Hexarelin

What Hexarelin is, structurally

Hexarelin is a hexapeptide with a free N-terminal amine and a C-terminal amide. Two of its six residues are D-configured, and one of those carries a methyl group that does not occur on any natural amino acid.

The formula reconciles precisely, and on a molecule with modified residues that is worth doing explicitly. Twelve nitrogens comes from six backbone amides, three for the histidine, one each for the two indoles, one for the lysine side chain and one for the C-terminal amide.

The most consequential feature is two indole rings rather than one. Position two is 2-methyl-D-tryptophan, position four ordinary L-tryptophan. Tryptophan is the most oxidation-prone and photosensitive standard residue, so carrying two doubles that exposure in only six residues.

The methyl on the position-two indole sits at the ring carbon adjacent to the nitrogen, one of the more reactive sites on an indole. Substituting it blocks a route that would otherwise be open, while the unmodified tryptophan at position four stays fully exposed. The two indoles are not equivalent in reactivity.

The histidine at position one adds a property the rest of the sequence lacks. Its imidazole has a pKa near six, so net charge shifts measurably across the working pH range rather than staying fixed, and imidazole is a competent metal-coordinating group. With the lysine and free N-terminal amine the peptide is cationic and water soluble, though no quantitative figure is quoted here. There is no cysteine and no methionine, so the formula contains no sulfur.

Reconstitution and handling

Sterile water is the default solvent, and PBS or an assay buffer are reasonable, with one qualification: the histidine coordinates transition metals, and trace metal contamination promotes tryptophan oxidation. On a molecule that binds metals and carries two oxidisable indoles those properties compound, so a clean diluent matters more here than usual.

Add diluent down the inside wall of the vial, swirl gently, and let the solution clarify. Work in subdued light and do not leave solutions standing under illumination.

Adsorption onto plasticware is worth allowing for at low concentration, and low-protein-binding tubes reduce measured loss. Three aromatic rings and a cationic charge give this peptide both hydrophobic and electrostatic routes to a surface.

This is laboratory preparation chemistry, not dosing, administration, or protocol guidance of any kind.

Storage and stability

Store the lyophilized powder at -20 degrees C, sealed, desiccated and protected from light, and let a cold vial warm before opening. Reconstituted, hold at 2 to 8 degrees C, or aliquot and freeze rather than thawing repeatedly.

The weak point is indole oxidation, with two sites rather than the usual one. Nothing else competes: no cysteine, no methionine, no asparagine or glutamine, no aspartate. Air, light and trace metals drive it, and the histidine's metal affinity is why the third deserves more weight here than usual.

The two D-residues give the backbone resistance to proteolysis, so the shape of the picture is simple even with the oxidation risk doubled: a robust backbone with two vulnerable side chains.

These are storage conditions for the material, not dosing or administration guidance.

How Hexarelin is tested

Reversed-phase HPLC establishes chromatographic purity as area percent. Two indoles and a benzene ring give strong absorbance near 280 nm, so detection there is straightforward alongside the low-UV amide measurement at 214 nm.

Area percent is a chromatographic measure rather than peptide content by weight. Solid-phase synthesis delivers a salt, commonly trifluoroacetate or acetate, associating with the basic sites. Residual trifluoroacetate and deletion sequences are the impurity classes to resolve.

Mass spectrometry confirms identity and reads the oxidation directly, with a complication worth anticipating. Each indole can take up oxygen independently, so oxidised material appears at plus sixteen and plus thirty-two above the molecular ion, and a plus-sixteen peak does not say which of the two rings was hit. The two are not equally reactive, since one carries a blocking methyl, so distinguishing them needs fragmentation rather than intact mass. Two further limits apply: D-residues cannot be verified by mass, being identical in weight to their L-forms, and the position-two methyl adds fourteen units, so a molecular ion fourteen light indicates unmethylated tryptophan rather than oxidation.

These describe general methodology, not a claim about any particular batch.

Handling FAQ

Why does trace metal contamination matter more for this peptide? Because the histidine coordinates metals and the two tryptophans are oxidisable. Bound transition metal near an oxidisable side chain promotes exactly the degradation this molecule is most prone to, so the two features reinforce each other rather than being separate concerns.

A molecular ion fourteen units lighter than expected: what is that? Most likely unmethylated tryptophan at position two rather than any degradation. The methyl group that distinguishes this compound weighs fourteen, so its absence points to a synthesis-related impurity carrying ordinary tryptophan in that position.

Full specifications for Hexarelin.