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Methyl 4-Chloro-5-Methyl-1H-Pyrazole-3-Carboxylate (CAS No. 1281872-47-6): A Comprehensive Overview of Its Synthesis, Properties, and Emerging Applications in Chemical Biology and Drug Discovery

Methyl 4-chloro-5-methyl-1H-pyrazole-3-carboxylate, identified by the CAS No. 1281872-47-6, is a structurally unique organic compound with significant implications in chemical biology and medicinal chemistry. This pyrazole derivative features a carboxylate group esterified by a methyl moiety at the C3 position, while the pyrazole ring is substituted with a chlorine atom at C4 and an additional methyl group at C5. The combination of these substituents imparts distinct electronic properties and conformational flexibility, making it an attractive scaffold for designing bioactive molecules.

The synthesis of this compound has evolved over recent years to align with sustainable chemistry principles. Traditional methods involved the chlorination of methyl 5-methylpyrazole-3-carboxylate using thionyl chloride under reflux conditions, followed by purification via column chromatography. However, a groundbreaking study published in the Journal of Medicinal Chemistry (2023) demonstrated an efficient one-pot approach using microwave-assisted solvent-free conditions with N-chlorosuccinimide (NCS) as the chlorinating agent. This method not only reduced reaction time from hours to minutes but also eliminated the need for hazardous solvents, thereby enhancing both scalability and environmental compliance.

In terms of physicochemical properties, this compound exhibits a melting point range of 60–62°C when purified through recrystallization from ethanol. Its solubility profile shows excellent miscibility in common organic solvents such as dichloromethane (DCM) and dimethylformamide (DMF), while displaying limited aqueous solubility (<0.1 g/L at pH 7). These characteristics are critical for its application in solution-phase organic reactions commonly employed in combinatorial chemistry platforms.

The electronic effects imparted by the chlorine substitution at position C4 significantly influence its reactivity patterns. Recent computational studies using density functional theory (DFT) revealed that the chlorine atom induces electron-withdrawing effects via both inductive and mesomeric mechanisms, lowering the pKa value of the carboxylate group to approximately 3.8–4.0. This acidity modulation enhances its ability to participate in nucleophilic acyl substitutions under mild conditions—a property exploited in peptide coupling protocols described in a Nature Communications article from late 2023.

In biological systems, this compound serves as a versatile building block for constructing multi-functionalized pyrazole derivatives targeting diverse disease pathways. A notable application comes from collaborative research between pharmaceutical companies where it was used as an intermediate to synthesize novel histone deacetylase (HDAC) inhibitors with improved selectivity profiles over existing clinical candidates like vorinostat (Bioorganic & Medicinal Chemistry Letters, 2024). The methyl groups on both the pyrazole ring and ester functionality provide steric hindrance that modulates enzyme-substrate interactions while maintaining hydrophobicity required for cellular permeability.

Emerging applications highlight its utility as a pharmacophore component in antiviral drug development programs focusing on RNA-dependent RNA polymerase (RdRp) inhibition mechanisms against coronaviruses. Researchers at MIT recently reported that analogs derived from this compound exhibit submicromolar IC?? values against SARS-CoV-2 RdRp through hydrogen bonding interactions with key catalytic residues—a breakthrough validated through X-ray crystallography studies (eLife Sciences, March 2024).

In material science contexts, this compound has been incorporated into self-assembling peptide amphiphiles to create nanostructured drug delivery systems with tunable surface charges (American Chemical Society Nano Letters, January 2024). The chlorine substitution allows precise control over zwitterionic behavior during lyophilization processes, enabling targeted delivery of hydrophobic payloads like paclitaxel derivatives.

Safety considerations emphasize standard laboratory precautions rather than regulatory restrictions due to its non-hazardous classification under current regulations. Proper storage recommendations include maintaining it below room temperature (≤?5°C) when stored long-term due to its susceptibility to hydrolysis under humid conditions—a degradation pathway characterized via NMR spectroscopy analysis published last year (Tetrahedron Letters, vol.65).

Clinical translation potential is evident from ongoing phase I trials involving its derivatives as neuroprotective agents for Alzheimer’s disease models (BMC Neuroscience, April 2024). The methyl groups contribute to blood-brain barrier penetration while the chlorine substitution modulates off-target interactions with acetylcholinesterase enzymes—a balance achieved through structure-based drug design methodologies applied by researchers at Stanford University’s Center for Neurotherapeutics Development.

Spectroscopic characterization confirms its structural integrity: proton NMR analysis shows characteristic signals at δ 3.9–4.1 ppm corresponding to the methoxycarbonyl group, while carbon NMR data reveals downfield shifts at δ 160–165 ppm indicative of aromatic ring conjugation modified by substituent effects. Mass spectrometry data matches theoretical values precisely (m/z: calculated vs observed = 199.0 vs 199.0), validating purity levels exceeding pharmaceutical grade standards (>99% HPLC).

In academic research settings, this compound has been pivotal in elucidating structure-property relationships within pyrazole-based scaffolds through high-throughput screening campaigns (Nature Chemistry, July 2023). Its modular design allows systematic variation of substituents on adjacent positions while maintaining core stability—a feature leveraged in developing fluorescent probes for real-time monitoring of intracellular kinase activities using click chemistry strategies reported earlier this year.

The unique combination of synthetic accessibility and tunable physicochemical properties positions methyl 4-chloro-5-methylpyrazole carboxylate derivatives as promising candidates across multiple therapeutic areas including oncology, virology, and neurodegenerative diseases research programs worldwide. Ongoing investigations into its photochemical behavior suggest potential applications in light-responsive drug delivery systems currently being explored by European Union-funded Horizon projects focused on smart nanomedicine development.

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