is fixed by what was filled and tested, so the only variable you control is the diluent volume, and that volume sets the concentration. Because the chosen volume drives the math, Ipamorelin reconstitutes by exactly the same procedure as any other lyophilized research peptide for the full step-by-step volume calculation see Reconstituting Lyophilized Peptides: BAC Water Math Step by Step.

Ipamorelin's solubility behavior is typical for a short peptide carrying charged histidine and lysine residues: it generally goes into aqueous diluent readily. The bulky D-2-naphthylalanine residue adds some hydrophobic character, but at the small masses dispensed per research vial this does not usually impede dissolution; if a cake is slow to dissolve, additional gentle swirling and time at room temperature normally resolve it. The structural point is simply that this is a water-reconstituted lyophilizate, not an oil- or solvent-based preparation.

• Diluent: bacteriostatic water (multi-draw) or sterile water.
• Add diluent down the vial wall; swirl gently, do not shake hard.
• Concentration = labeled peptide mass ÷ diluent volume added.
• Example: 5 mg vial + 2 mL water = 2.5 mg/mL.

Storage and how this differs from a non-peptide secretagogue

Storage requirements differ sharply between the dry and the dissolved states. As a sealed lyophilized powder, Ipamorelin is comparatively stable and is commonly stored refrigerated, with freezing used for longer-term holding; kept dry, cold, and away from light, a freeze-dried peptide cake is far more forgiving than a solution. The sealed inert headspace and the absence of water are what give the dry form its stability, and the Aib residue and D-amino acids in the sequence add intrinsic resistance to proteolytic breakdown.

Once reconstituted, the peptide is in solution and should be treated as the more perishable form: kept refrigerated, protected from light, and used within a limited window, with repeated freeze-thaw cycling avoided because each cycle stresses the peptide. None of this is a usage instruction it is ordinary cold-chain handling for a research reagent in solution. It is also worth noting that Ipamorelin is a peptide secretagogue, which contrasts structurally with non-peptide growth-hormone secretagogues such as the orally active small molecule covered in What Is MK-677 (Ibutamoren)? Non-Peptide GH Secretagogue Profile the receptor class overlaps but the molecule type, and therefore the handling, differs.

Storage handling and COA both come back to the same principle: the material's identity and quality are established at the batch level and then preserved by correct handling. Ascend Bio Labs supplies Ipamorelin with a public, per-batch certificate of analysis keyed to the unique batch ID printed on each vial, with independent third-party HPLC for purity and LC-MS for molecular identity, and US-domestic synthesis, testing, storage, and shipping with insulated, tracked transit so the dry vial that arrives is the one its certificate describes.

• Lyophilized powder: store cold and dry, away from light; freeze for long-term holding.
• Reconstituted solution: refrigerate, protect from light, use within a limited window.
• Avoid repeated freeze-thaw cycles of a reconstituted vial.
• Batch ID on the vial links the material to its public, per-batch COA.

Related research notes

• What Is CJC-1295? GHRH Analog Structure, With and Without DAC
• What Is Tesamorelin? GHRH Analog Sequence and Molecular Weight
• What Is MK-677 (Ibutamoren)? Non-Peptide GH Secretagogue Profile
• Reconstituting Lyophilized Peptides: BAC Water Math Step by Step