| Aad | α-Aminoadipic acid |
| βAad | β-Aminoadipic acid |
| Abu | α-Aminobutyric acid |
| Aib | α-Aminoisobutyric acid; α-methylalanine |
| βAla | β-Alanine; 3-aminopropionic acid (avoid Bal) |
| Asu | α-Aminosuberic acid |
| Aze | Azetidine-2-carboxylic acid |
| Cha | β-cyclohexylalanine |
| Cit | Citrulline; 2-amino-5-ureidovaleric acid |
| Dha | Dehydroalanine (also ΔAla) |
| Gla | γ-Carboxyglutamic acid |
| Glp | pyroglutamic acid; 5-oxoproline (also pGlu) |
| Hph | Homophenylalanine (Hse=homoserine, and so on). Caution is necessary over the use of the prefix homo in relation to α-amino-acid names and the symbols for homo-analogues. When the term first became current, it was applied to analogues in which a side-chain CH2 extension had been introduced. Thus homoserine has a side-chain CH2CH2OH, homoarginine CH2CH2CH2NHC(NH)NH2, and so on. In such cases, the convention is that a new three-letter symbol for the analogue is derived from the parent, by taking H for homo and combining it with the first two characters of the parental symbol – hence, Hse, Har and so on. Now, however, there is a considerable literature on β-amino acids which are analogues of α-amino acids in which a CH2 group has been inserted between the α-carbon and carboxyl group. These analogues have also been called homo-analogues, and there are instances for example not only of ‘homophenylalanine', NH2CH(CH2CH2Ph)CO2H, abbreviated Hph, but also ‘homophenylalanine', NH2CH(CH2Ph)CH2CO2H abbreviated Hph.Further, members of the analogue class with CH2 interpolated between the α-carbon and the carboxyl group of the parent α-amino acid structure have been called both ‘α-homo'- and ‘β-homo’. Clearly great care is essential, and abbreviations for ‘homo’ analogues ought to be fully defined on every occasion. The term ‘β-homo’ seems preferable for backbone extension (emphasizing as it does that the residue has become a β-amino acid residue), with abbreviated symbolism as illustrated by βHph for NH2CH(CH2Ph)CH2CO2H. |
| Hyl | δ-Hydroxylysine |
| Hyp | 4-Hydroxyproline |
| αIle | allo-Isoleucine; 2S, 3R in the l-series |
| Lan | Lanthionine; S-(2-amino-2-carboxyethyl)cysteine |
| MeAla | N-Methylalanine (MeVal=N-methylvaline, and so on). This style should not be used for α-methyl residues, for which either a separate unique symbol (such as Aib for α-methylalanine) should be used, or the position of the methyl group should be made explicit as in αMeTyr for α-methyltyrosine. |
| Nle | Norleucine; α-aminocaproic acid |
| Orn | Ornithine; 2,5-diaminopentanoic acid |
| Phg | Phenylglycine; 2-aminophenylacetic acid |
| Pip | Pipecolic acid; piperidine-s-carboxylic acid |
| Sar | Sarcosine; N-methylglycine |
| Sta | Statine; (3S, 4S)-4-amino-3-hydroxy-6-methyl-heptanoic acid |
| Thi | β-Thienylalanine |
| Tic | 1,2,3,4-Tetrahydroisoquinoline-3-carboxylic acid |
| αThr | allo-Threonine; 2S, 3S in the l-series |
| Thz | Thiazolidine-4-carboxylic acid, thiaproline |
| Xaa | Unknown or unspecified (also Aaa) |
| Aad | α-Aminoadipic acid |
| βAad | β-Aminoadipic acid |
| Abu | α-Aminobutyric acid |
| Aib | α-Aminoisobutyric acid; α-methylalanine |
| βAla | β-Alanine; 3-aminopropionic acid (avoid Bal) |
| Asu | α-Aminosuberic acid |
| Aze | Azetidine-2-carboxylic acid |
| Cha | β-cyclohexylalanine |
| Cit | Citrulline; 2-amino-5-ureidovaleric acid |
| Dha | Dehydroalanine (also ΔAla) |
| Gla | γ-Carboxyglutamic acid |
| Glp | pyroglutamic acid; 5-oxoproline (also pGlu) |
| Hph | Homophenylalanine (Hse=homoserine, and so on). Caution is necessary over the use of the prefix homo in relation to α-amino-acid names and the symbols for homo-analogues. When the term first became current, it was applied to analogues in which a side-chain CH2 extension had been introduced. Thus homoserine has a side-chain CH2CH2OH, homoarginine CH2CH2CH2NHC(NH)NH2, and so on. In such cases, the convention is that a new three-letter symbol for the analogue is derived from the parent, by taking H for homo and combining it with the first two characters of the parental symbol – hence, Hse, Har and so on. Now, however, there is a considerable literature on β-amino acids which are analogues of α-amino acids in which a CH2 group has been inserted between the α-carbon and carboxyl group. These analogues have also been called homo-analogues, and there are instances for example not only of ‘homophenylalanine', NH2CH(CH2CH2Ph)CO2H, abbreviated Hph, but also ‘homophenylalanine', NH2CH(CH2Ph)CH2CO2H abbreviated Hph.Further, members of the analogue class with CH2 interpolated between the α-carbon and the carboxyl group of the parent α-amino acid structure have been called both ‘α-homo'- and ‘β-homo’. Clearly great care is essential, and abbreviations for ‘homo’ analogues ought to be fully defined on every occasion. The term ‘β-homo’ seems preferable for backbone extension (emphasizing as it does that the residue has become a β-amino acid residue), with abbreviated symbolism as illustrated by βHph for NH2CH(CH2Ph)CH2CO2H. |
| Hyl | δ-Hydroxylysine |
| Hyp | 4-Hydroxyproline |
| αIle | allo-Isoleucine; 2S, 3R in the l-series |
| Lan | Lanthionine; S-(2-amino-2-carboxyethyl)cysteine |
| MeAla | N-Methylalanine (MeVal=N-methylvaline, and so on). This style should not be used for α-methyl residues, for which either a separate unique symbol (such as Aib for α-methylalanine) should be used, or the position of the methyl group should be made explicit as in αMeTyr for α-methyltyrosine. |
| Nle | Norleucine; α-aminocaproic acid |
| Orn | Ornithine; 2,5-diaminopentanoic acid |
| Phg | Phenylglycine; 2-aminophenylacetic acid |
| Pip | Pipecolic acid; piperidine-s-carboxylic acid |
| Sar | Sarcosine; N-methylglycine |
| Sta | Statine; (3S, 4S)-4-amino-3-hydroxy-6-methyl-heptanoic acid |
| Thi | β-Thienylalanine |
| Tic | 1,2,3,4-Tetrahydroisoquinoline-3-carboxylic acid |
| αThr | allo-Threonine; 2S, 3S in the l-series |
| Thz | Thiazolidine-4-carboxylic acid, thiaproline |
| Xaa | Unknown or unspecified (also Aaa) |