Synthesis and Antiviral Evaluation of Carbocyclic Nucleoside Analogs of Nucleoside Reverse Transcriptase...

MK-8591 (4'-ethynyl-2-fluoro-2'-deoxyadenosine) is a novel nucleoside analog that displays a differentiated mechanism of action as a nucleoside reverse transcriptase translocation inhibitor (NRTTI) compared to approved NRTIs. Herein, we describe our recent efforts to explore the impact of structural changes to the properties of MK-8591 through the synthesis and antiviral evaluation of carbocyclic derivatives. Synthesized analogs were evaluated for their antiviral activity, and the corresponding triphosphates were synthesized and evaluated in a biochemical assay. 4'-Ethynyl-G derivative (±)-29 displayed a promising IC₅₀ of 33 nM in a hPBMC cell-based antiviral assay, and its triphosphate (TP), (±)-29-TP, displayed an IC₅₀ of 324 nM in a biochemical RT-polymerase assay. Improved TP anabolite delivery resulting in improved in vitro potency was achieved by preparing the corresponding phosphoramidate prodrug of single enantiomer 29b, with 6-ethoxy G derivative 34b displaying a significantly improved IC₅₀ of 3.0 nM, paving the way for new directions for this novel class of nucleoside analogs.