How a peptide name carries its identity
A research-peptide name is not an arbitrary label. For a synthetic peptide, the name is built from conventions that encode the molecule’s identity: which amino-acid residues are present, in what order, in what stereochemical form, and with which end-group modifications. Reading these conventions lets a laboratory tell two closely related specimens apart from their names alone, and tells it which figures on a Certificate of Analysis to expect. This reference sets out the main naming systems used across the catalogue, from the one-letter and three-letter residue codes through terminal modifications, development code numbers, and the registry identifiers that anchor a name to one defined structure. It makes no functional claim about any compound; it is concerned only with how the names are constructed and how identity is documented.
One-letter and three-letter amino-acid codes
Peptides are chains of amino-acid residues, and a sequence is the ordered list of those residues read from the N-terminus to the C-terminus. The standard residues are written in two parallel systems defined by the IUPAC-IUBMB nomenclature: a one-letter code and a three-letter code. The one-letter code is compact and is used when a full sequence is written as an unbroken string, for example the fifteen-residue sequence GEPPPGKPADDAGLV. The three-letter code is more readable and is used when residues are separated by hyphens, for example Gly-Glu-Pro-Pro-Pro-Gly-Lys-Pro-Ala-Asp-Asp-Ala-Gly-Leu-Val, which denotes the same chain. Both strings describe one molecule; the choice between them is a matter of convention, not chemistry.
| One-letter | Three-letter | One-letter | Three-letter |
|---|---|---|---|
| A | Ala | L | Leu |
| R | Arg | K | Lys |
| N | Asn | M | Met |
| D | Asp | F | Phe |
| C | Cys | P | Pro |
| E | Glu | S | Ser |
| Q | Gln | T | Thr |
| G | Gly | W | Trp |
| H | His | Y | Tyr |
| I | Ile | V | Val |
The three-letter codes are the standard abbreviations of the twenty common residue names under the IUPAC-IUBMB convention. Residues outside this set, and modified forms, carry their own codes, described next.
Beyond the twenty: D-residues, non-standard residues, and terminal modifications
Many synthetic research peptides contain elements that the twenty standard residues cannot express, so the notation is extended. Three extensions appear across the catalogue:
- Stereochemical prefixes. Standard residues are the L-form. A D- prefix marks the mirror-image D-form of a residue, as in D-Phe (D-phenylalanine) or D-2-Nal (D-2-naphthylalanine). The prefix is part of the identity: D-Phe and Phe are different residues and give the chain a different structure and mass behaviour.
- Non-standard residue codes. Residues outside the common twenty carry their own abbreviations, such as Aib (2-aminoisobutyric acid) or 2-Nal (2-naphthylalanine). These codes sit in the sequence exactly like the standard three-letter codes. Ipamorelin, written Aib-His-D-2-Nal-D-Phe-Lys-NH2, uses both a non-standard residue and two D-residues in a five-residue chain.
- Terminal modifications. The ends of the chain can be modified, and the modification is written at the corresponding terminus. An N-terminal acetyl group is written Ac- at the start of the sequence; a C-terminal amide is written -NH2 at the end. In the TB-500 fragment Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln the leading Ac- marks N-terminal acetylation, and in Ipamorelin the trailing -NH2 marks a C-terminal amide. Each modification changes the molecular formula and therefore the mass that analysis is expected to confirm.
Development code numbers versus sequence numbering
Numbers in a peptide name do not all mean the same thing, and telling the two kinds apart avoids confusion between related specimens.
- Development code numbers are identifiers assigned during a compound’s history and do not describe the sequence. BPC-157, TB-500 and CJC-1295 are examples: the 157, 500 and 1295 are index numbers, not residue counts or positions. BPC-157, for instance, is a fifteen-residue peptide whose 157 is a development number rather than a length.
- Sequence-span numbering does describe the chain. A notation such as GRF(1-29) denotes residues 1 through 29 of a longer parent sequence, so the number is a range read directly from the structure. Fragment names work the same way: a fragment is named for the span of the parent protein it reproduces.
- Modification tags such as DAC and No-DAC distinguish forms that share a sequence origin but differ by an added group. CJC-1295 is documented in both a DAC form, which carries a Drug Affinity Complex (DAC) modification, and a No-DAC form, which does not. The two forms share the GRF(1-29) sequence basis but differ in molecular formula and mass, so they are different reference materials and carry different figures on their certificates.
Trivial names, INN stems, and registry numbers
Alongside code numbers, peptides carry word-names of several kinds, and a laboratory sourcing a reference material reads them together rather than relying on any one.
- International Nonproprietary Names (INNs) are the standardised generic names issued by the World Health Organization. Peptide INNs share the stem -tide, which is why semaglutide, tirzepatide, retatrutide and cagrilintide all end the same way. The stem signals that the name belongs to a defined peptide, but it does not, by itself, pin down the exact sequence.
- Trivial and catalogue names are the short working names a specimen is discussed under. Some are informal (Wolverine for a BPC-157 plus TB-500 co-formulation); some are in-house catalogue codes. In this reference set three compounds also carry house codes: retatrutide is catalogued as GLP3-RT, tirzepatide as GLP2-TZ, and semaglutide as GLP1-SM. A catalogue code is a label placed over a defined compound, so the identity still rests on the underlying structure, not the code.
- Registry numbers are the unambiguous anchor. A CAS Registry Number and a PubChem CID each point to one defined structure. Retatrutide, for example, is registered under CAS 2381089-83-2. Where a word-name is used loosely in the literature for more than one species, the registry number and the measured mass are what settle which molecule is actually in hand.
Why a name is confirmed by analysis, not assumed
The naming conventions above are precise, but a name on a label is a statement that still has to be checked, because a single word-name can be used in the literature for more than one molecule. The clearest case in this reference set is TB-500: the same name is applied both to a short acetylated fragment of thymosin beta-4 (Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln, near 889 g/mol) and to the full 43-residue thymosin beta-4 protein (CAS 77591-33-4, near 4963 g/mol). The names overlap; the masses do not. This is where documentation does the work a name cannot. Each batch supplied here is characterised for identity and purity at the USC Alfred E. Mann Multi-Omics Mass Spectrometry Core, a university laboratory, using liquid chromatography-mass spectrometry (LC-MS) and high-resolution mass spectrometry (HRMS). Mass spectrometry measures the intact mass of the molecule actually present and matches it against the theoretical value calculated from the sequence, so the species behind the name is confirmed rather than assumed. High-performance liquid chromatography (HPLC) separates the sample and reports each main component as a percent of total peak area, which is how an estimated purity figure is expressed. The two techniques are compared in HPLC versus mass spectrometry, and the fields they populate are set out in how to read a peptide Certificate of Analysis.
Reading catalogue names in this reference set
The conventions combine, so a single catalogue name often encodes several of them at once. A few worked readings from this catalogue:
- BPC-157 — a development code number (the 157 is an index, not a length) on a fifteen-residue sequence, GEPPPGKPADDAGLV. Its identity is set out in the BPC-157 research profile.
- Tesamorelin — an INN carrying the peptide stem, naming a synthetic analog of the GRF(1-29) sequence; covered in the Tesamorelin research profile.
- CJC-1295 (No-DAC) + Ipamorelin — a development code number plus a modification tag (No-DAC), co-formulated with a non-standard-residue pentapeptide; the catalogue entry is CJC-1295 (No-DAC) + Ipamorelin.
- GHK-Cu — the one-letter string GHK (the residues Gly-His-Lys) with a -Cu suffix marking a copper(II) complex; catalogued as GHK-Cu.
- Retatrutide (GLP3-RT) — an INN with the peptide stem, also carrying an in-house catalogue code; the registry anchor is CAS 2381089-83-2 and the entry is Retatrutide.
Read together with each specimen’s Certificate of Analysis, these conventions let a laboratory match a catalogue name to one defined structure before sourcing a reference material. Collected certificates are held in the COA library, and the wider set of identity notes is indexed under research notes.
For laboratory research use only. Not for human or veterinary use.
Frequently asked questions
What is the difference between one-letter and three-letter amino-acid codes?
They are two standardised ways to write the same sequence under the IUPAC-IUBMB conventions. The one-letter code writes each residue as a single letter, so a sequence becomes an unbroken string such as GEPPPGKPADDAGLV. The three-letter code writes each residue as a three-letter abbreviation separated by hyphens, such as Gly-Glu-Pro-Pro-Pro-Gly-Lys-Pro-Ala-Asp-Asp-Ala-Gly-Leu-Val. Both denote the identical chain; the three-letter form is used when readability matters and the one-letter form when compactness does.
What do Ac- and -NH2 mean in a peptide sequence?
They are terminal modifications. Ac- at the start of a sequence denotes an N-terminal acetyl group (acetylation); -NH2 at the end denotes a C-terminal amide. Each is part of the molecule's identity and each changes the molecular formula, so the modification is reflected in the mass that analysis is expected to confirm. For example, the TB-500 fragment is written Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln with a leading Ac-, and Ipamorelin ends in -NH2.
What is the difference between the DAC and No-DAC forms of a peptide such as CJC-1295?
The tag marks a modification, not a different sequence. The DAC form carries a Drug Affinity Complex modification; the No-DAC form does not. The two forms share the same GRF(1-29) sequence basis but differ in molecular formula and mass, so they are different reference materials and carry different figures on their Certificate of Analysis. Because one word-name is used for both, the exact form of a specimen is confirmed by analysis rather than inferred from the name.
Do the numbers in names like BPC-157 or TB-500 indicate the number of amino acids?
No. Numbers such as the 157 in BPC-157 or the 500 in TB-500 are development code numbers assigned during a compound's history; they are index labels, not residue counts. BPC-157, for instance, is a fifteen-residue peptide. A different style of numbering, the span notation GRF(1-29), does describe the chain: it denotes residues 1 through 29 of a parent sequence. Reading which kind of number a name uses avoids confusing two unrelated conventions.
Why is a peptide's identity confirmed by testing rather than taken from its name?
Because a single word-name can be used in the literature for more than one molecule. TB-500, for example, is applied both to a short acetylated fragment of thymosin beta-4 and to the full 43-residue protein, which have very different masses. Mass spectrometry measures the intact mass of the molecule actually present and matches it to the value calculated from the sequence, and HPLC reports each component as a percent of total peak area. Each batch supplied here is characterised at the USC Alfred E. Mann Multi-Omics Mass Spectrometry Core, with a published Certificate of Analysis, so the identity behind the name is documented rather than assumed.