Fluorescent Puromycin Derivatives Containing Functionalized Adenosine Analogues—Synthesis, Photophysics, and Biological Applications
ABSTRACT OF THE DISSERTATION
Synthesis and Analysis of Fluorescent Antibiotics Containing Emissive Adenosine Surrogates
Doctor of Philosophy
University of California, San Diego, 2022
Professor Yitzhak Tor, Chair
The synthesis, photophysical analysis, and biological investigation of puromycin analogues containing fluorescent adenosine derivatives are discussed. We analyzed the photophysical properties of two novel fluorophores, N,N-dimethylthieno[3,4-d]pyrimidin-4-amine and isothiazolo[4,3-d]pyrimidine-7(6H)-thione. While the photophysical properties of these two compounds were found to be lackluster, substitution of the dimethylamine substituents for modified and unmodified azetidines were found to significantly augment the brightness of the fluorophores by nearly three orders of magnitude in the thienopurines and two orders of magnitude in the isothiazolo derivatives. We then synthesized C-nucleoside analogues of puromycin employing a thieno[3,4-d]pyrimidine heterocycle in place of the native purine, along with other derivatives employing azetidine and 2,2-difluoroazetidine at the 6 position (following native purine numbering). A convergent synthesis utilizing lithium halogen exchange between a halogenated thiophene-based purine analogue and a benzyl protected 3’-deoxy-3’-azido-ribolactone produced a desired C-glycoside with reactive handles at the 3’position of the sugar (for peptide coupling) and at the 6-position of the modified purine (for SnAr reactions) providing synthetic accessibility to numerous fluorescent antibiotic scaffolds. Biological evaluation of the synthesized antibiotics indicates similar bioactivity of the novel fluorophores compared to native puromycin, both in in vitro protein expression systems and bactericidal assays. Treatment of the modified derivatives in HEK293T cells indicated localization of the compounds with ribosomes following fixation immunofluorescence treatments. One derivative, the 2,2-difluoroazetidine modified analogue, exhibited fluorescence in live cells and neurons at sub-cytotoxic concentrations, one of the first and few times a fluorescent nucleoside derivative has been used in this context given the effect of size restriction on the chromophores in question.