Thymosin Alpha-1: Structure, Identity and Handling

For laboratory research use only. Not for human or veterinary use.

Thymosin alpha-1 is unusual in a research catalogue. It is not a designed analogue or a synthetic construct — it is a naturally occurring human peptide fragment, produced synthetically, and it has a real pharmaceutical history under the name thymalfasin. It also has two structural features that change how it must be handled and tested, and neither is widely mentioned.

Identity#

The sequence:

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

It corresponds to the first 28 residues of prothymosin alpha, a larger human protein. Thymosin alpha-1 is the proteolytic fragment; the synthetic material reproduces it.

The acetyl group is not optional#

Note the Ac- at the front of the sequence. The N-terminal acetylation is part of the molecule's definition, not a manufacturing flourish, and it is present on the natural fragment.

An acetyl group is C₂H₂O: 42 Da. So a correctly made thymosin alpha-1 has a mass of 3108.28, and a 28-residue peptide of the same sequence without the acetyl group comes in at roughly 3066 — a different compound that happens to share a sequence.

This is the first thing to check on a certificate. If the mass spectrometry result reads near 3066 rather than 3108, the acetylation step did not happen or did not go to completion. The gap is large enough to be unambiguous and small enough to be missed by anyone not looking for it.

It has no aromatic residues — which breaks the usual assay#

This is the structural feature with the largest practical consequence, and it is almost never mentioned.

Read the sequence again. There is no tryptophan, no tyrosine and no phenylalanine anywhere in it.

Peptide concentration is routinely measured by ultraviolet absorbance at 280 nm. That method works because tryptophan and tyrosine absorb strongly at that wavelength. Thymosin alpha-1 contains neither, so A280 quantification does not work on this peptide — it will read essentially nothing regardless of how much peptide is present.

Quantification has to go via the peptide bond itself at around 214 nm, or via amino acid analysis. If a supplier's certificate reports concentration or net peptide content by A280, that number cannot be right for this compound. It is a good test of whether the certificate describes actual work.

A strongly acidic peptide#

Counting the charged residues: nine acidic (three aspartate, six glutamate) against four basic (all lysine, no arginine or histidine). The molecule carries a substantial net negative charge at neutral pH.

Two consequences worth knowing. It is very soluble in water, which makes preparation straightforward — no organic co-solvent, no coaxing. And it is sensitive to pH near its isoelectric point, which sits low; buffers drifting acidic move it toward neutrality and toward falling out of solution.

It also contains no cysteine, so there are no disulfide bonds to scramble and no oxidation pathway through free thiols — one of the more common degradation routes simply does not apply here. Combined with the absence of tryptophan, which is the residue most vulnerable to light, this is a comparatively robust peptide.

Regulatory position — stated plainly#

Thymosin alpha-1 is marketed as a medicine under the name thymalfasin (brand name Zadaxin) and is approved in a number of countries.

It is not licensed as a medicine in the United Kingdom. Pioneer supplies it as a research compound for laboratory use only. Nothing on this page describes or implies any human or veterinary application, and the existence of a licensed product elsewhere does not change what is being supplied here or what it may be used for.

What to check on the certificate#

• Mass: 3108.28, not ~3066. The acetylation check, specific to this compound.
• Purity method named. HPLC as measured on that batch, with the method stated.
• Quantification method. Anything reported by A280 is not measuring this peptide.
• Net peptide content. Distinct from purity. A highly acidic peptide of this length carries appreciable counter-ion and water; net peptide content is how much of the vial is peptide.
• Counter-ion. Acetate or trifluoroacetate, from purification. It affects the net peptide figure.

Ask about the documentation for the batch we would ship before you order. See also how to read a COA and what a purity figure means.

Handling#

Standard peptide handling applies: it ships lyophilised because the powder is far more stable than the solution, and it should be stored cold, dry and sealed. Bring a cold vial to room temperature before opening. Reconstitute by running solvent down the vial wall rather than onto the powder, and never shake.

It dissolves readily in water or aqueous buffer. Given the absence of cysteine and tryptophan, it is less demanding on light protection and inert atmosphere than many peptides of comparable length — though there is no reason to be casual about either.

What Pioneer supplies#

Thymosin alpha-1 is stocked as a lyophilised vial. It ships from the UK with same-day dispatch on orders before 2pm, alongside bacteriostatic or sterile water and transfer equipment.

Quality comes first#

With a peptide whose correct form differs from an incorrect one by a single 42 Da group, the certificate is the only way to know which you have. Ask about the documentation for the batch we would ship before you order.

Sources#

Status elsewhere: Licensed as thymalfasin in more than 35 countries (as of 2009), though not in the UK.

Each entry links to its PubMed record, where the title and abstract can be read. The descriptions are ours: they say what each paper examined, not what it is claimed to show. Records checked on PubMed on 28 October 2026.

1. Goldstein AL, Low TL, McAdoo M, et al. (1977). Proc Natl Acad Sci U S A 74(2):725–9. Isolation and sequencing of thymosin alpha-1 from calf thymus: 28 residues, heat-stable and highly acidic. PubMed 265536
2. Goldstein AL, Goldstein AL (2009). Expert Opin Biol Ther 9(5):593–608. Review of the clinical use of thymosin alpha-1 by the group that discovered it. States that it was approved in over 35 countries. PubMed 19392576
3. Dominari A, Hathaway D, Pandav K, et al. (2020). World J Virol 9(5):67–78. Review of the biochemistry of thymosin alpha-1 and its clinical history under the name thymalfasin. PubMed 33362999
4. Wu J, Zhou L, Liu J, et al. (2013). Crit Care 17(1):R8. Randomised trial in 361 intensive-care patients at six Chinese hospitals. 28-day mortality was 26% against 35%, a borderline result that the larger 2025 trial below was set up to test. PubMed 23327199
5. Wu J, Pei F, Zhou L, et al. (2025). BMJ 388:e082583. Phase 3 double-blind placebo-controlled trial in 1,106 intensive-care patients at 22 centres in China. No difference in its primary outcome, 28-day mortality. Part-funded by SciClone Pharmaceuticals, the company that markets thymalfasin. PubMed 39814420

In our catalogue#

• Thymosin alpha-1 — 28-amino-acid peptide, immune signalling research
• TB-500 — thymosin beta-4 fragment — a different compound, see the guide above
• KPV — tripeptide alpha-MSH fragment, inflammatory pathway research

Pioneer Research Peptides — UK supplier of research peptides for laboratory use. Ask about batch documentation before you order.

For laboratory research use only — not for human consumption. 18+.