Tryptophan

l-Tryptophan
	Skeletal formula of L-tryptophan
ball-and-stick model	space-filling model
Names
	IUPAC name Tryptophan
	Systematic IUPAC name 2-Amino-3-(1H-indol-3-yl)propanoic acid
	Other names 2-Amino-3-(1H-indol-3-yl)propionic acid
Identifiers
CAS Number	73-22-3 ;
3D model (JSmol)	Interactive image; Zwitterion: Interactive image;
ChEBI	CHEBI:16828;
ChEMBL	ChEMBL54976 ;
ChemSpider	6066 ;
DrugBank	DB00150 ;
ECHA InfoCard	100.000.723
IUPHAR/BPS	717;
KEGG	D00020 ;
PubChem CID	6305;
UNII	8DUH1N11BX ;
CompTox Dashboard (EPA)	DTXSID5021419 ;
	InChI InChI=1S/C11H12N2O2/c12-9(11(14)15)5-7-6-13-10-4-2-1-3-8(7)10/h1-4,6,9,13H,5,12H2,(H,14,15)/t9-/m0/s1 Key: QIVBCDIJIAJPQS-VIFPVBQESA-N ;
	SMILES c1[nH]c2ccccc2c1C[C@H](N)C(=O)O; Zwitterion: c1[nH]c2ccccc2c1C[C@H]([NH3+])C(=O)[O-];
Properties
Chemical formula	C11H12N2O2
Molar mass	204.229 g·mol−1
Solubility in water	Soluble: 0.23 g/L at 0 °C,; 11.4 g/L at 25 °C,; 17.1 g/L at 50 °C,; 27.95 g/L at 75 °C
Solubility	Soluble in hot alcohol, alkali hydroxides; insoluble in chloroform.
Acidity (pKa)	2.38 (carboxyl), 9.39 (amino)
Magnetic susceptibility (χ)	−132.0·10−6 cm3/mol
Pharmacology
ATC code	N06AX02 (WHO)
Supplementary data page
	Tryptophan (data page)
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Tryptophan (symbol Trp or W) is an α-amino acid that is used in the biosynthesis of proteins. Tryptophan contains an α-amino group, an α-carboxylic acid group, and a side chain indole, making it a polar molecule with a non-polar aromatic beta carbon substituent. Tryptophan is also a precursor to the neurotransmitter serotonin, the hormone melatonin, and vitamin B₃ (niacin). It is encoded by the codon UGG.

Like other amino acids, tryptophan is a zwitterion at physiological pH where the amino group is protonated (–NH⁺
₃; pK_a = 9.39) and the carboxylic acid is deprotonated ( –COO⁻; pK_a = 2.38).

Humans and many animals cannot synthesize tryptophan: they need to obtain it through their diet, making it an essential amino acid.

Tryptophan is named after the digestive enzymes trypsin, which were used in its first isolation from casein proteins. It was assigned the one-letter symbol W based on the double ring being visually suggestive to the bulky letter.