SS-31 or Elamipretide? One Compound, Several Naming Conventions

SS-31 is listed under at least four names depending on which document you are holding. A supplier catalogue will usually say SS-31. A pharmacology paper will usually say elamipretide. A development-era document may say MTP-131. An older one may use a trade name that no longer appears on anything current. All four point at the same tetrapeptide, and the confusion this creates is the reason people end up comparing a certificate against a reference entry for something slightly different. This article sets out the identity, explains where each name came from, and covers the two things about this molecule that change how it is analyzed.

The compound, on paper

Where the names came from

SS-31 is a series designation. The SS prefix refers to the two researchers whose laboratory characterized the series, and the number is the position of this particular analogue within it. That is why you will also encounter SS-02, SS-20 and other members of the same family in the literature: they are related structures from the same numbering scheme, not alternative names for the same compound. Confusing SS-31 with SS-20 because both begin with SS is a real and avoidable error, and the sequences differ.

Elamipretide is the international nonproprietary name, assigned when the compound entered formal development. MTP-131 is a development code from that period. A nonproprietary name and a series designation can coexist indefinitely, and neither supersedes the other in the way a corrected spelling would. If a certificate says SS-31 and a reference entry says elamipretide, that is not a discrepancy to resolve; it is two naming conventions describing one structure. The CAS registry number is the field that settles it, and it is the field worth checking first when two documents disagree on the name.

Two structural features that matter analytically

This is a short peptide, four residues, but it is not a conventional one. Two features change how it behaves on an analytical column.

The first is stereochemistry. The N-terminal arginine is the D-enantiomer, not the L form found in ribosomally synthesized peptides. A D-residue does not change the molecular formula or the nominal mass, which means mass spectrometry alone will not distinguish the intended compound from a batch where that position has the wrong configuration. Chiral or otherwise stereochemistry-aware methods are what separate them. A certificate reporting mass confirmation and HPLC purity has established the mass and the proportion of target material under that method; it has not, on its own, established configuration at that position unless the method was chosen to do so.

The second is the Dmt residue. Dmt is 2,6-dimethyltyrosine, a modified aromatic amino acid rather than a standard proteinogenic one. It contributes most of the compound ultraviolet absorbance and is a substantial part of why the molecule retains as it does in reverse-phase conditions. It is also the residue most likely to be the point of difference between SS-31 and a related analogue, so a method developed for a standard tyrosine-containing tetrapeptide is not automatically a suitable method here.

Salt form and net peptide content

Short, strongly basic peptides are isolated as salts, commonly acetate or trifluoroacetate. The counter-ion contributes to the mass on the balance without contributing to the peptide, which means a vial labelled 10 mg and a vial containing 10 mg of peptide are not necessarily the same thing across suppliers reporting against different conventions. Where a certificate reports net peptide content separately from purity, those are two different determinations answering two different questions: how much of what is in the vial is peptide, and how much of that peptide is the target sequence. Comparing a purity figure from one document against a net peptide content figure from another produces a difference that is entirely an artefact of the comparison.

Which document belongs to which vial

Batch documents live on the certificates of analysis page. Because a certificate describes one batch rather than one product, the cap colour and the crimp colour on the vial are what identify the correct document; the compound name narrows it to a product line and stops there. Coverage is partial, in that not every product and not every batch has a published certificate, and the batches we do publish are run by HPLC as well as purity testing. What is promised and what is deliberately not claimed are both written out on the purity guarantee page.

Stocked in Canada

SS-31 10mg is stocked in Canada in a single 10 mg presentation. It sits in the mitochondrial and cellular compounds category alongside the MOTS-C and NAD listings, which are frequently compared against it in sourcing decisions for no better reason than category adjacency. They are unrelated structures with unrelated analytical requirements. Current pricing across the range is on the Canadian price index.

If you take one thing from this

SS-31, elamipretide and MTP-131 are one tetrapeptide under three conventions, and CAS 736992-21-5 is the field that proves it. SS-20 and SS-02 are different compounds that share the prefix. The D-arginine and the Dmt residue are the two features that make a generic peptide method inappropriate here, and mass alone will not catch a stereochemical error. 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.