Sermorelin, Tesamorelin and CJC-1295: The Identity Data Side by Side

Sermorelin, Tesamorelin and CJC-1295 are all built on the same parent sequence, which is why they get compared, and why the comparison so often goes wrong. Two of the three have masses within ten units of each other despite differing at four positions. The third is fifty per cent heavier than either. And the modification that distinguishes one of them is invisible to a mass measurement but obvious in the molecular formula, if you know which character to look at. This article puts the three side by side as identity data, and points out where a certificate can mislead you.

The parent sequence

Growth-hormone-releasing factor, GRF, is a 44-residue peptide. Its biological activity resides in the N-terminal region, which is why almost every analogue in this group is built on either the first 29 residues or the full 44. That single fact explains most of the family. Sermorelin is GRF 1-29 with nothing changed. CJC-1295 without DAC is GRF 1-29 with four substitutions. Tesamorelin is the full GRF 1-44 with a group attached at the N-terminus. Everything else is detail.

The three, side by side

Ten units apart, and how to tell them anyway

Sermorelin and CJC-1295 without DAC differ by four substituted residues and by ten grams per mole. On molecules of roughly 3360, that is a difference of about three parts in a thousand. A mass determination that resolves it is doing fine work; one reported to the nearest few units does not separate them at all.

The molecular formulas do, and the tell is a single character. Look at the end of each: C149H246N44O42S against C152H252N44O42. Sermorelin contains one sulfur atom. CJC-1295 without DAC contains none. That sulfur is the methionine at position 27 of the native sequence, and one of the four substitutions in the CJC-1295 modification replaces it with leucine. Methionine is also the residue most prone to oxidation in peptide chemistry, which is part of why the substitution exists.

So a document reporting the molecular formula is more informative than one reporting only a rounded mass, for this particular pair. And if you are reconciling a certificate for a sulfur-free formula against a reference entry for Sermorelin, the discrepancy is not an error in the document; it is a sign that the two are describing different compounds.

The other three substitutions, D-alanine at position 2, glutamine at 8 and alanine at 15, are stereochemical and isobaric changes of the sort that mass measurement handles poorly in general. The D-alanine in particular has the same formula and mass as the L form. These are the reason CJC-1295 without DAC is also written as Mod GRF 1-29, a name that describes what it is rather than assigning it a code, and which you will encounter on certificates and in literature interchangeably with the CJC-1295 label.

Tesamorelin is a different size of molecule

At 5136 g/mol, Tesamorelin is over 1700 units heavier than either of the 1-29 analogues. It carries the full 44-residue sequence rather than the truncated one, plus a trans-3-hexenoyl group at the N-terminus. There is no mass-resolution problem in distinguishing it from the other two; there is no plausible instrument on which those numbers are confusable.

What is worth noting instead is that a larger peptide with an acyl modification is a harder synthesis and a harder purification, and that the impurity profile of a 44-residue peptide is not the impurity profile of a 29-residue one. Deletion sequences, the peptides that result when a coupling step fails, are more numerous the longer the chain, and they sit closer to the target in both mass and retention. A purity figure on a 44-mer and a purity figure on a 29-mer are the same number measuring a different degree of difficulty.

The DAC question

CJC-1295 is listed both with and without DAC, and they are different products, not packaging variants. The DAC version adds a linker designed to bind albumin, and it changes the mass substantially. We have covered that distinction in detail in CJC-1295 with DAC or without DAC. For the purposes of this comparison, the entry in the table above is the version without DAC, which is the one that sits ten units from Sermorelin.

Getting the right document onto the right vial

Three white lyophilized powders with similar names and, in two cases, near-identical masses is precisely the situation in which paperwork ends up attached to the wrong vial. Our published batch documents are on the certificates of analysis page, and the match is made on cap colour and crimp colour rather than on the printed compound name. Not every product and not every batch has a published certificate. Batches that are tested go through HPLC as well as purity testing. The purity guarantee page records both what we commit to and what we decline to claim.

Ordering the three in Canada

All three are stocked in Canada under growth hormone secretagogues: Sermorelin 5mg and 10mg, CJC-1295 without DAC 5mg, and Tesamorelin 10mg. The CJC-1295 no DAC and Ipamorelin blend pairs the 1-29 analogue with a compound from a different structural class entirely; Ipamorelin is a five-residue molecule at 711.9 g/mol and is not a GRF analogue. Current pricing across the group is on the Canadian price index.

Where this leaves you

All three are GRF-derived. Sermorelin is the unmodified 1-29 at 3357.9. CJC-1295 without DAC is the same fragment with four substitutions at 3367.9, ten units away, and the reliable discriminator is the sulfur atom Sermorelin has and it does not. Tesamorelin is the full 1-44 with an N-terminal hexenoyl group at 5136, a different size of problem to both synthesize and analyze. Check formulas, not just masses, and check the cap and crimp colours before assuming a certificate belongs to the vial in front of you.

All compounds referenced here are supplied by ExoLabz for laboratory research use only. They are not for human or veterinary use, are not authorised by Health Canada as a drug or natural health product, and nothing on this page is guidance on preparation, administration or use.