Semax: structure and analysis

What it is

Semax is a synthetic heptapeptide based on the 4-7 fragment of adrenocorticotropic hormone, extended with a proline-glycine-proline tail. Seven residues in total: a four-residue active fragment plus a three-residue stabilising extension.

It shares its design logic with Selank — a short active sequence joined to a tail that slows enzymatic degradation — while deriving from an entirely different parent hormone.

The N-terminal residue of the ACTH(4-7) fragment is methionine, and that single fact drives most of what is analytically distinctive about this compound.

How it is produced

Assembled by solid-phase peptide synthesis: the chain is built one residue at a time on an insoluble resin support, then cleaved from the resin, deprotected and purified — most commonly by reversed-phase high-performance liquid chromatography. The purified material is lyophilized to a dry solid.

The impurity profile that appears on a certificate is a record of where that process was imperfect: deletion sequences from an incomplete coupling, truncated chains, and species retaining a protecting group.

Confirming identity

Mass spectrometry confirms the seven-residue chain including the proline-glycine-proline extension. A truncated species lacking the tail is well separated in mass and readily identified.

Methionine oxidation is the modification an identity method will most often encounter here. The sulfoxide is sixteen mass units heavier than the parent, which is unambiguous at high resolution.

Analytical considerations

Methionine sulfoxide is the characteristic impurity for this compound, and its position at the N-terminus leaves it relatively exposed. A purity method for Semax needs to resolve the sulfoxide from the parent peptide, and a method that does not will report a purity figure that quietly includes it.

This is the clearest example in the catalogue of why a purity number needs its method attached. Two laboratories can analyse the same lot and report different figures depending on whether their gradient separates an oxidation product that differs from the target by a single oxygen atom.

The compound is otherwise chromatographically well behaved: seven residues is long enough for solid reversed-phase retention and short enough that deletion products remain resolvable.

What its certificate reports

A certificate for a lot of this material names the lot, names the issuing laboratory, and states for each parameter both the method used and the specification the result was measured against. Identity and purity are the two core results; net peptide content states how much of the fill weight is actually peptide.

A certificate belongs to a lot, not to a product line. When a new lot is released it is tested again, and the certificate published against it is that lot's certificate — a previous lot's result is never carried forward.

Research use only

This page describes structure and analysis. It makes no claim about what this compound does, and none should be inferred from it. Material is supplied for laboratory research use only: it is not a drug, food, dietary supplement, cosmetic or medical device, it is not for human or veterinary consumption, and no dosing, administration or reconstitution guidance is provided for any such use.