ARA-290 identity: structure, molecular weight and form

• ARA-290 is a linear synthetic undecapeptide with an average molecular weight of 1257.3 g/mol.
• The sequence features a closed pyroglutamate ring at the N-terminus, rendering it invisible to standard colorimetric ninhydrin tests.
• Because it lacks aromatic amino acids, high-performance liquid chromatography must evaluate the peptide bonds directly at 210 to 215 nanometres.
• The material is supplied as a lyophilised powder, where a failure in the freeze-drying step leaves residual moisture that skews net peptide mass calculations.
• Laboratory mass spectrometry must confirm a mass of 1257.3 Daltons; an 18-Dalton deviation indicates a failed cyclisation during synthesis.

Before you open a lab report, it pays to know what the mass spectrometer is supposed to be looking for. ARA-290 is an eleven-amino-acid chain engineered to mimic the solvent-exposed spatial configuration of a specific section of a parent glycoprotein. But unlike that massive parent protein with its complex glycosylation and disulfide bridges, ARA-290 is a discrete synthetic fragment. Its primary sequence is defined as pGlu-Glu-Gln-Leu-Glu-Arg-Ala-Leu-Asn-Ser-Ser.

The defining feature of this sequence is right at the start. The N-terminus is capped by a pyroglutamate residue, often written as pGlu or Pyr. This is not a standard building block pulled off a shelf. It is formed by an intramolecular dehydration reaction where an N-terminal glutamine or glutamic acid closes its nitrogen into a pyrrolidone ring. This little ring changes everything about how the molecule behaves in an analytical laboratory.

Because the N-terminus is cyclised, the peptide lacks a free primary amine at the first position. If you send a sample of ARA-290 to a sequencing lab asking for a classic Edman degradation, they will return a blank report. The reagent cannot attach to a closed ring. Without that free amine, the peptide will not turn purple in a standard ninhydrin colour test. This "N-terminally blocked" structure is the reason why identity verification relies entirely on advanced mass spectrometry. If a seller provides a certificate claiming they chemically sequenced the sequence residue by residue, they are simply bluffing.

The empirical molecular formula for the free base of ARA-290 is C51H84N16O21, carrying an average molecular weight of 1257.3 g/mol PubChem. This number is the anchor point for every legitimate certificate of analysis.

Mass spectrometry must establish that the dominant peak in the vial matches this theoretical mass. When looking at a mass spectrum, you are checking whether the synthesis machinery did its job. The formation of the pyroglutamate ring requires the loss of a small molecule, typically water, which weighs about 18 Daltons. If the N-terminal residue fails to undergo this intramolecular cyclisation during synthesis or when cleaved with TFA, the resulting chain remains open. An open-ring peptide has a mass of 1275.3 g/mol. A certificate showing a dominant peak at 1275 Daltons is not demonstrating an acceptable margin of error; it is describing a different molecule representing a process impurity.

The mass spectrometer evaluates the observed mass-to-charge ratio. In positive ion mode, a clean sample typically presents the singly charged ion near 1257.6 and the doubly charged ion near 629.3. If those numbers are missing from the report, the document is nothing more than decoration.

Laboratory ARA-290 is manufactured using solid-phase peptide synthesis, where amino acids are coupled sequentially onto a resin support Advances in Fmoc solid-phase peptide synthesis. Following synthesis, cleavage and purification, the peptide is supplied as a white lyophilised powder. It looks uniform and static in the vial, but the freeze-drying step is a controlled process.

The liquid solution is frozen and subjected to a deep vacuum, allowing the ice to sublimate directly into vapour without passing through a liquid phase. This primary and secondary drying determines the residual moisture left in the solid cake Design of freeze-drying processes for pharmaceuticals: practical advice. Residual moisture is not just a storage concern; it directly impacts the net peptide mass. A vial containing 10 milligrams of solid material never contains 10 milligrams of the pure ARA-290 sequence.

Synthesised peptides are recovered as salts to ensure solubility. Because the single arginine residue provides a basic site, ARA-290 is usually supplied as a trifluoroacetate or acetate salt. When you weigh the powder to prepare a molar solution, the mass includes the peptide, the counterions and the bound water. The actual net peptide content typically hovers between 70 percent and 85 percent of the total powder mass. Nitrogen determination or amino acid analysis is required to correct for this weight when precision is the goal.

While mass spectrometry confirms identity, high-performance liquid chromatography determines purity. A chromatogram is a race where every synthesis truncation, deletion sequence and degradation product has to cross the finish line in public. Reversed-phase chromatography separates these molecules based on their interaction with a stationary phase, usually under an acetonitrile and water gradient HPLC analysis and purification of peptides.

ARA-290 presents a unique challenge for standard chromatography. The sequence contains no aromatic amino acids like tryptophan or phenylalanine. As a result, it does not absorb ultraviolet light at the common 280-nanometre wavelength. An analyst running the column must evaluate purity by reading the absorbance of the peptide bonds themselves, typically monitored at 210 to 215 nanometres. If a vendor supplies a chromatogram tracked only at 280 nanometres, they are measuring a flat line and calling it perfect purity.

For demanding laboratory applications, purity specifications are defined. The independent testing for NuuVive's ARA-290 verified the material at ≥99% purity (99.822%, Janoshik #110953) with a measured amount of 11.00 mg of solid material in the vial. You can verify the current lot specification, third-party lab reports and pricing directly on the ARA-290 catalogue page.

1. HPLC analysis and purification of peptides (Methods in Molecular Biology 386). Springer
2. Advances in Fmoc solid-phase peptide synthesis (Journal of Peptide Science). Wiley
3. Design of freeze-drying processes for pharmaceuticals: practical advice (Pharmaceutical Research). Springer
4. nih.gov. National Library of Medicine