Noncanonical Amino Acids

Unnatural amino acid library

A source-linked reference for representative noncanonical amino acid building blocks used in peptide design, synthesis, and modification-aware curation.

37 database-mapped amino acids Identity and 2D structure linked to PubChem

Scope

TPDB 3D structure viewers are intended for standard-residue peptide models. This library records individual noncanonical amino acid building blocks as 2D molecules rather than predicting modified peptide 3D structures.

Data provenance

Molecular identity, stereochemistry, and 2D depictions are mapped to specific PubChem compound records. Each entry links directly to its source database record; the short note is a conservative chemical and peptide-design summary.

Browse by type

Noncanonical amino acid classes

Showing all 37 entries

D-amino acids

5 entries
2D structure of D-Alanine
D-Ala

D-Alanine

The D stereoisomer of alanine; D-residue substitution is used to reduce protease susceptibility.

Source database PubChem CID 71080
2D structure of D-Phenylalanine
D-Phe

D-Phenylalanine

An aromatic phenylalanine residue with D stereochemistry, used in stability-oriented peptide design.

Source database PubChem CID 71567
2D structure of D-Tryptophan
D-Trp

D-Tryptophan

An indole-bearing tryptophan residue with D stereochemistry for membrane-interacting peptide design.

Source database PubChem CID 9060
2D structure of D-Lysine
D-Lys

D-Lysine

A lysine residue with D stereochemistry that retains a basic, positively charged side chain.

Source database PubChem CID 57449
2D structure of D-Arginine
D-Arg

D-Arginine

A guanidinium-bearing arginine residue with D stereochemistry for cationic peptide design.

Source database PubChem CID 71070

Conformationally restricted

4 entries
2D structure of 2-Aminoisobutyric acid
Aib

2-Aminoisobutyric acid

An achiral alpha,alpha-disubstituted amino acid associated with restricted, helix-favoring conformations.

Source database PubChem CID 6119
2D structure of L-Tetrahydroisoquinoline-3-carboxylic acid
L-Tic

L-Tetrahydroisoquinoline-3-carboxylic acid

A rigid cyclic aromatic amino acid used to restrict peptide backbone and side-chain geometry.

Source database PubChem CID 2733226
2D structure of L-Pipecolic acid
L-Pip

L-Pipecolic acid

A six-membered cyclic imino acid and ring-expanded homolog of proline.

Source database PubChem CID 439227
2D structure of 1-Aminocyclopropane-1-carboxylic acid
Ac3c

1-Aminocyclopropane-1-carboxylic acid

An achiral cyclopropane alpha-amino acid that fixes the alpha-carbon substituents in a compact geometry.

Source database PubChem CID 535

Side-chain analogs

8 entries
2D structure of L-Ornithine
L-Orn

L-Ornithine

A basic non-proteinogenic amino acid whose side chain is one methylene shorter than lysine.

Source database PubChem CID 6262
2D structure of L-Citrulline
L-Cit

L-Citrulline

A neutral ureido amino acid structurally related to arginine.

Source database PubChem CID 9750
2D structure of L-Norleucine
L-Nle

L-Norleucine

A straight-chain, sulfur-free amino acid commonly used as a methionine analog.

Source database PubChem CID 21236
2D structure of L-2-Aminobutyric acid
L-Abu

L-2-Aminobutyric acid

A small aliphatic amino acid with a side chain one carbon longer than alanine.

Source database PubChem CID 80283
2D structure of 3-Cyclohexyl-L-alanine
L-Cha

3-Cyclohexyl-L-alanine

A hydrophobic phenylalanine analog containing a saturated cyclohexyl side chain.

Source database PubChem CID 712421
2D structure of 1-Naphthyl-L-alanine
1-Nal

1-Naphthyl-L-alanine

A bulky aromatic alanine analog containing a 1-naphthyl side chain.

Source database PubChem CID 2724883
2D structure of L-Homoarginine
L-hArg

L-Homoarginine

An arginine homolog with one additional methylene group in the side chain.

Source database PubChem CID 9085
2D structure of L-Homophenylalanine
L-hPhe

L-Homophenylalanine

A phenylalanine homolog with one additional methylene group before the phenyl ring.

Source database PubChem CID 2724505

Beta-amino acids

4 entries
2D structure of Beta-alanine
beta-Ala

Beta-alanine

An achiral beta-amino acid with the amino group on the beta carbon, extending the peptide backbone.

Source database PubChem CID 239
2D structure of (S)-3-Aminobutyric acid
beta-hAla

(S)-3-Aminobutyric acid

A chiral beta-amino acid with a methyl substituent on the amino-bearing beta carbon.

Source database PubChem CID 2761506
2D structure of (3S)-Beta-leucine
beta-Leu

(3S)-Beta-leucine

A branched-chain beta-amino acid containing an isopropyl side chain.

Source database PubChem CID 439734
2D structure of (S)-3-Amino-4-phenylbutanoic acid
beta-hPhe

(S)-3-Amino-4-phenylbutanoic acid

An aromatic beta-amino acid containing a benzyl substituent on the amino-bearing carbon.

Source database PubChem CID 2761537

N-methyl amino acids

4 entries
2D structure of N-Methyl-L-alanine
N-Me-L-Ala

N-Methyl-L-alanine

An N-methylated alanine that changes backbone hydrogen-bonding and conformational behavior.

Source database PubChem CID 5288725
2D structure of N-Methyl-L-phenylalanine
N-Me-L-Phe

N-Methyl-L-phenylalanine

An aromatic N-methyl amino acid used to alter backbone hydrogen bonding and conformation.

Source database PubChem CID 6951135
2D structure of Sarcosine
Sar

Sarcosine

N-Methylglycine, the simplest achiral N-methyl amino acid building block.

Source database PubChem CID 1088
2D structure of N-Methyl-L-leucine
N-Me-L-Leu

N-Methyl-L-leucine

A hydrophobic N-methylated leucine derivative with altered backbone hydrogen-bonding capacity.

Source database PubChem CID 2777993

Halogenated amino acids

4 entries
2D structure of 4-Fluoro-L-phenylalanine
4-F-L-Phe

4-Fluoro-L-phenylalanine

A para-fluorinated phenylalanine analog with modified aromatic electronic properties.

Source database PubChem CID 716312
2D structure of 4-Chloro-L-phenylalanine
4-Cl-L-Phe

4-Chloro-L-phenylalanine

A para-chlorinated phenylalanine analog with a halogenated aromatic side chain.

Source database PubChem CID 736190
2D structure of 4-Bromo-L-phenylalanine
4-Br-L-Phe

4-Bromo-L-phenylalanine

A para-brominated phenylalanine analog with a larger halogen substituent.

Source database PubChem CID 671214
2D structure of 4-Iodo-L-phenylalanine
4-I-L-Phe

4-Iodo-L-phenylalanine

A para-iodinated phenylalanine analog with an iodine-substituted aromatic ring.

Source database PubChem CID 134497

Bioorthogonal amino acids

4 entries
2D structure of L-Azidohomoalanine
Aha

L-Azidohomoalanine

An azide-bearing methionine analog used as a bioorthogonal labeling handle.

Source database PubChem CID 147480
2D structure of L-Propargylglycine
L-Pra

L-Propargylglycine

A terminal-alkyne amino acid used as a handle for click-chemistry conjugation.

Source database PubChem CID 168091
2D structure of p-Azido-L-phenylalanine
pAzF

p-Azido-L-phenylalanine

A phenylalanine analog bearing a para-azide group as a bioorthogonal reaction handle.

Source database PubChem CID 3080772
2D structure of L-Homopropargylglycine
Hpg

L-Homopropargylglycine

A methionine analog bearing a terminal alkyne for bioorthogonal labeling and conjugation.

Source database PubChem CID 11344028

Modified residues

4 entries
2D structure of trans-4-Hydroxy-L-proline
L-Hyp

trans-4-Hydroxy-L-proline

A 4-hydroxylated proline residue found prominently in collagen-derived sequences.

Source database PubChem CID 5810
2D structure of O-Phospho-L-serine
pSer

O-Phospho-L-serine

The phosphorylated form of L-serine and a common post-translationally modified residue.

Source database PubChem CID 68841
2D structure of N6-Acetyl-L-lysine
AcK

N6-Acetyl-L-lysine

An L-lysine residue acetylated at the side-chain amino group, representing lysine acetylation.

Source database PubChem CID 92832
2D structure of O-Sulfo-L-tyrosine
sTyr

O-Sulfo-L-tyrosine

An L-tyrosine residue sulfated at the phenolic oxygen, representing tyrosine sulfation.

Source database PubChem CID 514186