Synthesis Of Guaianolide Analogues With A Tunable Alpha-Methylene-Gamma-Lactam Electrophile And Correlating Bioactivity With Thiol Reactivity

alpha-Methylene-gamma-lactones are present in similar to 3% of known natural products, and compounds comprising this motif display a range of biological activities. However, this reactive lactone limits informed structure-activity relationships for these bioactive molecules. Herein, we describe chemically tuning the electrophilicity of the alpha-methylene-gamma-lactone by replacement with an alpha-methylene-gamma-lactam. Guaianolide analogues having alpha-methylene-gamma-lactams are synthesized using the allenic Pauson-Khand reaction. Substitution of the lactam nitrogen with electronically different groups affords diverse thiol reactivity. Cellular NF-kappa B inhibition assays for these lactams were benchmarked against parthenolide and a synthetic alpha-methylene-gamma-lactone showing a positive correlation between thiol reactivity and bioactivity. Cytotoxicity assays show good correlation at the outer limits of thiol reactivity but less so for compounds with intermediate reactivity. A La assay to detect reactive molecules by nuclear magnetic resonance and mass spectrometry peptide sequencing assays with the La antigen protein demonstrate that lactam analogues with muted nonspecific thiol reactivities constitute a better electrophile for rational chemical probe and therapeutic molecule design.