Prodrugs of the Phosphoribosylated Forms of Hydroxypyrazine­carboxamide Pseudobase T‑705 and Its De-Fluoro Analogue T‑1105 as Potent Influenza Virus Inhibitors

We here disclose chemical synthesis of ribonucleoside 5′-monophosphate (RMP), -diphosphate (RDP), and -triphosphate (RTP) and cycloSal-, DiPPro-, and TriPPPro nucleotide prodrugs of the antiviral pseudobase T-1105. Moreover, we include one nucleoside diphosphate prodrug of the chemically less stable T-705. We demonstrate efficient T-1105-RDP and -RTP release from the DiPPro and TriPPPro compounds by esterase activation. Using crude enzyme extracts, we saw rapid phosphorylation of T-1105-RDP into T-1105-RTP. In sharp contrast, phosphorylation of T-1105-RMP was not seen, indicating a yet unrecognized bottleneck in T-1105’s metabolic activation. Accordingly, DiPPro and TriPPPro compounds displayed improved cell culture activity against influenza A and B virus, which they retained in a mutant cell line incapable of activating the nucleobase parent. T-1105-RTP had a strong inhibitory effect against isolated influenza polymerase, and DiPPro-T-1105-RDP showed 4-fold higher potency in suppressing one-cycle viral RNA synthesis versus T-1105. Hence, our T-1105-RDP and -RTP prodrugs improve antiviral potency and achieve efficient metabolic bypass.