Synthesis of T-705-Ribonucleoside and T-705-Ribonucleotide and Studies of Chemical Stability.

T-705 (favipiravir) is a fluorinated hydroxypyrazine carboxamide that exhibits antiviral activities against a variety of RNA viruses. Given the lack of potent agents to combat these infections caused by a large number of high-impact pathogens, significant emphasis has been put on studies of the antiviral properties of T-705 and its mechanism of action. T-705 acts as a nucleobase analogue; it is therefore metabolized to the corresponding ribonucleoside triphosphate intracellularly. Herein we report a reliable synthesis of T-705-ribonucleoside as well as its 5'-monophosphate. Moreover, we disclose detailed studies on the remarkable lability of the heterocycle when attached to ribose under very mild conditions, as typically applied in biochemical studies.