1199809-32-9

A compound or salt thereof having the following structure useful for the treatment of hepatitis C virus (HCV): wherein R 7 is C 1-6 alkyl or C 3-6 cycloalkyl and R 8 is -O(C 1-6 alkyl) or -O(C 3-6 cycloalkyl).

PSI-352938 is a novel 2′-deoxy-2′-α-fluoro-2′- β-C-methyl 3′,5′-cyclic phosphate nucleotide prodrug currently under investigation for the treatment of hepatitis C virus (HCV) infection. PSI-352938 demonstrated superior characteristics in vitro that include broad genotype coverage, superior resistance profile, and high levels of active triphosphate in vivo in the liver compared to our first and second generation nucleoside inhibitors of this class. Consequently, PSI-352938 was selected for further development and an efficient and scalable synthesis was sought to support clinical development. We report an improved, diastereoselective synthesis of a key 1′-β-nucleoside intermediate 13 via SN2 displacement of 1-α-bromo ribofuranose sugar 16 with the potassium salt of 6-chloro-2-amino purine and an efficient method to prepare cis-Rp cyclic phosphate (PSI-352938) in a highly stereoselective manner without any chromatographic purification. The 1-α-bromo sugar 16 was stereospecifically prepared from the corresponding 1-β-lactol in high yield under mild bromination conditions using CBr4/PPh3 (Appel reaction). The desired cis-Rp 3′,5′-cyclic phosphate construction was accomplished using isopropyl phosphorodichloridate readily obtained from POCl3 and isopropyl alcohol. The base combination of Et 3N/NMI was identified as a key factor for producing PSI-352938 as the major (>95%) diastereomer (cis-Rp) in high yield after the final cyclization step. The current route described in this article was successfully used to produce PSI-352938 on multikilogram scale.

A series of novel 2′-deoxy-2′-α-fluoro-2′-β-C- methyl 3′,5′-cyclic phosphate nucleotide prodrug analogs were synthesized and evaluated for their in vitro anti-HCV activity and safety. These prodrugs demonstrated a 10-100-fold greater potency than the parent nucleoside in a cell-based replicon assay due to higher cellular triphosphate levels. Our structure-activity relationship (SAR) studies provided compounds that gave high levels of active triphosphate in rat liver when administered orally to rats. These studies ultimately led to the selection of the clinical development candidate 24a (PSI-352938).