DSIP: structure and analysis

What is DSIP?

DSIP is a nonapeptide — a nine-amino-acid sequence — first isolated from mammalian brain tissue and produced synthetically here. The name records the context in which it was originally identified rather than describing a property of the material.

It is a short, highly polar sequence with several acidic residues, which governs how it behaves chromatographically.

How is DSIP 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.

What are the molecular figures for DSIP?

Calculated from the formula C35H48N10O15, not measured. The average molecular weight counts the natural abundance of each element's isotopes; the monoisotopic mass is the mass of the single most abundant isotopic composition, which is the figure a mass spectrometer is usually compared against.

The expected ions follow from the monoisotopic mass by adding one proton per charge. They are a starting point for recognising a spectrum, not a substitute for one: adducts, salts, modifications and multiply charged species all move the observed m/z, and the certificate reports what was actually measured for a batch.

Adducts, salts, modifications and multiply charged species all move an observed m/z away from any figure calculated here, and a certificate reports what was measured for a batch rather than what was expected of it.

What is the sequence of DSIP?

DSIP is 9 residues long. Written in the one-letter amino-acid code, as the cited record states it:

The sequence is what an identity test resolves. The mass a spectrometer is compared against is the mass this chain implies, which is why a single missing or substituted residue changes the result by an amount that cannot be mistaken for instrument variation — the deletion is detectable rather than invisible.

Sequence information describes the molecule, not the material in a vial. What establishes a specific batch is the identity method and result on its certificate.

How does DSIP compare with related compounds?

Related compounds are not interchangeable. Published figures differ between them, and in this catalogue three compounds share a GHRH backbone while several share the same structural class — which is exactly why identity is confirmed analytically rather than inferred from the label.

How is the identity of DSIP confirmed?

Mass spectrometry confirms the nine-residue chain. At this length the expected mass is small enough that high-resolution measurement gives a tight confirmation, and a single deletion is a large proportional change.

Which impurities can appear in DSIP?

Short, acidic and polar peptides are weakly retained under standard reversed-phase conditions, so a method developed for longer hydrophobic sequences will not resolve this one adequately. The gradient and ion-pairing conditions have to suit the molecule.

Purity figures for short polar peptides are therefore particularly method-dependent, which is why the method belongs on the certificate alongside the number.

What does a certificate of analysis for DSIP report?

A certificate for a batch of this material names the batch, 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 batch, not to a product line. When a new batch is released it is tested again, and the certificate published against it is that batch's certificate — a previous batch's result is never carried forward.

Is DSIP for human use?

No. 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.

References

• Delta sleep-inducing peptide — PubChem, National Library of Medicine
• Emideltide — ChEMBL, European Bioinformatics Institute
• Characterization, properties and multivariate functions of delta-sleep-inducing peptide (DSIP) — Eur Neurol, 1984