Palmitoyl Tripeptide-38 (Matrixyl Synthe'6)

1 Identity

Acylated cosmetic tripeptide (lipopeptide conjugate) carrying an oxidized sulfur center. A synthetic tripeptide Lys-Met-Lys in which the methionine side-chain thioether is fully oxidized to the sulfone, bearing a single C16:0 palmitoyl group amide-bonded to the N-terminal alpha-amino group. The oxidation state is part of the identity, not a degradation state: this article IS the sulfone, and the sulfoxide and the unoxidized thioether are different molecules with different masses. Sold as a topical bulk cosmetic ingredient and laboratory raw material. and 'Pal-KMO2K' as several ingredient databases render it. Two CAS numbers are in live circulation for this one INCI name: 1447824-23-8, carried by four reagent catalogs, and 1101448-24-1, carried by a general public reference work. Neither is treated here as settled, and the supplier is required to declare in writing which registry record and which sulfur oxidation state a lot corresponds to. 'Matrixyl Synthe'6' is a formulated blend containing this peptide at parts-per-million loading, not a synonym for the neat conjugate, and the same is true of the other trade names in this family.

Sequence

N-hexadecanoyl(palmitoyl)-L-Lys-L-Met(O2)-L-Lys-OH. One C16:0 palmitoyl group amide-bonded to the alpha-amino group of Lys1; the methionine side chain is the sulfone, -CH2CH2-S(=O)2-CH3; free C-terminal carboxylic acid on Lys3; no amidation, no cyclization, no disulfide; all three residues L. Methionine sulfone is a non-proteinogenic residue, which is why this record sits on panel P3 and not on P2 alongside the other palmitoyl cosmetic peptides. The sequence statement is incomplete without two further statements: the oxidation state of the sulfur, and the regiochemistry - there are two lysine epsilon-amines plus the N-terminal alpha-amine, three candidate acylation sites, and the mass distinguishes none of them.

Molecular formula

C33H65N5O7S for the neat conjugate as the sulfone. The sulfoxide is C33H65N5O6S and the unoxidized thioether is C33H65N5O5S; both are sold, both are one or two oxygens from this article, and neither is it. A reader assuming an ordinary methionine computes Pal-Lys-Met-Lys at 643.973, which is a different molecule shipping under the same INCI name. Free tripeptide Lys-Met(O2)-Lys C17H35N5O6S. Carrier dilutions in glycerin/water/hydroxypropyl cyclodextrin have no formula and must not be received against this specification.

Average mass

675.971 Da (C33H65N5O7S) on IUPAC 2021 abridged conventional atomic weights (C 12.011, H 1.008, N 14.007, O 15.999, S 32.06). The oxidation ladder is the whole problem and it is arithmetic: sulfone 675.971, sulfoxide 659.972, unoxidized thioether 643.973 - three articles 16.00 Da apart on one INCI name, and a certificate that prints a mass rounded to the nearest unit still separates them, while a certificate that prints no mass at all does not. For comparison on the same shelf, palmitoyl tripeptide-5 (Pal-KVK) is C33H65N5O5 at 611.913 - the same carbon and hydrogen count, no sulfur, and 64.06 Da below this article. Free tripeptide Lys-Met(O2)-Lys 437.556, exactly 238.42 Da lighter, which is the palmitoyl delta.

Monoisotopic mass

675.46047 Da neutral (C33H65N5O7S); [M+H]+ 676.46775; [M+2H]2+ m/z 338.73751; [M-H]- 675.45319. Identity window on [M+H]+ at plus or minus 5 ppm is plus or minus 0.0034 Da. Sulfoxide 659.46556 neutral, [M+H]+ 660.47284. Unoxidized thioether 643.47064 neutral, [M+H]+ 644.47792. Free tripeptide 437.23080 neutral, [M+H]+ 438.23808. C-terminal amide 674.47645 neutral, 0.984 Da below parent.

Salt / variant note

The oxidation ladder first, because it is the substitution that will actually happen. (1) sulfoxide Pal-Lys-Met(O)-Lys, C33H65N5O6S, 659.972 / 659.46556 - exactly 16.00 Da light, the incomplete-oxidation product of the same synthesis, and chromatographically close. (2) unoxidized thioether Pal-Lys-Met-Lys, C33H65N5O5S, 643.973 / 643.47064 - exactly 32.00 Da light, the cheapest article in the family because it skips the oxidation step entirely. A lot that is a mixture of all three passes a purity assay run at a wavelength that sees none of them. (3) des-palmitoyl free tripeptide Lys-Met(O2)-Lys, C17H35N5O6S, 437.556 / 437.23080 - 238.42 Da light, the incomplete-acylation failure. (4) regioisomers carrying no mass difference: acylation at either lysine epsilon-amine instead of the N-terminal alpha-amine gives the identical C33H65N5O7S and the identical 675.46047, and only MS/MS or co-elution against a qualified standard separates them. (5) DI-palmitoyl over-acylation C49H95N5O8S, 914.386 / 913.69014 - plus 238.42 Da, the other end of the same control failure and a plausible contributor to an out-of-specification content result. (6) C-terminal amide C33H66N6O6S, 674.987 / 674.47645 - 0.984 Da below parent, unresolved below about 30,000 resolving power. (7) nearest shelf-MATE, and the one that matters commercially: palmitoyl tripeptide-5 C33H65N5O5, 611.913 / 611.49857 - identical carbon and hydrogen counts, no sulfur, 64.06 Da below, sold by the same sellers at the same 200 mg size and at a lower price. (8) further same-shelf articles: palmitoyl tripeptide-1 578.799, Pal-AHK 592.826, palmitoyl tetrapeptide-7 694.919, palmitoyl pentapeptide-4 802.068. (9) name and presentation axis, the dominant real-world error: 'Matrixyl Synthe'6' is a formulated blend at parts-per-million peptide loading, not the neat conjugate, and a certificate for the blend presented against an order for neat peptide states no peptide loading at all. (10) registry axis: CAS 1447824-23-8 against CAS 1101448-24-1 on one INCI name, unreconciled, and no authenticated reference standard for this article has been located.

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 name - in vitro, animal or human - in cosmeceutical peptide reviews, in Cosmetic Ingredient Review safety assessments or in targeted searches on the INCI name. The governing point for this family is that 'Matrixyl 3000' and 'Matrixyl Synthe'6' are different commercial blends containing other peptides, including palmitoyl tripeptide-38, and are not interchangeable with pal-KTTKS - which means the human trial that exists in this family, Robinson et al., Int J Cosmet Sci 2005, PMID 18492182, a 93-subject 12-week double-blind placebo-controlled split-face randomized controlled trial, attaches to palmitoyl pentapeptide-4 and not to this molecule. Class-level citations kept separate on this page: Kraeling et al., PMID 24754410, in vitro excised human cadaver and hairless guinea pig skin; Choi et al., PMID 25143811, in vitro hairless mouse skin; Imhof and Leuthard, PMID 32882685, systematic review; Wang et al., PMID 39783908, solubility and delivery of palmitoylated cosmetic peptides; Chen et al., PMID 33748252, injection case report. No human trial of this article has been located and no registry number is quoted because none was found - an absence of located evidence rather than a demonstration that none exists. Literature volume by study type is printed at the head of the research page.

4 Storage & specification

Storage

Off-white to pale-tan lyophilized powder or friable waxy solid, acetate salt, packed in amber glass with a nitrogen headspace and a desiccant sachet; non-sterile, no sterility claim, no stoppered-and-crimped format. 2-8 degrees C, protected from light and moisture, with the jar equilibrated to room temperature sealed before opening so that atmospheric moisture does not condense onto a hygroscopic di-lysine powder. Nitrogen overlay after each withdrawal is a specification item and not a packaging preference, for a reason specific to this molecule: the sulfur center is already at its highest oxidation state, so the article cannot oxidize further, but the sulfoxide and thioether impurities can, which means the impurity profile of a partially oxidized lot moves under air while the main peak does not. Shipped ambient with a temperature-excursion indicator; excursions to 25 degrees C for up to 14 days cumulative are accepted against the stability protocol.

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 and accelerated at 25 degrees C / 60 percent RH. The stability-indicating attributes are free palmitic acid, des-palmitoyl free tripeptide, and the sulfoxide-to-sulfone ratio tracked as a pair rather than as a single number - the main peak is already fully oxidized and will not move, so a stability program that trends only assay will report a stable article while its impurity profile changes underneath. The interval is shortened on data and never extended without a completed dataset.