Hexarelin

GHRP-6 with 2-methyl-D-tryptophan in place of D-tryptophan at position 2: one added methyl group, 14.016 Da heavier. Every value on this page is calculated from the structure shown, by the method and constants in the sources below; measured values for a particular lot are on its certificate of analysis.

Structure

Three-letter code: H-His-D-Mrp-Ala-Trp-D-Phe-Lys-NH2

• 6 residues
• N-terminus: free amine
• C-terminus: amide
• 2 D-residues
• non-standard residues: 2-Methyltryptophan

Calculated properties

Calculated from the structure

Property	Value
Molecular formula	C47H58N12O6
CAS Registry Number	140703-51-1
Average molecular weight	887.06 g/mol
Monoisotopic mass	886.4602 Da
Net charge at pH 7	2.2
Isoelectric point	No acidic groups: the peptide carries a positive charge at every pH, so it has no isoelectric point.
Molar absorption coefficient, 280 nm	Not calculated: a non-standard aromatic residue also absorbs at 280 nm.
Hydropathy (GRAVY)	Not calculated: the scale covers the standard amino acids only

Net charge across the pH range

pH 2	pH 4	pH 6	pH 7	pH 8	pH 10	pH 12
3.0	3.0	2.8	2.2	1.8	0.9	0.1

Composition: Ala 1, His 1, Lys 1, Mrp 1, Phe 1, Trp 1.

Expected mass spectrometry ions

The protonated ions expected in positive-mode electrospray, from the monoisotopic mass, and the common sodium and potassium adducts. MALDI spectra show mainly [M+H]⁺.

Expected ions (monoisotopic)

Ion	m/z
[M+H]+	887.4675
[M+2H]2+	444.2374
[M+Na]+	909.4494
[M+K]+	925.4234

Isotope pattern

Natural carbon-13, nitrogen-15, oxygen-18, sulfur-34 and deuterium spread each ion over a cluster of peaks about 1 Da apart (1/z on the m/z scale). The monoisotopic peak is the most abundant.

Isotope peaks (relative abundance, most abundant = 100)

Peak	Abundance	Neutral mass	[M+H]+	[M+2H]2+
M (monoisotopic)	100.0	886.4602	887.4675	444.2374
M+1	56.1	887.4631	888.4704	444.7388
M+2	16.7	888.4659	889.4732	445.2402
M+3	3.5	889.4686	890.4759	445.7416
M+4	0.6	890.4712	891.4785	446.2429

Fragment ions (MS/MS)

Collision-induced fragmentation breaks peptide bonds along the backbone. Fragments that keep the N-terminus are b ions; those that keep the C-terminus are y ions. Reading the ladder confirms the sequence residue by residue. Singly charged monoisotopic values. The b ion containing every residue is rarely seen and the y ion containing every residue is the precursor itself, so neither is listed.

b and y ions

b#	b+	Residue	y+	y#
1	138.0662	His	—	6
2	338.1612	D-Mrp	750.4086	5
3	409.1983	Ala	550.3136	4
4	595.2776	Trp	479.2765	3
5	742.3460	D-Phe	293.1972	2
6	—	Lys	146.1288	1

Immonium ions (low-mass markers of the residues present): Ala 44.0495, Lys 101.1073, His 110.0713, Phe 120.0808, Trp 159.0917.

What to watch for analytically

Variants this sequence can give, from its chemistry. They are what an HPLC or mass spectrometry result for this peptide is read against; none is a statement about a particular lot. Where synthesis variants come from is explained in How synthetic peptides are made.

Sequence-specific variants

Variant	Mass change	Why
Tryptophan oxidation	+15.995 or +31.990 Da	Tryptophan at position 4 can oxidize, particularly on exposure to light and air.
Stereochemistry	0 Da	2 residues are in the D-configuration by design. An epimer at any position has the same mass, so stereochemical purity is a chromatographic question.
C-terminal amide	free-acid variant +0.984 Da	The C-terminus is an amide. The corresponding free acid, from synthesis or hydrolysis, differs by +0.984 Da, close to the isotope spacing, so it needs a resolved spectrum to tell apart.
Synthesis-related variants	minus a residue (deletion)	As for any synthetic peptide, deletion sequences and incompletely deprotected forms can occur.

Sources & Further Reading

1. Prohaska T, Irrgeher J, Benefield J, Böhlke JK, Chesson LA, Coplen TB, et al. Standard atomic weights of the elements 2021 (IUPAC Technical Report). Pure and Applied Chemistry 2022;94(5):573–600. doi:10.1515/pac-2019-0603
2. Wang M, Huang WJ, Kondev FG, Audi G, Naimi S. The AME 2020 atomic mass evaluation (II). Tables, graphs and references. Chinese Physics C 2021;45(3):030003. doi:10.1088/1674-1137/abddaf
3. Rice P, Longden I, Bleasby A. EMBOSS: the European Molecular Biology Open Software Suite. Trends in Genetics 2000;16(6):276–277. doi:10.1016/S0168-9525(00)02024-2
4. Pace CN, Vajdos F, Fee L, Grimsley G, Gray T. How to measure and predict the molar absorption coefficient of a protein. Protein Science 1995;4(11):2411–2423. doi:10.1002/pro.5560041120
5. Kyte J, Doolittle RF. A simple method for displaying the hydropathic character of a protein. Journal of Molecular Biology 1982;157(1):105–132. doi:10.1016/0022-2836(82)90515-0
6. Meija J, Coplen TB, Berglund M, Brand WA, De Bièvre P, Gröning M, et al. Isotopic compositions of the elements 2013 (IUPAC Technical Report). Pure and Applied Chemistry 2016;88(3):293–306. doi:10.1515/pac-2015-0503
7. Roepstorff P, Fohlman J. Letter to the editors: proposal for a common nomenclature for sequence ions in mass spectra of peptides. Biomedical Mass Spectrometry 1984;11(11):601. doi:10.1002/bms.1200111109
8. Biemann K. Contributions of mass spectrometry to peptide and protein structure. Biomedical and Environmental Mass Spectrometry 1988;16(1–12):99–111. doi:10.1002/bms.1200160119
9. Geiger T, Clarke S. Deamidation, isomerization, and racemization at asparaginyl and aspartyl residues in peptides. Succinimide-linked reactions that contribute to protein degradation. Journal of Biological Chemistry 1987;262(2):785–794. doi:10.1016/S0021-9258(19)75855-4
10. Manning MC, Chou DK, Murphy BM, Payne RW, Katayama DS. Stability of protein pharmaceuticals: an update. Pharmaceutical Research 2010;27(4):544–575. doi:10.1007/s11095-009-0045-6
11. D'Hondt M, Bracke N, Taevernier L, Gevaert B, Verbeke F, Wynendaele E, et al. Related impurities in peptide medicines. Journal of Pharmaceutical and Biomedical Analysis 2014;101:2–30. doi:10.1016/j.jpba.2014.06.012

Cosmic Peptides. (2026, October 25). Hexarelin: peptide reference entry. Cosmic Peptides Research Library. Retrieved October 26, 2026, from https://cosmicpeptides.com/research/peptides/hexarelin

@misc{cosmicpeptides_research_peptides_hexarelin,
  author       = {{Cosmic Peptides}},
  title        = {Hexarelin: peptide reference entry},
  howpublished = {Cosmic Peptides Research Library},
  year         = {2026},
  month        = oct,
  url          = {https://cosmicpeptides.com/research/peptides/hexarelin},
  urldate      = {2026-10-26},
  note         = {Last reviewed 2026-10-25}
}

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DA  - 2026/10/25
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Y2  - 2026/10/26
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