5-Methyl-3-phenylisoxazole-4-carboxylic acid
[CAS# 1136-45-4]

Identification

• Classification: Pharmaceutical intermediate >> Heterocyclic compound intermediate >> Pyrimidine compound >> Carboxylic acid
• Name: 5-Methyl-3-phenylisoxazole-4-carboxylic acid
• Synonyms: Oxacillin Related Compound C
• Molecular Formula: C₁₁H₉NO₃
• Molecular Weight: 203.20
• CAS Registry Number: 1136-45-4
• EC Number: 214-497-9
• SMILES: CC1=C(C(=NO1)C2=CC=CC=C2)C(=O)O

Properties

• Density: 1.3±0.1 g/cm³, Calc.^*
• Melting point: 192-193 °C (Expl.)
• Index of Refraction: 1.579, Calc.^*
• Boiling Point: 365.0±37.0 °C (760 mmHg), Calc.^*
• Flash Point: 174.5±26.5 °C, Calc.^*

^* Calculated using Advanced Chemistry Development (ACD/Labs) Software.

Safety Data

• Hazard Symbols: GHS07 Warning
• Risk Statements: H302
• Safety Statements: P264-P270-P301+P317-P330-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Acute toxicity	Acute Tox.	4	H302

Discovery and Applications

5-Methyl-3-phenylisoxazole-4-carboxylic acid is a heterocyclic compound that features an isoxazole ring substituted with a methyl group, a phenyl group, and a carboxylic acid functional group. This structure lends the compound significant reactivity and versatility, making it valuable in various domains of chemistry, including pharmaceuticals, agrochemicals, and materials science.

The discovery of 5-methyl-3-phenylisoxazole-4-carboxylic acid is rooted in the exploration of isoxazole derivatives, which have drawn considerable interest due to their diverse biological activities. Isoxazole synthesis typically involves cyclization reactions, and in this case, methods such as the 1,3-dipolar cycloaddition of nitrile oxides with alkynes or alkenes are commonly employed. Subsequent functional group modifications yield the desired substitution pattern. Recent advancements in synthetic methodologies have focused on green and sustainable routes to improve yield and reduce environmental impact.

In the pharmaceutical industry, 5-methyl-3-phenylisoxazole-4-carboxylic acid serves as a crucial intermediate for developing bioactive compounds. Isoxazole derivatives are known for their anti-inflammatory, antimicrobial, and anticancer properties, and the presence of the carboxylic acid group facilitates interactions with biological targets, enhancing efficacy. This compound has been used in the synthesis of small-molecule inhibitors and drugs targeting enzymes and receptors associated with inflammatory pathways and cancer cell proliferation.

In agrochemistry, 5-methyl-3-phenylisoxazole-4-carboxylic acid is employed in the development of herbicides and fungicides. Its isoxazole core and functional groups can be modified to enhance selectivity and potency against specific pests or pathogens, contributing to sustainable agricultural practices.

The compound's versatility also extends to materials science. Isoxazole derivatives like 5-methyl-3-phenylisoxazole-4-carboxylic acid are utilized in creating advanced polymers and coatings, where their rigid aromatic structure and reactive sites improve material properties such as durability and resistance to environmental degradation.

Recent research has focused on expanding the utility of this compound through combinatorial chemistry approaches. Its inclusion in compound libraries has facilitated high-throughput screening for potential drug candidates and functional materials. Moreover, modifications of its core structure are being investigated to explore new therapeutic and industrial applications.

References

2013. 5-Methyl-3-phenyl-isoxazole-4-carboxylic acid. Acta Crystallographica. Section E, Structure Reports Online.
DOI: 10.1107/s1600536813011410

2015. FT-IR, Laser-Raman spectra and computational analysis of 5-Methyl-3-phenylisoxazole-4-carboxylic acid. Spectrochimica Acta. Part A, Molecular and Biomolecular Spectroscopy.
DOI: 10.1016/j.saa.2014.12.023

1967. Synthesis of certain derivatives of 3-phenyl-5-methyl-4-isoxazolecarboxylic acid. Pharmaceutical Chemistry Journal.
DOI: 10.1007/bf00760824