Dihexa

1 Identity

Peptidomimetic — N-acylated dipeptide bearing a non-proteinogenic omega-amino amide extension; angiotensin IV analog. the PubChem systematic name N-(1-oxohexyl)-L-tyrosyl-N-(6-amino-6-oxohexyl)-L-isoleucinamide.

Sequence

Not a standard peptide sequence and it must not be written as one. The article is a hexanoylated L-Tyr-L-Ile dipeptide core extended at the C-terminus by 6-aminohexanamide: CH3(CH2)4CO-Tyr-Ile-NH-(CH2)5-CONH2. Two peptide bonds are present, plus a third amide at the terminal carboxamide, so the article is a peptidomimetic and not a small molecule, and the non-proteinogenic omega-amino acid is what places it on P3 rather than on any small-molecule panel. Derived by structural truncation from angiotensin IV (Val-Tyr-Ile-His-Pro-Phe) in the Washington State University analog series. Neutral and lipophilic: no free alpha-amino group, no free carboxylate, no disulfide, no metal center, and no salt form in the isolated material. Three stereocenters — the tyrosine alpha-carbon and both the alpha- and beta-carbons of isoleucine — so the isoleucine position alone admits four configurations (L-Ile, D-Ile, L-allo-Ile, D-allo-Ile), and the diastereomeric profile rather than the achiral purity figure is the principal analytical burden.

Molecular formula

C27H44N4O5, and the formula closes by atom count from the structure rather than being accepted from a listing: hexanoyl C6H11O contributes 6 C; the Tyr residue 9 C, 1 N, 2 O; the Ile residue 6 C, 1 N, 1 O; the 6-aminohexanamide tail 6 C, 2 N, 1 O; hydrogens 11 + 9 + 11 + 13. The count closes on C27H44N4O5 independently. PubChem CID 129010512 carries the same formula. No CAS Registry Number could be verified from a primary source, and none is asserted.

Average mass

504.672 Da from C27H44N4O5 on IUPAC 2021 conventional atomic weights. Listings commonly print 504.66 or 504.67; both round the same number and neither is wrong. The article is neutral and unsalted, so unlike most of this catalog the weighed mass and the molecular mass are the same quantity and no net peptide content adjustment applies.

Monoisotopic mass

504.33117 Da neutral. Working ions: [M+H]+ m/z 505.33845, [M+Na]+ m/z 527.32039, [M-H]- m/z 503.32389. A plus or minus 5 ppm window on the neutral is plus or minus 0.0025 Da. Positive mode is the sensible choice on a neutral molecule with three amide nitrogens and no acidic function. Note that accurate mass is worth very little as an identity test on this article: every diastereomer and every regioisomeric alternative to the hexanoyl cap and the aminohexanamide tail is exactly isobaric, which is why the panel demands NMR and why the NMR and chiral requirements are mandatory rather than advisory.

Salt / variant note

The confusable set here is stereochemical and isomeric, not mass-based — every entry below is exactly 504.33117 Da monoisotopic and none is separable by accurate mass. (1) The allo-isoleucine diastereomer, the most likely synthesis defect in this molecule, arising from epimerization at the Ile beta-carbon; identical formula, identical mass, different molecule, and a lot carrying it releases clean on any specification that stops at mass and gross purity. (2) D-Tyr and D-Ile epimers, singly and in combination — eight stereoisomers exist in total across three centers. (3) Regioisomeric acyl caps: any C6 acyl isomer in place of n-hexanoyl (2-methylpentanoyl, 4-methylpentanoyl) is isobaric. (4) Branched-chain alternatives at the aminohexanamide tail, likewise isobaric. (5) Angiotensin IV itself (Val-Tyr-Ile-His-Pro-Phe) and the wider Washington State University analog series, which are the parent chemistry and are separable by mass. (6) Norleucine-for-isoleucine substitution, isobaric again, and a known low-cost synthesis substitution.

2 Class & testing panel

Form

Single article

Testing panel

P3 — panel definition

3 Primary sources & evidence

The index reports the design and provenance of the literature, not a conclusion about effect.

In-vitro and animal literature only, by study type and identifier, with no statement here of what any study reported. Design and characterization: McCoy and colleagues, J Pharmacol Exp Ther 2013, PMID 23055539 — in vitro and rodent. Reagent-substitution use in human pluripotent stem-cell differentiation protocols: Siller and colleagues, Stem Cell Reports 2015, PMID 25937370; Mathapati and colleagues 2016, PMID 27532814; Pan and colleagues, Stem Cell Res Ther 2022, PMID 35410439 — in vitro, human cells. Uribe and colleagues, Front Cell Neurosci 2015, PMID 25674052 — in vitro and zebrafish. Sun and colleagues, Brain Sci 2021, PMID 34827486 — mouse. Wells and colleagues, J Huntingtons Dis 2024, PMID 38489193 — rat. Ho and colleagues, Neurosci Biobehav Rev 2018, PMID 29733881 — systematic review of preclinical studies. RETRACTION, which is the load-bearing fact: Benoist and colleagues, J Pharmacol Exp Ther 2014, PMID 25187433, the foundational mechanistic paper, was the subject of a Notice of Concern in 2021 (PMID 34551987) and was RETRACTED in 2025 (retraction notice PMID 40312093). The reason for retraction is not stated in the PubMed record and could not be verified; the fact of retraction is verified. No registered human trial of this compound was identified. FDA states it has identified no human exposure data by any route. Evidence grade D.

4 Storage & specification

Storage

Off-white amorphous to crystalline solid. Labeled: store at -20 degrees C plus or minus 5 degrees C, desiccated and protected from light, with 2 to 8 degrees C acceptable for working quantities held under 90 days. Both peptide bonds and the terminal carboxamide are hydrolytically robust at neutral pH in the solid state; the tyrosine phenol is the oxidation-sensitive feature and drives the light and headspace requirements.

Shelf life

Assigned at 36 months at -20 degrees C plus or minus 5 degrees C for a neutral amide of this stability class, on a 0/6/12/24/36-month protocol with tyrosine oxidation products as the tracked attribute and the epimeric ratio re-measured at each pull, since the stereochemical profile is the attribute that matters and it is not visible in a purity chromatogram. Each lot is dated from its date of manufacture and carries that retest date on its certificate.