Peptide Nomenclature FAQ

Contact the synthesis lab immediately before production begins. Most custom peptide suppliers review orders within 24–48 hours and will flag obvious errors (impossible sequences, undefined abbreviations), but transpositions (Gly-Ser vs Ser-Gly) often pass automated checks. A single-residue error discovered post-synthesis means reordering from scratch at full cost—peptide synthesis is sequence-specific with zero tolerance for "close enough." Our experience: 15–20% of first-time orders contain at least one nomenclature ambiguity that requires clarification before synthesis starts.

Use PubChem, UniProt, or the original publication describing the peptide. Search the trivial name in PubChem's compound database—most research-grade peptides have entries listing the full systematic sequence, modifications, and stereochemistry. Cross-check against at least two independent sources (original patent, peer-reviewed synthesis paper) because trivial names occasionally refer to multiple variants. For Thymalin, the systematic name specifies exact amino acid sequence and acetylation status—submitting "Thymalin" alone to a synthesis lab risks receiving a structurally similar but functionally distinct variant.

Request the full IUPAC systematic sequence from the supplier before reconstitution. Trivial names like "Ipamorelin" or "Sermorelin" don't specify modifications, stereochemistry, or cyclization—manufacturers sometimes ship variants (acetylated vs free N-terminus, L-form vs D-substituted) under the same trivial name. Cross-reference the provided sequence against peer-reviewed literature or the supplier's certificate of analysis. If the supplier can't or won't provide the systematic structure, you're working blind—biological activity data from literature won't map reliably to an unverified structure.

Choose one format and apply it uniformly throughout your submission. Regulatory agencies like the FDA do not require a specific hyphenation standard for peptide names. They require consistency within a single filing. If your initial investigational new drug (IND) application referred to the compound as LL37, continue using LL37 in all subsequent amendments, annual reports, and correspondence. If you accidentally switch between LL37 and LL-37 mid-document, include a clarifying note in the submission cover letter stating both names refer to the same 37-amino-acid cathelicidin peptide and provide the full amino acid sequence to eliminate ambiguity. Consistency matters more than which specific format you choose.

Check the experimental conditions and peptide purity, not the name. Apparent conflicts between LL37 and LL-37 studies almost always trace to differences in assay methodology, cell line selection, peptide concentration ranges, or post-synthesis modifications rather than the nomenclature itself. For example, some early LL-37 studies used crude synthetic peptides with 70–85% purity, while modern LL37 studies use HPLC-purified material at >98% purity. The impurity profile affects bioactivity far more than the hyphen. If you encounter conflicting MIC values or receptor-binding affinities between studies, compare the actual experimental protocols and peptide characterization data rather than assuming the name difference indicates a distinct molecule.

Order the LL37. They are the same peptide. Verify the amino acid sequence on the supplier's certificate of analysis matches the 37-residue cathelicidin fragment (LLGDFFRKSKEKIGKEFKRIVQRIKDFLRNLVPRTES). If the sequence, molecular weight (4493.3 Da), and purity specifications match your protocol requirements, the hyphen difference is irrelevant. Reputable peptide manufacturers synthesize to sequence, not to name formatting, so the biological activity will be identical. We've seen researchers delay studies by weeks trying to source "LL-37" specifically when their institution already had LL37 in inventory. The procurement confusion serves no scientific purpose.