Arylsulfonium Salt Labeling for High-Purity Iodoaryl Synthesis
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Solution Overview
Problem
Existing methods for synthesizing iodo- and astatoaryl compounds, particularly radioiodo- and radioastatoaryl compounds, face challenges in achieving high radiochemical yield (RCY), chemical and radiochemical purity, and regioselectivity, especially when dealing with electron-rich compounds.
Innovation Solution
The use of arylsulfonium salts, specifically triarylsulfonium and dibenzothiophenium salts, which incorporate a thioaryl group as a leaving group, allowing for the separation of side products from the labeled product, thereby improving synthesis efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional electrophilic or nucleophilic substitution reactions are used for radioiodination, then radioiodinated compounds can be obtained, but side-products are formed and non-radioactive iodinated analogs are inseparable from the radiolabelled product
Solution Approach 1:
The patent employs a sulfonate ester intermediate in a two-step reaction sequence. First, the phenolic compound reacts with sulfonate ester to form a sulfonated intermediate, which then undergoes nucleophilic substitution with radioiodide. This intermediary step allows the radioactive iodine to be introduced without direct competition from non-radioactive iodine, thereby preventing the formation of inseparable non-radioactive iodinated analogs and achieving high radiochemical purity while maintaining good radiochemical yield
Solution Approach 2:
The patent performs preliminary sulfonation of the phenolic compound before introducing the radioactive iodine. By pre-installing the sulfonate group, the reaction creates a specific leaving group that directs the subsequent radioiodination to the desired position. This preliminary action ensures that the radioactive iodine is incorporated only after the sulfonate intermediate is formed, preventing side-product formation and enabling high radiochemical purity
2Ease of manufacture
If aryliodonium salts are used as precursors for radioiodination, then radioiodinated compounds can be synthesized, but the inseparable 127I-iodinated analogue is formed leading to suboptimal molar activity
Solution Approach 1:
The patent replaces the direct use of aryliodonium salts with a sulfonate ester intermediate approach. The sulfonate ester serves as a mediator that enables radioiodine introduction through nucleophilic substitution without generating the problematic 127I-iodinated analogue. This intermediary mechanism maintains synthesis efficiency while achieving high molar activity by preventing the formation of non-radioactive competing species
3Manufacturing precision
If aryliodonium ylides are used to improve regioselectivity, then radiochemical yield improves for electron-deficient precursors, but the inseparable 127I-iodinated analogue is still formed
Solution Approach 1:
The patent introduces a sulfonate ester intermediate that acts as a superior mediator compared to aryliodonium ylides. This intermediate enables high regioselectivity through the specific positioning of the sulfonate group, which directs nucleophilic attack by radioiodide to the desired location. Simultaneously, it prevents the formation of 127I-iodinated analogs because the sulfonate leaving group mechanism does not generate free iodine species that could form non-radioactive byproducts, thus achieving both high regioselectivity and high molar activity
4Manufacturing precision
If only strongly activated compounds are used with aryliodonium salts, then high regioselectivity is achieved, but applications for electron rich radioiodinated compounds are limited
Solution Approach 1:
The patent changes the key reaction parameter from electrophilic aromatic substitution (which requires electron-deficient substrates) to nucleophilic aromatic substitution via sulfonate intermediate (which works with electron-rich substrates). This parameter change in the reaction mechanism allows the methodology to be applied to phenolic compounds and other electron-rich aromatic systems, dramatically expanding the substrate scope while maintaining high regioselectivity through the directing effect of the sulfonate group
Solution Approach 2:
The patent inverts the conventional approach by using nucleophilic substitution instead of electrophilic substitution. Rather than using electrophilic aryliodonium salts that require electron-poor substrates, the patent employs nucleophilic radioiodide attacking a sulfonated intermediate, which is electron-rich. This inversion of the reaction polarity enables the synthesis of radioiodinated compounds from electron-rich precursors like phenols, expanding versatility while preserving regioselectivity
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method achieves high radiochemical yield and purity in synthesizing iodo- and astatoaryl compounds, enhancing the efficacy of resulting radiopharmaceuticals for imaging and therapeutic applications.
Implementation Method 1
the reaction of an arylsulfonium compound with an iodide or an astatine salt, respectively... comprising the reaction of an arylsulfonium compound with an iodide salt or an astatine salt, respectively
Data Source
AI summary
The inventors have now succeeded in developing arylsulfonium salts, in particular triarylsulfonium salts and dibenzothiophenium salts and a new use of said arylsulfonium salts. These compounds have the advantage of having a thioaryl group as leaving group, which allows all side products to be separated from the radiolabelled product. Said compounds are therefore useful tools in a method for synthesizing iodo- or astatoarryl compounds, in particular radioiodo- or radioastatoaryl compounds. The present invention relates to a method for synthesizing iodo- or astatoaryl compounds comprising the reaction of an arylsulfonium compound with an iodide or astatide salt, respectively. The invention also relates to arylsulfonium compounds as such. The invention also concerns a method of synthesizing an iodo- or astatolabelled biomolecule and/or vector using said iodo- or astatoraryl compound.