Discovery of ß-D-2'-deoxy-2'-α-fluoro-4'-α-cyano-5-aza-7,9-dideaza adenosine as a potent nucleoside inhibitor of respiratory syncytial virus with excellent selectivity over mitochondrial RNA and DNA polymerases.

Novel 4'-substituted ß-d-2'-deoxy-2'-α-fluoro (2'd2'F) nucleoside inhibitors of respiratory syncytial virus (RSV) are reported. The introduction of 4'-substitution onto 2'd2'F nucleoside analogs resulted in compounds demonstrating potent cell based RSV inhibition, improved inhibition of the RSV polymerase by the nucleoside triphosphate metabolites, and enhanced selectivity over incorporation by mitochondrial RNA and DNA polymerases. Selectivity over the mitochondrial polymerases was found to be extremely sensitive to the specific 4'-substitution and not readily predictable. Combining the most potent and selective 4'-groups from N-nucleoside analogs onto a 2'd2'F C-nucleoside analog resulted in the identification of ß-D-2'-deoxy-2'-α-fluoro-4'-α-cyano-5-aza-7,9-dideaza adenosine as a promising nucleoside lead for RSV.

Use of 2'-spirocyclic ethers in HCV nucleoside design.

Conformationally restricted 2'-spironucleosides and their prodrugs were synthesized as potential anti-HCV agents. Although the replicon activity of the new agents containing pyrimidine bases was modest, the triphosphate of a 2'-oxetane cytidine analogue demonstrated potent intrinsic biochemical activity against the NS5B polymerase, with IC50 = 8.48 µM. Activity against NS5B bearing the S282T mutation was reduced. Phosphoramidate prodrugs of a 2'-oxetane 2-amino-6-O-methyl-purine nucleoside demonstrated potent anti-HCV activity in vitro, and the corresponding triphosphate retained similar potent activity against both wild-type and S282T HCV NS5B polymerase.

ß-D-2'-α-F-2'-ß-C-Methyl-6-O-substituted 3',5'-cyclic phosphate nucleotide prodrugs as inhibitors of hepatitis C virus replication: a structure-activity relationship study.

The 3',5'-cyclic phosphate prodrug 9-[ß-d-2'-deoxy-2'-α-fluoro-2'-ß-C-methylribofuranosyl]-2-amino-6-ethoxypurine, PSI-352938 1, has demonstrated promising anti-HCV efficacy in vitro and in human clinical trials. A structure-activity relationship study of the nucleoside 3',5'-cyclic phosphate series of ß-d-2'-deoxy-2'-α-fluoro-2'-ß-C-methylribofuranosyl nucleoside prodrugs was undertaken and the anti-HCV activity and in vitro safety profile were assessed. Cycloalkyl 3',5'-cyclic phosphate prodrugs were shown to be significantly more potent as inhibitors of HCV replication than branched and straight chain alkyl 3',5'-cyclic phosphate prodrugs. No cytotoxicity and mitochondrial toxicity for prodrugs 12, 13 and 19 were observed at concentrations up to 100 µm in vitro. Cycloalkyl esters of 3',5'-cyclic phosphate nucleotide prodrugs demonstrated the ability to produce high levels of active triphosphate in clone-A cells and primary human hepatocytes. Compounds 12, 13 and 19 also demonstrated the ability to effectively deliver in vivo high levels of active nucleoside phosphates to rat liver.

Synthesis of stable isotope labeled analogs of the anti-hepatitis C virus nucleotide prodrugs PSI-7977 and PSI-352938.

In order to support bioanalytical LC/MS method development and plasma sample analysis in preclinical and clinical studies of the anti-hepatitis C-virus nucleotides, PSI-7977 and PSI-352938, the corresponding stable isotope labeled forms were prepared. These labeled compounds were prepared by addition reaction of the freshly prepared Grignard reagent (13)CD(3)MgI to the corresponding 2 '-ketone nucleosides followed by fluorination of the resulting carbinol with DAST. As expected, these 2 '-C-(trideuterated-(13)C-methyl) nucleotide prodrugs showed similar anti-HCV activity to that of the corresponding unlabeled ones.

Stereoselective synthesis of PSI-352938: a ß-D-2'-deoxy-2'-α-fluoro-2'-ß-C-methyl-3',5'-cyclic phosphate nucleotide prodrug for the treatment of HCV.

PSI-352938 is a novel 2'-deoxy-2'-α-fluoro-2'-ß-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'-ß-nucleoside intermediate 13 via S(N)2 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-ß-lactol in high yield under mild bromination conditions using CBr(4)/PPh(3) (Appel reaction). The desired cis-Rp 3',5'-cyclic phosphate construction was accomplished using isopropyl phosphorodichloridate readily obtained from POCl(3) and isopropyl alcohol. The base combination of Et(3)N/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.

Discovery of PSI-353661, a Novel Purine Nucleotide Prodrug for the Treatment of HCV Infection.

Hepatitis C virus afflicts approximately 180 million people worldwide, and the development of direct acting antivirals may offer substantial benefit compared to the current standard of care. Accordingly, prodrugs of 2'-deoxy-2'-fluoro-2'-C-methylguanosine monophosphate analogues were prepared and evaluated for their anti-HCV efficacy and tolerability. These prodrugs demonstrated >1000 fold greater potency than the parent nucleoside in a cell-based replicon assay as a result of higher intracellular triphosphate levels. Further optimization led to the discovery of the clinical candidate PSI-353661, which has demonstrated strong in vitro inhibition against HCV without cytotoxicity and equipotent activity against both the wild type and the known S282T nucleoside/tide resistant replicon. PSI-353661 is currently in preclinical development for the treatment of HCV.

2'-deoxy-2'-α-fluoro-2'-ß-C-methyl 3',5'-cyclic phosphate nucleotide prodrug analogs as inhibitors of HCV NS5B polymerase: discovery of PSI-352938.

A series of novel 2'-deoxy-2'-α-fluoro-2'-ß-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).

An efficient and diastereoselective synthesis of PSI-6130: a clinically efficacious inhibitor of HCV NS5B polymerase.

R7128 is the prodrug of 2'-deoxy-2'-fluoro-2'-C-methylcytidine (PSI-6130), a potent and selective inhibitor of HCV NS5B polymerase. Currently, R7128 is in clinical trials for the treatment of HCV infection. To support clinical development efforts, we needed an efficient and scalable synthesis of PSI-6130. We describe an improved, diastereoselective synthetic route starting with protected d-glyceraldehyde. No chiral reagents or catalysts were used to produce the three new contiguous stereocenters. Introduction of fluorine at the C-2 tertiary carbon was accomplished in a highly regio- and stereoselective manner through nucleophilic substitution on a cyclic sulfate. Scale-limiting chromatographic purifications were eliminated through the use of crystalline intermediates.

Synthesis and biological activity of 5',9-anhydro-3-purine-isonucleosides as potential anti-hepatitis C virus agents.

In order to study structure-activity relationships among the derivatives and congeners of 5',9-anhydro-3-(beta-D-ribofuranosyl)xanthine for anti-hepatitis C virus activity, a series of 5',9-anhydro-purine-isonucleosides with a substituent (s) at 6- or/and 8-position of the purine moiety were synthesized, and their anti-hepatitis C virus activity and cytotoxicity were evaluated and discussed.

N4-hydroxycytosine dioxolane nucleosides and their activity against hepatitis B virus.

Novel racemic, D- and L-beta-dioxolane N4-hydroxycytosine nucleosides have been synthesized and evaluated for their activity against hepatitis B virus. None of the synthesized nucleosides demonstrated selective anti-HBV activity.

Unusual olefin formation by PhSe-F trans-elimination.

A new approach to the synthesis of 2',3'-didehydro-2',3-dideoxynucleosides was described in excellent yield through unusual olefin formation by PhSe-F trans-elimination.

Ring-expanded analogues of natural oxetanocin: (+) and (-) hydroxymethyl isodideoxyadenosine.

New enantiomeric isonucleoside analogues related to natural oxetanocin have been synthesized from D-glucosamine and D-glucose. The structures of the target compounds were confirmed by NMR, HRMS, UV, single crystal X-ray, and optical rotation data. Stability studies with respect to purine nucleoside phosphorylase and adenosine deaminase show that these compounds are not substrates. Antiviral results are discussed.

Synthesis and structure-activity relationships of novel anti-hepatitis C agents: N3,5'-cyclo-4-(beta-D-ribofuranosyl)-vic-triazolo[4,5-b]pyridin-5-one derivatives.

Several 6- and 7-monosubstituted N3,5'-cyclo-4-(beta-d-ribofuranosyl)-vic-triazolo[4,5-b]pyridin-5-one derivatives as well as the 5-thiono analogue were synthesized, providing structure-anti-hepatitis C virus (HCV) activity relationships for the series. Among the compounds synthesized, the 6-bromo, 7-methylamino, and 5-thiono analogues exhibited more potent anti-HCV activity in an HCV subgenomic replicon cell based assay (EC90 = 1.9, 7.4, and 10.0 microM, respectively) than the lead compound N3,5'-cyclo-4-(beta-D-ribofuranosyl)-vic-triazolo[4,5-b]pyridin-5-one (EC90 = 79.8 microM).

Synthesis of 5'-C-methyl-1',3'-dioxolan-4'-yl nucleosides.

Novel racemic 5'-C-methyl-1',3'-dioxolan-4'-yl nucleosides were synthesized from the key intermediate, 2-benzoyloxymethyl-4-oxo-5-C-methyl-1,3-dioxolane, which was prepared from racemic lactic acid.