A manganese-catalyzed decarboxylative fluorination platform for synthesizing complex fluorinated molecules and PET tracers

Background

Fluorination of organic molecules is a critical transformation in the fields of pharmaceuticals, agrochemicals, and medical imaging, particularly due to the unique properties that fluorine imparts to bioactive compounds. The introduction of fluorine atoms can significantly enhance metabolic stability, bioavailability, and binding affinity of drug candidates, while radioactive fluorine isotopes, such as [18F], are essential for positron emission tomography (PET) imaging. As a result, efficient and selective methods for incorporating fluorine into complex molecules, especially at late stages of synthesis, are highly sought after to streamline the development of new therapeutics and diagnostic agents.

Current approaches to fluorination, however, face significant challenges. Traditional electrophilic fluorination methods often require harsh conditions, expensive reagents, or are incompatible with sensitive functional groups, limiting their utility for late-stage modification of complex molecules. Nucleophilic fluorination, while more cost-effective and functional group tolerant, typically struggles with poor reactivity and selectivity, especially when targeting unactivated carbon centers. Radiochemical fluorination with [18F] is further complicated by the need for rapid, high-yielding reactions under mild conditions due to the isotope’s short half-life, and often involves laborious precursor synthesis or time-consuming drying steps. These limitations collectively hinder the efficient synthesis of fluorinated pharmaceuticals and PET tracers, underscoring the need for more practical and broadly applicable fluorination technologies.

Technology

This technology is a manganese-catalyzed process for the decarboxylative fluorination of organic compounds, enabling the direct replacement of aliphatic, benzylic, and aryloxy carboxylic acid groups with fluorine atoms—including radioactive [18F]—under mild conditions. The system employs a manganese(III) porphyrin or salen catalyst, an iodine(III) oxidant such as iodosylbenzene, and a nucleophilic fluoride source like triethylamine trihydrofluoride or potassium fluoride. The reaction is typically carried out in solvents such as 1,2-dichloroethane at moderate temperatures, with the option to add benzoic acid to enhance yields. This method demonstrates broad substrate scope and high tolerance for diverse functional groups, including heterocycles, amides, esters, ketones, and electron-rich aromatics, making it suitable for late-stage fluorination of complex pharmaceuticals, agrochemicals, and the synthesis of PET imaging tracers.

What differentiates this technology is its unique combination of mild, metal-catalyzed decarboxylation and nucleophilic fluorination, which overcomes the limitations of traditional electrophilic fluorination methods. By targeting carboxylic acids—a common motif in drug molecules—it allows for direct late-stage fluorination without the need for extensive precursor synthesis. The use of nucleophilic fluoride sources not only reduces cost but also enhances compatibility with sensitive functional groups. For PET radiochemistry, the protocol streamlines [18F] labeling by eliminating the need for azeotropic drying, enabling efficient, high-specific-activity radiopharmaceutical production. Mechanistic studies confirm a radical-based pathway, ensuring selective C–F bond formation and broad applicability to structurally complex molecules, thereby providing a practical and versatile solution for both synthetic and radiochemical applications.

Benefits

• Enables efficient and selective replacement of aliphatic carboxylic acid groups with fluorine atoms, including radioactive [18F], under mild conditions.
• Utilizes a cost-effective nucleophilic fluoride source, improving compatibility with sensitive functional groups compared to electrophilic fluorination methods.
• Exhibits high functional group tolerance, allowing fluorination of complex bioactive molecules with diverse functionalities such as heterocycles, ketones, and alkenes.
• Facilitates late-stage fluorination, streamlining the synthesis of pharmaceuticals, agrochemicals, and PET imaging tracers without extensive precursor modification.
• Simplifies radiolabeling protocols by eliminating the need for azeotropic drying of [18F]fluoride and enabling direct use from cyclotron-produced fluoride.
• Achieves high radiochemical conversion and specific activity suitable for producing high-quality PET radiopharmaceuticals.
• Operates via a well-understood radical mechanism catalyzed by manganese porphyrin or salen complexes, ensuring reproducibility and scalability.

Applications

• Late-stage pharmaceutical fluorination
• Radiopharmaceutical PET tracer synthesis
• Agrochemical fluorinated compound production
• Complex bioactive molecule labeling

Additional info

This manganese-catalyzed protocol facilitates decarboxylative fluorination, converting aliphatic carboxylic acids into C–F bonds. Utilizing manganese porphyrin catalysts, iodine(III) oxidants, and nucleophilic fluoride, the reaction generates transient carbon radicals trapped by manganese-bound fluoride. This methodology enables late-stage functionalization of complex bioactive molecules and the synthesis of high-specific-activity [18F]-labeled radiopharmaceuticals for PET imaging, offering high functional group tolerance under mild reaction conditions.