What Is Thymosin Alpha-1? Sequence, MW & CAS Number

By the Zen Well Labs Research Team · Last reviewed October 2026 · For laboratory research reference only

Short answer: Thymosin alpha-1 (INN name thymalfasin) is a synthetic N-acetylated peptide of 28 amino acids, sequence Ac-SDAAVDTSSEITTKDLKEKKEVVEEAEN, with molecular formula C129H215N33O55, average molecular weight ≈3108.3 Da and primary CAS number 62304-98-7 (PubChem CID 16130571; FDA UNII W0B22ISQ1C). It was first isolated as a component of thymosin fraction 5 from calf thymus by Goldstein, Low and colleagues. It is chemically distinct from thymosin beta-4 / TB-500. Published work is largely cell-culture and animal-model research. Thymosin alpha-1 is not approved by the FDA for any use. Zen Well Labs sells Thymosin Alpha-1 (10 mg) as a laboratory reagent for in-vitro research only.

Thymosin alpha-1 at a glance

Common names	Thymosin alpha-1, thymosin α1, Tα1, thymalfasin (INN/USAN)
Type	Synthetic linear peptide, 28 residues, N-terminally acetylated
Sequence (one-letter)	Ac-SDAAVDTSSEITTKDLKEKKEVVEEAEN
Sequence (three-letter)	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
Molecular formula	C129H215N33O55
Molecular weight (average)	≈3108.3 Da
Monoisotopic mass	≈3106.5 Da
CAS number	62304-98-7 (primary PubChem synonym; alternate registry numbers also appear)
PubChem CID	16130571
FDA UNII	W0B22ISQ1C
Historical origin	Component of thymosin fraction 5 (calf thymus)
Distinct from	Thymosin beta-4 / TB-500 (different sequence and mass)
Typical supplied form	Lyophilized powder (Zen Well Labs: 10 mg vial)
US regulatory status	Not FDA-approved for any use; research chemical

Where does thymosin alpha-1 come from?

Thymosin alpha-1 is a discrete, defined peptide. Its laboratory history starts with crude thymic extracts. Goldstein, Guha and colleagues (Proceedings of the National Academy of Sciences, 1972) purified thymosin activity from calf thymus. Later fractionation yielded thymosin fraction 5, a mixture of polypeptides. From that mixture, Low, Thurman and colleagues (Journal of Biological Chemistry, 1979) isolated and characterised thymosin alpha-1 and another component (polypeptide β1). Low and Goldstein (Journal of Biological Chemistry, 1979) then reported the amino-acid sequence: 28 residues with an N-terminal acetylserine.

Commercial research vials are produced by solid-phase peptide synthesis of that acetylated 28-mer, not by extracting thymus tissue. Identity should be confirmed by mass spectrometry against the theoretical mass (≈3108.3 Da average; ≈3106.5 Da monoisotopic) and by chromatographic purity, not by trade name alone.

The INN/USAN name for the synthetic peptide is thymalfasin. Catalogue labels may say thymosin alpha-1, Tα1 or thymalfasin; for purchasing and methods sections, treat those as the same defined sequence only when the COA mass matches.

Sequence and chemical identity

One-letter code (N-acetylated): Ac-SDAAVDTSSEITTKDLKEKKEVVEEAEN.

Three-letter code: 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.

Notes that matter at the bench:

The N-terminal acetylation is part of the native sequence definition (acetylserine), not an optional catalogue modification. Unacetylated 28-mers are different chemical entities.
The peptide is acidic (multiple Asp and Glu residues). Low and Goldstein (1979) reported an isoelectric point of about 4.2 for the natural isolate.
Free-acid versus salt form (for example acetate) changes the formula weight of the supplied solid. The COA should state the form so that milligrams of powder are not confused with milligrams of free peptide.

PubChem lists the compound under CID 16130571 (title “Thymalfasin”) with formula C129H215N33O55 and average molecular weight 3108.3. The primary CAS synonym on that record is 62304-98-7; other registry numbers (including 69521-94-4) also appear in databases. Prefer the CAS and observed mass printed on the batch COA when writing a methods section.

Thymosin alpha-1 versus thymosin beta-4 / TB-500

These names share “thymosin” and are easy to confuse in catalogues. They are not interchangeable reagents:

Feature	Thymosin alpha-1 (thymalfasin)	Thymosin beta-4 / TB-500
Length	28 residues, N-acetylated	43 residues (full-length β4)
Approx. average mass	≈3108 Da	≈4963 Da (PubChem CID 45382195)
Origin in the literature	Thymosin fraction 5 component	Separate β-thymosin family peptide
Mass check on COA	Near 3108 Da	Near 4963 Da (or the fragment mass if a truncated catalogue analogue is sold)

An MS result near 3108 Da supports thymosin alpha-1. An MS result near 4963 Da supports full-length thymosin beta-4. See our TB-500 reference page and the BPC-157 vs TB-500 comparison for the β4/TB-500 side of the catalogue.

What has the published research looked at?

The thymosin alpha-1 literature is large and spans decades. Themes that appear repeatedly in cell-culture and animal-model work include:

Sequence definition and fraction-5 origin. Low & Goldstein (1979) and the companion isolation paper (Low et al., 1979) established the 28-residue acetylated sequence from thymosin fraction 5 and reported that a chemically synthesised molecule matched the natural isolate in the bioassay systems then in use.
Immune-cell culture readouts. Historical and later papers examine endpoints related to T-cell maturation markers and related in-vitro immune-cell assays. These are model-specific laboratory observations. They do not establish a clinical effect for research-grade material.
Analytical identity of the synthetic peptide. Because the molecule is defined by sequence and mass, modern laboratory use depends on HPLC purity and MS confirmation rather than on extract nomenclature.

These are mechanistic and preclinical research themes. They do not show that thymosin alpha-1 from any supplier has a health effect in people, and they do not create an approved drug product.

Regulatory status

In the United States, thymosin alpha-1 / thymalfasin is not an FDA-approved drug, food, cosmetic or dietary supplement. FDA has approved no drug product containing thymosin alpha-1. Zen Well Labs lists it as a research chemical for in-vitro use only.

Outside the United States, finished pharmaceutical products under the INN thymalfasin (historically including the brand Zadaxin in some markets) have a different regulatory history. We note that only as background. Registration or marketing authorisation in other countries does not create FDA approval, equivalence or any authorised human use for research-grade catalogue material in the United States, and it has no bearing on how Zen Well Labs material may be used.

Orphan-drug designations that have been granted for thymalfasin in the US regulatory record are not product approvals. Designation is not the same as marketing authorisation.

What is missing

US product approval. There is no FDA-approved drug product under these research-chemical trade names.
Transfer from models to people. Cell-culture and animal-model findings depend on the assay, cell type, species and endpoint. They do not transfer automatically to human use, and Zen Well Labs material is not sold for that purpose.
Name confusion. Extract labels (thymosin, fraction 5), the defined 28-mer (thymosin alpha-1 / thymalfasin) and thymosin beta-4 / TB-500 must be kept separate in purchasing and methods sections.

Storage and stability in the laboratory

Store thymosin alpha-1 as sealed lyophilized powder: keep vials closed, dry and protected from light, at −20 °C for long-term storage. Short periods at 2–8 °C are generally tolerated for sealed dry material. Let a cold vial reach room temperature before opening so moisture does not condense on the powder, and reseal promptly. Record the batch number and date of first opening. See our guide to lyophilized peptide storage and stability for the general principles.

How are identity and purity verified?

Reversed-phase HPLC reports purity as percent peak area. Mass spectrometry confirms identity: the observed mass should be consistent with ≈3108.3 Da (average) or ≈3106.5 Da (monoisotopic) for the free peptide, allowing for the ionisation adducts your instrument reports. A Certificate of Analysis should report both results and a batch number, and ideally the CAS number used. Because thymosin alpha-1 and thymosin beta-4 differ by roughly 1.8 kDa, an MS result settles most labelling mix-ups at once.

Our explainer on how to read a peptide COA walks through each field. For how HPLC purity and MS identity complement each other, see also HPLC vs mass spec for peptide identity (planned related page).

Chemical features that matter for identity checks

Several residues and modifications shape how thymosin alpha-1 appears on a COA:

N-terminal acetylserine is required for the defined sequence. An unacetylated 28-mer would be lighter by 42 Da (loss of the acetyl group) and is not the thymalfasin reference described here.
No methionine or tryptophan in the standard sequence, so the classic +16 Da methionine-sulfoxide problem seen with some other research peptides is not the primary oxidation watch-point for this molecule. Aspartic and glutamic acid–rich regions can still form other process impurities (for example aspartimide-related species) during synthesis; HPLC impurity profiles matter for that reason.
Multiple lysine residues contribute basic sites, but the overall peptide remains acidic because of the Asp/Glu content — consistent with the low isoelectric point reported for the natural isolate (Low & Goldstein, 1979).
Salt form. Research vials are often supplied as the acetate salt of the lyophilized peptide. The peptide mass on MS still tracks ≈3108 Da for the free peptide ion series; the salt affects weight percent peptide in the powder, which is why some COAs also list counter-ion or net peptide content as separate fields. See how to read a peptide COA and HPLC vs mass spec for peptide identity.

Catalogue and methods hygiene

When thymosin alpha-1 appears in a purchasing cart or a methods section, keep the documentation trail simple:

Write the sequence (Ac-SDAAVDTSSEITTKDLKEKKEVVEEAEN) or the INN thymalfasin, not only a trade nickname.
Record CAS 62304-98-7 (or the CAS printed on that lot’s COA) and PubChem CID 16130571 if your inventory system uses registry IDs.
File the batch COA with HPLC percent peak area and observed MS mass next to the vial.
Do not substitute TB-500 / thymosin beta-4 documentation for thymosin alpha-1, or vice versa — the masses differ by about 1.8 kDa.

Zen Well Labs supplies Thymosin Alpha-1 as a 10 mg lyophilized research vial. It is intended only for in-vitro laboratory research under your institution’s protocols.

Frequently asked questions

What is the amino acid sequence of thymosin alpha-1?

Ac-SDAAVDTSSEITTKDLKEKKEVVEEAEN — 28 residues with an N-terminal acetyl group. The INN name is thymalfasin.

What is the molecular weight and CAS number of thymosin alpha-1?

About 3108.3 Da (formula C129H215N33O55), CAS 62304-98-7, PubChem CID 16130571, UNII W0B22ISQ1C. Salt forms have higher formula weights.

Is thymosin alpha-1 the same as TB-500 or thymosin beta-4?

No. Thymosin alpha-1 is the 28-residue acetylated peptide described above. Thymosin beta-4 / TB-500 is a different sequence with a much higher mass (full-length β4 ≈4963 Da). See What is TB-500?.

Is thymosin alpha-1 the same as thymosin fraction 5?

No. Fraction 5 is a historical multi-peptide thymic extract. Thymosin alpha-1 is one defined component that was isolated from that mixture and is now made synthetically.

Is thymosin alpha-1 FDA-approved?

No. It is not approved by the FDA for any use. Finished pharmaceutical products sold under the INN thymalfasin in some other countries do not change the US status of research-grade material.

What is Zen Well Labs Thymosin Alpha-1 10 mg intended for?

In-vitro laboratory research only. It is not for human or veterinary use.

References

Goldstein AL, Guha A, Zatz MM, Hardy MA, White A. Purification and biological activity of thymosin, a hormone of the thymus gland. Proceedings of the National Academy of Sciences of the USA. 1972;69(7):1800–1803.
Low TL, Thurman GB, McAdoo M, McClure J, et al. The chemistry and biology of thymosin. I. Isolation, characterization, and biological activities of thymosin alpha1 and polypeptide beta1 from calf thymus. Journal of Biological Chemistry. 1979;254(3):981–986.
Low TL, Goldstein AL. The chemistry and biology of thymosin. II. Amino acid sequence analysis of thymosin alpha1 and polypeptide beta1. Journal of Biological Chemistry. 1979;254(3):987–995.
PubChem Compound Summary, CID 16130571 (Thymalfasin). National Center for Biotechnology Information.
PubChem Compound Summary, CID 45382195 (Thymosin Beta 4). National Center for Biotechnology Information.
NCATS Inxight Drugs / UNII W0B22ISQ1C (THYMALFASIN).

Research use only. All products sold by Zen Well Labs are intended strictly for in-vitro laboratory research. They are not drugs, foods, cosmetics or dietary supplements, are not approved by the FDA for any use, and are not for human or veterinary use. Nothing on this page is medical advice, and nothing here describes or recommends administration to humans or animals.

What Is Thymosin Alpha-1?