Samarium Diiodide Catalysis for Novel Bioiosteres

The concept of bioisosteric replacement of arene pharmacophores in drug candidates has garnered increasing attention as a powerful tool to circumvent the production of toxic metabolites through detrimental metabolic modifications of the arene backbone. Replacement of the arene core in drug candidates with rigid, C(sp3)-rich bioisosteric scaffold improves their metabolic stability, potency, lipophilicity, and solubility. Crucially, cage-like structures with defined exit vectors renders them bioisosteres with superior ability to dock in the chiral binding pocket of the target receptor. Therefore, the demand for C(sp3)-rich bioisosteric replacements is skyrocketing and recent endeavors have provided a variety of decorated saturated systems mimicking substituted arenes. While initial studies were mostly directed towards bioisosteres of mono- and para-substituted arenes, recent efforts have focussed more on bioisosteres for ortho- and meta-substituted aromatic rings. Despite the significant development of synthetic strategies for preparing already proven bioisosteres, the lack of synthetic methods to access many unexplored analogues, such as bicyclo[2.2.1]heptanes (BCHeps), renders their potential undetermined to date. Consequently, developing general, catalytic, sustainable methods for rapidly accessing 1,2-BCHeps is an urgent necessity. Recent breakthroughs from the Procter group have set a new benchmark by applying radical relay catalysis using SmI2 for accessing bioisosteric scaffolds. Sam-4-Bio will integrate this novel concept with the group’s recent finding of enhancing catalytic efficiency of SmI2 by photoactivation, to develop a catalytic platform for accessing unexplored bioisosteres of ortho-arenes like 1,2-BCHeps. Challenging insertion of alkene into the bridgehead bond of strained housane ketones under SmI2-catalysis will deliver key intermediates for downstream manipulation en route to new saturated analogues of validated drugs with superior bioactivity.