Site-Divergent Oxidations within Venerable Macrolide Antibiotic Scaffolds Unveil Compounds with Broad Spectrum and Anti-MRSA Activities

The synthesis of bioactive compounds with differential, and ideally enhanced, activities presents persistent and growing challenges for the field of organic synthesis. By leveraging Nature’s ability to build complex, stereochemically rich, and biologically active molecular scaffolds, site-selective modification of natural products can deliver analogs without the need for lengthy de novo syntheses. Yet, achieving selective reactivity at a single desired position is complicated by the presence of multiple iterations of similar reactive functional groups, thus precluding widespread adoption of catalyst-controlled site-selective modification. Herein we describe the development of complementary systems for the oxidation of secondary alcohols on erythromycin A, clarithromycin, and azithromycin using a newly designed azaadamantyl oxoammonium catalyst, wherein different hydroxyl groups show disparate reactivities under the same conditions. The application of this methodology has enabled the generation of a suite of oxidized macrolide antibiotics and derivatives that take advantage of the newly installed carbonyls. Antimicrobial activity testing revealed that multiple compounds retain activity against a broad range of pathogens consistent with erythromycin A coverage. Additionally, three of the compounds reported herein display antibiotic activity against CA-MRSA and MRSA(mph(C)), for which the clinical analogs erythromycin A, clarithromycin, and azithromycin exhibit no activity at tested concentrations.