Guide
Selank vs Semax: A Research Comparison
Selank and Semax are both synthetic heptapeptides, both end in the same Pro-Gly-Pro extension, and both come out of the same Russian peptide-chemistry research tradition. From there they diverge: different parent molecules, different sequences, and different in vitro research contexts. This comparison lays out the differences the way an analytical chemist would, strictly for laboratory research context.
Two heptapeptides, two parent molecules
Selank (Thr-Lys-Pro-Arg-Pro-Gly-Pro, CAS 129954-34-3) is built on tuftsin, an endogenous tetrapeptide fragment of immunoglobulin G. Semax (Met-Glu-His-Phe-Pro-Gly-Pro, CAS 80714-61-0) is built on the ACTH(4-7) fragment of adrenocorticotropic hormone.
That parentage is the cleanest way to keep them apart: Selank descends from an immune-system peptide, Semax from a pituitary hormone fragment. The two share no sequence overlap in their first four residues.
The shared Pro-Gly-Pro motif
Both peptides carry the same C-terminal Pro-Gly-Pro extension, and it is there for the same reason in each: the tripeptide tail slows enzymatic breakdown of the parent fragment, extending its usable life in laboratory preparations.
This shared design element is why the two are so often discussed together. It reflects a common stabilization strategy applied to two unrelated parent sequences, not a chemical or functional equivalence.
Molecular identity at a glance
Selank: C33H57N11O9, molecular weight 751.89 g/mol, seven residues, no sulfur. Semax: C37H51N9O10S, molecular weight 813.92 g/mol, seven residues, one methionine and therefore one sulfur atom.
That single methionine is the practical analytical difference. Methionine can oxidize during synthesis or storage, so a Semax report has one extra failure mode to rule out that a Selank report does not.
Different in vitro research contexts
In cell-based research, Selank appears as a model neuropeptide in receptor-signaling assays, neurotrophin gene-expression studies, and peptidase-stability work centered on that Pro-Gly-Pro tail.
Semax appears in melanocortin-receptor pathway studies, neurotrophic-factor expression models, and peptide-hydrolysis research. These are in vitro applications only; no medical claims are made here, and this comparison does not cover preparation or use of any kind.
Verifying either one
The verification checklist is identical for both compounds: an HPLC purity percentage, a mass-spectrometry identity confirmation, and a traceable lot number with a test date. For Semax, the mass-spectrometry step is doing extra work, since an oxidized methionine shifts the observed mass.
Whichever compound a study calls for, the batch you receive should come with its own report, not a brand-level summary. If the supplier lets you look up that batch’s document by lot number, you can match the paperwork to the vial in hand. Our COA reading guide walks through each field.