Tryptophan

C 11
H 12
N 2
O 2

Ball-and-stick Stick Space-filling

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27 atoms, 28 bonds.

IUPAC name: (2S)-2-amino-3-(1H-indol-3-yl)propanoic acid
Molar mass: 204.229(28) g/mol
Atoms: 27
SMILES: C1=CC=C2C(=C1)C(=CN2)CC(C(=O)O)N
InChIKey: QIVBCDIJIAJPQS-VIFPVBQESA-N
PubChem CID: 6305

Made of

C H N O

Structural formula of tryptophan. Each unlabelled corner is a carbon atom, and the eight hydrogens on carbon are not drawn. Wedges come toward you, hashes go back. It shows which atoms are joined to which, not the shape. The model above shows the shape.

Tryptophan carries an indole group, two rings fused along one edge, the smaller holding a nitrogen atom. Its IUPAC name, (2S)-2-amino-3-(1H-indol-3-yl)propanoic acid, places that group on the third carbon of a three-carbon acid, with an amino group on the second. Eleven carbon, twelve hydrogen, two nitrogen and two oxygen atoms add up to 204.23 g/mol. The (2S) fixes one of two mirror-image forms, L-tryptophan, a building block of proteins; a D form also exists.

The pure compound is a white powder with no smell and a flat, slightly bitter taste. Heated, it decomposes at 282 °C, or at 289 °C when heated rapidly. Its solubility in water rises with temperature, from 11.4 g/L at 25 °C to 49.9 g/L at 100 °C. The US Centers for Disease Control and Prevention (CDC) calls it an essential amino acid and notes that it is normally taken in as part of dietary protein.

Structure and bonding

Nine of the model’s 27 atoms make the indole rings: a six-membered carbon ring fused along one bond to a five-membered ring of four carbons and an N–H. A CH₂ links the smaller ring to a carbon holding NH₂, H and COOH. In Ball-and-stick, both chain carbons point four single bonds at the corners of a tetrahedron, as Chem1 describes.

Turned edge-on, the two rings shrink to a thin line: in PubChem’s computed model all nine ring atoms sit within 0.002 Å of one plane. Space-filling swells them into a broad slab; Stick leaves only the bonds.

The model fixes four C=C bonds, three in the six-membered ring and one in the five, alternating with single bonds. Chem1 calls such alternation a conjugated system, its double-bond electrons delocalised, spread over the rings (benzene shows why). The drawing is the uncharged molecule; glycine covers the charged forms.

Where it turns up

The US National Cancer Institute’s thesaurus names dairy products, meat, fish, brown rice and soybeans as foods that contain it. It takes part in the metabolism of the yeast Saccharomyces cerevisiae, of plants, of Escherichia coli and of people, and has been reported in the plant Bupleurum chinense. In the epidermis, the outer layer of skin, proteins containing tryptophan and tyrosine are among the absorbers of shorter-wavelength ultraviolet light.

Farms put niacin or tryptophan into the concentrated feed of intensively reared poultry and pigs, according to the Hazardous Substances Data Bank (HSDB). Laboratories use it as a probe of protein structure and motion. The US Food and Drug Administration (FDA) permits it as an additive placed directly in food. The Environmental Protection Agency allows it as an inert ingredient in pesticides not used on food, and cosmetics use it as an antistatic agent.

Why it matters

Mammals can turn tryptophan into the vitamin niacin, though inefficiently, according to MeSH, the National Library of Medicine’s subject headings. Corn falls short twice: its niacin is bound and unusable, and it is low in tryptophan. Diets heavy in corn therefore brought pellagra, a niacin deficiency, HSDB explains. In Hartnup disease, a failure to absorb certain amino acids from food, MeSH traces the light-sensitive, pellagra-like rash to tryptophan lost in urine. MedlinePlus links many of its features to a shortage of tryptophan and niacin.

On 30 October 1989, New Mexico health officials learned of three L-tryptophan users with eosinophilia, an eosinophil count far above normal, and severe myalgia, or muscle pain. On 11 November the FDA advised consumers to stop taking L-tryptophan tablets and capsules, then recalled them six days later. By 24 August 1990 the CDC had 1,536 reported cases of eosinophilia-myalgia syndrome and 27 deaths. Peak 97, the trace compound most predictive of the implicated lots, was DTAA, made from tryptophan and acetaldehyde: two tryptophan units bridged through their ring nitrogens. Whether it caused the illness stayed unsettled.

Properties

Properties of tryptophan Molar mass summed from IUPAC/CIAAW 2024 standard atomic weights; formula, atom and bond counts and PubChem's molecular weight from PubChem CID 6305.
Property	Value	Unit	Source
Molecular formula (Hill order)	C₁₁H₁₂N₂O₂
Molar mass	204.229(28) g/mol	g/mol	IUPAC/CIAAW 2024
Carbon atoms	11
Hydrogen atoms	12
Nitrogen atoms	2
Oxygen atoms	2
Bonds	28
Single bonds	23
Double bonds	5
PubChem molecular weight	204.22 g/mol	g/mol	PubChem

Safety

Eaten as part of dietary protein, tryptophan is essentially harmless. Under the Globally Harmonized System it went unclassified in 222 of 225 reports to the European Chemicals Agency. Toxic fumes come off it when it is heated to decomposition. These cautions sit in the PubChem Laboratory Chemical Safety Summary for tryptophan.

Questions

Why is tryptophan's indole ring flat?

Each of the ring system's eight carbons is drawn with a double bond. Chem1 describes such a carbon as bonded to three neighbours in one flat, trigonal arrangement, formed from sp² hybrid orbitals; hybridisation, it adds, is a mathematical treatment rather than a physical process. In PubChem's computed model the nine ring atoms, nitrogen included, share a single plane, and the CH₂ link joins that flat unit to the amino-acid end.

What does the body make from tryptophan?

A vitamin, a neurotransmitter and a hormone, among other products. The Hazardous Substances Data Bank (HSDB) names it as the starting material for niacin, serotonin, tryptamine and melatonin, a hormone of the pineal gland. The route to serotonin runs through 5-hydroxytryptophan (5-HTP). In the liver, the enzymes tryptophan pyrrolase and tryptophan hydroxylase break it down, and plants use it to build indole alkaloids.

Does tryptophan help you sleep?

MeSH, the National Library of Medicine's subject vocabulary, ties its use as a sleep aid and antidepressant to serotonin, which the body makes from it. NCCIH, the US National Center for Complementary and Integrative Health, reports that L-tryptophan has sedative effects, but how they work is unclear and the data on its effects on insomnia are very limited.

Where does commercial tryptophan come from?

Fermentation with the bacterium Corynebacterium glutamicum builds it from natural or biologically available feedstocks, and an enzyme route uses microbial tryptophanase to assemble it from indole, pyruvic acid and ammonia. Chemical syntheses start from compounds such as hydantoin or 3-indoleacetonitrile. In 1977 the United States made none commercially and imported 2.34 × 10⁷ g, about 23 tonnes. The Hazardous Substances Data Bank lists nutrition and research, medicine, dietary supplements and cereal enrichment among its uses.

Made of the same elements

C₁₀H₁₂N₂O Serotonin 25 atoms, 26 bonds.
C₉H₁₁NO₂ Phenylalanine 23 atoms, 23 bonds.
C₈H₁₁NO₂ Dopamine 22 atoms, 22 bonds.
C₉H₁₃NO₃ Epinephrine 26 atoms, 26 bonds.
C₉H₁₁NO₃ Tyrosine 24 atoms, 24 bonds.
C₁₃H₁₆N₂O₂ Melatonin 33 atoms, 34 bonds.
C₈H₉NO₂ Acetaminophen 20 atoms, 20 bonds.
C₈H₁₀N₄O₂ Caffeine 24 atoms, 25 bonds.

All 25 compounds made of carbon, hydrogen, nitrogen and oxygen

C₆H₁₃NO₂ Isoleucine 22 atoms, 21 bonds.
C₆H₁₃NO₂ Leucine 22 atoms, 21 bonds.
C₁₂H₁₇NO DEET 31 atoms, 31 bonds.
C₁₄H₁₈N₂O₅ Aspartame 39 atoms, 39 bonds.
C₅H₉NO₄ Glutamic acid 19 atoms, 18 bonds.
C₅H₆N₂O₂ Thymine 15 atoms, 15 bonds.
C₁₃H₂₁NO₃ Albuterol 38 atoms, 38 bonds.
C₃H₇NO₂ Alanine 13 atoms, 12 bonds.
C₁₄H₂₂N₂O Lidocaine 39 atoms, 39 bonds.
C₄H₄N₂O₂ Uracil 12 atoms, 12 bonds.
C₄H₅N₃O Cytosine 13 atoms, 13 bonds.
C₁₇H₂₁NO Diphenhydramine 40 atoms, 41 bonds.
C₂H₅NO₂ Glycine 10 atoms, 9 bonds.
C₅H₅N₅O Guanine 16 atoms, 17 bonds.
C₅H₄N₄O₃ Uric acid 16 atoms, 17 bonds.
CO(NH₂)₂ Urea 8 atoms, 7 bonds.
C₂₀H₂₄N₂O₂ Quinine 48 atoms, 51 bonds.