Amino Acid Abbreviations HEADING_TITLE

Table of Amino Acid Abreviations

Please use these abreviations to enter your custom peptide sequence.

Amino Acid Single Letter Multiple Letter D-Amino Acid   Unusual Amino Acid Multiple Letter D-Amino Acid
Alanine A Ala d-Ala   3-(1-Naphthyl)alanine 1-Nal d-1-Nal
Arginine R Arg d-Arg   3-(2-Naphthyl)alanine 2-Nal d-2-Nal
Asparagine N Asn d-Asn   Norleucine


Aspartic Acid D Asp d-Asp   Norvaline Nva d-Nva
Cysteine C Cys d-Cys   Octahydroindole-2-carboxylic acid Oic d-Oic
Glutamine Q Gln d-Gln   4-Oxo-Proline 4-Oxo-Pro d-4-Oxo-Pro
Glutamic Acid E Glu d-Glu   Ornithine Orn d-Orn
Glycine G Gly     Penicillamine Pen d-Pen
Histidine H His  d-His   4-Bromophenylalanine Phe(4-Br) d-Phe(4-Br)
Isoleucine I Ile d-Ile   2-Chlorophenylalanine Phe(2-Cl) d-Phe(2-Cl)
Leucine L Leu d-Leu   3-Chlorophenylalanine Phe(3-Cl) d-Phe(3-Cl)
Lysine K Lys d-Lys   4-Chlorophenylalanine Phe(4-Cl) d-Phe(4-Cl)
Methionine M Met d-Met   3,4-Dichlorophenylalanine Phe(3,4-diCl) d-Phe(3,4-diCl)
Phenylalanine F Phe d-Phe   3-Cyanophenylalanine Phe(3-CN) d-Phe(3-CN)
Proline P Pro d-Pro   4-Cyanophenylalanine Phe(4-CN) d-Phe(4-CN)
Serine S Ser d-Ser   2-Fluorophenylalanine Phe(2-F)  d-Phe(2-F)
Threonine T Thr d-Thr   4-Fluorophenylalanine Phe(4-F) d-Phe(4-F)
Tryptophan W Trp d-Trp   4-Iodophenylalanine Phe(4-I) d-Phe(4-I)
Tyrosine Y Tyr d-Tyr   4-Methylphenylalanine Phe(4-Me) d-Phe(4-Me)
Valine V Val d-Val   4-Aminophenylalanine Phe(4-NH2) d-Phe(4-NH2)
          4-Nitrophenylalanine Phe(4-NO2) d-Phe(4-NO2)
 Allylglycine    Allylgly  d-Allylgly   Phenylglycine Phg d-Phg
beta-Alanine   b-Ala     4-Hydroxyphenyglycine Phe(4-OH) d-Phe(4-OH)
2-Aminobutyric acid   2-Abu d-2-Abu   Phosphoserine pSer d-pSer
2-Aminoisobutyric acid   Aib     Phosphothreonine pThr d-pThr
6-Aminohexanioc acid   6-Ahx     Phosphotyrosine pTyr d-pTyr
Citrulline   Cit  d-Cit   3-(2-Pyridyl)alanine 2-Pal d-2-Pal
Cyclohexylalanine   Cha d-Cha   3-(3-Pyridyl)alanine 3-Pal d-3-Pal
Cyclohexylglycine   Chg d-Chg   3-(4-Pyridyl)alanine 3-Pal d-3-Pal
2,4-Diaminobutyric acid   Dab d-Dab   Pyroglutamic acid Pyr d-Pyr
2,3-Diaminopropionic acid   Dap d-Dap   Sarcosine Sar  
Homoarginine   HArg d-HArg   2,3,4,5-Tetrahydroisoquinoline-3-carboxylic acid Tic d-Tic
Homocysteine   HCys d-HCys   tert-Leucine Tle d-Tle
Homoleucine   HLeu d-HLeu   allo-Threonine aThr d-aThr
Homophenylalanine   HPhe d-HPhe   O-Methyl Tyrosine Tyr(Me) d-Tyr(Me)
Homoserine   HSer d-HSer   3-Chlorotyrosine Tyr(3-Cl) d-Tyr(3-Cl)
Homotyrosine   HTyr d-HTyr   3-Iodotyrosine Tyr(3-I) d-Tyr(3-I)
4-trans-Hydroxyproline   Hyp d-Hyp   3,5-Diiodotyrosine Tyr(3,5-I2) d-Tyr(3,5-I2)
Isonipecotic acid   Inp     3-Nitrotyrosine Tyr(3-NO2) d-Tyr(3-NO2)
allo-Isoleucine   aIle d-aIle   3,5-Dinitrotyrosine Tyr(3,5-diNO2) d-Tyr(3,5-diNO2)



Alanine is the simplest optically active amino acid.  It is nonpolar and contributes a hydrophobic character when incorporated into a peptide, although the unprotected amino acid is water soluble.  Alanine is a strong α-helix forming amino acid and does not significantly contribute to turn or β-sheet formation.  AAPPTec provides Fmoc, Boc, and Z protected alanine as well as alanine esters with 99+% purity.  High purity amino acid derivatives from AAPPTec produce higher peptide yields and purer peptides.


Arginine is a basic, hydrophilic amino acid.  The guanidinium group in the sidechain is strongly basic and is protonated in most conditions.  Arginine is a common component of cell-penetrating peptides which are utilized to transport larger molecules and particles into cells.  In proteins, arginine can play a regulatory role.  Arginine residues may be mono- or di-methylated on the sidechain or may be converted to citrulline. Regulatory modifications of arginine residues are often observed in histone proteins.  AAPPTec offers a variety of high purity Fmoc or Boc protected arginine derivatives for solid phase peptide synthesis.  AAPPTec also provides many high quality arginine derivatives for solution phase synthesis.


Asparagine is a polar, hydrophilic amino acid with a strong turn forming influence and is a moderate contributor to β-sheet formation.  It does not contribute significantly to α-helix formation, but is often located near the beginnings or ends of α-helices.  Asparagine derivatives can be utilized in peptide synthesis without sidechain protection, but side reactions, namely dehydration to the nitrile, may occur during coupling.  Protecting the side chain of asparagine residues avoids the side reactions and also increases the solubility of the asparagine derivatives.  AAPPTec offers high purity Fmoc, Boc, and Z asparagine derivatives either with or without sidechain protection.

Aspartic Acid

Aspartic acid is an acidic, hydrophilic amino acid that occurs primarily on the surface of water-soluble proteins.  It has a strong turn-forming influence but does not contribute to β-sheet formation. Aspartic acid residues, with lysine or ornithine residues, can be used to introduce cyclic structure into peptides by formation of amide bonds.  Aspartic acid residues can cyclize, forming aspartimide, which can reopen forming undesired β-aspartyl peptides.  In Boc chemistry, this side reaction can be suppressed by utilizing Asp(OcHx).  In Fmoc chemistry, this side reaction is most prevalent when aspartic acid follows Gly or another Asp residue.  In these cases, utilizing N-Dmb or N-Hmb protected derivatives for the residue preceding Asp prevents aspartimide formation.  Please see the Dmb and Hmb Derivatives section for AAPPTec’s selection of these derivatives for high yield, high purity peptide production.


Cysteine is a small, hydrophobic amino acid that can readily form disulfide bonds.  It has a significant role in forming and stabilizing the tertiary structure of proteins and large peptides.  Some complex peptide structures include as many as three disulfide bridges.  Synthesis of these complex peptides requires differently protected cycteine derivative that can be selectively deprotected.  AAPPTec offers many high quality cysteine derivatives suitable for preparing peptides with complex disulfide bridging.

Since cysteine can be readily oxidized, it plays a role in antioxidants such as glutathione.  The thiol group of the cysteine side chain is highly nucleophilic and often participates in enzymatic reactions.  The thiol group is also a metal chelator and cysteine residues often occur in the metal binding sites of metal-containing enzymes. 


Glutamine is an acidic, hydrophilic amino acid.  It contributes to the stability of α-helices, turns, and β-sheets, but does not promote the formation of a single type of secondary structure.  As an N-terminal residue, glutamine can cyclize to form pyroglutamic acid.  Glutamine, like aspargine, is susceptible to nitrile formation by dehydration.  As with asparagine, side-chain protection blocks this side reaction in increases the solubility of the derivative in organic solvents.  AAPPTec provides Fmoc, Boc, or Z-protected glutamine derivates with 99+% purity.  AAPPTec high purity amino acid derivatives improve peptide yield and purity and improve your chances for success.

Glutamic Acid

Glutamic acid is an acidic, hydrophilic amino acid.  As the amino acid, glutamic acid has important roles as a neurotransmitter and a flavor component.  In peptides, glutamic acid residues may be utilized to form cyclic structures through amide bond formation with a lysine residue side chain.  In addition to high quality glutamic acid derivatives for standard solid phase peptide synthesis, AAPPTec offers specially protected high purity derivatives that can be selectively deprotected on resin for further elaboration.


Glycine is the simplest amino acid.  It lacks a sidechain, thus is achiral.  As a free amino acid, glycine is very water soluble due to its small size and strong hydrogen bonding ability of the acid and amine functions.  Incorporated into a peptide, glycine contributes a small hydrophobic character to the peptide.  Glycine strongly contributes to turn formation, but is a weak contributor to α-helix or β-sheet formation.  AAPPtec provides 99+% pure glycine derivatives for solid phase or solution phase peptide synthesis.  AAPPTec high purity amino acid products produce higher yields with fewer byproducts.  AAPPTec amino acid derivative improve your chances for success.


Histidine is a mildly basic, moderately hydrophobic amino acid.  Histidine residues often play important roles in enzymes.  The histidine side chain can activate serine, threonine or cysteine residues as nucleophiles by abstracting a proton.  It can also quickly remove a proton from a substrate molecule and transfer it to another molecule, forming a cationic intermediate.  The imidazole ring of histidine is a good
metal chelator and histidine residues are often part of the metal binding site of enzymes with metal ion cofactors.  Polyhistidine tags are used to isolate and purify recombinant proteins on nickel ion columns.  The polyhistidine tag binds to the immobilized metal ions, then the tagged protein is released from the column with excess imidazole. 

Histidine is susceptible to racemization during coupling.  In Fmoc chemistry, trityl (Trt) protection on the imidazole ring of the side chain suppresses enaniomerization except when coupling is slow.  In Boc chemistry, His(Bom) should be utilized when histidine racemization is critical.  AAPPTec offers high purity histidine derivatives for solid phase and solution phase peptide synthesis. 


Isoleucine is hydrophobic and promotes the formation of β-sheets.  Isoleucine is one of only two common amino acids with two chiral centers.  Racemization of L-isoleucine forms D-allo-isoleucine.  AAPPtec provides both the L and the D configurations of isoleucine, as well as the diasteromeric isomer allo-isoleucine.


Leucine is hydrophobic and contributes to forming both α-helices and β-sheets.  AAPPTec provides N-protected leucine derivates in greater than 99% purity for optimum solid phase peptide synthesis.  In addition, AAPPTec also offers other high quality leucine derivates, including esters, for solution phase synthesis.  AAPPTec high quality products improve peptide synthesis yield, peptide purity and reduce the time and effort required for purification.  AAPPTec products enhance the chances for success.


Lysine is a basic amino acid with very low hydrophobicity.  Lysine residues are a convenient site for attaching biotin and other types of tags.  The primary amine group of the side chain reacts readily with isothiocyanates, acid chlorides or activated esters.  The lengthy side chain imposes some distance between the tag and the peptide.   Lysine residues are sometimes utilized to form cyclic peptides by forming a amide bond between lysine and aspartic or glutamic acid residues.  Methylation and acetylation of the lysine side chain is involved in regulation, notably in histone proteins.

AAPPTec provides a variety of high-purity labeled or specially protected lysine derivatives for preparing lysine-modified peptides.  Available AAPPTec lysine derivatives include sidechain methylated or acetylated products.


Methionine is nonpolar and hydrophobic, yet contributes more significantly to α-helix formation than β-sheet formation.  Methionine can be oxidized to methionine sulfoxide.  The oxidation can be reversed by methionine oxide reductase enzymes.  AAPPTec offers 99+% pure Fmoc, Boc, or Z protected methionine derivatives in addition to high purity methionine esters.


Phenylalanine is non-polar and very hydrophobic with strong β-sheet forming and moderate α-helix forming properties.  AAPPTec supplies high purity N-protected phenylalanine and phenylalanine derivativesRing-substituted phenylalanine derivatives are often utilized in synthetic peptides to enhance potency or receptor selectivity.  AAPPTec offers a range of high purity substituted phenylalanine derivatives for peptide synthesis.  Please see the Unusual Amino Acid section for AAPPTec’s selection of substituted phenylalanine derivatives. 


Proline is the only natural amino acid that incorporates the α-amine into a ring.   Because of this unique structure, proline residues introduce a “kink” into the backbone structure of peptides.  Proline disrupts β-sheet formation and promotes turn formation.  This property of the proline residue is exploited in pseudoproline derivatives utilized to disrupt peptide aggregation and product higher yield and higher purity peptides with difficult sequences.  (See the Pseudoproline Dipeptide section for AAPPTec’s pseudoproline products).  Since proline does not contain a primary amine, Kaiser test (ninhydrin test) results may give false positive results when testing coupling to proline.  Alternative tests, such as the 2,4,6-trinitobezoic acid test, should be considered.

AAPPTec provides 99+% pure proline derivatives for solid phase and solution phase synthesis.  Utilizing AAPPTec high quality N-protected proline derivates and proline esters improves peptide yield and purity.


Serine, as the free amino acid, is highly water soluble and the mono-protected derivatives also display a high affinity for water.  Within a peptide sequence, however, isolated serine residues display moderate hydrophilicity.  Common modifications of serine are phosphorylation and glycosylation.  Phosphoserine residues play a role in cell signaling and glucoserine residues can significantly increase metabolic stability of peptides (T. Yamamoto, et al, J. Med. Chem., 2009, 52, 5164-75.).  AAPPTec provides high quality Fmoc-Ser derivatives that can be selectively deprotected to permit site-specific peptide modification in addition to optically pure, high quality Fmoc-Ser(tBu) for standard peptide synthesis.


Threonine is one of two natural amino acids that has two chiral centers.  Raceimization of L-threonine produces D-allo-threonine.  Threonine is polar and within a peptide sequence, threonine residues are moderately hydrophilic.  Like serine, common modifications of threonine are phosphorylation and glycosylation.  AAPPTec provides a selection of 99+% protected threonine derivatives for solid phase peptide synthesis.  AAPPTec also carries high purity threonine esters and Z-threonine derivative for solution phase synthesis.


Tryptophan is an aromatic, nonpolar hydrophobic amino acid.  The indole ring of tryptophan can be modified during the cleavage and deprotection of the peptide.  These side reactions can be avoided by utilizing Trp(Boc) in Fmoc synthesis and Trp(Formyl) or Trp(Hoc) in Boc synthesis.  Tryptophan has significant absorbance at 280 nm and can be used to estimate peptide concentration.  Tyrosine and cystine (but not cysteine) also absorb at 280 nm, but not as strongly as trytophan.

AAPPTec provides high purity protected tryptophan derivatives for solid phase and solution phase synthesis.  All AAPPTec Fmoc amino acids are 99+% pure for optimum peptide synthesis yields.


Tyrosine is moderately hydrophobic and contributes strongly to β-sheet formation.  Tyrosine phosphorylation is a key process in signal transduction and enzyme regulation.  Sulfation of tyrosine plays a critical role in the recognition of CCK-A sites.  Increased nitrotyrosine levels in proteins is an indicator of oxidative stress.

AAPPTec supplies high purity tyrosine derivatives for solid phase or solution phase peptide synthesis.  AAPPTec high purity amino acid derivatives produce higher yields and purer peptides.


Valine is a non-polar, highly hydrophobic residue that strongly participates in β-sheet formation.   Valine substitution for glutamic acid in hemoglobin results in abnormal aggregation, the cause of sickle-cell disease.  AAPPTec’s 99+% Fmoc, Boc, or Z-protected valine derivatives maximize peptide yield and purity while minimizing undesired byproducts.