Peptide names, codes, and registry numbers can be confusing, especially when the same compound appears under several names. This guide explains the conventions researchers use to identify a peptide precisely.
Writing a sequence
Sequences are always written from the N-terminus (free amine end) to the C-terminus (carboxyl end). Each amino acid has a three-letter code and a one-letter code. For example, the 15-residue sequence of BPC-157 can be written either way:
- Three-letter: Gly-Glu-Pro-Pro-Pro-Gly-Lys-Pro-Ala-Asp-Asp-Ala-Gly-Leu-Val
- One-letter: GEPPPGKPADDAGLV
Common modifications
- C-terminal amidation (-NH2): replaces the terminal carboxylic acid with an amide. Ipamorelin, for example, is Aib-His-D-2-Nal-D-Phe-Lys-NH2.
- N-terminal acetylation (Ac-): caps the N-terminal amine.
- D-amino acids: mirror-image forms of the natural L-amino acids, written with a “D-” prefix. CJC-1295 (No DAC), also called Modified GRF (1-29), carries D-alanine at position 2.
- Unnatural residues: building blocks such as Aib (α-aminoisobutyric acid) or 2-Nal (2-naphthylalanine) that aren’t among the 20 standard amino acids.
- Cyclization: a ring formed within the peptide, for example by a lactam bridge between side chains, written with “cyclo” and brackets. PT-141 is Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-OH.
- Disulfide bonds: links between two cysteine residues, as in AOD-9604.
CAS Registry Numbers
A CAS Registry Number is a unique identifier assigned by the Chemical Abstracts Service to a specific substance. It’s the most reliable way to confirm two documents refer to the same compound. Note that different forms of the same molecule get different CAS numbers:
- Free peptide vs. metal complex: the tripeptide GHK is 49557-75-7, while its copper complex, GHK-Cu, is 89030-95-5.
- Free base vs. salt: tesamorelin is 218949-48-5, while its acetate salt is listed separately as 901758-09-6.
When comparing documentation, check that the CAS number matches the exact form being supplied.
Molecular formula and molecular weight
The molecular formula lists the atoms in one molecule (BPC-157 is C62H98N16O22). Molecular weight can be reported as the average mass (natural isotope abundance, used for weighing) or the monoisotopic mass (most abundant isotopes, used to interpret mass spectra). A COA’s mass spectrometry section compares the observed mass to the theoretical value derived from the formula.
Code names and synonyms
Many research peptides are known by development codes or abbreviations, such as “BPC” for Body Protection Compound or “GRF” for growth hormone-releasing factor. Because names vary between suppliers, rely on the sequence and CAS number, not the name, to confirm identity. Every product page in our catalog lists these details where they apply.
The Pure Vial Co. supplies research materials for laboratory, analytical, and scientific research use only. Nothing in this guide is medical advice or an indication that any material is suitable for human or veterinary use. See our Research Disclaimer.
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