Is thymalfasin the same as thymosin alpha-1?

Yes, for testing purposes. PubChem describes thymalfasin as a chemically synthesised version of thymosin alpha-1 that is identical to the human peptide, and lists both names on the same record, CID 16130571. Both should match the acetylated 28-residue sequence and an average mass of 3108.3 g/mol on a certificate.

What mass should a thymosin alpha-1 certificate show?

PubChem gives an average molecular weight of 3108.3 g/mol and a monoisotopic mass of 3106.50 Da. Raw spectra show several multiply charged ions, which software converts to one neutral mass. A main mass lower by about one acetyl group suggests non-acetylated material, and a small companion peak only slightly heavier than the main one fits deamidation.

Why is asparagine 28 singled out in thymosin alpha-1 testing?

Because most of its known impurities come from that residue. A 2022 metrology study of thymalfasin materials found that over half of the related impurities it identified arose directly or indirectly from the C-terminal asparagine. The authors even proposed deleting or replacing that residue in future molecules. A report that addresses Asn28 directly answers the most relevant question for this peptide.

Can recombinant thymosin alpha-1 fail an identity test?

It can if the acetyl group is missing. One recombinant E. coli fusion protein came out only partly N-alpha-acetylated, and other routes add the acetyl chemically after expression. Non-acetylated chains are lighter than thymalfasin by one acetyl group, so mass spectrometry shows them as a separate signal. A good report states the ratio if both forms appear.

Is a single HPLC purity figure enough for thymosin alpha-1?

It is a start, not a full answer. Even a pharmacopoeia reference standard was found to contain 23 related impurities above 0.1 mg/g, some of them isomers with the same mass as the main peptide. A purity figure supported by an impurity profile, with masses for the larger peaks, tells you far more about what the vial holds.

Why does a thymosin alpha-1 label sometimes mention acetate?

Peptides are usually supplied as salts, and PubChem lists thymosin alpha1 acetate among the synonyms for thymalfasin. That acetate is a counter-ion, separate from the acetyl group bonded to the N-terminus, and it adds weight without adding peptide. The lesson on net peptide content and counterions explains how a report accounts for it.

One of the 30 compound testing profiles

Thymosin alpha-1

Thymosin alpha-1 is a 28-amino-acid peptide (C129H215N33O55, average mass 3108.3 g/mol) with an acetylated N-terminus; a test should confirm that mass, show the acetyl group is present, and look closely at the C-terminal asparagine, the source of most of its known impurities.

Thymalfasin is a chemically synthesised version of thymosin alpha-1, an acetylated 28-residue polypeptide identical to the human sequence, originally found in a thymus gland extract (PubChem).

Test your Thymosin alpha-1

Identity card

Formula: C129H215N33O55
Average mass: 3,108.3 g/mol
Monoisotopic mass: 3,106.5 Da
Length: 28 residues
Modifications: N-terminal acetyl on Ser1; Free C-terminal acid on Asn28
Also sold as: Thymalfasin, Thymosin alpha 1, TA1, Talpha1
Sequence: SDAAVDTSSEITTKDLKEKKEVVEEAEN
Note: PubChem records thymalfasin with the line notation Ac-Ser-Asp-Ala-...-Glu-Asn-OH and lists a monoisotopic mass of 3106.50 Da. Thymosin alpha-1 and thymalfasin are listed as synonyms of the same record.

Source: Thymalfasin compound record (CID 16130571).

Check a certificate's mass against these values with the mass checker, prefilled for Thymosin alpha-1.

What usually goes wrong with Thymosin alpha-1. Documented failure modes, with sources.

Deamidation and succinimide at the C-terminal Asn28

The single asparagine sits at the end of the chain and is the peptide's main weak point. A 2022 LC-HRMS study from China's National Institute of Metrology examined a China Pharmacopoeia thymalfasin standard and three commercial materials, and found that over half of the thymalfasin-related impurities arose directly or indirectly from the labile C-terminal Asn (Cheng et al., 2022). The major impurity types it reported were deamination, amination, succinimide, amino acid insertion or deletion, dimers and isomers. Asparagine deamidation runs through a succinimide intermediate (Reissner and Aswad, 2003), so related species can sit in the same sample.

Isomers that keep the same mass

Beta-linked isoaspartyl bonds form through a succinimide, either from asparagine deamidation or from aspartate dehydration (Reissner and Aswad, 2003). Thymosin alpha-1 has aspartic acid at positions 2, 6 and 15 as well as Asn28, and isomers were among the major impurity types in thymalfasin materials (Cheng et al., 2022). An isomer has the same formula as its parent, so intact mass cannot see it. HPLC separation, and where needed fragment data that localise the change, is what reveals it.

A long impurity list even in reference material

The same study separated, identified and quantified twenty-three thymalfasin-related impurities above 0.1 mg/g in the China Pharmacopoeia standard alone, and the authors stressed that comprehensive impurity determination is needed to avoid bias when assigning purity (Cheng et al., 2022). If reference material carries that many related species, a single purity number without an impurity profile tells only part of the story for any vial.

Material that is missing the N-terminal acetyl group

A 2010 review notes that clinical thymosin alpha-1 is made by solid-phase synthesis, while recombinant E. coli routes struggle with this modification because the bacteria lack efficient post-translational modification systems: one fusion protein came out only partly N-alpha-acetylated, and another route acetylated the peptide chemically after expression (Li et al., 2010). A non-acetylated chain is lighter by one acetyl group, so a mixture shows as two related signals on a mass spectrum, which a report should list separately.

Which tests matter most

HRMSDeamidation of Asn28 changes the mass only slightly on a 3108 g/mol peptide; the published impurity work on thymalfasin relied on LC-HRMS for this reason.
LC-MSConfirms the acetylated 28-residue chain and assigns masses to insertion, deletion, succinimide and dimer impurities.
HPLC-UVSeparates same-mass isoaspartyl isomers from the main peak and gives the purity figure.
Peptide mappingDigesting the chain localises a modification to the C-terminal Asn28 or to an Asp elsewhere in the sequence.

Reading Thymosin alpha-1 results

At about 3108 g/mol, electrospray gives several multiply charged ions, each resolved into an isotope cluster on a high-resolution instrument. A report should give a deconvoluted mass and say whether it compares against the average (3108.3 g/mol) or monoisotopic (3106.50 Da) value (PubChem). The mass checker and reading a mass spectrum explain both.

The sequence is strongly acidic: nine of its 28 residues are aspartic or glutamic acid, against four lysines (PubChem). Trifluoroacetate from synthesis and purification pairs with positively charged groups such as lysine (Erckes et al., 2025), and PubChem lists acetate and trifluoroacetate salt names among the synonyms. A net peptide content result is what turns a powder weight into a peptide weight.

Public Tested.ph results

No public Thymosin alpha-1 records yet

Each public Thymosin alpha-1 record will appear here with its identity, HPLC purity and measured amount against the label, once the first vial is tested.

FIG 13Amount against the label

Questions about testing Thymosin alpha-1

Is thymalfasin the same as thymosin alpha-1?: Yes, for testing purposes. PubChem describes thymalfasin as a chemically synthesised version of thymosin alpha-1 that is identical to the human peptide, and lists both names on the same record, CID 16130571. Both should match the acetylated 28-residue sequence and an average mass of 3108.3 g/mol on a certificate.
What mass should a thymosin alpha-1 certificate show?: PubChem gives an average molecular weight of 3108.3 g/mol and a monoisotopic mass of 3106.50 Da. Raw spectra show several multiply charged ions, which software converts to one neutral mass. A main mass lower by about one acetyl group suggests non-acetylated material, and a small companion peak only slightly heavier than the main one fits deamidation.
Why is asparagine 28 singled out in thymosin alpha-1 testing?: Because most of its known impurities come from that residue. A 2022 metrology study of thymalfasin materials found that over half of the related impurities it identified arose directly or indirectly from the C-terminal asparagine. The authors even proposed deleting or replacing that residue in future molecules. A report that addresses Asn28 directly answers the most relevant question for this peptide.
Can recombinant thymosin alpha-1 fail an identity test?: It can if the acetyl group is missing. One recombinant E. coli fusion protein came out only partly N-alpha-acetylated, and other routes add the acetyl chemically after expression. Non-acetylated chains are lighter than thymalfasin by one acetyl group, so mass spectrometry shows them as a separate signal. A good report states the ratio if both forms appear.
Is a single HPLC purity figure enough for thymosin alpha-1?: It is a start, not a full answer. Even a pharmacopoeia reference standard was found to contain 23 related impurities above 0.1 mg/g, some of them isomers with the same mass as the main peptide. A purity figure supported by an impurity profile, with masses for the larger peaks, tells you far more about what the vial holds.
Why does a thymosin alpha-1 label sometimes mention acetate?: Peptides are usually supplied as salts, and PubChem lists thymosin alpha1 acetate among the synonyms for thymalfasin. That acetate is a counter-ion, separate from the acetyl group bonded to the N-terminus, and it adds weight without adding peptide. The lesson on net peptide content and counterions explains how a report accounts for it.

Sources

Thymalfasin compound record (CID 16130571), PubChem, US National Library of Medicine
Cheng Y et al. Identification and determination of structurally related peptide impurities in thymalfasin by LC-HRMS. Anal Bioanal Chem. 2022;414(28):8035-8045, Analytical and Bioanalytical Chemistry (PubMed)
Li J et al. Thymosin alpha 1: biological activities, applications and genetic engineering production. Peptides. 2010;31(11):2151-8, Peptides (PMC)
Reissner KJ, Aswad DW. Deamidation and isoaspartate formation in proteins. Cell Mol Life Sci. 2003;60(7):1281-95, Cellular and Molecular Life Sciences (PubMed)
Erckes V et al. Towards a consensus for the analysis and exchange of TFA as a counterion in synthetic peptides. Pharmaceuticals. 2025;18(8):1163, Pharmaceuticals (PMC)

Last reviewed 6 Oct 2026.