Tesamorelin is a synthetic analogue of growth hormone-releasing hormone, the hypothalamic signal that tells the pituitary to release growth hormone. The molecule is the natural 44-residue sequence with one addition: a short unsaturated fatty acid attached to the N-terminus. (Reference: Wang & Chanoine, 2009)

What the fatty acid is for

Native GHRH is cleared quickly. The first two residues are a known cleavage site for dipeptidyl peptidase IV, the same enzyme that limits how long the incretin hormones last in circulation. (Reference: Mentlein, 1999)

Attaching a trans-3-hexenoyl group to the N-terminus blocks that end. The design goal is a molecule that behaves like GHRH at its receptor while surviving longer than the native sequence. (Reference: Spooner & Olin, 2012) Chemically this is the same strategy as a D-residue substitution or a backbone constraint: the peptide is modified where the enzyme cuts, not where the receptor binds.

Which receptor family

The GHRH receptor belongs to the secretin-like class of G protein-coupled receptors, the same structural family as the GIP, GLP-1 and glucagon receptors. (Reference: Mayo et al., 2003) Family membership is why selectivity within the group is a measurement and not an assumption, a point our note on agonists and antagonists develops.

Tesamorelin acts on the receptor directly, which separates it from the growth hormone secretagogues that work through the ghrelin receptor instead. Two compounds described as raising growth hormone can therefore be doing it through different receptors, and our note on secretagogues covers the distinction.

Identity on paper

Tesamorelin is C221H366N72O67S, 5135.9 g/mol, CAS 218949-48-5. The CAS number passes the check digit and resolves in PubChem to a record whose formula matches, which is the pair of checks worth doing on any compound: run the arithmetic with our validator, then look the number up and read back which substance it returns.

At forty-four residues this is a long peptide, and the single sulfur in the formula comes from its one methionine. That residue oxidises, and each oxidation adds sixteen mass units, which is a specific thing to look for on a mass spectrum.

A sequence calculator cannot handle this compound, and the reason is instructive. Our molecular weight calculator works from the twenty standard amino acids, and the hexenoyl group is not one of them. The calculator would return the unmodified peptide, which is a different molecule. This is the same limit that stops it seeing a bound metal or an amidated terminus.

"GHRH analogue" names a family, not a molecule

Several compounds in catalogues are described this way, and they differ in how much of the natural sequence they keep and what was done to the ends. Tesamorelin keeps all forty-four residues and modifies the N-terminus. Others use the first twenty-nine residues, the shortest fragment that still acts at the receptor, with substitutions inside the chain.

Two products under the same description can therefore differ by fifteen residues and several substitutions, which changes the formula, the mass and what a certificate has to report. The label is a category; the sequence is the compound. Comparing two of them means comparing sequences, not descriptions.

What a certificate should show

Purity from RP-HPLC with the column, gradient and detection wavelength written out. Identity from mass spectrometry, with observed and theoretical mass both given, because on a molecule of five thousand daltons a rounded figure cannot distinguish close relatives.

Length is the reason purity deserves attention here. Forty-four residues means forty-three coupling steps in synthesis, each one a chance for an incomplete reaction, and the resulting deletion sequences differ from the target by a single residue and leave the column at nearly the same time. Long peptides are often assembled from fragments joined afterwards for this reason.

Net peptide content belongs on the document separately from chromatographic purity. Our note on what else is in the vial explains the gap.

Two vial strengths, one compound

Tesamorelin is listed here at 10 mg and 20 mg per vial. That is a packaging difference and nothing else: same sequence, same formula, same CAS number, same certificate fields. The batch number is what distinguishes one lot from another, and a 20 mg vial carries its own batch number exactly as a 10 mg vial does.

Worth saying because a strength on a label is a quantity of powder, and the share of that powder which is peptide is a separate figure. Two vials of different stated strength and identical net content percentage hold proportionally different amounts of peptide; two vials of the same strength and different net content do not hold the same amount at all.

The acylation is also an analytical question

A modification at one end of a long chain is a small fraction of the total mass, so the difference between the acylated molecule and the unacylated one is about ninety-six daltons out of five thousand. That is well within what a mass spectrometer resolves, but only if the document reports the measured value instead of a verdict.

A certificate that says "conforms" has told you someone looked. One that gives the observed mass next to the theoretical mass has told you what they saw, and the second is checkable against the public record.

Storage is a longer conversation on a long peptide

Degradation routes that depend on chain length have more chain to work on here. Hydrolysis of the backbone, deamidation of asparagine and glutamine, and oxidation of the single methionine all proceed with time and temperature. (Reference: Manning et al., 2010)

The acyl group adds one more site to think about, since an ester or amide linkage is itself hydrolysable. A certificate is dated because a result belongs to a moment, and what happens between that date and your bench is a matter of handling. Our note on storage sets out the routes.

Research use only

All products sold by Codex Research are strictly for laboratory research and development. They are not for human or animal consumption and are not intended to diagnose, treat, cure, or prevent any disease.

The compound at Codex Research

Tesamorelin, 10 mg per vial · batch-verified, with its certificate of analysis.

Frequently asked questions

What is tesamorelin?

A synthetic analogue of growth hormone-releasing hormone: the natural 44-residue sequence with a short unsaturated fatty acid, trans-3-hexenoyl, attached to the N-terminus.

Why does tesamorelin carry a fatty acid group?

The first two residues of native GHRH are a cleavage site for dipeptidyl peptidase IV. Blocking that end with an acyl group is a design aimed at surviving longer than the native sequence while still acting at the receptor.

What is the formula and mass of tesamorelin?

C221H366N72O67S, 5135.9 g/mol, CAS 218949-48-5. The CAS number passes the check digit and resolves in PubChem to a record with a matching formula.

Can a sequence calculator give the mass of tesamorelin?

No. A calculator works from the twenty standard amino acids, and the hexenoyl group is not one of them, so it would return the unmodified peptide instead, which is a different molecule.

Does tesamorelin work through the same receptor as a secretagogue?

No. It acts at the GHRH receptor, while growth hormone secretagogues act through the ghrelin receptor. Two compounds described as raising growth hormone can be doing it through different receptors.

Why does the length matter for purity?

Forty-four residues means forty-three coupling steps, each a chance for an incomplete reaction. The resulting deletion sequences differ from the target by one residue and elute at nearly the same time, which is why long peptides are often assembled from fragments.

References

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