SS-31 (Elamipretide)

What SS-31 is, structurally

SS-31 is a tetrapeptide, and the product page states that it contains a D-arginine, carries positive charge, and holds two aromatic rings. Each has a distinct practical consequence, and the first is most easily overlooked.

A D-residue means the stereochemistry must be preserved, and it introduces a failure mode with an awkward property: a peptide that epimerises at that centre becomes a diastereomer with an identical formula and mass. Mass spectrometry cannot see it. Chromatography can, because diastereomers, unlike enantiomers, separate on an ordinary reversed-phase column. This mirrors the disulfide-scrambling problem on the cysteine-containing products: the identity check most readers trust is the one blind to it.

Epimerisation is also a synthesis-side impurity class rather than only a storage concern, so a chromatographic profile matters more here than the formula alone would suggest.

The charge picture follows from the nitrogen count. Nine nitrogens across four residues is a great many: four backbone and one C-terminal amide account for five, leaving four on side chains, of which an arginine alone carries three. The molecule is strongly basic on a very small frame, giving it unusually high charge density.

That has the usual consequence for dissolution, in the direction opposite to an acidic peptide. Lowering the pH raises the net positive charge and with it solubility, so mildly acidic conditions assist.

Two further points. There is no sulfur, so no disulfide chemistry, no thiol oxidation and no methionine sulfoxide. And the average residue mass is about 160, high and consistent with the large aromatic and basic residues the page describes, where ordinary peptides average nearer 110.

Reconstitution and handling

Sterile water is the default solvent, and a small, strongly basic peptide should dissolve readily. Where a vial resists, mildly acidic conditions are the correct escalation.

Add diluent slowly down the inside wall of the vial, swirl gently, and let the solution clarify. Do not vortex; it introduces foam without dissolving anything faster.

No reducing agent is needed, since the formula contains no sulfur.

Adsorption deserves particular attention here. A small molecule carrying this much positive charge binds readily to negatively charged surfaces, so ordinary borosilicate glass is a poor choice and low-protein-binding polypropylene is the better default.

This is laboratory preparation chemistry, not dosing, administration, or protocol guidance of any kind.

Storage and stability

Store the lyophilized powder at -20 degrees C, sealed, desiccated and protected from light, and let a cold vial warm before opening. Reconstituted, hold at 2 to 8 degrees C, or aliquot and freeze rather than thawing repeatedly.

With no sulfur present, the oxidation routes that dominate many peptides are closed, and air exposure matters correspondingly less.

Epimerisation is the liability specific to this molecule. Racemisation at a stereocentre is base-catalysed and accelerated by heat, so alkaline conditions and elevated temperature are the two things worth avoiding, and near-neutral cold storage is the control. Because the product of that reaction has the same mass as the starting material, a stability study that relies on mass alone will not detect it.

Deamidation does not arise here at all. The stated sequence carries neither asparagine nor glutamine, so the reaction has no site to act on, which is a definite statement rather than an inference from composition.

These are storage conditions for the material, not dosing or administration guidance.

How SS-31 is tested

Reversed-phase HPLC establishes chromatographic purity as area percent, and here it carries more weight than usual: it is the method capable of resolving the stereochemical impurity mass spectrometry cannot.

Detection is available at 280 nm as well as 214 nm, since the page describes two aromatic rings, and the higher wavelength gives a cleaner baseline.

A small, strongly basic peptide retains weakly on a standard C18 column, so high-aqueous starting conditions or an ion-pairing mobile phase should be expected. Trifluoroacetic acid serves both purposes.

Area percent is a chromatographic measure and not peptide content by weight. On a peptide of only 640 daltons carrying multiple basic centres, the counter-ion is a large proportional share of the vial contents, larger than on most products in this catalogue.

Mass spectrometry confirms identity against 639.80. What it will not confirm is stereochemistry, and that limitation is worth stating explicitly rather than leaving implied.

These describe general methodology, not a claim about any particular batch.

Handling FAQ

Will a mass spectrum confirm this material is correct? Only partly. It confirms the composition, but the molecule contains a D-residue, and a peptide epimerised at that centre has an identical formula and mass. Only chromatography separates the two, so a clean mass result alone is not sufficient evidence of correct stereochemistry.

Does the counter-ion matter more on a peptide this small? Yes, proportionally. Solid-phase synthesis delivers a salt, and on a 640-dalton peptide with several basic centres the counter-ion accounts for a larger fraction of the vial contents than it would on a peptide several times the size.

Full specifications for SS-31.