SS-31 10mg

At a glance

Strength

10 mg

Also known as

Elamipretide; MTP-131; Bendavia; SS31; Szeto-Schiller peptide

CAS number

736992-21-5

Molecular formula

C32H49N9O5

Molecular weight

639.8 g/mol (free peptide)

Sequence

D-Arg-Dmt-Lys-Phe-NH2 (Dmt = 2,6-dimethyl-L-tyrosine)

PubChem CID

11764719

What SS-31 is

SS-31 belongs to a series of short peptides with alternating cationic and aromatic residues that enter cells and target mitochondria ¹. The series is known as the Szeto-Schiller peptides, after Szeto and Schiller, who appear together on early papers from Cornell University in New York ². A 2005 paper by that group studied one related Dmt tetrapeptide, [Dmt1]DALDA, where Dmt is 2,6-dimethyltyrosine. Using isolated mouse liver mitochondria, the authors reported that one fluorescent analog of it was retained in the inner mitochondrial membrane and that the unlabeled parent peptide behaved like that analog ². SS-31 has carried several names over its development: MTP-131, Bendavia and, as its nonproprietary name, elamipretide. All refer to the same molecule. Stealth BioTherapeutics developed it as a mitochondrial cardiolipin binder ³.

Chemical identity and salt form

PubChem (CID 11764719) gives SS-31 the formula C32H49N9O5, a molecular weight of 639.8 g/mol and CAS number 736992-21-5, all for the free peptide. The four residues are D-arginine, 2,6-dimethyl-L-tyrosine, L-lysine and L-phenylalaninamide. FDA's label for Forzinity describes the drug substance as elamipretide hydrochloride, C32H49N9O5 with three HCl, molecular weight 749.2. Synthetic peptides in general are supplied as hydrochloride, acetate or trifluoroacetate salts. Each salt carries a different counter-ion mass, so the same mass of powder holds different amounts of peptide. A certificate should name the salt and report net peptide content.

Regulatory status

On September 19, 2025, FDA granted accelerated approval to Forzinity (elamipretide), sponsored by Stealth BioTherapeutics under new drug application 215244. The approved indication is set out in the FDA label, available on DailyMed. Under the accelerated approval pathway, the label states that continued approval may depend on a confirmatory trial. The drug substance in Forzinity is elamipretide hydrochloride.

SS-31 sold for research is not Forzinity. It is not made under that application, has not been reviewed by FDA, and is not an approved medicine. It is supplied for laboratory research use only.

Laboratory research

Most laboratory work concerns how SS-31 interacts with mitochondrial membranes. A 2020 study used chemical cross-linking with mass spectrometry in mitochondria to find the proteins SS-31 contacts. The authors identified two groups of interacting proteins, all of them known cardiolipin binders, and mapped the cross-linked residues ⁴. A 2022 study compared SS-31 with three analogs that differ in aromatic side chains and sequence order. Using NMR and molecular dynamics, the authors built the first structural models for this class and reported that, unlike the analogs, SS-31 did not adopt a compact reverse-turn shape when bound to membranes ¹. The same study measured how each peptide bound cardiolipin-containing membranes and changed membrane surface charge ¹.

Clinical development

Elamipretide has been through human clinical development, which led to the 2025 accelerated approval, and further phase 3 programs were under way when a 2026 review of the approval was written ³. Trial reports are indexed in PubMed under the names elamipretide and MTP-131. This page does not summarize them, because the research material sold here is not the approved medicine and is not for human use.

What is not known

The mechanism is not settled. Authors of the 2020 cross-linking study wrote that mechanistic details of the peptide's pharmacological effects were unknown, even though cardiolipin binding is the main reported interaction ⁴. Structure-activity work shows that changes in side chains or sequence order alter membrane behavior, so findings for one SS peptide do not transfer automatically to another ¹. For research-grade material, nothing published compares its impurity profile or salt form with pharmaceutical elamipretide.

Storage and quality testing

FDA's Forzinity label specifies refrigerated storage at 2 to 8 °C and says not to freeze; that instruction applies to the licensed product only. For research SS-31, store the vial as stated on the certificate of analysis and product label, keep it sealed and dry, protect it from light, and let it reach room temperature before opening.

A certificate should confirm identity by mass spectrometry; PubChem gives a monoisotopic mass of 639.386 Da for the free peptide. Purity should be measured by HPLC with the method stated. The D-arginine is a stereocenter that mass spectrometry cannot check, since an all-L epimer has the same mass, so the HPLC method should separate that epimer. The certificate should also report the counter-ion, water content, net peptide content and lot number.