Pentapeptide-18 (Leuphasyl)

1 Identity

Cosmetic pentapeptide containing a D-amino acid. A synthetic linear pentapeptide with a free N-terminal alpha-amino group and a free C-terminal carboxylic acid, no acylation, no amidation, no cyclization, no disulfide and no metal, in which the second residue is D-alanine — a non-L residue, which is the whole reason this record sits on panel P3 and not on P1. One tyrosine and one phenylalanine give it a genuine aromatic chromophore, which is unusual in this cosmetic block and useful analytically. Sold as a topical bulk cosmetic ingredient and laboratory raw material. Structurally related and not synonyms, each a separate article with a separate mass: Leu-enkephalin (Tyr-Gly-Gly-Phe-Leu).

Sequence

H-L-Tyr-D-Ala-Gly-L-Phe-L-Leu-OH. Free N-terminal alpha-amino group, free C-terminal carboxylic acid; no acetylation, no amidation, no cyclization, no disulfide. Residue 2 is D-alanine; glycine at position 3 is achiral; Tyr1, Phe4 and Leu5 are L. The configuration is the identity. The all-L peptide, the D-Ala2 peptide of this specification and the D-Ala2/D-Leu5 peptide (DADLE) all carry the identical formula C29H39N5O7 and the identical 569.28495 monoisotopic mass, so mass spectrometry at any resolution establishes nothing whatever about stereochemistry; a chiral method is therefore the load-bearing identity test on this article and not a supplementary one, and P3 is the panel that proves a D-residue. The D-Ala2 assignment rests on ingredient-database and registry documentation, no institutional supplier publishes a formula under the INCI name, and no authenticated standard has been located, so the assignment is derived rather than confirmed and remains a supplier claim until it is proved on the first lot.

Molecular formula

C29H39N5O7 as the free peptide. As the 1:1 acetate salt the formula unit is C31H43N5O9 at 629.711; as the 1:1 trifluoroacetate, C31H40F3N5O9 at 683.681. The counterion is not folded into the identity and is specified as a percentage range.

Average mass

569.659 Da (C29H39N5O7), on IUPAC 2021 abridged conventional atomic weights (C 12.011, H 1.008, N 14.007, O 15.999) from the formula and independently reconstructed residue-by-residue from Tyr-Ala-Gly-Phe-Leu; the two routes agree to the digit. The arithmetic that matters on this shelf: Leu-enkephalin (YGGFL) is C28H37N5O7 at 555.632 — exactly 14.03 Da, one methylene, below this article, and it is the cheaper and far more widely available peptide; dalargin (YAGFLR) is C35H51N9O8 at 725.848, exactly 156.19 Da above. No cosmetic-ingredient document and no supplier document located for this article publishes a verified mass, so the figure printed here is built from the formula and reconstructed from the residues.

Monoisotopic mass

569.28495 Da neutral (C29H39N5O7); [M+H]+ 570.29223; [M+2H]2+ m/z 285.64975; [M-H]- 569.27767. Identity window on [M+H]+ at plus or minus 5 ppm is plus or minus 0.0029 Da. Leu-enkephalin 555.26930 neutral, [M+H]+ 556.27658. Dalargin 725.38606 neutral. The C-terminal amide is 568.30093 neutral, 0.984 Da below parent. DADLE, the D-Leu5 diastereomer, is 569.28495 — identical to the digit, at every resolution, forever.

Salt / variant note

(1) the stereochemical axis, and it is invisible to mass at any resolution and at any accuracy. All-L Tyr-Ala-Gly-Phe-Leu, the D-Ala2 article of this specification, and DADLE (D-Ala2, D-Leu5) all carry C29H39N5O7 and 569.28495 monoisotopic. So does every other epimer of the four chiral residues — sixteen diastereomers, one mass. Only a validated chiral method, or co-elution against an authenticated D-Ala2 standard, separates them, and a certificate whose identity section is a mass has established nothing about this article at all. (2) LEU-ENKEPHALIN (YGGFL), C28H37N5O7, 555.632 / 555.26930, [M+H]+ 556.27658 — exactly 14.03 Da light, the des-methyl parent, cheap, widely stocked and the obvious substitution; it is also the all-L peptide and therefore fails nothing that a chiral method is not run to catch. (3) DALARGIN (YAGFLR), C35H51N9O8, 725.848 / 725.38606 — this sequence plus a C-terminal Arg, 156.19 Da heavy, and the article this one is described in the trade as a shortened analog of. (4) MET-ENKEPHALIN (YGGFM), C27H35N5O7S, 573.665 / 573.22572 — 4.0 Da heavy of this article at nominal mass and easily confused on a low-resolution document. (5) C-terminal amide C29H40N6O6, 568.675 / 568.30093 — 0.984 Da below the free acid, unresolved below about 30,000 resolving power, and a genuinely different article in the enkephalin trade. (6) tyrosine degradants: oxidation at plus 15.995 Da, and dityrosine crosslinking on light exposure; the phenol is the photolabile center. (7) salt axis: 1:1 acetate formula unit 629.711 against 1:1 trifluoroacetate 683.681 — a 9.6 percent content difference, and trifluoroacetate is refused. (8) same-shelf cosmetic articles offered at the same 200 mg size and at the same list price: Vialox (pentapeptide-3), Syn-AKE, Syn-Coll (palmitoyl tripeptide-5, 611.913), Pal-GHK (578.799), Pal-AHK (592.826), palmitoyl tetrapeptide-7 (694.919), AHK-Cu, Nonapeptide-1, Decapeptide-12 and "Lipopeptide" — the last of which is not an identity at all but a structural class.

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.

No compound-specific primary literature has been located for this article under its own INCI name — in vitro, animal or human — across cosmeceutical peptide reviews, Cosmetic Ingredient Review safety assessments and targeted INCI-name searching, and the eleven-ingredient group grades F on that basis. One commercial claim is worth stating with its status: the assertion that this ingredient is synergistic with acetyl hexapeptide-8 is a testable pharmacological claim requiring a factorial design, no such study has been retrieved, and the claim appears to originate in supplier literature. Class-level citations, kept separate on the catalog page and belonging to other molecules: Kraeling et al., Cutan Ocul Toxicol 2015, PMID 24754410, in vitro, excised human cadaver and hairless guinea pig skin, the only rigorous human-skin penetration study of a peptide in this class; Choi et al., Biomol Ther 2014, PMID 25143811, in vitro, hairless mouse skin; Imhof and Leuthard, Dermatology 2021, PMID 32882685, systematic review of over-the-counter topical antiaging agents; Chen et al., World J Clin Cases 2021, PMID 33748252, case report on injection of a cosmetic peptide. Separately, and not to be conflated with the INCI-name literature: a large mid-twentieth-century neuroscience literature exists on enkephalin analogs under their chemical names; the INCI name and the chemical name address two different supplier markets and two different literatures, and that body of work is not enumerated on this page. No human trial of this article has been located and no NCT number is quoted because none was found. No Cosmetic Ingredient Review safety assessment for this specific ingredient has been located, in searching that did return such assessments for other peptide ingredients. Literature volume by study type is printed at the head of the research page.

4 Storage & specification

Storage

White to off-white lyophilized powder, acetate salt, in amber glass with a nitrogen headspace and a desiccant sachet; non-sterile, no sterility claim, no stoppered-and-crimped injection format, no dose-shaped vial. 2-8 degrees C, protected from light and moisture. Amber glass is a specification item and not a packaging preference on this molecule: the tyrosine phenol is the photolabile center and dityrosine crosslinking is a light-driven degradation pathway, so a clear vial on a bench under fluorescent light is a stability excursion that no thermometer records. The jar is equilibrated to room temperature sealed before opening. Shipped ambient with a temperature-excursion indicator; excursions to 25 degrees C for up to 14 days cumulative are accepted against the stability protocol and recorded on the lot record. Unlike the palmitoylated articles on the same shelf, this peptide is water-soluble and needs no co-solvent, which is a handling fact and nothing more.

Shelf life

The retest interval is 24 months at 2-8 degrees C and 36 months at -20 degrees C plus or minus 5 degrees C for the retained reference portion, supported by this company's own ICH Q1A-format study on three production lots — long-term at 5 degrees C plus or minus 3 degrees C, accelerated at 25 degrees C and 60 percent RH, and photostability under ICH Q1B option 2 because the phenol is the identified labile center. The stability-indicating attributes are the tyrosine oxidation product at plus 15.995 Da and dityrosine species, tracked on the 275-280 nm channel, together with chiral purity at ALA2, which is trended on stability and not only at release: base-catalyzed epimerization is slow but real on a peptide whose identity is a single D-center. The interval is shortened on data and never extended without a completed dataset.