Bremelanotide (PT-141)

1 Identity

Melanocortin receptor ligands. CAS 189691-06-3 (free base), CAS 1607799-13-2 (mono-acetate).

Sequence

Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-OH. A synthetic cyclic heptapeptide: N-terminally acetylated on norleucine at position 1, cyclized head-to-side-chain through a lactam bridge between the Asp2 beta-carboxyl and the Lys7 epsilon-amine, terminating in a free C-terminal carboxylic acid. Two features govern the entire analytical approach and neither is carried in the mass: D-phenylalanine at position 4, and NORLEUCINE at position 1, a non-proteinogenic residue isobaric with both leucine and isoleucine at 113.08406 Da. The lactam is an amide bond formed with loss of water and is not a disulfide; there is no cysteine in this molecule. Trp6 provides the only 280 nm chromophore and is also the principal photolabile feature. Supplied as the acetate salt.

Molecular formula

C50H68N14O10 (free base); C52H72N14O12 (mono-acetate salt, separately registered as CAS 1607799-13-2)

Average mass

1025.182 Da (C50H68N14O10) as the free base; 1085.234 Da (C52H72N14O12) as the mono-acetate, both on IUPAC 2021 conventional atomic weights. Listings commonly print 1025.16, 1025.18 and 1085.22 - the spread arises entirely from which atomic-weight table was used and is not a structural disagreement, and a single atomic-weight table is used across all documents here so that a 0.02 Da bookkeeping difference is never mistaken for a finding.

Monoisotopic mass

1024.5243 Da neutral. Working ions: [M+H]+ m/z 1025.5316, [M+2H]2+ m/z 513.2694. A plus or minus 5 ppm identity window on [M+H]+ is plus or minus 0.0051 Da. Every mass on a certificate for this article must name the ion and the charge state, because the principal confusable sits 0.984 Da away and the unqualified number '1024.5' is simultaneously this molecule's monoisotopic neutral and melanotan II's protonated ion.

Salt / variant note

Four chemically distinct articles trade around this one name and the arithmetic separating them is unforgiving. (1) the free base, C50H68N14O10, 1025.182 avg / 1024.5243 mono, [M+H]+ 1025.5316 - the article. (2) the mono-acetate as a separately registered substance, CAS 1607799-13-2, C52H72N14O12, formula weight 1085.234 - exactly 60.052 Da heavier, so a lot certified against the acetate formula weight but assayed as free base is 5.5% out on every content and concentration figure derived from it. (3) melanotan II, C50H69N15O9, 1024.198 avg / 1023.54027 mono, [M+H]+ 1024.5475 - the same seven residues, the same acetyl cap and the same lactam bridge, differing only in that the C-terminal carboxamide has not been hydrolyzed to the free acid. Set the numbers side by side: this article's monoisotopic neutral is 1024.5243 and melanotan II's protonated ion is 1024.5475, 0.023 Da apart; a certificate printing 'MW 1024.2' under the name bremelanotide has printed melanotan II's average mass. (4) the all-L stereoisomer: identical formula, identical exact mass to every decimal place, and completely invisible to every achiral method on the panel - this is the mass-silent variant and the whole reason P3 is mandatory. (5) The linear uncyclized precursor, C50H70N14O11, 1043.197 avg / 1042.53485 mono, +18.011 Da. (6) Trp6 oxidation products at +15.995 and +31.990 Da. (7) Leu or Ile substituted for Nle at position 1 - isobaric, zero dalton shift, separable only by co-elution against a certified norleucine standard or by characteristic MS/MS fragmentation.

2 Class & testing panel

Form

Single article

Testing panel

P3 — panel definition

3 Primary sources & evidence

The index reports the design and provenance of the literature, not a conclusion about effect.

A complete regulatory development file sits behind NDA 210557, including two sponsor-run phase 3 trials (the RECONNECT program) and the supporting non-clinical package - the deepest human evidence base of any article in this catalog, and all of it pertaining to an approved finished drug product made under an approved application. Behind it sits an academic melanocortin literature going back to the 1980s and 1990s: receptor pharmacology in vitro, structure-activity work on cyclic lactam analogues, and rodent studies. Nothing published describes the research-market article itself - no peer-reviewed analysis of gray-market bremelanotide identity, stereochemical purity or impurity profile has been published. This is a description of what has been published and registered, by study type and identifier.

4 Storage & specification

Storage

White lyophilized powder, acetate salt, in amber glass with a nitrogen headspace and in-pack desiccant, stored at -20 degrees C plus or minus 5 degrees C, desiccated and protected from light. The tryptophan indole makes photostability a specification item rather than a preference, and the lactam bridge is the other watched feature. Excursions to 2 to 8 degrees C of up to 30 days cumulative are permitted and recorded on the lot record; shipment on gel packs with a temperature logger filed against the shipment.

Shelf life

Provisional 24-month retest interval at -20 degrees C plus or minus 5 degrees C, assigned by protocol rather than by measurement pending a three-lot ICH Q1A study with an ICH Q1B option 2 photostability arm, long-term at -20 degrees C and accelerated at 25 degrees C / 60 percent relative humidity, with the melanotan II amide species, the linear uncyclized precursor and the Trp6 oxidation products all tracked as indicating impurities. That study replaces the assumed interval at the 12-month data point.