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Pyridine-3-sulfonic acid acts as a competitive antagonist of nicotinic acid and its analogues. The compound is known to antagonize the growth-promoting effects of nicotinamide and nicotinic acid by competing with these essential metabolites for the enzymes involved in their further utilization, due to its similarity in chemical structure. Evidence indicates that the compound acts by preventing the utilization of p-aminobenzoic acid, considered an essential metabolite, by competing with it for the enzymes involved in its conversion. In biological systems, it has also been shown to inhibit squalene epoxidase in human HepG2 cells (IC50 = 150 nM) and to reduce hepatic cholesterol synthesis in rats, though it lacks cholesterol-lowering activity. Additionally, it inhibits nitrate reductase in bacteria and chloroperoxidase in plants. At concentrations ≥10-⁴ M, it can substitute for nicotinamide in bacterial growth assays.
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| ln Vitro |
Pyridine-3-sulfonic acid exhibits significant in vitro enzyme inhibitory activity. It potently inhibits squalene monooxygenase (squalene epoxidase) in human HepG2 cells with an IC50 of 150 nM, as demonstrated in enzyme inhibition assays using pig liver enzyme preparations. The compound also functions as a nicotinic acid antagonist, competitively inhibiting enzymes involved in the utilization of this essential vitamin. At concentrations as low as 10-⁴ M, it has been shown to substitute for nicotinamide and promote bacterial growth in Staphylococcus species, indicating that it can act as a growth factor under certain conditions. In bacterial systems, it inhibits nitrate reductase, while in plant systems, it inhibits chloroperoxidase activity, though no effect on mammalian enzymes beyond those involved in nicotinate metabolism has been reported. The compound also reduces hepatic cholesterol synthesis in rat models.
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| ln Vivo |
In vivo studies have demonstrated that Pyridine-3-sulfonic acid reduces hepatic cholesterol synthesis in rats, though it lacks cholesterol-lowering activity. The compound is orally active, as shown by its effects on cholesterol metabolism following oral administration. In bacterial models, it has been observed to promote growth at certain concentrations by substituting for nicotinamide, indicating that it can be metabolized or utilized in vivo as a growth factor. As a nicotinic acid antagonist, it may interfere with niacin-dependent metabolic pathways in vivo. However, formal efficacy studies in animal disease models have not been published. The compound is not a drug candidate, and its in vivo effects have been characterized primarily in the context of understanding its mechanism as a vitamin antagonist and its effects on cholesterol synthesis.
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| Enzyme Assay |
A standard protocol for cell-free enzyme inhibition assays for Pyridine-3-sulfonic acid, based on squalene epoxidase inhibition studies: (1) Prepare a reaction mixture containing 50 mM potassium phosphate buffer (pH 7.4), 1 mM EDTA, 1 mM DTT, 0.1% Triton X-100, and purified squalene epoxidase enzyme (from pig liver). (2) Add varying concentrations of Pyridine-3-sulfonic acid (0.1 nM to 10 uM) dissolved in DMSO (final DMSO concentration ≤1%). (3) Add the substrate, [3H]squalene (approximately 20 uM, 0.1 uCi/assay). (4) Incubate the reaction at 37degC for 60 minutes in a shaking water bath. (5) Stop the reaction by adding 1 mL of 10% KOH in 50% ethanol and heat at 65degC for 30 minutes to saponify the mixture. (6) Extract the unsaponifiable lipids (including squalene epoxide) with petroleum ether. (7) Analyze the products by thin-layer chromatography (TLC) using silica gel plates and a solvent system of hexane:ethyl ether:acetic acid (70:30:1). (8) Quantify the radioactivity corresponding to squalene epoxide by liquid scintillation counting. (9) Calculate IC50 values by plotting percent inhibition vs. log inhibitor concentration.
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| Cell Assay |
A standard cellular protocol for evaluating the effects of Pyridine-3-sulfonic acid on cell proliferation, based on its use as a nicotinic acid antagonist: (1) Culture Staphylococcus aureus or other susceptible bacterial strains in a defined medium lacking nicotinic acid, such as a synthetic medium containing glucose, ammonium salts, and essential minerals. (2) Grow cells overnight at 37degC with shaking. (3) Dilute the overnight culture to an OD600 of 0.01-0.05 in fresh defined medium. (4) Aliquot 200 uL of the diluted culture into wells of a 96-well microplate. (5) Add varying concentrations of Pyridine-3-sulfonic acid (0.1-1000 uM) and a fixed concentration of nicotinic acid or nicotinamide (e.g., 1 uM) to each well. (6) Include control wells with nicotinamide only (positive growth control) and without nicotinic acid (negative control). (7) Incubate the plate at 37degC for 16-24 hours with shaking. (8) Measure bacterial growth by reading absorbance at 600 nm using a microplate reader. (9) Alternatively, measure cell viability using a resazurin or alamarBlue assay. (10) Determine the concentration required to inhibit 50% of growth promotion (IC50) by comparing growth in the presence of the antagonist to the nicotinamide-only control. In bacterial models, Pyridine-3-sulfonic acid can substitute for nicotinamide at ≥10-⁴ M.
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| Animal Protocol |
Pyridine-3-sulfonic acid has been studied in vivo for its effects on cholesterol synthesis in rats. A standard animal protocol: (1) Male Sprague-Dawley rats (150-200 g) are acclimated for one week on standard laboratory chow. (2) The rats are fasted overnight (12-16 hours) prior to the experiment. (3) Pyridine-3-sulfonic acid is formulated in a suitable vehicle such as 0.5% carboxymethylcellulose (CMC) or water (the compound is water-soluble). (4) Administer the compound by oral gavage at doses of 10-100 mg/kg body weight. (5) For cholesterol synthesis studies, administer a radiolabeled precursor such as [14C]acetate (20 uCi/kg) by intraperitoneal injection 30-60 minutes before sacrifice. (6) Euthanize the animals 2-4 hours after compound administration by CO2 asphyxiation. (7) Collect liver tissue and saponify in 10% KOH in 50% ethanol. (8) Extract the nonsaponifiable lipids (including cholesterol) with petroleum ether. (9) Quantify the incorporation of [14C]acetate into cholesterol by liquid scintillation counting and express as dpm/g liver or as percent of control. (10) Measure serum cholesterol levels using an enzymatic colorimetric assay kit. The compound reduces hepatic cholesterol synthesis but does not lower serum cholesterol levels.
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| ADME/Pharmacokinetics |
Pharmacokinetic properties of Pyridine-3-sulfonic acid have not been systematically characterized. The compound is orally active, as demonstrated by its ability to reduce hepatic cholesterol synthesis in rats following oral administration. Its molecular weight is 159.16, and it is highly soluble in water (almost transparency in water at 20degC) but poorly soluble in organic solvents including methanol, ether, and benzene. The pKa values are approximately 1.4 (for the sulfonic acid group) and 4.8 (for the pyridine nitrogen), indicating that the compound exists primarily as a zwitterion or negatively charged species at physiological pH. These physicochemical properties suggest low membrane permeability and poor oral absorption. In bacterial growth assays, concentrations as low as 10-⁴ M were required for growth-promoting effects, consistent with moderate cellular uptake. For storage, the powder should be kept at room temperature in a tightly sealed container, protected from moisture. Long-term storage at -20degC is recommended. Stock solutions can be prepared in water (10-50 mg/mL) and stored at 4degC for up to one week or at -80degC for longer periods.
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| Toxicity/Toxicokinetics |
Published toxicological data for Pyridine-3-sulfonic acid are limited. According to safety data sheets, the compound may cause eye, skin, and respiratory tract irritation. Standard precautionary measures include avoiding contact with skin and eyes, wearing appropriate personal protective equipment (gloves, goggles, lab coat), and working in a well-ventilated area or fume hood. The compound should not be ingested or inhaled. No data are available regarding acute toxicity (LD50) values in animals, nor are there studies on carcinogenicity, genotoxicity, or reproductive toxicity. As an antagonist of nicotinic acid (vitamin B3), chronic exposure could theoretically interfere with niacin-dependent metabolic pathways. However, the compound is used exclusively as a research chemical and is not intended for human consumption. Standard laboratory safety protocols should be followed, including washing hands thoroughly after handling and disposing of waste according to local regulations. Spills should be cleaned up promptly using appropriate absorbent materials.
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| References | |
| Additional Infomation |
Pyridine-3-sulfonic acid (CAS 636-73-7) is a versatile biochemical reagent and synthetic building block. It is also known as 3-pyridinesulfonic acid or pyridine-3-sulphonic acid and is prepared by the sulfonation of pyridine using fuming sulfuric acid (oleum) at elevated temperatures (230-240degC) in the presence of a mercury catalyst. The compound is structurally related to nicotinic acid (pyridine-3-carboxylic acid), which explains its ability to act as a competitive antagonist of this vitamin. It is also a precursor for the synthesis of pyridine-3-sulfonamide and other sulfonamide derivatives with potential pharmacological activities. In analytical chemistry, it serves as a standard for titration methods (neutralization titration) due to its high purity (≥98% by titration). The compound is also listed as a metabolite in biological pathway databases such as MetaCyc. It has no FDA approval, no clinical trial history, and is not intended for human therapeutic use.
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| Molecular Formula |
C5H5NO3S
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| Molecular Weight |
159.16
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| Exact Mass |
158.999
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| CAS # |
636-73-7
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| PubChem CID |
69468
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| Appearance |
Solid powder
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| Density |
1.5±0.1 g/cm3
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| Melting Point |
>300 °C(lit.)
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| Flash Point |
> 66
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| Index of Refraction |
1.576
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| LogP |
-0.62
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| Hydrogen Bond Donor Count |
1
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| Hydrogen Bond Acceptor Count |
4
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| Rotatable Bond Count |
1
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| Heavy Atom Count |
10
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| Complexity |
193
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| Defined Atom Stereocenter Count |
0
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| SMILES |
C1=CC(=CN=C1)S(=O)(=O)O
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| InChi Key |
DVECLMOWYVDJRM-UHFFFAOYSA-N
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| InChi Code |
InChI=1S/C5H5NO3S/c7-10(8,9)5-2-1-3-6-4-5/h1-4H,(H,7,8,9)
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| Chemical Name |
pyridine-3-sulfonic acid
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| Synonyms |
Pyridine-3-sulphonic acid
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| HS Tariff Code |
2934.99.9001
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| Storage |
Powder -20°C 3 years 4°C 2 years In solvent -80°C 6 months -20°C 1 month |
| Shipping Condition |
Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)
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| Solubility (In Vitro) |
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
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| Solubility (In Vivo) |
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.
Injection Formulations
Injection Formulation 1: DMSO : Tween 80： Saline = 10 : 5 : 85 (i.e. 100 μL DMSO stock solution → 50 μL Tween 80 → 850 μL Saline)(e.g. IP/IV/IM/SC) *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). View More
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)] Oral Formulations
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). View More
Oral Formulation 3: Dissolved in PEG400 (Please use freshly prepared in vivo formulations for optimal results.) |
| Preparing Stock Solutions | 1 mg | 5 mg | 10 mg | |
| 1 mM | 6.2830 mL | 31.4149 mL | 62.8299 mL | |
| 5 mM | 1.2566 mL | 6.2830 mL | 12.5660 mL | |
| 10 mM | 0.6283 mL | 3.1415 mL | 6.2830 mL |
*Note: Please select an appropriate solvent for the preparation of stock solution based on your experiment needs. For most products, DMSO can be used for preparing stock solutions (e.g. 5 mM, 10 mM, or 20 mM concentration); some products with high aqueous solubility may be dissolved in water directly. Solubility information is available at the above Solubility Data section. Once the stock solution is prepared, aliquot it to routine usage volumes and store at -20°C or -80°C. Avoid repeated freeze and thaw cycles.
Calculation results
Working concentration： mg/mL；
Method for preparing DMSO stock solution： mg drug pre-dissolved in μL DMSO (stock solution concentration mg/mL). Please contact us first if the concentration exceeds the DMSO solubility of the batch of drug.
Method for preparing in vivo formulation:：Take μL DMSO stock solution, next add μL PEG300, mix and clarify, next addμL Tween 80, mix and clarify, next add μL ddH2O，mix and clarify.
(1) Please be sure that the solution is clear before the addition of next solvent. Dissolution methods like vortex, ultrasound or warming and heat may be used to aid dissolving.
(2) Be sure to add the solvent(s) in order.
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