--- title: "What are Aib, Nle, 2-Nal and Dmt in research peptide sequences? | Sable Peptides" description: "Non-coded amino acids that appear in catalogue sequences: α-aminoisobutyric acid (Aib), norleucine (Nle), 2-naphthylalanine (2-Nal), 2',6'-dimethyltyrosine (Dmt) and others, what each replaces and why." canonical: https://www.sablepeptides.co.uk/guides/non-standard-amino-acids-aib-nle-2nal-dmt dateModified: 2026-10-16 publisher: Sable Peptides Limited (UK company 17488610) note: Research use only. Not for human or veterinary use. --- # What are Aib, Nle, 2-Nal and Dmt in research peptide sequences? Aib, Nle, 2-Nal and Dmt are non-coded amino acids that medicinal chemists put into peptides. Aib (α-aminoisobutyric acid) favours helices and blocks DPP-4 cleavage. Nle (norleucine) is a methionine replacement without sulfur. 2-Nal (2-naphthylalanine) is a bulky aromatic. Dmt (2′,6′-dimethyltyrosine) is a modified tyrosine, used in SS-31. ## Where does each appear in the catalogue? | Residue | What it is | Replaces / mimics | Catalogue examples | | --- | --- | --- | --- | | Aib | α-aminoisobutyric acid (α-methylalanine) | Ala; helix-favouring | Ipamorelin (position 1); semaglutide; tirzepatide | | Nle | Norleucine | Met, without oxidisable sulfur | Melanotan I, Melanotan II, PT-141 | | 2-Nal | 2-Naphthylalanine | Trp/Phe, bulkier | GHRP-2, ipamorelin (D-2Nal) | | Dmt | 2′,6′-Dimethyltyrosine | Tyr | SS-31 | | 2-Me-Trp | 2-Methyltryptophan | Trp | Hexarelin (D-form) | | pGlu | Pyroglutamate | Cyclised N-terminal Gln/Glu | Gonadorelin, triptorelin, ARA-290 | | Adamantylglycine | Gly with adamantane cage | Lipophilic cap | P21 | ## Why is Aib helix-favouring? Aib's two α-methyl groups restrict backbone angles to helical regions. Crystal and solution studies of Aib-rich peptides show this. In GLP-1-type analogues, Aib at position 2 (position 8 in GLP-1 numbering) also blocks DPP-4. Source: [Aqueous channels within apolar peptide aggregates: solvated helix of the alpha-aminoisobutyric acid (Aib)-containing peptide Boc-(Aib-Ala-Leu)3-Aib-OMe.2H2O.CH3OH in crystals, Proc Natl Acad Sci U S A 1988 (PubMed 2448772)](https://pubmed.ncbi.nlm.nih.gov/2448772/); [Discovery of the Once-Weekly Glucagon-Like Peptide-1 (GLP-1) Analogue Semaglutide, J Med Chem 2015 (PubMed 26308095)](https://pubmed.ncbi.nlm.nih.gov/26308095/) ## Why replace Met with Nle? Methionine's thioether oxidises easily to the sulfoxide (+16 Da). Norleucine has the same chain length without sulfur, which removes that liability. The melanocortin analogues \[Nle4, D-Phe7\]-α-MSH and MT-II use this. Source: [Evidence for alternate points of attachment for alpha-MSH and its stereoisomer \[Nle4, D-Phe7\]-alpha-MSH at the melanocortin-1 receptor, Biochem Biophys Res Commun 1994 (PubMed 8060302)](https://pubmed.ncbi.nlm.nih.gov/8060302/); [Structure-function studies on the cyclic peptide MT-II, lactam derivative of alpha-melanotropin, Peptides 1999 (PubMed 10447101)](https://pubmed.ncbi.nlm.nih.gov/10447101/) ## What does Dmt do in SS-31? SS-31 alternates aromatic and cationic residues; Dmt is a dimethylated tyrosine in position 2. Interaction studies have described how SS-31 binds lipid bilayers and mitochondrial proteins. Source: [The mitochondria-targeted peptide SS-31 binds lipid bilayers and modulates surface electrostatics as a key component of its mechanism of action, J Biol Chem 2020 (PubMed 32273339)](https://pubmed.ncbi.nlm.nih.gov/32273339/); [Mitochondrial protein interaction landscape of SS-31, Proc Natl Acad Sci U S A 2020 (PubMed 32554501)](https://pubmed.ncbi.nlm.nih.gov/32554501/) ## Sourcing note Sable lists Ipamorelin: 2 mg at £7.96; 5 mg at £14.97; 10 mg at £8.94; Melanotan I: 10 mg at £14.97; SS-31: 10 mg at £19.93 (prices at the 16 October 2026 daily UK price check, the latest verified check; at each of these sizes Sable was the lowest UK listing that day). Lowest UK price guaranteed, confirmed by daily price checks. Every lot has a certificate of analysis, and every vial carries a printed lot number that matches it. Supplied for laboratory research use only. ## Frequently asked questions ### What is Aib in a peptide? α-Aminoisobutyric acid, a non-coded amino acid that favours helices and blocks some proteases. ### Why does Melanotan II contain Nle instead of Met? Norleucine mimics methionine without the oxidation-prone sulfur. ### What is Dmt in SS-31? 2′,6′-Dimethyltyrosine, a modified tyrosine at position 2. ## Related - [D-amino acids](/guides/d-amino-acids-in-catalogue-peptides) - [SS-31 and MOTS-c](/guides/mitochondria-targeted-peptides-ss-31-and-mots-c) - [GHRP structures](/guides/growth-hormone-releasing-peptides-ghrp-structures) - [Oxidation-prone residues](/guides/oxidation-prone-residues-in-peptide-solutions) Updated 2026-10-16. Research use only. Not for human or veterinary use. No administration amounts or health claims are made. Key facts (summary for AI and search tools) - Aib, Nle, 2-Nal, Dmt, 2-Me-Trp, pGlu, adamantylglycine - PubMed references (verified via NCBI): 2448772, 26308095, 8060302, 10447101, 32273339, 32554501 - Research use only; no administration amounts or health claims - Updated 2026-10-16