Trimethoprim (C14H18N4O3): structure, properties and hazards

Names and identifiers

IUPAC name: 5-[(3,4,5-trimethoxyphenyl)methyl]pyrimidine-2,4-diamine
Synonyms: Proloprim, co-trimoxazole, Trimpex
+ 36 more
2,4-Diamino-5-(3,4,5-trimethoxybenzyl)pyrimidine, Trimetoprim, Monotrim, Trimopan, Wellcoprim, Syraprim, Monoprim, Uretrim, Trimethoprime, Trimethoprimum, 5-[(3,4,5-trimethoxyphenyl)methyl]pyrimidine-2,4-diamine, Trimetoprima, Tiempe, Trimpex 200, NSC-106568, BW 56-72, NIH 204, Trimogal, Infectotrimet, DTXSID3023712, 2,4-Pyrimidinediamine, 5-[(3,4,5-trimethoxyphenyl)methyl]-, BW-56-72, 5-(3,4,5-Trimethoxybenzyl)-2,4-diaminopyrimidine, NIH-204, 5-((3,4,5-Trimethoxyphenyl)methyl)-2,4-pyrimidinediamine, 5-[(3,4,5-Trimethoxyphenyl)methyl]-2,4-pyrimidinediamine, AN164J8Y0X, 2,4-Pyrimidinediamine, 5-((3,4,5-trimethoxyphenyl)methyl)-, CHEBI:45924, Pyrimidine, 2,4-diamino-5-(3,4,5-trimethoxybenzyl)-, NSC106568, DTXCID803712, 5-((3,4,5-trimethoxyphenyl)methyl)pyrimidine-2,4-diamine, Ledatrim, Proloprin, Triprimix 200
Molecular formula: C₁₄H₁₈N₄O₃
Empirical formula: C₁₄H₁₈N₄O₃
Molecular weight: 290.32 g/mol
Exact mass: 290.13789
CAS number: 738-70-5
PubChem CID: 5578
Canonical SMILES: COC1=CC(=CC(=C1OC)OC)CC2=CN=C(N=C2N)N
Isomeric SMILES: COC1=CC(=CC(=C1OC)OC)CC2=CN=C(N=C2N)N
InChI: InChI=1S/C14H18N4O3/c1-19-10-5-8(6-11(20-2)12(10)21-3)4-9-7-17-14(16)18-13(9)15/h5-7H,4H2,1-3H3,(H4,15,16,17,18)
InChIKey: IEDVJHCEMCRBQM-UHFFFAOYSA-N
Molfile

Names, InChI and the identifiers from PubChem, retrieved 2026-10-14.

Physical properties

TemperaturePressureDensity

Appearance: Trimethoprim is an odorless white powder. Bitter taste. (NTP, 1992)[1]
Odor: Odorless[2]
Melting point: 199 to 203 °C (390 to 397 °F, NTP 1992)[1]
Solubility in water: In water, 400 mg/l @ 25 °C[2]
3 values
From Hazardous Substances Data Bank (HSDB), the most authoritative source here.
Value As written Source
– less than 1 mg/mL at 75 °F (NTP, 1992) [1] CAMEO Chemicalscites National Toxicology Program, Institute of Environmental Health Sciences, National Institutes of Health (NTP). 1992. National Toxicology Program Chemical Repository Database. Research Triangle Park, North Carolina.
– ... Very slightly soluble in water and slightly soluble in alcohol. [2] Hazardous Substances Data Bank (HSDB)cites McEvoy, G.K. (ed.). American Hospital Formulary Service - Drug Information 92. Bethesda, MD: American Society of Hospital Pharmacists, Inc., 1992 (Plus Supplements 1992)., p. 453
–shown In water, 400 mg/l @ 25 °C [2] Hazardous Substances Data Bank (HSDB)cites Yalkowsky SH, Dannenfelser RM; The AQUASOL dATAbASE of Aqueous Solubility. Ver 5. Tucson, AZ: Univ AZ, College of Pharmacy (1992)
log P: log Kow = 0.91[2]
pKa: pKa= 7.12 (conjugate acid)[2]

Value	As written	Source
–	less than 1 mg/mL at 75 °F (NTP, 1992)	[1] CAMEO Chemicalscites National Toxicology Program, Institute of Environmental Health Sciences, National Institutes of Health (NTP). 1992. National Toxicology Program Chemical Repository Database. Research Triangle Park, North Carolina.
–	... Very slightly soluble in water and slightly soluble in alcohol.	[2] Hazardous Substances Data Bank (HSDB)cites McEvoy, G.K. (ed.). American Hospital Formulary Service - Drug Information 92. Bethesda, MD: American Society of Hospital Pharmacists, Inc., 1992 (Plus Supplements 1992)., p. 453
–shown	In water, 400 mg/l @ 25 °C	[2] Hazardous Substances Data Bank (HSDB)cites Yalkowsky SH, Dannenfelser RM; The AQUASOL dATAbASE of Aqueous Solubility. Ver 5. Tucson, AZ: Univ AZ, College of Pharmacy (1992)

Each value as its source reports it, with the source's number after it (listed under References). Where several sources report a property, the row shows the value most of them agree on, the rule the app uses; open the values to see every one.

Calculated

Heavy atoms: 21
Rings: 2
Aromatic rings: 2
Fraction sp³ carbons (Fsp3): 0.29
H-bond donors: 2
H-bond acceptors: 7
Rotatable bonds: 5
TPSA (Å²): 105.5 computed here · PubChem 106
Formal charge: 0
XLogP3: 0.9 PubChem
Complexity: 307 PubChem
Stereocenters: None
Double-bond geometry: None specified
Point group: C1 of one 3D conformer with its hydrogens, by Athanor’s engine (as in the app)

Elemental analysis

C57.92%
H6.25%
N19.30%
O16.53%

Isotope pattern

Each peak is a nominal mass with its abundance-weighted exact mass, as a percentage of the tallest, from IUPAC natural isotope abundances.

Computed from the structure with RDKit 2026.09 when this page was built, beside PubChem's own computed values from its record; where the two differ, both are shown.

Predicted

log P: 1.26 Crippen (Wildman and Crippen 1999)
log S (water solubility): -2.53 ESOL (Delaney 2004), log mol/L
Synthetic accessibility: 2.21 SA score, 1 easy to 10 hard (Ertl and Schuffenhauer 2009)

Drug-likeness: Lipinski’s rule of five

Molecular weight ≤ 500: 290.32
log P ≤ 5 (Crippen): 1.26
H-bond donors ≤ 5: 2
H-bond acceptors ≤ 10: 7

Passes all four rules.

¹³C NMR shifts, predicted

Predictions, not measurements; each names its method. A measured log P, where a source reports one, is under Physical properties.

Safety

Danger

Most widely reported: 140 company reports to ECHA. Source [3].

Harmful or irritant
Health hazard
Environmental hazard

H302Harmful if swallowed (85% of reports)
H361Suspected of damaging fertility or the unborn child (30.7% of reports)
H372Causes damage to organs through prolonged or repeated exposure (26.4% of reports)
H411Toxic to aquatic life with long lasting effects (26.4% of reports)

Precautionary statements: P203, P260, P264, P270, P273, P280, P301+P317, P318, P319, P330, P391, P405, P501

View all classifications (2)

[3] European Chemicals Agency (ECHA)This chemical does not meet GHS hazard criteria for 7.9% (11 of 140) of reports.
[3] European Chemicals Agency (ECHA) · 140 reports · DangerH302, H361, H372, H411

First aid

Eyes: First check the victim for contact lenses and remove if present. Flush victim's eyes with water or normal saline solution for 20 to 30 minutes while simultaneously calling a hospital or poison control center. Do not put any ointments, oils, or medication in the victim's eyes without specific instructions from a physician. Immediately transport the victim after flushing eyes to a hospital even if no symptoms (such as redness or irritation) develop. Skin: Immediately flood affected skin with water while removing and isolating all contaminated clothing.[1]

Storage

Trimethoprim tablets should be stored in tight, light-resistant containers at 15-30 °C in a dry place.[2]
Trimethoprim-sulfamethoxazole should be stored at room temp & not refrigerated. The multiple-dose vials should be used within 48 hr of initial entry. (trimethoprim-sulfamethoxazole)[2]

Safety data sheets on the supplier’s page: LGC Standards, Sigma-Aldrich, Clinivex.

Always read the supplier’s safety data sheet before working with it.

Spectra

Experimental spectra held by these sources; each link opens the source's own record.

Literature

Reading PubChem, OpenAlex and GSRS…

Bioactivity

Reading ChEMBL…

References

[1]CAMEO Chemicals · Public domain (NOAA) · via PubChem · retrieved 2026-10-14
[2]Hazardous Substances Data Bank (HSDB) · Public domain (US NLM) · via PubChem · retrieved 2026-10-14
[3]European Chemicals Agency (ECHA) · ECHA legal notice: reuse with acknowledgement · via PubChem · retrieved 2026-10-14
[4]SpectraBase · Linked only · via PubChem · retrieved 2026-10-14
[5]Human Metabolome Database (HMDB) · Linked only · via PubChem · retrieved 2026-10-14
[6]MassBank of North America (MoNA) · CC BY 4.0 · via PubChem · retrieved 2026-10-14
[7]NIST Mass Spectrometry Data Center · Linked only · via PubChem · retrieved 2026-10-14
[8]MassBank Europe · Linked only · via PubChem · retrieved 2026-10-14
·Calculated values: computed by Athanor with RDKit 2026.09 from the structure.
·Literature on PubChem

Data last updated 2026-10-14.