Drug compounds have included stable heavy isotopes of carbon, hydrogen, and other elements, mostly as tracers that influence measurement during the drug development process. It's possible that the pharmacokinetics and functional range of medications contribute to the concern over mutagenesis [1].

Absorption, Distribution and Excretion
We conducted diffusion cell experiments on aniline (ANI), o-toluidine (OT), 4,4'-methylenediphenylamine (MDA), and N-phenyl-2-naphthylamine (PBNA). Human skin was exposed to amino acid solutions of varying concentrations containing water and solvent. Within 24 hours, the recovery rates of ANI in the recipient fluid were approximately 20-38%, and the recovery rate of MDA was 15%. PBNA was not detected in the recipient fluid. We also referenced data from recent studies on OT and β-naphthylamine (BNA). We derived a semi-quantitative ranking of amino acid transdermal absorption as follows: BNA > OT > ANI > MDA > PBNA. For saturated concentrations of ANI in aqueous solution, a linear relationship between exposure dose and permeation was observed. However, the linear extrapolation of pure compound flux, often recommended in risk assessment policies, significantly underestimates transdermal absorption. In vitro data support… the findings of a study of rubber industry workers that transdermal absorption may significantly increase overall AA exposure.
...This study used a diffusion cell to investigate the effects of two skin barrier creams (SBC) and one skin cream (SCC) on the transdermal penetration of aniline (ANI) and o-toluidine (OT), as well as a mixture of OT and workplace-specific lubricants. Experiments were conducted on untreated skin and skin treated with the skin cream. Compared to untreated skin, treated skin showed significantly enhanced transdermal penetration of the test compounds; the enhancement was most significant on skin treated with SBC (water-in-oil emulsion-based) (mean enhancement factor 6.2–12.3 times). Skin treated with SCC showed the lowest enhancement (mean enhancement factor 4.2–9.7 times). In vitro data support...the phenomenon observed in workers where the transdermal absorption of aromatic amines is significantly increased when skin cream is applied. The effectiveness of skin cream in protecting the transdermal penetration of aromatic amines has not yet been confirmed...
...Using a diffusion cell...the penetration of o-toluidine (OT) through human skin was measured. OT is rapid (lag time: approximately 0.8 hours) and has high penetration (50% penetration of the administered dose within 24 hours). Therefore, the use of a moisturizing cream is reasonable…
The distribution of the carcinogen o-toluidine (OT) in rats was studied using diazotization. Three days after the last administration (total treatment duration of 8 months), the level of free amines was 1.5–2 times that of the control group. The highest concentrations were observed in the target tissue gland (Zymbal gland). Furthermore, the concentration of conjugated amines in the gland was also significantly increased (8 times that of the control group). Similar results were reported seven days after the last OT administration: the level of free amines at the same site was 7 times that of the control group. The increased concentrations of free and conjugated amines may indicate their excretion via the Zymbal gland ducts. This may also promote their carcinogenesis.
For more data on the absorption, distribution, and excretion (complete) of 2-aminotoluene (21 in total), please visit the HSDB record page.

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Metabolism/Metabolites
Male F344 rats were subcutaneously injected with 50 or 400 mg/kg of o-[methyl-(14)C]toluidine… The results showed that the main metabolic pathway of o-toluidine in rats was N-acetylation and 4-hydroxylation. Secondary pathways included 6-hydroxylation, methyl oxidation, and amino oxidation. The ratio of sulfate conjugate to glucuronide was 6:1. Substances detected in urine included o-toluidine, azotoluene, o-nitrosotoluene, N-acetyl-o-toluidine, N-acetyl-o-aminobenzyl alcohol, 4-amino-m-cresol, N-acetyl-4-amino-m-cresol, o-aminobenzoic acid, N-acetyl-o-aminobenzoic acid, 2-amino-m-cresol, and unidentified substances. Substances excreted in feces or exhaled air were not mentioned. Four dogs over one year of age received intravenous injection of o-toluidine hydrochloride at a dose of 0.77 mM/kg body weight (equivalent to 111.1 mg/kg body weight), dissolved in water. Blood concentrations of o-toluidine were observed over 6 hours… N-oxidation products were extracted from the blood using carbon tetrachloride… Hemoglobin was estimated by measuring the increase in absorbance at 550 μm after adding cyanide to a blood solution at pH 6.8. The plasma elimination half-life was approximately half an hour. Approximately 10 μg of o-toluidine was detected per milliliter of blood 7 hours after administration. The proportion of hemoglobin to total hemoglobin increased with time after administration, reaching a maximum at 6 hours, indicating the presence of reactive oxidation products. The carbon tetrachloride extract was free of o-nitrosotoluene. Male F344 rats (weighing 230–260 g) were subcutaneously injected with 0.82 mmol/kg body weight o-toluidine (corn oil solution). Urine was collected over 6 hours. All urine samples were analyzed using high-performance liquid chromatography-electrochemical detection within 4 hours of collection. In rats treated with 0.82 mmol/kg body weight of o-toluidine, the concentration of N-hydroxytoluidine in urine ranged from 0.04 to 0.36 μmol from 0 to 6 hours. The activities of metabolic enzymes in the liver, kidneys, and lungs of rats were determined. Male Wistar rats, weighing 200-250 g (n=6 per group), were intraperitoneally injected with 0.75 mg/kg body weight of o-toluidine (dissolved in sunflower oil) for 3 consecutive days. After the last administration, the rats were sacrificed after fasting for 12 hours. On the fourth day, the rats were decapitated, and the liver, kidneys, and lungs were immediately removed, weighed, and homogenized. Analysis was performed (methods not mentioned); a p-value < 0.05 was considered statistically significant. Changes in enzyme activity in various organs: Liver: Cytochrome b5: 0.545 vs 0.447 nmol/mg protein; NADPH cytochrome c reductase: 201.3 vs 165.8 nmol/mg protein/min; Aromatic hydrocarbon hydrolase (AHH): 654 vs 295 pmol/mg protein/min; Glutathione S-transferase to AHH activity ratio: 1926 vs 3969 nmol/mg protein/min; Epoxide hydrolase to AHH activity ratio: 1.85 vs 3.35 nmol/mg protein/min. Kidney: AHH: 70.35 vs 2.91 pmol/mg protein/min; glutathione S-transferase to AHH activity ratio: 2840 vs 63780 nmol/mg protein/min; epoxide hydrolase to AHH activity ratio: 1.24 vs 34.02 nmol/mg protein/min. Lung: AHH: 9.49 vs 4.75 pmol/mg protein/min; glutathione S-transferase to AHH activity ratio: 5184 vs 12484 nmol/mg protein/min; epoxide hydrolase to AHH activity ratio: 4.00 vs 9.89 nmol/mg protein/min.
For more complete data on the metabolisms/metabolites of 2-aminotoluene (14 in total), please visit the HSDB record page.

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Biological Half-Life
In rats (strain not specified), the plasma elimination half-life after oral administration of 500 mg/kg body weight of toluidine was 12 to 15 hours; in dogs, the plasma elimination half-life after intravenous injection of approximately 111 mg/kg body weight was half an hour.

Toxicity Summary
Compound Identification: o-Toluidine is a synthetic chemical, a pale yellow liquid at room temperature. It is primarily used in dye manufacturing, but also in the production of rubber, chemicals, and pesticides, and as a curing agent in epoxy resin systems. Human Exposure: In occupational settings, o-toluidine may exhibit significant carcinogenicity and genotoxicity. Animal Studies: The acute toxicity of o-toluidine is low to moderate, potentially causing mild skin irritation and mild irritation. Information regarding skin or respiratory sensitization by o-toluidine is currently unavailable. The main toxic symptom following short-term acute exposure to this chemical is methemoglobinemia and its associated effects on the spleen. These effects were observed in rats after administration of o-toluidine at a dose of 225 mg/kg body weight/day for 5 consecutive days. The No Observed Adverse Effect Dose (NOEL) has not been determined. In several carcinogenicity studies, oral administration of o-toluidine to rats and mice resulted in a significant increase in the incidence of benign and malignant tumors in various tissues. o-Toluidine is generally not mutagenic in standard bacterial mutagenicity tests, but it is chromosomal breakage-inducing in in vitro mammalian cells. The in vivo genotoxicity of o-toluidine is uncertain; however, some positive results have been reported. Based on the widespread distribution of tumors in animals exposed to o-toluidine and the chromosome breakage activity observed in in vitro mammalian studies, o-toluidine may have genotoxic carcinogenic effects. No information was found related to assessing the risk of reproductive or developmental effects of o-toluidine.

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Toxicity Data
LC50 (rat) = 862 ppm/4hInteractions
Concurrent subcutaneous injection of benzidine and o-toluidine into 116 rats resulted in earlier tumor development. The latency of aniline was twice that of the combined administration (548.6 days vs. 264.1 days, respectively).

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Non-human toxicity values
Oral LD50 in rats: 940 mg/kg
Oral LD50 in rats: 670 mg/kg
Wistar oral LD50 in rats: 0.75 mL/kg body weight (750 mg/kg body weight)
Intraperitoneal LD50 in male Sprague-Dawley rats: 164 mg/kg body weight
For more complete non-human toxicity data for 2-aminotoluene (out of 15), please visit the HSDB records page.

[1]. Impact of Deuterium Substitution on the Pharmacokinetics of Pharmaceuticals. Ann Pharmacother. 2019 Feb;53(2):211-216.

According to an independent committee of scientific and health experts, o-toluidine is potentially carcinogenic. o-Toluidine appears as a colorless or pale yellow transparent liquid. It may turn reddish-brown upon exposure to air and light. Its flash point is 85 degrees Celsius (185 degrees Fahrenheit). Its density is similar to water, and it is slightly soluble in water. Its vapor is heavier than air. It has been identified as a carcinogen. o-Toluidine is an aminotoluene, in which the amino substituent is located ortho-to the methyl group. It is a carcinogen. o-Toluidine is primarily used in dye manufacturing. o-Toluidine is highly toxic to humans through skin absorption, inhalation of vapors, or ingestion. Acute (short-term) exposure to o-Toluidine can affect the blood (e.g., methemoglobinemia) and cause clinical symptoms of central nervous system depression. Long-term exposure to o-Toluidine can cause chronic (long-term) effects such as anemia, anorexia, weight loss, skin lesions, central nervous system depression, cyanosis, and methemoglobinemia. Animal studies have shown that long-term exposure to o-toluidine can damage the spleen, liver, bladder, and blood. Occupational exposure to dyes (including o-toluidine) is associated with an increased risk of bladder cancer. 2-Methylaniline hydrochloride (the hydrochloride salt of o-toluidine) is carcinogenic to rats and mice. O-toluidine has been classified as a Group 2 carcinogen by the U.S. Environmental Protection Agency (EPA), meaning it is likely carcinogenic to humans. O-toluidine has been reported to be present in tea (Camellia sinensis), and relevant data exist. O-toluidine is a synthetic, light-colored, light-sensitive liquid, slightly soluble in water, and miscible with carbon tetrachloride, ether, and ethanol. O-toluidine hydrochloride is a synthetic, light-sensitive white crystalline powder, soluble in dimethyl sulfoxide and ethanol. O-toluidine and its hydrochloride are primarily used as intermediates in the production of dyes and pigments. O-toluidine decomposes upon heating, releasing toxic nitrogen oxide fumes, while the hydrochloride salt also produces hydrochloric acid. Four studies on workers exposed to o-toluidine reported an increased incidence of bladder cancer. o-Toluidine and its hydrochloride are likely human carcinogens. (NCI05)
Toluidine's chemical properties are very similar to aniline and share properties with other aromatic amines. Due to the amino group attached to the aromatic ring, toluidine is weakly basic. All toluidine compounds have low solubility in pure water, but will dissolve in acidic solutions due to the formation of ammonium salts, as is typical for organic amines. At room temperature and pressure, o-toluidine and m-toluidine are viscous liquids, while p-toluidine is a flaky solid. This can be explained by the more symmetrical molecule of p-toluidine, making it easier to form a crystal structure. p-Toluidine can be prepared by reducing p-nitrotoluene. p-Toluidine reacts with formaldehyde to form the Trog base.

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Mechanism of Action
The mechanism of DNA damage caused by the carcinogen o-toluidine metabolites in the presence of metals was studied using DNA sequencing technology with 32P-labeled human DNA fragments. The main metabolite, 4-amino-3-methylphenol, causes DNA damage in the presence of Cu(II). The primary DNA cleavage sites are thymine and cytosine residues. o-Nitrotoluene is a minor metabolite that does not induce DNA damage even in the presence of Cu(II), but the addition of NADH induces DNA damage very effectively. Its DNA cleavage pattern is similar to that of 4-amino-3-methylphenol. Bartophenonelin and catalase inhibit DNA damage induced by these o-toluidine metabolites, indicating that Cu(I) and H₂O₂ are involved in the DNA damage process. Typical hydroxyl radical scavengers have no inhibitory effect on DNA damage. In the presence of Cu(II), o-toluidine metabolites increase the formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine in calf thymus DNA. UV-Vis and electron spin resonance (ESR) spectroscopy studies show that 4-amino-3-methylphenol undergoes auto-oxidation in the presence or absence of Cu(II) to generate aminomethylphenoxy radicals, while o-nitrosotoluene is reduced to o-toluenehydronitrooxy radicals under the action of NADH. Therefore, these free radicals are thought to react with O₂ to generate O₂⁻, which in turn generates H₂O₂, and the reactive species produced by the reaction of H₂O₂ with Cu(I) are involved in DNA damage. The metal-dependent DNA damage mediated by H₂O₂ via o-toluidine metabolites appears to be associated with the carcinogenicity of o-toluidine. This study investigated the in vivo covalent binding of o-toluidine and p-toluidine to rat liver macromolecules to determine whether there was a correlation between the degree of binding of each isomer and its carcinogenic potency. The ortho isomer has been shown to have stronger hepatotoxicity than the para isomer. In addition to macromolecular binding, the tissue distribution of each isomer was measured. The degree of binding of both isomers to liver macromolecules appeared to reach its maximum 24–28 hours post-administration. At 24 hours post-administration, the binding level of o-toluidine to DNA was approximately 1.2 times lower than that of p-toluidine. The binding of o-toluidine to RNA and proteins was also lower than that of p-toluidine, but the difference was not as significant as the difference in DNA binding. The tissue distribution of the two isomers showed subtle differences. However, contrary to the macromolecular binding data, the area under the plasma concentration-time curve for o-toluene was approximately 1.8 times greater than that for p-toluene. Based on the results of these studies, there is no direct correlation between the degree of macromolecular binding and carcinogenic potency.

C7H2D7N

114.20

114.117

68408-22-0

97917-08-3;636-21-5 (hydrochloride)

7242

Colorless to light yellow liquid

2.7 °F (NTP, 1992)
-14.41 °C
Melting point: -23.7 °C (alpha form); -14.7 °C (beta form)
-16.3 °C
-16 °C (beta-form)
2.7 °F
6 °F

2.158

1

1

0

8

70.8

0

[2H]C1=C([2H])C([2H])=C(N)C(C([2H])([2H])[2H])=C1[2H]

RNVCVTLRINQCPJ-UHFFFAOYSA-N

InChI=1S/C7H9N/c1-6-4-2-3-5-7(6)8/h2-5H,8H2,1H3

2-methylaniline

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

May dissolve in DMSO (in most cases), if not, try other solvents such as H2O, Ethanol, or DMF with a minute amount of products to avoid loss of samples

Note: Listed below are some common formulations that may be used to formulate products with low water solubility (e.g. < 1 mg/mL), you may test these formulations using a minute amount of products to avoid loss of samples.

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Injection Formulation 1: DMSO : Tween 80： Saline = 10 : 5 : 85 (i.e. 100 μL DMSO stock solution → 50 μL Tween 80 → 850 μL Saline)
*Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH ₂ O to obtain a clear solution.
Injection Formulation 2: DMSO : PEG300 ：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL DMSO → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)
Injection Formulation 3: DMSO : Corn oil = 10 : 90 (i.e. 100 μL DMSO → 900 μL Corn oil)
Example: Take the Injection Formulation 3 (DMSO : Corn oil = 10 : 90) as an example, if 1 mL of 2.5 mg/mL working solution is to be prepared, you can take 100 μL 25 mg/mL DMSO stock solution and add to 900 μL corn oil, mix well to obtain a clear or suspension solution (2.5 mg/mL, ready for use in animals).

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Injection Formulation 4: DMSO : 20% SBE-β-CD in saline = 10 : 90 [i.e. 100 μL DMSO → 900 μL (20% SBE-β-CD in saline)]
*Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.
Injection Formulation 5: 2-Hydroxypropyl-β-cyclodextrin : Saline = 50 : 50 (i.e. 500 μL 2-Hydroxypropyl-β-cyclodextrin → 500 μL Saline)
Injection Formulation 6: DMSO : PEG300 : castor oil : Saline = 5 : 10 : 20 : 65 (i.e. 50 μL DMSO → 100 μLPEG300 → 200 μL castor oil → 650 μL Saline)
Injection Formulation 7: Ethanol : Cremophor : Saline = 10： 10 : 80 (i.e. 100 μL Ethanol → 100 μL Cremophor → 800 μL Saline)
Injection Formulation 8: Dissolve in Cremophor/Ethanol (50 : 50), then diluted by Saline
Injection Formulation 9: EtOH : Corn oil = 10 : 90 (i.e. 100 μL EtOH → 900 μL Corn oil)
Injection Formulation 10: EtOH : PEG300：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL EtOH → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)

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Oral Formulation 1: Suspend in 0.5% CMC Na (carboxymethylcellulose sodium)
Oral Formulation 2: Suspend in 0.5% Carboxymethyl cellulose
Example: Take the Oral Formulation 1 (Suspend in 0.5% CMC Na) as an example, if 100 mL of 2.5 mg/mL working solution is to be prepared, you can first prepare 0.5% CMC Na solution by measuring 0.5 g CMC Na and dissolve it in 100 mL ddH2O to obtain a clear solution; then add 250 mg of the product to 100 mL 0.5% CMC Na solution, to make the suspension solution (2.5 mg/mL, ready for use in animals).

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Oral Formulation 3: Dissolved in PEG400
Oral Formulation 4: Suspend in 0.2% Carboxymethyl cellulose
Oral Formulation 5: Dissolve in 0.25% Tween 80 and 0.5% Carboxymethyl cellulose
Oral Formulation 6: Mixing with food powders

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Note: Please be aware that the above formulations are for reference only. InvivoChem strongly recommends customers to read literature methods/protocols carefully before determining which formulation you should use for in vivo studies, as different compounds have different solubility properties and have to be formulated differently.

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 (Please use freshly prepared in vivo formulations for optimal results.)