FOXO4-DRI — also sold under the name Proxofim — is by a wide margin the most structurally unusual peptide in a typical research catalogue. This article explains what the designation means, what the material is, and why almost every analytical shortcut that works on an ordinary peptide fails on this one. It makes no claim about what the compound does and contains no preparation, handling or dosing guidance.
What the name encodes
“DRI” stands for D-retro-inverso, and unlike most peptide trade names this one is genuinely informative. A retro-inverso peptide is built by two simultaneous inversions of a parent sequence: the residue order is reversed, and every residue is switched from the L to the D enantiomer. The result is a molecule whose side chains sit in approximately the same spatial arrangement as the parent while the backbone runs the other way.
FOXO4-DRI is a 46-residue peptide built entirely from D-amino acids, with an average mass of approximately 5,358 g/mol. That makes it an order of magnitude larger than the short bioregulator peptides and roughly four times the size of a decapeptide like Gonadorelin.
Two segments, not one
The sequence is functionally two pieces joined together. The first stretch is derived from a FOXO4 interaction motif; the tail is a highly basic arginine- and lysine-rich stretch of the kind used as a cell-penetrating carrier. That basic tail dominates the physical chemistry of the whole molecule and is the single most important fact for anyone reading an analysis of it.
Why the analysis is harder than for an ordinary peptide
Chromatography is dominated by the basic tail. A long run of arginines and lysines interacts strongly with residual silanols and depends heavily on ion-pairing additive for a usable peak shape. Broad or tailing peaks are common and are frequently a method artefact rather than a purity finding. Column choice matters more here than almost anywhere else in a peptide catalogue.
Counter-ion load is enormous. Every basic side chain can carry a counter-ion. On a peptide with this many of them, trifluoroacetate can account for a substantial fraction of the mass of the powder in the vial. This is the compound where the difference between “98% pure by HPLC” and net peptide content is at its most severe, and buying on the purity figure alone will systematically mislead you about how much peptide you have.
Routine chirality checks do not apply. Standard amino-acid analysis after hydrolysis will return the expected composition whether the residues are L or D. Confirming that a material is genuinely all-D requires chiral analysis, which is not part of a routine certificate. A supplier claiming DRI material without a method that could distinguish it is claiming something their data does not establish — and since an all-L peptide of the same composition would show the same mass and a similar amino-acid analysis, this is not a theoretical concern.
Mass alone does not separate retro from parent. A retro-inverso peptide and its parent sequence are composed of the same residues, so they share a molecular formula and a nominal mass. Mass spectrometry confirms composition here; it does not confirm the isomer.
Naming
FOXO4-DRI, FOXO4 D-retro-inverso and Proxofim all refer to the same construct in catalogue usage. Note that some listings render the name with a zero — “FOX04” — which is a transcription error rather than a different compound, though it does mean search results for the two spellings will not overlap.
What an analysis should show
Column chemistry and dimensions, mobile phase and gradient with the ion-pairing additive named, detection wavelength, retention time, integrated peak area with a visible integration window, and a mass confirmation near 5,358 g/mol. Reported separately: net peptide content and the declared counter-ion form. On this compound, treat net peptide content as the number that tells you what you bought.
How FOXO4-DRI is supplied here
FOXO4-DRI 10mg is supplied as a lyophilised powder in a sealed vial, with an independent reverse-phase HPLC analysis published on the product page alongside net peptide content, counter-ion form and vial size. Vials carry no batch or lot numbers and are matched to their published test by crimp and cap colour.
Frequently asked questions
Is Proxofim the same thing as FOXO4-DRI?
Yes. Proxofim is a trade name for the same D-retro-inverso construct.
How many amino acids is FOXO4-DRI?
46 residues, all in the D configuration, with an average mass of about 5,358 g/mol.
What does D-retro-inverso mean?
The parent sequence is reversed in order and every residue is replaced by its D enantiomer, which approximately preserves the spatial arrangement of the side chains while reversing the backbone direction.
Can a certificate of analysis prove the peptide is all-D?
Not a routine one. Mass and standard amino-acid analysis cannot distinguish D from L. Establishing chirality requires a chiral method, and it is fair to ask a supplier whether they have run one.
Why is the net peptide content so much lower than the purity figure?
Because the sequence carries a large number of basic residues, each capable of binding a counter-ion. On a heavily basic peptide the counter-ion is a large share of the powder mass, which is exactly why the two numbers must be reported separately.
Research use only. All products supplied by Battle Born Peptides are laboratory reference materials for in-vitro research and analytical use by qualified professionals. They are not drugs, foods, dietary supplements, cosmetics or medical devices; they are not approved by the FDA or any other regulator for use in humans or animals; and they are not intended to diagnose, treat, cure, mitigate or prevent any disease, or to affect the structure or any function of the body of humans or animals. Nothing in this article is preparation, handling or dosing guidance. See our full research-use terms.