Three-component assembly of stabilized fluorescent isoindoles

A fluorescence-based assay for measuring polyamine biosynthesis aminopropyl transferase-mediated catalysis

Polyamines are polycationic molecules that are crucial in a wide array of cellular functions. Their biosynthesis is mediated by aminopropyl transferases (APTs), which are promising targets for antimicrobial, antineoplastic, and antineurodegenerative therapies. A major limitation in studying APT enzymes, however, is the lack of high-throughput assays to measure their activity. We have developed the first fluorescence-based assay, diacetyl benzene (DAB)-APT, for the measurement of APT activity using 1,2-DAB, which forms fluorescent conjugates with putrescine, spermidine, and spermine, with fluorescence intensity increasing with the carbon chain length. The assay has been validated using APT enzymes from Saccharomyces cerevisiae and Plasmodium falciparum, and the data further validated by mass spectrometry and TLC. Using mass spectrometry analysis, the structures of the fluorescent putrescine, spermidine, and spermine 1,2-DAB adducts were determined to be substituted 1,3-dimethyl isoindoles. The DAB-APT assay is optimized for high-throughput screening, facilitating the evaluation of large chemical libraries. Given the critical roles of APTs in infectious diseases, oncology, and neurobiology, the DAB-APT assay offers a powerful tool with broad applicability, poised to drive advancements in research and drug discovery.

Synthesis and Atropisomeric Properties of Benzoazepine-Fused Isoindoles

Atropisomeric, bench-stable benzoazepine-fused isoindoles were synthesized via oxidation from isoindoline precursors. Using the isoindoles 5d-f as models, the stereochemistry and conformational folding of the systems were examined. Chiral UHPLC was used to analyze the rate of racemization and calculate the Gibbs free energy of enantiomerization (ΔG^‡_Enant). X-ray crystallography, ¹H NMR spectroscopy, and DFT calculations were used to elucidate the three axes of chirality and clarify the structural factors contributing to ΔG^‡_Enant. Tandem rotation around the axes of chirality precludes the formation of diastereomers, with rotational restriction of the C_aryl-N_sulfonamide bond determined as the moderator of atropisomeric stability in the system, affected primarily by steric hindrance as well as by π-stacking interactions facilitated by the folded conformation of the sulfonamide over the isoindole moiety.