Synthesis And Characterization Of Heteroatom-Substituted TAM Radicals

Objective:In recent years,tetrathiatriarylmethyl?TAM?radicals such as OX063 and CT-03 have accepted intense attention in the fields of magnetic resonance spectroscopy and imaging owing to their long relaxation times(>10^-6 s),good water solubility,high biocompatibility,and sharp EPR singlet signal?30-50 mG?.Due to the complex structure of TAM radicals,it is very challenging to derivatize these stable radicals without compromising their properties,therefore greatly limiting their biomedical applications.Therefore,in the present thesis,a series of heteroatom-substituted TAM radicals were efficiently synthesized by optimizing their synthetic methods with the purpose o f obtaining novel TAM radicals with excellent properties,providing a basis for biomedical applications of TAM radicals.Methods:Triarylmethanol as a starting material was deprotonated by n-butyllithium,followed by reaction with dimethyl carbonate to afford the corresponding diester compounds.The treatment of the diesters with trifluoromethanesulfonic acid led to the generation of trityl cations which were further attacked by the P-,S-,N-and O-nucleophiles to produce the dimethyl ester derivatives of TAM radicals.Finally,the resulting dimethyl esters were hydrolyzed by LiOH to give heteroatom-substituted asymmetric TAM radicals as the target products.The compounds obtained were separated and purified by column chromatography,high performance liquid chromatography?HPLC?,and their molecular structure and physicochemical properties were characterized by means of nuclear magnetic resonance,mass spectrometry,ultraviolet-visible spectroscopy and electron paramagnetic resonance?EPR?spectroscopy.Thereafter,monophosphonated TAM radicals were PEGylated and deuterated,and the potential application of the resulting TAM radicals as pH probes was comprehensively studiedResults:?1?The carbocation-based synthetic method of TAM radicals was developed and eight heteroatom-substituted unsymmetrical TAM radicals were successfully obtained;?2?Monophosphonated TAM radicals were efficiently synthesized,overcoming the limitation of the previously reported methods.The PEGylation and deuteration of monophosphonated TAM radicals led to a dual-function EPR probe for simultaneous detection of pH and O₂ under physiological conditions;?3?TAM 1 and TAM 3 could function as superoxide probes having different reaction mechanisms with the previously reported TAM-based superoxide probes;Two products were observed in the reactions of TAM 1 or TAM 3 with superoxide radical;?4?Both TAM4 and TAM 7 are sensitive to pH and O₂ and thus are potential pH/O₂ dual-function EPR probes;it is worth noting that TAM 7 with cyanoacetic acid group is the first carbon-centered TAM pH probe;?5?DCT as a diamagnetic analogue of TAM radical can be reduced to generate TAM radical which can also be oxidized back to DCT;therefore,DCT shows great potential to measure redox states.Conclusion:This article mainly focuses on the research on heteroatom-substituted asymmetric TAM radicals.?1?In the synthesis,a variety of stable,heteroatom-substituted,asymmetric,water-soluble TAM radicals were obtained from triarylmethanol via the carboncation mechanism.This new approach was high synthesis efficiency and good repeatability,and provided a simple route for the large-scale synthesis of these compounds;?2?It has been found that these probes show great application potentials in superoxide,pH or redox detection and it is expected to expand TAMs'biomedical applications in the future;?3?The direct access to modify aromatic rings partially also provide new ideas for the development of TAMs'derivatization.