Where to Buy Thymosin Alpha-1 in 2026: Sizes, Purity and Verification

Thymosin alpha-1 (INN thymalfasin) is a synthetic, N-acetylated 28-residue peptide that shares a name with thymosin beta-4 (TB-500) and nothing else. This guide covers what it is chemically, how Pepta Labs lists it, what a purity report for a 3.1 kDa peptide should show, and how to store it.

What Is Thymosin Alpha-1?

The one-letter sequence Ac-SDAAVDTSSEITTKDLKEKKEVVEEAEN-OH corresponds to residues 2-29 of prothymosin alpha. The Ac- prefix means the N-terminal serine carries an acetyl group, so the peptide has no free N-terminal amine; the acetyl adds 42.01 Da and is part of the identity that mass spectrometry confirms. A listing that omits the Ac- prefix, or a report whose mass is 42 Da low, describes the des-acetyl peptide, which is a different compound. The C-terminus is a free carboxylic acid, not an amide. Registry numbers for the whole catalog are collected in the CAS number and molecular weight table.

Charge, salt form and net peptide content

The sequence contains three aspartate and six glutamate residues against four lysines and no free N-terminal amine, so the peptide carries a strongly negative net charge at neutral pH. It is still isolated as an acetate or trifluoroacetate salt after purification, with counter-ions paired to the lysine side chains, and it holds bound water. Net peptide content, the fraction of the vial's gross mass that is peptide rather than counter-ion and water, is therefore below 100%, so a 5 mg vial by gross weight holds somewhat less than 5 mg of peptide. The salt form and net peptide content are stated on the analytical report; the TFA versus acetate article sets out the arithmetic.

Not the same as thymosin beta-4 (TB-500)

Thymosin alpha-1 and thymosin beta-4 share only the historical name. Thymosin beta-4 is a separate 43-residue peptide of about 4963 g/mol (CAS 77591-33-4), covered in the TB-500 buying guide. The two have different sequences, masses and CAS numbers, and a report for one cannot substantiate a listing for the other. The quick check is the deconvoluted mass: near 3108 for thymosin alpha-1, near 4963 for TB-500.

How Pepta Labs Lists Thymosin Alpha-1

Thymosin alpha-1 is supplied as 5 mg of lyophilized powder in a sealed glass vial and is listed in the thymic category. The product page shows the reported RP-HPLC purity for the sourced production run, and identity is confirmed by mass spectrometry. Both results come from an independent laboratory commissioned through a cooperative purchasing group; Pepta Labs does not test in-house. The analytical report (COA) is available by email on request, before or after purchase. Free US shipping, and most orders ship the next business day. The Testing and Documentation page describes the arrangement.

How to Verify a Thymosin Alpha-1 Listing

What the HPLC report shows

Reversed-phase HPLC with UV detection at 214-220 nm separates the peptide from its synthesis-related impurities, and purity is reported as the main-peak area divided by total peak area. For a 28-residue synthetic peptide the likely minor peaks are deletion sequences (one residue missing, eluting close to the main peak), incompletely deprotected species and the des-acetyl peptide. Area percent does not measure water, counter-ion or absolute quantity, which is why a 99.1% purity and an 85% net peptide content can both be correct for the same vial: they describe different things.

What the mass spectrometry report shows

A 3.1 kDa peptide ionizes under electrospray as a series of multiply charged ions, which the instrument software deconvolutes to a single mass. At this size the most abundant isotope peak sits one or two mass units above the monoisotopic peak, so a reported 3107.5 or 3108.3 is consistent with the formula C129H215N33O55, as is a monoisotopic 3106.5. A value near 3066 is 42 Da low and indicates the missing acetyl group. Satellite peaks 114 Da above the main mass are trifluoroacetate adducts, common for TFA salts, not a different peptide. The expected mass table lists the same figures for the rest of the catalog.

Production-run report versus lot-specific COA

The report Pepta Labs supplies covers the sourced production run, the batch from which the vials were filled, and may name the purchasing group or the source as the client rather than Pepta Labs. A manufacturer's lot-specific COA is tied to a numbered lot instead. In either case the lot or run reference on the document should match the reference on the vial label; a certificate with no reference, or one whose mass belongs to thymosin beta-4, should be rejected. The COA verification guide and the HPLC versus mass spectrometry article explain each field.

Storage and Shipping

• Ships as a lyophilized powder at ambient temperature; a few days in transit at room temperature is standard for a sealed, dry peptide.
• Refrigerate at 2-8 C on arrival. For storage longer than a few months, keep the sealed vial at -20 C.
• Protect from light and moisture. Keep the vial sealed and let it reach room temperature before opening so that condensation does not form on the powder.

US Regulatory Status

Thymalfasin is the INN and USAN for thymosin alpha-1, and PubChem records Zadaxin as a trade name for the same substance. An openFDA Drugs@FDA query for thymalfasin returns no application records, consistent with there being no US-approved product under that name. In compounding regulation, the FDA page on bulk drug substances that may present significant safety risks (content current as of April 22, 2026) lists Thymosin-alpha 1 (Ta1) under the heading "Bulk drug substances nominated but withdrawn", described there as substances previously in Category 2 of the section 503A interim policy whose nominations were withdrawn by the nominators; the peptide does not appear in the current 503A nominations document (updated May 14, 2026). Those entries concern compounding pharmacies, not the sale of a research reference material; the general framework for research compounds is in Peptide Legal Status 2026.

Frequently Asked Questions

Is thymosin alpha-1 the same as thymalfasin?

Yes. Thymalfasin is the international nonproprietary name for the synthetic N-acetylated 28-residue peptide; both names refer to CAS 62304-98-7, formula C129H215N33O55, 3108.3 g/mol.

What does the Ac- prefix mean?

It denotes an acetyl group on the N-terminal serine, so there is no free N-terminal amine. The acetyl adds 42.01 Da and is part of the identity confirmed by mass spectrometry; a peptide without it is a different compound.

Why does a 5 mg vial contain less than 5 mg of peptide?

The 5 mg figure is the gross weight of lyophilized salt. Counter-ions (acetate or trifluoroacetate) and bound water make up the balance, and the peptide fraction is reported as net peptide content on the analytical report.

All products are supplied for laboratory research use only and are not for human or animal use.