Fragment 176-191

1 Identity

Synthetic disulfide-cyclized peptide fragment of the human growth hormone chain. AOD-9604 is Tyr-hGH(177-191) and is a distinct compound routinely conflated with this one and routinely shipped under this name.

Sequence

H-Phe-Leu-Arg-Ile-Val-Gln-Cys-Arg-Ser-Val-Glu-Gly-Ser-Cys-Gly-Phe-OH (FLRIVQCRSVEGSCGF), 16 residues, all-L, corresponding to residues 176-191 of the 191-residue human growth hormone chain, with one intramolecular disulfide closing the loop between Cys182 and Cys189. It is not A linear peptide and must never be specified as one. Residue 176 is phenylalanine on the reference chain; the cysteines of the full chain fall at 53, 165, 182 and 189. No non-proteinogenic residue and no D-residue. Two Arg plus the N-terminal amine against one Glu side chain and the C-terminal carboxyl. Two Phe give a weak 257 nm signal, but there is no Trp and no Tyr, so this peptide has NO useful 280 nm chromophore — which is itself a discriminator against AOD-9604, whose N-terminal tyrosine does absorb there, and which makes the 280 nm trace a free discriminator between the two. Supplied as a lyophilized acetate or trifluoroacetate salt.

Molecular formula

C78H123N23O22S2 (disulfide-closed) / C78H125N23O22S2 (reduced, open chain). AOD-9604 for contrast: C78H123N23O23S2 (closed) / C78H125N23O23S2 (reduced).

Average mass

1799.101 Da closed (C78H123N23O22S2); 1801.117 Da reduced (C78H125N23O22S2). AOD-9604 for comparison: 1815.100 Da closed and 1817.116 Da reduced. All four follow from the two sequences on IUPAC 2021 conventional atomic weights. Tabulations built on pre-2021 atomic weights print 1799.08, 1801.10, 1815.08 and 1817.10; the 0.019 Da spread across all four is convention, not error, and neither set is a correction of the other. Four species live inside an 18 Da window, and the closed-to-reduced gap is only 2.016 Da, so mass alone will not exclude the open chain. One further point, because it is often written up as scientific uncertainty and is not: the reference chain settles that hGH residue 176 is phenylalanine. What is inconsistent is seller usage of the name, and that is a commercial fact about suppliers rather than an open question in chemistry.

Monoisotopic mass

1797.86544 Da closed; 1799.88109 Da reduced. AOD-9604: 1813.86036 Da closed; 1815.87601 Da reduced. Working ions on the closed article: [M+H]+ m/z 1798.87272, [M+2H]2+ m/z 899.94000, [M+3H]3+ m/z 600.29576. A plus or minus 5 ppm window on the closed neutral is plus or minus 0.0090 Da — which is four times wider than nothing and still nine times narrower than the 2.016 Da disulfide gap, so a high-resolution instrument does separate closed from reduced. The trap that mass spectrometry cannot solve: phenylalanine plus one oxygen is elementally tyrosine, so a mono-oxidized disulfide-closed hGH(176-191) has formula C78H123N23O23S2 — exactly the formula and exactly the mass of disulfide-closed AOD-9604, 1813.86036 monoisotopic. The two are not near-isobaric; they are elementally identical. Only MS/MS, which localizes the extra oxygen to the N-terminal residue or elsewhere, or co-elution against both authentic standards, separates them.

Salt / variant note

Multi-molecule name, and this is the best-documented substitution in the catalog: the market ships AOD-9604 under the 176-191 name, on its own printed datasheets. Four species live inside an 18 Da window. (1) Disulfide-closed hGH(176-191): C78H123N23O22S2, 1799.101 / 1797.86544. (2) Reduced hGH(176-191): C78H125N23O22S2, 1801.117 / 1799.88109 — only 2.016 Da from the closed form. (3) Disulfide-closed AOD-9604: C78H123N23O23S2, 1815.100 / 1813.86036. (4) Reduced AOD-9604: C78H125N23O23S2, 1817.116 / 1815.87601. What is actually sold under the name, recorded exactly as found: one seller lists "Fragment 176-191" in 5 mg units, prints C78H125N23O23S2 and MW 1817.12, describes a tyrosine at the N-terminus, and states in its own text that the article is also known as tyr-hGH 177-191 or AOD-9604. A second seller lists "Fragment 176-191" in 5 mg units and prints C78H123N23O23S2 against MW 1817.1 — the formula for closed AOD-9604 paired with the mass of reduced AOD-9604, internally inconsistent by exactly the disulfide, and belonging to the wrong molecule for the name either way. A third catalogs "HGH Fragment (176-191)" with the sequence printed outright as YLRIVQCRSVEGSCGF and MW 1817.01. A trade aggregator page for "HGH Fragment 176-191" states MW 1817.12. Four independent sellers, one name, and every one of them is describing AOD-9604.

2 Class & testing panel

Form

Single article

Testing panel

P1 — panel definition

3 Primary sources & evidence

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

No citation set is assembled for this article, and the reason is itself the finding. The fragment has been presented on the basis of data pertaining to AOD-9604, a modified form of it, so the citation set circulating under the 176-191 name substantially describes a different molecule, and attaching it here would repeat the error this record exists to document. Any literature search for this article must be run against the disulfide-closed 16-residue sequence FLRIVQCRSVEGSCGF and against hGH residue numbering, not against the trade name, and each retrieved paper must be checked for which of the four species it used. No statement is made here about what the compound does in any body.

4 Storage & specification

Storage

Supplied as the lyophilized solid in amber glass with a desiccant sachet and a tamper-evident closure, stored at -20 degrees C plus or minus 5 degrees C, desiccated and protected from light, with the headspace displaced and the closure kept intact between withdrawals. The condition is chosen for the disulfide: the closed loop that distinguishes this article from the open chain is held by keeping the solid cold, dry and dark.

Shelf life

Each lot is dated from its date of manufacture and carries a retest date on its certificate, set on the company's own stability data for the lot. The stability-indicating attributes that govern the interval are free-thiol content, since disulfide reduction is the reaction that converts the article into a different species 2.016 Da away, and oxidation at the two phenylalanines in a sequence that carries no methionine, which converts it into something elementally identical to a different marketed compound. Both are invisible in a gross purity figure, so both are trended by name.