Introduction
Sulfonyl fluorides have emerged as indispensable tools in modern click chemistry, particularly in the context of sulfur(VI) fluoride exchange (SuFEx) — a reaction pioneered by Nobel laureate K. Barry Sharpless and colleagues. Among the diverse sulfonyl fluoride building blocks, 5-chloropyridine-2-sulfonyl fluoride (CAS 1780694-70-3) stands out as a versatile reagent with significant applications in chemical biology and drug discovery.
This article provides a comprehensive overview of 5-chloropyridine-2-sulfonyl fluoride, including its chemical properties, synthetic routes, and emerging applications in bioconjugation and activity-based protein profiling (ABPP).
Chemical Profile
5-Chloropyridine-2-sulfonyl fluoride is a heteroaromatic sulfonyl fluoride featuring both a pyridine ring and a reactive SO₂F group. Its molecular structure combines the electronic properties of the pyridine nitrogen (which can serve as a hydrogen bond acceptor or coordination site) with the chemoselective reactivity of the sulfonyl fluoride moiety.
| Property | Value |
|---|---|
| CAS Number | 1780694-70-3 |
| Molecular Formula | C₅H₃ClFNO₂S |
| Molecular Weight | 195.602 g/mol |
| InChIKey | TUILXSYMSYXYSW-UHFFFAOYSA-N |
| Category | Sulfonyl Fluorides (SuFEx Building Blocks) |
The presence of the chlorine atom at the 5-position provides an additional handle for further functionalization via cross-coupling reactions, making this compound a valuable intermediate in multi-step syntheses.
Synthesis Routes
Three primary synthetic routes have been documented for 5-chloropyridine-2-sulfonyl fluoride, each offering distinct advantages in terms of yield, scalability, and starting material availability.
Route 1: Fluoride Exchange from Sulfonyl Chloride
The most straightforward approach involves the direct conversion of 5-chloropyridine-2-sulfonyl chloride (CAS 885277-08-7) to the corresponding fluoride using potassium hydrogen difluoride (KHF₂) as the fluoride source.
Reaction Conditions:
- Reagents: 5-Chloropyridine-2-sulfonyl chloride + KHF₂
- Solvent: Water/acetonitrile mixture
- Time: 2 hours
- Yield: ~370 mg (reported)
- Key Reference: Chatelain et al., Angewandte Chemie International Edition 2021, 60(48), 25307–25312. DOI: 10.1002/anie.202111977
This route benefits from the commercial availability of the sulfonyl chloride precursor and mild reaction conditions, making it suitable for laboratory-scale preparations.
Route 2: Oxidative Fluorination from Thiol
An alternative pathway starts from 5-chloropyridine-2-thiol (CAS 40771-41-3), which undergoes simultaneous oxidation and fluorination to directly yield the sulfonyl fluoride.
Reaction Conditions:
- Reagents: 5-Chloropyridine-2-thiol + KF + NaOCl
- Catalyst: Tetrabutylammonium hydrogensulfate (phase-transfer catalyst)
- Solvent: Dichloromethane/water biphasic system
- Temperature: −5 to 0 °C
- Time: 40 minutes
- Yield: 30%
- Key Reference: Nielsen et al., Journal of the American Chemical Society 2015, 137(30), 9571–9574. DOI: 10.1021/jacs.5b06307
This method, developed by the Doyle group, represents a significant advance in direct sulfonyl fluoride synthesis from thiols, bypassing the need for pre-formed sulfonyl chlorides.
Route 3: Selectfluor-Mediated Fluorination
A more recent approach employs Selectfluor as both oxidant and fluorine source, converting lithium 5-chloropyridine-2-sulfinate directly to the sulfonyl fluoride.
Reaction Conditions:
- Reagents: Lithium 5-chloropyridine-2-sulfinate + Selectfluor
- Solvent: Water/acetonitrile
- Key Reference: Shevchuk et al., Chemistry – A European Journal 2026, 32(13). DOI: 10.1002/chem.70739
This route demonstrates the continued innovation in sulfonyl fluoride synthesis, with 2026 publications highlighting the ongoing interest in this compound class.
Applications in Click Chemistry
SuFEx Bioconjugation
5-Chloropyridine-2-sulfonyl fluoride participates readily in SuFEx reactions with nucleophilic amino acid residues (tyrosine, lysine, histidine) in proteins. The pyridine nitrogen can modulate the electrophilicity of the SO₂F group, potentially offering enhanced selectivity compared to simple benzenesulfonyl fluorides.
Typical SuFEx Conditions:
- Nucleophile: Tyrosine-containing peptides or proteins
- Base: BTMG (2-tert-butyl-1,1,3,3-tetramethylguanidine) or DIPEA
- Solvent: DMSO, DMF, or aqueous buffer
- Temperature: Room temperature
- Time: 1–24 hours
Activity-Based Protein Profiling (ABPP)
Sulfonyl fluorides have been widely adopted as activity-based probes for covalent labeling of enzyme active sites. The 5-chloropyridine-2-sulfonyl fluoride scaffold can be incorporated into probe molecules designed to target specific enzyme families, such as serine hydrolases or kinases.
Drug Discovery
The pyridine-containing sulfonyl fluoride motif appears in several drug candidates and chemical probes. The chlorine substituent provides an opportunity for late-stage diversification via palladium-catalyzed cross-coupling reactions (Suzuki, Buchwald-Hartwig), enabling rapid generation of compound libraries for screening.
Advantages Over Traditional Sulfonyl Chlorides
Compared to the analogous sulfonyl chloride, 5-chloropyridine-2-sulfonyl fluoride offers several practical advantages:
- Enhanced Stability: Sulfonyl fluorides are significantly more stable to moisture and nucleophilic attack than sulfonyl chlorides, facilitating storage and handling.
- Improved Chemoselectivity: The SO₂F group reacts selectively with specific nucleophiles under mild conditions, reducing off-target reactions in complex biological systems.
- Biocompatibility: SuFEx reactions can be performed in aqueous media at physiological pH, making them suitable for live-cell applications.
Recent Advances and Future Directions
The field of SuFEx click chemistry continues to expand rapidly, with 4 peer-reviewed publications specifically addressing 5-chloropyridine-2-sulfonyl fluoride and its applications. Key trends include:
- Development of new catalytic systems for SuFEx reactions, including organocatalysts and transition-metal catalysts
- Integration with other click reactions (CuAAC, SPAAC) for multi-modal bioconjugation strategies
- Application in PROTAC technology for targeted protein degradation
- Use in covalent inhibitor design for challenging drug targets
Conclusion
5-Chloropyridine-2-sulfonyl fluoride (CAS 1780694-70-3) represents a valuable addition to the click chemistry toolbox, offering a unique combination of reactivity, stability, and functionalization potential. Its role in SuFEx bioconjugation and drug discovery is likely to expand as new synthetic methods and applications continue to emerge.
For researchers interested in exploring this compound further, detailed synthesis routes and characterization data are available in our product catalog.
Tags: #SuFEx #ClickChemistry #SulfonylFluorides #Bioconjugation #DrugDiscovery #ChemicalBiology #CAS1780694703
Category: Product Spotlight, Research Updates
Featured Image Alt Text: Molecular structure of 5-chloropyridine-2-sulfonyl fluoride, a key SuFEx click chemistry building block
sqkyzdwpjvnmdivqujhdloipxnwhni