Chemical Structure and Physical Properties of Sepiwhite MSH

Sepiwhite MSH is the trade name used by Seppic for Undecylenoyl Phenylalanine, a lipoamino-acid cosmetic active designed primarily for skin-brightening applications. Seppic lists its INCI name as Undecylenoyl Phenylalanine.

1. Chemical identity

The molecular formula, molecular weight, stereochemistry, and systematic chemical identity are documented in PubChem and the FDA Substance Registration System.

2. Molecular structure

Sepiwhite MSH consists essentially of two structural portions:

• L-phenylalanine portion — provides the amino-acid backbone and phenyl aromatic ring.

• Undecylenoyl portion — a long C11 fatty-acid-derived chain containing a terminal carbon–carbon double bond.

The structure can therefore be viewed as a lipid-modified phenylalanine, which is why it is classified as a lipoamino acid. Seppic describes it specifically as a lipoamino-acid derived from phenylalanine and an α-MSH-antagonist concept.

A simplified structural representation is:

CH₂=CH–(CH₂)₈–CO–NH–CH(CH₂–C₆H₅)–COOH

Its canonical SMILES is:

C=CCCCCCCCCC(=O)N[C@@H](CC1=CC=CC=C1)C(=O)O

The molecule contains one defined stereocenter, corresponding to the L-phenylalanine configuration.

3. Important physicochemical characteristics

Molecular weight: approximately 331.4 g/mol.

Lipophilicity: PubChem reports a calculated XlogP3-AA of approximately 5.2, indicating substantial lipophilic character. This is consistent with its long hydrocarbon chain and aromatic phenyl group.

Hydrogen bonding: the molecule has approximately 2 hydrogen-bond donors and 3 hydrogen-bond acceptors, associated mainly with its carboxylic-acid and amide functionalities.

Topological polar surface area: approximately 66.4 Ų.

Rotatable bonds: approximately 13, reflecting the flexible undecylenoyl chain and other single bonds.

4. Melting point and physical state

Undecylenoyl phenylalanine is reported as a white to off-white crystalline powder, with a melting point around 109–112 °C in commonly reported chemical-property databases.

The relatively high melting point compared with simple fatty acids reflects the presence of the amino-acid/amide portion and its intermolecular interactions.

5. Solubility

Sepiwhite MSH has an unusual amphiphilic character: it combines a lipophilic hydrocarbon/aromatic region with polar amino-acid and amide groups.

Reported behavior includes:

• Poor water solubility under acidic/low-pH conditions

• Greater water compatibility when appropriately ionized at higher pH

• Solubility in certain organic solvents

• Compatibility with some cosmetic solvent systems such as alcohols and propanediol, depending on concentration and formulation conditions.

For formulation work, the pH-dependent ionization of its carboxylic acid is particularly important. A predicted pKa of approximately 3.6 has been reported, although formulation-grade behavior can depend on the actual medium and salt form.

6. Structural features related to cosmetic function

The structure is particularly interesting because it combines:

Long hydrophobic chain → increases lipophilic character and affinity for lipid environments

Phenylalanine aromatic group → contributes hydrophobic and molecular-recognition characteristics

Amide linkage → connects the fatty-acid-derived group to phenylalanine

Carboxylic acid → provides an ionizable polar group

This combination gives Sepiwhite MSH properties quite different from those of unmodified phenylalanine.

Its cosmetic activity is associated with modulation of the α-MSH/melanogenesis pathway, including inhibition of the metabolic activation of tyrosinase according to Seppic. Experimental research has also investigated undecylenoyl phenylalanine as an α-MSH antagonist and skin-brightening compound.

7. Key takeaway

Sepiwhite MSH = Undecylenoyl Phenylalanine (C₂₀H₂₉NO₃, MW ≈331.4 g/mol). It is a lipophilic, chiral lipoamino acid consisting of an L-phenylalanine core chemically acylated with an undecylenoyl chain. Its long hydrocarbon chain gives it considerable lipophilicity, while the amide and carboxylic-acid groups provide polarity and hydrogen-bonding capacity. These structural characteristics are important both for its formulation behavior and its biological interaction with pigmentation pathways.