Pentapeptide-18 (Leuphasyl)

Sequence and stereochemistry

Pentapeptide-18 uses the Tyr-D-Ala-Gly-Phe-Leu sequence associated with [D-Ala2]leucine-enkephalin. The D-alanine changes protease susceptibility and conformation, so an all-L sequence is not an equivalent control. Identity documentation should preserve stereochemistry rather than reducing the sequence to the one-letter string YAGFL. Confirming the configuration takes a chiral method: routine amino acid analysis after acid hydrolysis reports alanine without telling you which enantiomer it was, unless a chiral derivatising agent is used. Enkephalins are endogenous opioid peptides described in the pharmacology literature as acting at delta- and mu-opioid receptors, and structure–activity work identifies the N-terminal tyrosine as central to that recognition, which is a practical reason to protect the free amine and the phenol from oxidation and from incidental derivatisation.

Research context

Comparison panel

• Argireline and SNAP-8 as SNARE-complex-related sequence analogs
• Syn-AKE as a diaminobutyroyl benzylamide compound modeled after waglerin research
• Vialox as a GPRPA pentapeptide studied at postsynaptic nicotinic receptors
• Native leucine-enkephalin as the all-L reference point for any stability comparison
• Vehicle-only and cytotoxicity controls to distinguish reduced activity from cell injury
• Time-course measurements to separate immediate signaling changes from longer-term matrix effects

Interpretation

Limits of the evidence

Support for the contraction-associated cosmetic models is thinner than product summaries imply. Much of it originates from supplier-generated work, small uncontrolled panels, or finished formulations in which the individual contribution of the pentapeptide cannot be isolated. Skin is also not a neuromuscular junction, and a hydrophilic five-residue peptide is not expected to cross an intact stratum corneum efficiently, so penetration is something to measure rather than assume. Reporting null results alongside positive markers is what keeps a comparison panel interpretable.

Let the vial reach room temperature before opening, then dissolve the powder with water or a neutral laboratory buffer and mix gently. Protect prepared material from prolonged light because the sequence contains tyrosine and phenylalanine. Record the D-alanine stereochemistry, solvent, pH, lot and preparation date. Store the sealed vial at −20 °C and use refrigerated working solutions within the defined study window; aliquot material needed across multiple sessions.