Thymosin alpha-1 (thymalfasin): structure and US status
Thymosin alpha-1 is a 28-residue, N-acetylated peptide cut from prothymosin alpha. Its sequence, why it is read at 214 nm, what FDA's 2024 compounding review concluded, and its US status as of November 2026.
Thymosin alpha-1 is a 28-residue peptide with an acetylated N-terminus: Ac-SDAAVDTSSEITTKDLKEKKEVVEEAEN-OH, residues 2 to 29 of the human protein prothymosin alpha. Its international nonproprietary name is thymalfasin. PubChem gives the formula C129H215N33O55 and a molecular weight of 3108.3, under CAS 62304-98-7. No drug containing it is approved in the United States: Drugs@FDA lists none, and FDA's own review of it for the Pharmacy Compounding Advisory Committee in December 2024 says it "is not approved in the United States." Ours is sold for laboratory research use only.
Where it comes from
Goldstein's group isolated thymosin alpha-1 from thymosin fraction 5, a calf-thymus preparation, and reported its sequence in 1977. FDA's 2024 review summarizes the history in two lines: the peptide was "originally isolated from thymosin fraction-5 of calf thymus in 1977", and the chemically produced version, named thymalfasin, "is identical in amino acid sequence to natural Ta1."
In the human proteome it is the N-terminal end of a larger protein. UniProt entry P06454, prothymosin alpha, is 111 residues long; after the initiator methionine is removed, residues 2 to 29 form the thymosin alpha-1 peptide, and the serine at position 2 carries an N-acetyl group. That acetyl cap is part of the molecule's identity, not a modification added later.
Thymosin alpha-1 is not related to thymosin beta-4 or to TB-500. The shared word comes from the same calf-thymus extract, not from a shared gene or sequence. Our article on TB-500 and thymosin beta-4 sets the three side by side. Thymalin, which we list as a separate product, is described as a thymus peptide complex and is not thymosin alpha-1 either.
The sequence, and what it means for testing
Ac-Ser-Asp-Ala-Ala-Val-Asp-Thr-Ser-Ser-Glu-Ile-Thr-Thr-Lys-Asp-Leu-Lys-Glu-Lys-Lys-Glu-Val-Val-Glu-Glu-Ala-Glu-Asn-OH
Three features of the sequence matter when reading a certificate.
It is strongly acidic. It carries nine acidic side chains (three aspartates and six glutamates) plus the free C-terminal carboxyl, against four lysines, and the acetylated N-terminus carries no charge. At neutral pH the net charge is about minus six.
It has no aromatic residues. There is no tryptophan, tyrosine or phenylalanine, so the peptide barely absorbs at 280 nm, the wavelength often used for proteins. Purity has to be read from the peptide bond's absorbance at around 214 nm. That is the wavelength on our certificate, and a thymosin alpha-1 chromatogram read at 280 nm would show very little. Reading a chromatogram explains why the wavelength matters.
It has no cysteine and no methionine, so there are no disulfide bonds to form or break and no methionine to oxidize. FDA's 2024 review lists the impurities to expect as peptide-related impurities and those left by the synthesis process, such as starting materials, residual solvents and coupling reagents.
For identity, the monoisotopic mass of C129H215N33O55 is 3106.50. By electrospray the peptide shows as multiply charged ions, for example m/z 1554.26 with two protons and 1036.51 with three. The average mass, 3108.3, is the figure PubChem lists.
US status as of November 7, 2026
No approved drug. A search of Drugs@FDA, FDA's database of approved drugs, by active ingredient returns no product containing thymalfasin or thymosin alpha-1. FDA's December 4, 2024 review for its Pharmacy Compounding Advisory Committee states: "Ta1 is not approved in the United States, Japan, or Europe (except Italy)." The same review names Zadaxin, SciClone Pharmaceuticals' thymosin alpha-1 product, and notes that FDA "is unable to independently verify these claims of approval in all the specified countries."
Compounding. Thymosin alpha-1 and its acetate salt were nominated for the list of bulk drug substances that pharmacies may compound under section 503A. FDA's review records that "the nomination was withdrawn, and FDA is evaluating the substances at its discretion." Its recommendation to the committee was that "a balancing of the four evaluation criteria weighs against Ta1 (free base) and Ta1 acetate being added to the 503A Bulks List." Among the reasons it gave was that they "are not well characterized from a physicochemical perspective." Where it sits on FDA's category lists is tracked in our explainer on Category 1, Category 2 and the 503A bulks list.
Not part of the October 2026 notice. The HHS notice of October 30, 2026 (91 FR 68526) set out enforcement discretion for 503A compounding with six named peptides: BPC-157, epitalon, KPV, MOTS-c, Semax and TB-500. Thymosin alpha-1 is not one of them, and the notice is not an approval for any of the six.
None of this concerns research material, which is sold for laboratory research use only and is not for human or veterinary use. Our status table keeps thymosin alpha-1 alongside the other compounds FDA has reviewed.
What our certificate shows
Our 10 mg size has a current certificate of analysis from Bioviridian Inc., the testing laboratory: lot TA1-10-0803, 99.78% purity by reversed-phase HPLC at 214 nm, identity by LC-MS/MS reported as conforming, and a measured content of 10.87 mg. It is certificate COA7585, issued August 28, 2026, and the certificate number can be checked on the laboratory's own site.
Storage
FDA's 2024 review records that the manufacturer of the acetate "recommends storage in a sealed container at 2°C to 8°C in a refrigerator or freezer", and that the acetate is publicly reported to stay stable in a freezer below -20 °C. Our thymosin alpha-1 is supplied as a lyophilized powder and listed for storage at -20 °C, desiccated.
Common questions
Is thymosin alpha-1 the same as thymalfasin?
Yes. Thymalfasin is the international nonproprietary name for synthetic thymosin alpha-1, which FDA's 2024 review describes as identical in sequence to the natural peptide. PubChem lists both names for CID 16130571.
Is thymosin alpha-1 FDA approved?
No. Drugs@FDA lists no product containing it (checked November 7, 2026), and FDA's December 2024 compounding review states that it is not approved in the United States. FDA's recommendation at that review weighed against adding it to the 503A bulks list.
What is the amino acid sequence of thymosin alpha-1?
Ac-SDAAVDTSSEITTKDLKEKKEVVEEAEN-OH: 28 residues, an N-acetylated serine at the start and a free acid at the end. It matches residues 2 to 29 of human prothymosin alpha (UniProt P06454).
Is thymosin alpha-1 related to TB-500?
No. TB-500 is a fragment of thymosin beta-4, a different protein from a different gene. The two share only the name "thymosin", from the calf-thymus extract both were first found in.
Why is thymosin alpha-1 purity measured at 214 nm?
It has no tryptophan, tyrosine or phenylalanine, so it absorbs almost nothing at 280 nm. At 214 nm the peptide bonds absorb, which makes the main peak and its impurities visible.
Sources
- Thymalfasin, CID 16130571, PubChem
- UniProt P06454, Prothymosin alpha (human), UniProt Consortium
- Goldstein AL, Low TL, McAdoo M, et al. Thymosin alpha1: isolation and sequence analysis of an immunologically active thymic polypeptide. Proc Natl Acad Sci USA, 1977
- Thymosin Alpha-1 (Ta1) Related Bulk Drug Substances, FDA presentation to the Pharmacy Compounding Advisory Committee, December 4, 2024
- December 4, 2024 meeting of the Pharmacy Compounding Advisory Committee, FDA
- Enforcement Discretion Policy Regarding 503A Compounding Using Certain Peptide Bulk Drug Substances, HHS notice, 91 FR 68526, October 30, 2026
- openFDA drugsfda endpoint, searched by active ingredient, FDA, November 7, 2026
For laboratory research use only. Not a drug, not a supplement, and nothing here is a claim about what any of this material does in a person or an animal.
