Expanding the Toolbox: Exploring the Lewis Acid Assisted 19F/18F-Isotopic Exchange Radiochemistry of BODIPY Dyes, and DiPODS: Development of a Novel Bioconjugation Reagent.
Shannon, Whitney Estella M. M.
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Radiochemical diagnostics and therapeutics benefit from pairing with a compliment second imaging modality. However, methods to radiolabel and link these molecules to targeting vectors are problematic. In this dissertation, I explored new radiosynthetic strategies for producing fluorophore-based bimodal agents and new bioconjugation reagents for antibody drug conjugation with improved in vivo stability. 18F-radiolabeled 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) fluorophores are hypothetically ideal bimodal imaging candidates. Preliminary experiments focused on facilitating 19F/18F-transfluorination of Pseudomonas aeruginosa-selective BODIPY dye, CDy11, using Lewis acidic [18F]F-BODIPY labeling strategies described in literature. However, the conventionally applied tin(IV)-chloride (SnCl4) Lewis acid’s instability affords reaction yield variability, and further promoted degradation of the CDy11. Thus, research transitioned towards investigating an alternative Lewis acid. To our knowledge, we are the first to use hydrated magnesium nitrate [Mg(NO3)2] as an air-stable substitute for promoting 18F-fluorination of commercially-available BODIPY dyes. Order of reagent addition significantly affected the 19F/18F-isotopic exchange reaction; with addition of azeotropically dried [18F]F-TBAF to a mixture of the commercial dye and Lewis acidic agent proving most effective. 19F/18F-transfluorination was achieved using both SnCl4 and Mg(NO3)2 to varying degrees. Increasing the equivalences of applied Mg(NO3)2 salt generally improved radiochemical yields. Bioconjugation chemistry enables the covalent attachment of molecules of interest to larger proteins such as antibodies. While conjugation with thiol groups (cysteine) in antibodies is common, conventional maleimide-based coupling agents are prone to in vivo hydrolysis. Price lab research efforts sought to develop radioimmunoconjugates that operate through two phenyloxadiazolyl methyl sulfone (DiPODS) functionality to form irreversible bonds with antibody cysteine pairs. My contribution was to assist in synthesizing several of the multistep synthesis products and apply spectroscopic methods towards analysis of the initial step’s product mixture, which was hypothesized to exist as a rotameric mixture. Several intermediate agents were successfully synthesized to produce the desired DIPODS end product. The three components of the 5-[[(1,1-dimethylethoxy)carbonyl]amino]-1,3-dimethyl ester (compound 1)product mixture were attributed to an inseparable mixture of rotamers, doubly-di-tert-butyl decarbonate (Boc)-protected derivative of the compound, and imidic acid tautomers using spectroscopic methods including variable temperature 1H NMR. Lastly, an additional chemical species was observed via 1H NMR as temperature was increased to 75 °C and attributed to a second set of product rotamers. Ultimately, this thesis served to improve future radiotherapeutic agents and radio-diagnostics through the investigation of alternative and reproducible [18F]F-BODIPY labeling strategies and radioimmunoconjugates of improved stability.
DegreeMaster of Science (M.Sc.)
SupervisorPrice, Eric; Siciliano, Steven
CommitteePhenix, Christopher; Ruzzini, Tony; Scott, Robert
Copyright DateMarch 2021
[18F]F-BODIPY, Lewis acid-assisted [19F/18F]- isotopic exchange, Radioimmunoconjugation