SS-31: structure and analysis

What is SS-31?

SS-31, also known as elamipretide, is a synthetic tetrapeptide carrying an alternating aromatic-cationic motif. That alternating pattern is not incidental — it is the structural feature that causes the molecule to concentrate at the inner mitochondrial membrane.

The sequence includes D-amino acid residues: the mirror-image stereoisomers of the naturally occurring L-forms. Their presence is a deliberate design choice, since proteases are stereospecific and a D-residue is not a substrate for enzymes that act on L-peptides.

At four residues it is among the shortest compounds in this catalogue, alongside the tripeptides.

How is SS-31 produced?

Assembled by solid-phase peptide synthesis: the chain is built one residue at a time on an insoluble resin support, then cleaved from the resin, deprotected and purified — most commonly by reversed-phase high-performance liquid chromatography. The purified material is lyophilized to a dry solid.

The impurity profile that appears on a certificate is a record of where that process was imperfect: deletion sequences from an incomplete coupling, truncated chains, and species retaining a protecting group.

What are the molecular figures for SS-31?

Calculated from the formula C32H49N9O5, not measured. The average molecular weight counts the natural abundance of each element's isotopes; the monoisotopic mass is the mass of the single most abundant isotopic composition, which is the figure a mass spectrometer is usually compared against.

The expected ions follow from the monoisotopic mass by adding one proton per charge. They are a starting point for recognising a spectrum, not a substitute for one: adducts, salts, modifications and multiply charged species all move the observed m/z, and the certificate reports what was actually measured for a batch.

Adducts, salts, modifications and multiply charged species all move an observed m/z away from any figure calculated here, and a certificate reports what was measured for a batch rather than what was expected of it.

What is the sequence of SS-31?

No one-letter amino-acid sequence is published for SS-31 on this page. The tetrapeptide contains a D-arginine and a dimethylated tyrosine, so the standard one-letter codes do not describe it.

What establishes the material in a specific vial is the identity method and result stated on that batch's certificate, not a notation on a reference page.

How does SS-31 compare with related compounds?

Related compounds are not interchangeable. Published figures differ between them, and in this catalogue three compounds share a GHRH backbone while several share the same structural class — which is exactly why identity is confirmed analytically rather than inferred from the label.

How is the identity of SS-31 confirmed?

Mass spectrometry confirms the four-residue composition, and for a tetrapeptide the measurement is very tightly constrained.

But mass spectrometry cannot confirm the most important thing about this molecule. A D-amino acid and its L-counterpart have identical molecular masses, so a diastereomer arising from incorrect stereochemistry is isobaric with the intended compound and completely invisible to a mass measurement.

Which impurities can appear in SS-31?

Stereochemical integrity is therefore the analytical question specific to SS-31, and it falls entirely to chromatography. Diastereomers can be resolved on a suitably developed method, but they will not be separated by a gradient that was not built to do it.

This makes SS-31 the compound in this catalogue where the method statement on a certificate is most load-bearing. A purity figure produced by a method that cannot resolve diastereomers is not addressing the impurity most worth knowing about, however high the number is.

The alternating cationic character also makes the molecule strongly basic and weakly retained under standard reversed-phase conditions, which is a second reason a purpose-built method is required.

What does a certificate of analysis for SS-31 report?

A certificate for a batch of this material names the batch, names the issuing laboratory, and states for each parameter both the method used and the specification the result was measured against. Identity and purity are the two core results; net peptide content states how much of the fill weight is actually peptide.

A certificate belongs to a batch, not to a product line. When a new batch is released it is tested again, and the certificate published against it is that batch's certificate — a previous batch's result is never carried forward.

Is SS-31 for human use?

No. This page describes structure and analysis. It makes no claim about what this compound does, and none should be inferred from it. Material is supplied for laboratory research use only: it is not a drug, food, dietary supplement, cosmetic or medical device, it is not for human or veterinary consumption, and no dosing, administration or reconstitution guidance is provided for any such use.

References

• Elamipretide (SS-31) — PubChem, National Library of Medicine
• Elamipretide — ChEBI, European Bioinformatics Institute
• Elamipretide — ChEMBL, European Bioinformatics Institute