Epitalon vs Thymalin: A Synthetic Tetrapeptide and a Thymic Peptide Complex

One program, two kinds of material

Both names come from the St. Petersburg Institute of Bioregulation and Gerontology. That group first made complex peptide preparations by extracting animal tissues: Epithalamin from the pineal gland and Thymalin from the thymus. It later designed short synthetic peptides based on the amino acid composition of those extracts ^[1].

Epitalon is one of those synthetic peptides, built from the composition of the pineal extract Epithalamin ^[2]. Thymalin stayed an extract. So the comparison is less "peptide A vs peptide B" and more "a defined molecule vs a tissue-derived mixture."

Chemistry at a glance

• Epitalon: Ala-Glu-Asp-Gly (AEDG), formula C14H22N4O9, listed molecular weight about 390.3 Da. Linear, free N- and C-termini, two acidic residues, so it carries a net negative charge at neutral pH.
• Thymalin: a polypeptide complex extracted from calf thymus, so it has no single sequence or molecular weight. The dipeptides Lys-Glu (KE) and Glu-Trp (EW) are named in the literature as active components of the preparation ^[4].
• Practical consequence: Epitalon can be described by one formula and one mass; Thymalin is described by its source, preparation and component profile.

What the cell-culture literature examines

Epitalon papers from the originating group include a 2003 report of telomerase expression and activity in cultured human fetal fibroblasts ^[3]. A 2025 review collects the in vitro, animal and in silico work and notes that physico-chemical and structural studies of the peptide remain limited ^[2].

Thymalin papers focus on immune-cell models. A 2023 study combined molecular docking of the KE and EW dipeptides with cytokine measurements in stimulated human blood mononuclear cells ^[4]. A 2022 study in the THP-1 monocyte cell line tested Thymalin and Epitalon side by side with three other peptides from the same program and measured kinase phosphorylation and LPS-stimulated cytokine expression ^[5].

Most of this record comes from one research school and its collaborators, so it is best read as preliminary. The Epitalon and Thymalin research overviews list the papers and their limits.

Characterizing each in the lab

Epitalon is small and defined, so identity is a straightforward Mass spectrometry check: the [M+H]+ ion sits near m/z 391.15. A Belgian public-health laboratory has reported identifying Epitalon in two illegal pharmaceutical preparations, an example of this kind of analytical identity work ^[6]. Purity is reported as HPLC area percent, and the peptide molecular weight estimator reproduces its mass from the four-letter sequence.

A mixture like Thymalin does not have one expected mass or one main HPLC peak, so "purity" in the single-compound sense does not apply. Characterization relies on a consistent chromatographic profile, the presence of named components and general tests such as endotoxin testing, which matters for any tissue-derived material used in cell assays.

Solution arithmetic differs

For Epitalon, a known molecular weight means mg/mL can be converted to Molarity; the Epitalon reconstitution calculator does that arithmetic. For Thymalin, there is no single molecular weight, so concentrations are stated by mass (mg/mL) only, and the concentration calculator handles that case.

Both are supplied as lyophilized powders and stored sealed and frozen. Thymalin is listed now; Epitalon is coming soon. For a different thymus-related comparison, see Thymosin Alpha-1 vs Thymosin Beta-4.