DALDA

DALDA is the first four residues of dermorphin rebuilt with D-arginine at position 2 and lysine at position 4, giving a compact tetrapeptide with a net +3 charge. That charge makes it extremely hydrophilic and a poor blood-brain-barrier substrate, so systemically it behaves as a peripherally restricted mu agonist — of interest historically as a way to get opioid analgesia without central reward or respiratory depression. Replacing the N-terminal tyrosine with 2,6-dimethyltyrosine gives DMT-DALDA, which is orders of magnitude more potent and, unexpectedly, penetrates cells and mitochondria. That cell-penetrating cationic tetrapeptide observation is the direct lineage of the Szeto-Schiller peptides: SS-31 (elamipretide) is a DALDA-derived analogue with the opioid pharmacophore deliberately removed. So DALDA's real modern significance is chemical ancestry rather than analgesia.

Targets: Mu opioid receptor (OPRM1), peripheral terminals, Cardiolipin and inner mitochondrial membrane (for the Dmt1 analogues)

• · DALDA has never been dosed in humans outside of research settings and no dose-finding exists. Animal work uses mg/kg intrathecal and systemic doses that do not translate.

Work out your exact syringe units →

• commonConstipation and GI slowing— Peripheral mu agonism hits gut receptors directly.
• commonPruritus and histamine release— Cationic peptides are prone to mast-cell degranulation.
• commonTolerance with repeated dosing— Seen in animal models.
• uncommonRespiratory depression at high systemic exposure— Lower risk than dermorphin because of poor CNS entry, but 'peripherally restricted' is a matter of degree, not an absolute.

• Concurrent opioids or CNS depressants — the peripheral restriction is incomplete and the risk is additive.
• Any expectation of a documented human safety profile; there isn't one.

• redundantdermorphin — Same family, same receptor, same risk; there is no reason to combine them.
• cautionss-31 — SS-31 is a DALDA-derived analogue built to remove opioid activity; running both re-adds the opioid pharmacology that SS-31 was designed to shed.

• · No human monitoring protocol exists. In any research context the relevant measures are respiratory rate, GI transit and evidence of tolerance.

Not approved anywhere; sold only as a research chemical. Its mu-agonist activity raises the same controlled-substance analogue questions as any potent opioid peptide.

• Schiller et al., DALDA and DMT-DALDA — highly selective mu opioid peptide agonists (preclinical)
• Zhao, Szeto et al., cell-permeable cationic tetrapeptides derived from DMT-DALDA (preclinical)

DALDA is best understood as a deliberate experiment in charge. Take the first four residues of dermorphin, put D-arginine at position 2 for protease resistance, put lysine at position 4, amidate the C-terminus, and you have a tetrapeptide carrying roughly +3 net charge. At the mu receptor it remains a highly selective, highly potent agonist — the pharmacophore is intact. But a +3 peptide has no passive route across the blood-brain barrier, and Szeto's sheep work confirmed the consequence directly: the apparent volume of distribution was only 50 to 80 mL/kg, essentially confined to the blood compartment, with minimal CNS entry. So systemically DALDA behaves as a peripherally restricted mu agonist. That was the point — peripheral opioid analgesia without central reward or respiratory depression, the same logical move difelikefalin later made successfully at the kappa receptor. Given intrathecally, where the barrier is bypassed, the same molecules are reported to be roughly three thousand times more potent than morphine, which tells you the receptor pharmacology was never the limitation. The scientifically important part came from an accident. Replacing the N-terminal Tyr with 2,6-dimethyltyrosine to boost potency produced [Dmt1]DALDA, and that compound turned out to penetrate cells and to concentrate in mitochondria, associating with cardiolipin in the inner membrane — behaviour nobody designed for and nobody predicted from an opioid peptide. Szeto and Schiller followed the cell-penetrating property rather than the opioid one, systematically stripped the opioid pharmacophore out, and arrived at SS-31 (elamipretide), a cardiolipin-binding mitochondrial peptide with no opioid activity that has been through multiple clinical trials in mitochondrial myopathy, Barth syndrome and geographic atrophy. That is DALDA's actual significance. It is not an analgesic that failed to be developed; it is the chemical ancestor of an entirely different drug class, and the alternating-cationic-aromatic motif that makes SS-31 work is DALDA's motif.

The framing error is what goes wrong first. People encounter DALDA through the SS-31 lineage, conclude it is a mitochondrial peptide, and dose it accordingly — but DALDA is the opioid ancestor, not the mitochondrial descendant, and it retains full mu agonist activity that SS-31 was specifically engineered to lack. The second error is trusting 'peripherally restricted' as a safety guarantee. Szeto's sheep data shows an apparent volume of distribution confined to blood, which is genuinely reassuring at ordinary exposures, but exclusion by charge is a gradient rather than a wall and there is no human dose above which it fails, because there is no human dose at all. Third, animal work uses mg/kg intrathecal and systemic dosing, and there is no valid arithmetic that converts an intrathecal rodent mg/kg into a human subcutaneous dose — a compound reported as three thousand times morphine's potency intrathecally is not a compound to estimate on. Fourth, constipation and GI slowing are close to guaranteed rather than possible, because peripheral restriction means the gut receptors get proportionally more drug than they would with a centrally acting opioid. And fifth, as with every potent mu agonist peptide, the 'research chemical' label does not answer the legal question; mu agonist activity raises controlled-substance analogue issues in multiple jurisdictions.

• Mu opioid receptor (OPRM1), predominantly peripheral terminals — High and highly mu-selective. Specific Ki values are published in the Schiller group's medicinal chemistry papers but I did not resolve a primary source in this session, so no number is asserted here.

  Full agonism with standard Gi/Go coupling. Reported as roughly three thousand times more potent than morphine when administered intrathecally, where the blood-brain barrier is not a factor — which shows the peripheral restriction is a delivery property, not a potency limitation.

• Blood-brain barrier — exclusion by charge — Not a target, a constraint. Szeto's sheep pharmacokinetics found an apparent volume of distribution of 50-80 mL/kg, essentially blood volume.

  Minimal CNS entry after systemic dosing. This is the designed feature: peripheral mu analgesia with limited central effect. 'Peripherally restricted' is a matter of degree, though, not an absolute, and at high systemic exposure central effects including respiratory depression become possible.

• Cardiolipin and the inner mitochondrial membrane — for [Dmt1]DALDA specifically — Not receptor-mediated. Association with the anionic phospholipid cardiolipin, driven by the alternating cationic-aromatic motif.

  Mitochondrial accumulation, stabilisation of cristae architecture and reduction of oxidative damage. This property, not the opioid activity, is what was carried forward into SS-31 / elamipretide.

• Gut mu opioid receptors — Directly accessible — peripheral restriction means the gut gets a relatively larger share of the dose.

  Constipation and slowed GI transit. The predictable price of peripheral mu agonism, and the reason peripherally restricted mu agonists never became useful analgesics while peripherally restricted mu antagonists (methylnaltrexone, naloxegol) became useful laxatives.

Rapid after parenteral dosing in animal models, with a terminal half-life of roughly 1.5 hours in sheep — genuinely longer-lived than dermorphin or the native opioid peptides, which is the practical payoff of the D-Arg and C-terminal amide. Clinically this is unanswerable: no human has been dosed in a published study, so onset, peak effect and duration in a person are unknown.

There is no human stack for DALDA because there is no human dose. The pharmacologically meaningful notes are two. First, combining DALDA with any CNS depressant is the same additive respiratory hazard as with any mu agonist — the peripheral restriction reduces central exposure, it does not eliminate it, and 'mostly peripheral' becomes 'partly central' at high systemic doses. Second, and more specific to this compound: running DALDA alongside SS-31 / elamipretide is self-defeating in a precise way. SS-31 is a DALDA-derived analogue from which the opioid pharmacophore was deliberately removed, because the whole point was to keep the mitochondrial targeting and lose the opioid activity. Adding DALDA back puts the opioid pharmacology into a stack that was designed to be free of it, which means constipation, tolerance and respiratory risk in exchange for nothing SS-31 was not already providing. Stacking with dermorphin or the endomorphins is redundant — same receptor, no added mechanism, multiplied risk.

Put DALDA next to difelikefalin and you have the same idea separated by thirty years and a development programme. Both are all- or partly-D-amino-acid peptides deliberately made too charged to enter the brain, so that opioid receptor agonism can be harvested peripherally without central side effects. DALDA did it at mu in the 1990s and never got a human dose; difelikefalin did it at kappa in the 2010s and got FDA approval. The difference is not mechanistic elegance — DALDA's is arguably more elegant — it is that peripheral mu agonism turns out not to be a very useful analgesic (most opioid analgesia is central, and what you get peripherally is mainly constipation), whereas peripheral kappa agonism turns out to be a genuinely useful antipruritic. That is a lesson about target choice, not about chemistry. Against SS-31 / elamipretide, DALDA is the ancestor: same cationic-aromatic scaffold, opposite design intent. And against dermorphin, DALDA is the truncated, charge-modified descendant — first four residues only, D-Arg instead of D-Ala, engineered to stay out of the brain rather than to get into it. Understanding DALDA is mostly useful as a way of understanding the two much more important molecules on either side of it.

Deliberately not priced. DALDA is a research reagent sold in milligram quantities for laboratory use. There is no human protocol, so a monthly cost would imply a dosing pattern that does not exist.

• ?No human pharmacokinetics, no human dosing and no human safety data exist. Everything in the pharmacokinetics section here comes from sheep.
• ?No Ki values at mu, delta or kappa are asserted, because I did not resolve a primary source for the Schiller group's binding data in this session.
• ?The 'three thousand times more potent than morphine' figure applies to intrathecal administration in animals and comes from the Szeto 2001 abstract; it does not translate to any systemic route or to humans.
• ?The molecular formula C30H45N9O5 and weight of approximately 611.7 Da were derived by composition arithmetic from the sequence and cross-checked against the Core record; I was unable to retrieve a PubChem record for DALDA under that name in this session.
• ?Protein binding, human half-life, human volume of distribution and bioavailability by any route are all genuinely uncharacterised.
• ?Whether tolerance develops at the same rate as with centrally acting mu agonists is unknown; it is reported in animal models but not quantified.

• In vivo pharmacokinetics of selective mu-opioid peptide agonists Szeto HH, Lovelace JL, Fridland G, et al., Journal of Pharmacology and Experimental Therapeutics, 2001 · PMID 11408525

  The one real pharmacokinetic dataset for this molecule. Sheep, intravenous: DALDA terminal half-life about 1.5 hours, [Dmt1]DALDA about 1.8 hours, clearance around 24 mL/kg/h (roughly ten-fold slower than DAMGO), apparent volume of distribution 50-80 mL/kg indicating confinement to the blood compartment. Also the source of the observation that these peptides are around three thousand times more potent than morphine intrathecally.

• Cell-permeable peptide antioxidants targeted to inner mitochondrial membrane inhibit mitochondrial swelling, oxidative cell death, and reperfusion injury Zhao K, Zhao GM, Wu D, et al., Journal of Biological Chemistry, 2004 · PMID 15178689

  The paper where the DALDA scaffold becomes something else entirely. This is the origin of the Szeto-Schiller mitochondrial peptides and therefore of SS-31 / elamipretide. If you want to understand why DALDA matters, this is the citation, not any of the analgesia work.

• Differential analgesic effects of a mu-opioid peptide, [Dmt(1)]DALDA, and morphine Shimoyama M, Szeto HH, Schiller PW, et al., Pharmacology, 2009 · PMID 18987489

  Direct comparison of [Dmt1]DALDA against morphine in animal analgesia models. Useful for seeing how the potency claims were actually generated and how route-dependent they are.

• Quantitative analysis of [Dmt(1)]DALDA in ovine plasma by capillary liquid chromatography-nanospray ion-trap mass spectrometry Wan H, Umstot ES, Szeto HH, et al., Journal of Chromatography B, 2004 · PMID 15026001

  The bioanalytical method behind the sheep pharmacokinetics. Included because it is the reason those PK numbers can be trusted at all — there is a validated assay behind them, which is more than most research peptides have.

• CNS delivery and pharmacokinetic evaluations of DALDA analgesic peptide analog administered in nano-sized oil-in-water emulsion formulation Shah L, Gattacceca F, Amiji MM, Pharmaceutical Research, 2014 · PMID 24297071

  A formulation attempt to force DALDA across the blood-brain barrier. Worth reading as evidence of how hard the exclusion is — people have built nanoemulsions specifically to overcome it, which is not something you do to a molecule that gets in on its own.