Views: 0 Author: Site Editor Publish Time: 2026-02-06 Origin: Site
In the pharmaceutical manufacturing landscape of 2026, 5-Methyl-4-isoxazolecarboxylic acid (CAS No. 42831-50-5) remains a high-value building block. It is primarily recognized as Leflunomide Impurity D, though its primary industrial role is far more critical: it serves as the essential heterocyclic intermediate for the synthesis of Leflunomide and its active metabolite, Teriflunomide.
These medications are cornerstones in the treatment of rheumatoid arthritis (RA) and multiple sclerosis (MS). By providing a stable isoxazole ring already functionalized with a carboxyl group, this compound allows for a streamlined, high-yield acylation process to create the final active pharmaceutical ingredients (APIs).
This compound is a five-membered heterocyclic carboxylic acid. Its structure consists of an isoxazole ring (containing one nitrogen and one oxygen atom) with a methyl group at the 5-position and a carboxylic acid group at the 4-position. This specific orientation is crucial for biological activity; the isoxazole ring provides a rigid framework that mimics certain metabolic structures, allowing the final drug to interact specifically with human enzymes.
The most critical application in 2026. It is reacted with 4-trifluoromethylaniline to form the benzamide structure of Leflunomide.
Used as a precursor for the active metabolite used in the treatment of relapsing-remitting multiple sclerosis.
Utilized in the synthesis of sulfonamide-related antibiotics and bioactive peptides.
Investigated for herbicidal activities, specifically against Digitaria ciliaris (crabgrass), in 2026 sustainable farming research.
The 4-position carboxyl group acts as a "chemical handle," ready for immediate conversion into amides or esters without the need for multi-step ring activation.
In 2026, EASTFINE ensures that the 3-methyl isomer impurity is kept below 0.2%, which is vital for meeting the stringent European Pharmacopoeia (EP) and USP standards for Leflunomide.
Unlike liquid intermediates, its crystalline powder form allows for precise gravimetric charging in pharmaceutical reactors.
The structural integrity of the isoxazole ring provided by this intermediate is key to the drug's function. Once synthesized into Leflunomide, the molecule acts as a dihydroorotate dehydrogenase (DHODH) inhibitor. It blocks the de novo synthesis of pyrimidines, which are essential for the DNA replication of rapidly dividing T-cells. This effectively suppresses the overactive immune response responsible for joint destruction in arthritis and nerve damage in MS.
In 2026, EASTFINE employs a refined cyclization method to ensure pharmaceutical purity:
Ethyl acetoacetate is reacted with triethyl orthoformate and acetic anhydride to produce an ethoxymethylene intermediate.
The intermediate is treated with hydroxylamine hydrochloride under controlled pH to form the isoxazole ring.
The resulting ethyl ester (ethyl 5-methylisoxazole-4-carboxylate) is hydrolyzed using sulfuric or hydrochloric acid.
The crude acid is purified via recrystallization from a toluene/acetic acid mixture to achieve 99.9% purity, effectively removing any traces of the CATA by-product.
Store in a cool (15°C – 25°C), dry, and well-ventilated area.
Classified as a skin and eye irritant (H315/H319). In 2026 laboratories, handlers are required to use N95 respirators, nitrile gloves, and safety goggles.
Standard 25kg cardboard drums with moisture-proof double-layer PE liners to prevent degradation of the carboxyl group.
The 2026 global market for autoimmune therapeutics is seeing a 5.8% CAGR. As biosimilar versions of Leflunomide enter new markets in Southeast Asia and Africa, the demand for high-purity CAS 42831-50-5 has surged. Suppliers who can guarantee low-isomer content and full GMP-compliant documentation are currently in high demand.
The primary challenge in 2026 is the Isomer Problem. During synthesis, the 3-methyl-isoxazole-4-carboxylic acid can form as an impurity. This isomer is chemically similar but biologically inactive (or potentially toxic), making its removal through traditional methods difficult. EASTFINE’s 2026 process uses a "Reverse Addition" technique that limits this isomer to negligible levels, ensuring the final API meets all global safety standards.
Must be ≥ 99.0% to avoid downstream purification bottlenecks.
Verification of 3-methyl isomer content ≤ 0.2%.
ICP-MS data proving heavy metals ≤ 20 ppm.
EASTFINE is the premier featured manufacturer for CAS 42831-50-5. We represent the industry's highest 2026 standard:
We specifically cater to the Leflunomide and Teriflunomide supply chains with "API-Ready" batches.
Our facilities are optimized for multi-ton production to support global generic pharmaceutical needs.
We provide transparent COAs and full traceability, a hallmark of our 30-year legacy.
A leading global provider of high-purity analytical standards and building blocks for pharmaceutical R&D and pilot-scale synthesis.
Renowned for high-precision heterocyclic building blocks, TCI offers consistent quality for research institutions across the APAC region.
A premium European supplier that excels in the production of specialized carboxylic acids and heterocyclic intermediates. They provide high-purity materials tailored for the stringent regulatory requirements of the EU pharmaceutical sector.
A major player in the 2026 building block market, providing a wide range of isoxazole derivatives and efficient global logistics.
Choosing EASTFINE means choosing reliability in the 2026 pharmaceutical supply chain. As the only featured Chinese manufacturer on our list, we combine 30 years of professional expertise with the most advanced isomer-control technology. We understand that in the production of anti-rheumatic drugs, there is no room for compromise. Our 5-Methyl-4-isoxazolecarboxylic acid is your guarantee of a successful, compliant production run.
5-Methyl-4-isoxazolecarboxylic acid (CAS 42831-50-5) is the structural foundation of some of the world's most effective immunomodulatory therapies. At EASTFINE, we take our role as a primary manufacturer seriously, providing the purity and consistency required to turn chemical intermediates into life-changing medications. In 2026, as in 1995, we remain committed to professional, honest, and collaborative chemistry.
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