Synthesis and Characterization of the Perthiatriarylmethyl Radical and Its Dendritic Derivatives with High Sensitivity and Selectivity to Superoxide Radical.

EPR spectroscopy, coupled with the use of tetrathiatriarylmethyl (TAM) radicals, has been a reliable method to detect the superoxide radical (O2.- ). However, the specificity and biocompatibility of TAM radicals need to be further improved. Although derivatization may overcome the drawbacks of current TAM radicals, esterification or amidation through the carboxylic groups greatly changes their redox properties and makes them inert to O2.- . Herein, the synthesis of a perthiatriarylmethyl (PST) radical and its dendritic derivatives, PST-TA and PST-NA, in which PST is covalently linked with dendrons containing three (TA) and nine (NA) carboxylic acids, respectively. The results show that PST rapidly reacts with O2.- to yield a unique quinone methide product. Dendritic modification of PST slightly decreases the reactivities of PST-TA and PST-NA, but notably increases their biostability toward various oxidoreductants. The detection limit of PST-NA to O2.- was estimated to be 2.1 nm min-1 over 60 min of detection. Importantly, PST-NA shows threefold higher sensitivity to O2.- in the presence and absence of ascorbic acid than that of the classic spin-trapping technique. In addition, the application of PST-NA to detect extracellular O2.- generation in stimulated RAW 264.7 macrophages was also explored. This study demonstrates that PST-NA has great potential for specific detection and quantitation of O2.- in extracellular sites.