Peptide Comparison | B2B Research-Grade Procurement Guide

Melanotan 1 vs Melanotan 2: Sequence, Selectivity, Quality Standards & Procurement Guide

A technical and commercial comparison for research-peptide procurement, analytical QC laboratories, cosmetic-channel compliance review, and anti-doping-aware sourcing teams.

Melanotan 1 vs Melanotan 2

Melanotan 1 (CAS 75921-69-6) is MT-I, a synthetic nine-residue cyclic melanocortin analogue modeled on gamma-MSH with near-selective MC1R activity; Melanotan 2 (CAS 121062-08-6) is MT-II, the shorter [Nle4, D-Phe7] alpha-MSH(4–10) cyclic heptapeptide that activates both MC1R and MC4R. MT-I has the molecular formula C₇₈H₁₁₁N₂₁O₁₉ (approx. 1,646.8 g/mol as the free peptide); MT-II is C₅₀H₆₉N₁₅O₉ (approx. 1,024.2 g/mol). The extra N-terminal extension of MT-I is what keeps it MC1R-selective, while MT-II loses that selectivity and gains MC4R-driven activity.

For procurement, the key distinction is regulatory, not just pharmacological: neither peptide is an approved therapeutic in most major markets, MT-II in particular is explicitly prohibited in sport (WADA Section S0 — non-approved substances) and is a controlled/restricted item in several jurisdictions, and the commercial market runs on research-grade material whose quality varies enormously by lot. Purity by HPLC, sequence confirmation by MS, acetate content, water content and TFA removal are the buying conversation — and cold-chain documentation decides whether the received vial still matches its CoA.

1. Quick Comparison

Comparison Parameter	Melanotan 1	Melanotan 2
Chemical class	Synthetic cyclic peptide; gamma-MSH analogue (9-mer, Asp7–Lys9 lactam ring, D-Phe7)	Synthetic cyclic peptide; [Nle4, D-Phe7] alpha-MSH(4–10) heptapeptide, same lactam pharmacophore
CAS Registry Number	75921-69-6	121062-08-6
Molecular formula	C₇₈H₁₁₁N₂₁O₁₉	C₅₀H₆₉N₁₅O₉
Molecular weight	Approx. 1,646.8 g/mol (free peptide)	Approx. 1,024.2 g/mol (free peptide; acetate-salt forms weigh more)
Receptor profile	Predominantly MC1R (skin/tanning axis)	MC1R + MC4R (tanning plus appetite/sexual-behavior axis)
Anti-doping status	Prohibited (S0 class, as an unapproved melanocortin agonist)	Prohibited at all times (WADA S0); the more frequently detected analyte
Primary commercial channel	Research-grade lyophilized peptide	Research-grade lyophilized peptide; largest grey-market volume of the two
Lewis structure guide	Melanotan 1 Lewis structure	Melanotan 2 Lewis structure
Chemical relationship	The longer gamma-MSH framework	The truncated core cyclic heptapeptide

Molecular weights are free-peptide values; commercial acetate salts add acetic-acid equivalents, which is why acetate-content data (or NMR/IC determination) belongs on the CoA. Receptor and WADA summaries reflect published classifications; confirm the current-year WADA list before any athlete-facing decision.

2. Core Definitions and Structural Differences

2.1 What Is Melanotan 1?

Melanotan 1 is a nine-amino-acid cyclic peptide whose design keeps the N-terminal extension of gamma-MSH while introducing the Asp–Lys lactam bridge and D-Phe7 that lock the bioactive conformation. That extension biases the molecule toward MC1R, the melanocyte receptor behind melanogenesis, which is why it was explored as a UV-photoprotection/tanning agent.

Commercially it is supplied as a lyophilized acetate salt, reconstituted with bacteriostatic water in research settings. Its peptide nature drives the whole quality conversation: sequence confirmation, aggregation/oxidation control, residual TFA from RP-HPLC purification, and water content that distorts mass-based dosing.

2.2 What Is Melanotan 2?

Melanotan 2 is the truncated core: the His–Phe–Arg–Trp–Lys–Pro region with Nle4 substitution and the same D-Phe7 lactam cyclization. Losing the N-terminal extension does not eliminate activity — it redistributes it. The compound becomes a potent MC4R agonist as well as an MC1R agonist, which is the pharmacological basis of both its popularity in unregulated channels (appetite and sexual-function claims) and its scrutiny by regulators and anti-doping agencies.

MC4R engagement also explains the side-effect profile repeatedly reported in the literature (nausea, flushing, appetite change). The approved-medicine comparator in this receptor area is setmelanotide (an MC4R-targeted drug), which is a useful reminder that melanocortin pharmacology is a real, safety-laden drug space, not a cosmetic curiosity.

2.3 Structural and Physicochemical Comparison

Property	Melanotan 1	Melanotan 2
Length	9 residues (nonapeptide with gamma-MSH extension)	7 residues (heptapeptide core analogue)
Cyclization	Asp7–Lys9 lactam bridge, D-Phe7 in the constrained ring	Asp–Lys lactam bridge, D-Phe7 in the constrained ring
Key substitutions	D-Phe7; Nle in the conserved position	Nle4, D-Phe7
Receptor bias	MC1R-selective	Balanced MC1R/MC4R
Mass per mole of “active ring”	Higher MW due to extension; molar dose must use 1,646.8	Lower MW; molar dose must use 1,024.2
Stability handling	Freeze-dried, cold storage, minimize freeze-thaw	Same handling class; oxidation/aggregation are the common lot failures

2.4 Why the Two Are Routinely Confused — and Must Not Be Substituted

Both peptides carry “melanotan,” both tan through MC1R, and grey-market listings frequently mislabel one for the other. But a 1,646.8 Da MC1R-selective agent and a 1,024.2 Da MC1R/MC4R agent produce measurably different outcomes: dosing in milligrams converts to very different molar amounts, and the MC4R activity of MT-II brings appetite and autonomic effects MT-I was designed not to have.

For any research program, the identity anchor is MS-confirmed sequence plus intact-mass match, not the catalog name. For any human-use question, the honest note is that neither peptide holds marketing authorization in the US, EU, UK or Australia, and supply outside a research context is a regulatory violation in several jurisdictions.

Molar-mass implication for dosing accuracy

A lot sold as “10 mg per vial” contains about 6.07 µmol of MT-I but 9.76 µmol of MT-II — a 1.6× difference driven entirely by molecular weight. Protocol transfers between the two peptides without molar recalculation silently over- or under-dose every subject.

3. Application Boundaries and Industrial Roles

3.1 Melanotan 1: Typical Roles

Photoprotection research: Tool compound for MC1R-mediated melanogenesis and UV-response studies.
Dermatology and pigment-cell biology: Melanocyte differentiation and melanin-pathway assays.
Reference-standard work: LC-MS method development where MC1R agonists must be screened (anti-doping panels frequently separate MT-I from MT-II).
Veterinary photoprotection exploration: Historical work in porphyria-adjacent models with appropriate oversight.

Melanotan 1 is not a consumer tanning product and has no approved human indication. Its legitimate commercial lane is research supply with documentation to match.

3.2 Melanotan 2: Typical Roles

MC4R signaling research: Appetite, energy-balance and sexual-function mechanism studies where the MC4R axis is the point.
Purinergic/melanocortin pharmacology tools: Comparative receptor-selectivity work against MT-I and afamelanotide-class compounds.
Anti-doping and forensic analytics: A routinely targeted analyte; reference material for assay validation.
Grey-market channel (risk, not role): The vast bulk of consumer-facing listings are MT-II; this is precisely the compliance exposure buyers must not legitimize.

Melanotan 2’s MC4R activity is not a side detail — it is the reason its safety and regulatory profile is worse than MT-I’s despite a smaller molecule. Procurement that treats the two as one “tanning peptide” SKU inherits the wrong risk file.

3.3 Applications That Require Extra Qualification

Any injectable, nasal or oral human-consumption concept for either peptide requires new-drug-pathway authorization; none exists in major markets, and several (Australia, UK, parts of the EU) have specific import/possession controls, especially for MT-II. Cosmetic-adjacent “tan booster” positioning does not downgrade the drug classification — it raises it. Documentation should state the research-only status on the CoA, label and invoice chain.

4. Commercial Procurement and Supply Chain Guide

4.1 Material Grade and Regulatory Compliance

For unapproved peptides, the only honest “grades” are analytical ones: research-grade with a full CoA package vs anything less. The buyer’s job is to demand the package and reject what is not in it.

Industry / Use	Target Grade	Essential Documentation and Checks
Receptor/pharmacology research	Research-grade with MS-confirmed sequence and intact mass	Per-batch CoA: HPLC purity (gradient, C18) with individual impurities listed, ESI-MS or MALDI intact mass, amino-acid analysis or sequence confirmation, TFA/acetate content, water/KF content, endotoxin data where cell-based work requires it.
Anti-doping / forensic reference work	Certified reference solution/solid with assignment uncertainty	Value assignment traceability, concentration accuracy, stability data, and no cross-contamination between MT-I and MT-II standards (the classic method artifact).
Cell-based melanogenesis assays	Low-endotoxin, sterile-filtered or aseptically processed material	Endotoxin (LAL) and bioburden per application, aggregation/oxidation profile (RP-LC plus size checks), carrier-free reconstitution guidance.
Comparative selectivity studies	Matched-purity lots for both peptides from documented routes	Lot-to-lot consistency evidence, same buffer/excipent basis when supplied as solutions, and stability (freeze-thaw count) records.
Any human-consumption context	No legal grade exists in major markets	Do not qualify. A supplier offering a “cosmetic” or “wellness” grade of either peptide is describing an unlawful channel; decline and document.

Regulatory note: WADA prohibits both melanocortin agonists under S0 (substances not approved for human use), with MT-II the more commonly detected. Australia’s customs/therapeutic-goods controls and UK Misuse-of-Drugs-adjacent enforcement have both targeted consumer MT-II shipments. Confirm current lists and local schedules before any transaction.

4.2 Critical COA Checkpoints and Impurity Audit

Peptide CoAs are marketing documents unless they contain the raw chromatograms and spectra. Insist on actual data, not summary ticks:

QC Attribute	Melanotan 1: Audit Focus	Melanotan 2: Audit Focus	Recommended Verification
Identity / sequence	Expected ions for the 9-mer framework; MS/MS fragment consistency	Expected ions for the 7-mer core; confirm Nle4 mass shift and D-Phe7 retention behavior	Intact MS within stated tolerance; trypsinase/digest fragment confirmation where available; reject CoAs that only say “matches”.
Purity (RP-HPLC)	Named individual impurities, not aggregate only; watch deletion sequences	Same; watch the MT-I cross-contamination peak (shared SPPS chemistry)	Gradient C18 with UV at 214/280 nm; each peak integrated above its reporting threshold; ≥98% typical research bar.
Acetate / counter-ion content	IC or NMR; drives mass-vs-molar math	Same	Salt form stated explicitly on the CoA; unreported salt state makes every molar dose guesswork.
TFA residual	Ion chromatography or NMR; relevant to cell-based assays	Same	TFA removal step documented; high residual TFA suppresses cell responses and biases bioassays.
Water content	KF or qNMR; hygroscopic acetate salts drift fast	Same	Batch-level water percentage on the CoA, with retest after opening; mass-based reconstitution must correct for it.
Aggregation / particulates	Visual + light-scatter or SEC where claimed	Same	Reconstituted-vial inspection SOP; aggregation is a leading cause of irreproducible peptide biology.

No Residual-Solvent Shortcut Here

SPPS-purified peptides carry acetonitrile, water and TFA/acetic-acid systems rather than classic pharmaceutical solvent sets. Apply ICH Q3C logic by declaring the actual purification solvents and their removal steps, with residual data where the assay is sensitive to them (cell and receptor work especially).

Impurity Strategy by Material

Melanotan 1: Deletion sequences (loss of the N-terminal residues) are the characteristic impurity family — they retain the cyclic pharmacophore and can still bind MC1R, so aggregate purity is not a functional metric.
Melanotan 2: Oxidation of Met-equivalent positions (Nle4 mitigates but does not eliminate), truncates, and any MT-I carry-over from shared SPPS/MS method development.
Both: Endotoxin and particulate controls belong to the application, not the catalog; TFA and water change what 10 mg actually means.

Important distinction: these are the audit targets for unapproved research peptides, not claims about any specific lot. The data package, not the purity headline, decides acceptance.

4.3 Buyer Caution: The “Same Tan, Different Drug” Substitution

Procurement warning: mislabeled “melanotan” lots are common, and MT-II inside a study expecting MT-I breaks both the science and the compliance file.

Grey-market and even research-channel listings have shipped MT-II labeled MT-I and vice versa — the intact-mass difference (about 622 Da) is trivially detectable by MS yet routinely invisible on summary CoAs. In receptor studies, the swapped peptide activates the wrong melanocortin subtype and every downstream conclusion inherits that error; in any athlete-facing context, the MT-II mislabel creates an anti-doping violation.

Prevention: accept only lots with per-batch intact-mass spectra, demand the MT-I/MT-II separation peak in the HPLC trace, and run your own identity confirmation (MS or, at minimum, retention comparison against a verified standard) before any material enters a study.

4.4 Regional Supply Chain Intelligence

The legitimate supply chain for these peptides is research-grade SPPS manufacture concentrated in China, India, the US and EU specialty peptide houses; the consumer-facing channel is a compliance problem, not a market.

China/India contract peptide labs: Large SPPS capacity and competitive pricing; qualification hinges on per-batch raw data (HPLC traces, MS), export documentation consistent with research-use declarations, and resistance to cross-contamination between the two sequences.
US/EU specialty suppliers: Better documentation norms and reference-grade assignment; useful for method validation and anti-doping work even at a premium.
Australia/UK enforcement: MT-II shipments are a named customs target; buyers and researchers must confirm local scheduling and import permits before ordering, not after seizure.
WADA/anti-doping context: Both compounds prohibited under S0; supply chains touching athlete populations require additional attestations and segregated storage from approved APIs.
Platform risk: General marketplaces continue to host these listings despite policies against them; procurement files should record the supplier’s legal manufacturing basis, not the storefront.

For programs requiring both peptides, qualify a single documented supplier with controlled SPPS scheduling rather than sourcing each from unvetted listings; the dominant quality failure is cross-sequence contamination.

4.5 Packaging, Storage and Shipping

Control	Procurement Recommendation
Container	Sealed vials under inert headspace with stopper integrity; lyophilized cake under vacuum or nitrogen.
Temperature	Cold storage (2–8 °C long-term; -20 °C for extended) with documented cold-chain transit for solution forms; dry peptide tolerates shorter ambient legs.
Reconstitution	Bacteriostatic water or specified buffer; minimize freeze-thaw; aliquot single-use volumes.
Light	Amber or light-barrier packaging; oxidation-sensitive residues demand exclusion.
Documentation	CoA with raw data attached, research-only statement, batch-level water and salt content, and cold-chain record on delivery.

5. Procurement Decision Matrix: Which Product Should You Request?

Request Melanotan 1 if…

Your protocol is MC1R-selective: photoprotection or melanocyte biology without MC4R confounds.
The method of record separates the 1,646.8 Da species and its deletion sequences.
Your compliance file requires documentation that the lot is not the MC4R-active MT-II.
You need CAS 75921-69-6 with free-peptide molecular weight approx. 1,646.8 g/mol.

Source Melanotan 1 →

Request Melanotan 2 if…

Your model targets MC4R mechanisms (appetite/energy-balance or sexual-function pathways).
You are building anti-doping or forensic assays where MT-II is the analyte of record.
Receptor-pharmacology work requires the balanced MC1R/MC4R agonist.
You need CAS 121062-08-6 with free-peptide molecular weight approx. 1,024.2 g/mol.

Source Melanotan 2 →

RFQ Checklist for Both Peptides

Peptide RFQs that omit the data package produce unreliable quotes. Specify:

Exact peptide name, CAS (research identifier), sequence and modification notes (Nle4/D-Phe7/lactam).
Free-peptide vs acetate-salt basis and expected MW on that basis.
Required HPLC purity with individual impurity reporting, plus intact-mass tolerance.
MS/MS or AAA sequence confirmation; TFA, acetate and water values on the CoA.
Endotoxin/bioburden limits for the intended cell-based use, if applicable.
Cold-chain transit terms and retest-after-opening guidance.
Research-only statement and any local import/schedule documentation needed.
Lot retention-sample availability and change-notification commitments.

B2B Chemical Sourcing

Source Documented Melanotan 1 or Melanotan 2 Lots

Compare suppliers on the raw data attached to each CoA and on their cross-contamination controls, then match the receptor profile your model actually requires.

Request Melanotan 1 RFQs Request Melanotan 2 RFQs

Request per-batch HPLC/MS data and cold-chain records directly from shortlisted suppliers; research use only, and verify local legal status before ordering.

7. Buyer and Researcher FAQs

Q1. MT-I vs MT-II: which one does my tanning-research protocol need?

If the mechanism question is melanocyte/MC1R biology alone, Melanotan 1 avoids the MC4R confound that appetite and autonomic effects introduce from Melanotan 2. If the question is the MC4R axis or comparative selectivity, Melanotan 2 is the tool. Either way, the molar dose must be recomputed from the actual peptide, because the same 10 mg delivers ~1.6× the moles of MT-II.

If the protocol has any human-consumption intent, neither is the answer — no marketing authorization exists in the major markets.

Q2. What is the minimum CoA evidence to trust a peptide lot?

Three raw-data attachments: (1) the analytical HPLC trace with every peak above the reporting threshold integrated, (2) the intact-mass spectrum with the measured value vs calculated value and tolerance, and (3) water plus salt (acetate/TFA) content by KF/IC or qNMR. A certificate that only lists “purity 99%, MS confirmed” with no data supports nothing.

For cell work add endotoxin; for bioanalytical work add a cross-contamination check for the sibling peptide.

Q3. Is it acceptable to reconstitute and refreeze in working volumes?

Reconstitution triggers hydrolysis and aggregation pathways that the dry cake is stable against. Standard practice: prepare a single concentrated stock, aliquot into single-use volumes immediately, store cold, and never refreeze a thawed aliquot. Record the freeze-thaw count as an attribute of the lot.

Peptide adsorption to plastic is real at low concentration; choose carrier-protein-free dilution strategies validated for the assay rather than assuming mass in equals mass available.

Q4. Does WADA treat the two peptides differently?

Both are prohibited as unapproved substances under S0 at all times (in and out of competition). Practically, MT-II is the analyte more often encountered in doping controls because of its consumer misuse; anti-doping laboratories separate MT-I from MT-II by mass and retention, so mislabeling a sample or a supply chain contaminates the record.

Confirm the current-year list before any supply, storage or disposal decision involving athlete populations.

8. References

PubChem, Melanotan I. Research identifier 75921-69-6, sequence, formula and property record. https://pubchem.ncbi.nlm.nih.gov/compound/Melanotan-I
PubChem, Melanotan II. Research identifier 121062-08-6, formula C₅₀H₆₉N₁₅O₉ and property record. https://pubchem.ncbi.nlm.nih.gov/compound/Melanotan-II
WADA Prohibited List (current year), Section S0. Non-approved substances including melanocortin agonists; verify annually. https://www.wada-ama.org/en/prohibited-list
FDA / EMA therapeutic-goods references on afamelanotide and setmelanotide. Approved-medicine context for the melanocortin pathway the two peptides target. https://www.fda.gov/ | https://www.ema.europa.eu/en
ICH Q3C/Q3D (framework) and peptide-purity guidance literature. Applied here to purification-solvent and elemental-impurity logic for SPPS peptides. ICH Quality Guidelines
TGA / MHRA import and scheduling notices on melanotan compounds. Jurisdiction-specific consumer-channel controls, especially MT-II. https://www.tga.gov.au/ | https://www.gov.uk/government/organisations/medicines-and-healthcare-products-regulatory-agency

Editorial and compliance note

These peptides are unapproved investigational/research substances in major markets. This guide supports analytical and procurement due diligence for lawful research use; it is not medical, legal or anti-doping compliance advice. Verify current schedules and lists before acquisition.

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Melanotan 1 Melanotan 2 Comparison