SS-31 (Elamipretide, MTP-131) explained: names, sequence and CAS numbers

SS-31 is a synthetic tetrapeptide with the sequence D-Arg-2′,6′-dimethylTyr-Lys-Phe-NH₂. It is also known as elamipretide, MTP-131 and the Szeto-Schiller peptide. The several names and two CAS numbers can make it look like more than one compound. This guide explains how they relate and what to check in the documentation.

SS-31 at a glance

Why does SS-31 have so many names?

The names come from different stages of its history. “SS” refers to Szeto and Schiller, the researchers after whom the Szeto-Schiller peptides are named, and SS-31 is one member of that series. MTP-131 is a development code, and elamipretide is the generic name. All of them refer to the same tetrapeptide.

Why are there two CAS numbers?

A peptide can exist as the free base or as a salt, in which the peptide is paired with a counter-ion such as acetate. The free base and the salt are registered separately, so each has its own CAS number. For SS-31 the free base is 736992-21-5 and the acetate salt is 1334953-95-5.

The peptide itself is the same in both. What differs is the counter-ion, which adds to the total weight of the powder. The quoted molecular weight of approximately 639.8 g/mol is for the free base. See how to read a peptide certificate of analysis for how salt form relates to net peptide content.

What is distinctive about the sequence?

The four residues alternate between aromatic and basic (positively charged) side chains. This alternating aromatic-cationic motif is the structural feature most often cited in the literature. Two of the residues are not standard amino acids: the first is the D-form of arginine, and the second is tyrosine carrying two added methyl groups. The NH₂ at the end indicates a C-terminal amide.

How is SS-31 supplied by Ascend Research?

The other compounds in the set are covered in the NAD+ guide and the MOTS-c guide.

What should the documentation show?

• The compound name and batch number match the vial label.
• Which form was tested, free base or acetate salt.
• An HPLC purity figure.
• A mass result consistent with approximately 639.8 g/mol for the peptide.

Batch documents are on the COAs page.

Frequently asked questions

Is SS-31 the same as elamipretide?

Yes. SS-31, elamipretide and MTP-131 are names for the same synthetic tetrapeptide.

What is the CAS number for SS-31?

The free base is CAS 736992-21-5. The acetate salt has the separate CAS number 1334953-95-5.

What does SS stand for in SS-31?

SS refers to Szeto and Schiller. SS-31 is one of the Szeto-Schiller peptides.

What is the sequence of SS-31?

D-Arg-2',6'-dimethylTyr-Lys-Phe-NH2, a four-residue sequence with a C-terminal amide.

What is the molecular weight of SS-31?

Approximately 639.8 g/mol for the free base.

All Ascend Research products are sold strictly for laboratory research use only. They are not for human or animal use, and nothing in this article is medical advice.

The Ascend Research team