Linker and Head-Group Exploration of Anti-MRSA Triaromatic Pleuromutilins

Based on hit 6, a triaromatic pleuromutilin (TAP) and potent bacterial protein synthesis inhibitor, we explored the chemical space surrounding its pharmacophore by synthesizing 45 new conjugates. Herein, the adenine head was exchanged for new heterocycles, and the benzyl linker exchanged for aniline-, ether-, amide-, and hydroxybenzyl linkages, with all of them successfully engaging the pharmacophore, a result which was mirrored in a strict 3D pharmacophore model. The aniline- and amide-linked conjugates moreover demonstrated greater stability in liver microsomes, while especially conjugate 21, but also 31, 43, 45, and 55 displayed excellent potency, with MRSA activities on par with 6 or better. Docking to the ribosome suggested a shifted engagement with C2469 for 21 over 6, resulting in greater multivalency, while 43/45 likely coordinates Mg²⁺. Lastly, conjugate 21 displayed efficacy equal to commercial Fucidin LEO (5) in a mouse Staphylococcus aureus skin infection model, highlighting its potential as a topical antibiotic lead.