Cognitive & Neuroprotection

Leu-Enkephalin

Leu-enkephalin is one of the body's two enkephalins — five-amino-acid opioid peptides released to quieten pain signalling — and it prefers the delta opioid receptor rather than the mu receptor that opioid drugs occupy. The interest is analgesia through a different door from morphine's. The human work on file is almost entirely about getting it there rather than about what it does on arrival: an intranasal nanoparticle formulation completed a study with no moderate or severe adverse events, and a gene-therapy approach reached Phase I. Most of its graded citations are chemistry, synthesis routes and stability assays, which is an accurate picture of where the effort has gone.

Last updated 12 August 2026

Studied forAnalgesia research · Mood and stress signalling · Opioid receptor pharmacology

Evidence on file2 animal studies · 4 in-vitro studies

Strongest sourceMet-enkephalin and other opioid peptides in the stress response of chickens: lessons from laboratory animals… (animal study)

Mechanism

Binds delta-opioid receptors preferentially and mu-opioid receptors weakly, inhibiting neuronal signalling through Gi-coupled pathways.

Reported effects

What sources associate with this compound. Reported categories, not outcomes we have graded — each would need its own citation and rung.

Analgesia research
Mood and stress signalling
Opioid receptor pharmacology

Dosing on file unverified

Envelta (nanotechnology delivery): human study completed; Dalargin (leu-enkephalin) in development; No established dose

Carried from a source that labels it unverified, and reproduced with that label attached. A record of what is reported, not a recommendation. No citation on this page establishes it.

Literature on file 6

in vitro
MALDI-induced fragmentation of leucine enkephalin, nitro-Tyr-leucine enkaphalin, and d5-Phe-nitro-Tyr-leucine enkephalin (2009, cited 21x) graded on: an in-vitro system — read from the indexed abstract — “in vitro”
in vitro
pH-induced transition of sponge-phase nanoparticles to micelles: The case of Leu-enkephalin-squalene lipopeptide prodrug. graded on: cell-free physicochemistry of Leu-enkephalin-squalene nanoparticle phase behaviour — read from the abstract — “abstract review”
in vitro
Amidine isosteric modification tunes proteolytic stability and activity. graded on: peptide backbone chemistry with proteolytic-stability assays — read from the abstract — “abstract review”
animal in vivo
Met-enkephalin and other opioid peptides in the stress response of chickens: lessons from laboratory animals and livestock. graded on: an animal model — “chickens”
in vitro
Cyclover-Assisted Liquid-Phase Peptide Synthesis Using T3P® as a Green Coupling Reagent. graded on: liquid-phase peptide synthesis methodology; cell-free chemistry — read from the abstract — “abstract review”
animal in vivo
Cytoprotective Effect of NOP Receptor Blockade in Primary Culture of Pulmonary Fibroblasts. graded on: an animal model — read from the indexed abstract — “rats”

Identity

Space-filling 3D model of Leu-Enkephalin, carbon grey, nitrogen blue, oxygen red — Built from the SMILES on this record — the atoms and bonds are exact. The shape is **one computed low-energy pose**, not a measured structure: a flexible peptide in solution has no single conformation, and where the SMILES leaves a stereocentre undefined the pose commits to one arbitrarily. The skeletal formula below claims connectivity and nothing more, which is what we actually know.

2D chemical structure of Leu-Enkephalin — Built from the SMILES on this record — the atoms and bonds are exact. The shape is **one computed low-energy pose**, not a measured structure: a flexible peptide in solution has no single conformation, and where the SMILES leaves a stereocentre undefined the pose commits to one arbitrarily. The skeletal formula below claims connectivity and nothing more, which is what we actually know.

Molecular weight: 555.6
Molecular formula: C28H37N5O7
CAS number: 58822-25-6
PubChem CID: 461776
UniProt: P01210 (precursor)
InChI key: URLZCHNOLZSCCA-VABKMULXSA-N
SMILES: CC(C)C[C@@H](C(=O)O)NC(=O)[C@H](CC1=CC=CC=C1)NC(=O)CNC(=O)CNC(=O)[C@H](CC2=CC=C(C=C2)O)N
InChI: InChI=1S/C28H37N5O7/c1-17(2)12-23(28(39)40)33-27(38)22(14-18-6-4-3-5-7-18)32-25(36)16-30-24(35)15-31-26(37)21(29)13-19-8-10-20(34)11-9-19/h3-11,17,21-23,34H,12-16,29H2,1-2H3,(H,30,35)(H,31,37)(H,32,36)(H,33,38)(H,39,40)/t21-,22-,23-/m0/s1

Notes unverified prose

Nanomerics completed human study with MET technology; Envelta for pain; no moderate-severe adverse events; Phase I gene therapy trial; Envelta intranasal (nanotechnology); dalargin

Not on file 2

1 of the 8 fields we track hold nothing on this record, and each says why. 1 further absence is named below. A blank field is a bug; a named absence is a finding.

amino-acid sequencenothing we hold supplies it
half-lifenothing we hold supplies it

Each field links to every other record missing the same thing. The full ledger holds 765 gaps across 163 records.