Synthesis of a Nucleobase-Modified ProTide Library

A new method for the construction of (aryloxy)­phosphoramidate nucleoside prodrugs is presented. An (aryloxy)­phosphoramidate ribose derivative as key building block was used for coupling with a number of nucleobases under Vorbrüggen reaction conditions yielding the protected ProTides in excellent yields. Selective hydrolysis of the acetoxy groups on the sugar moiety afforded a series of the desired ProTides. The advantage of this approach, when compared to classical procedures, is the greater flexibility for achieving structural variety of the nucleobase moiety

Synthesis of a C‑Nucleoside Phosphonate by Base-Promoted Epimerization

The efficient synthesis of a [2′S] C-nucleoside phosphonate and its corresponding prodrug has been realized. A phosphonomethoxy group was stereoselectively introduced at the anomeric 5′-carbon atom through glycosylation of a benzoyl protected [5′R]-acetoxy-[2′R]-9-deazaadenine. An unexpected epimerization at the 2′-position of the sugar moiety occurred upon removal of the protecting groups, but this was further exploited as a key reaction for improved synthesis of the target compound

Amidate Prodrugs of Cyclic 9‑(<i>S</i>)‑[3-Hydroxy-2-(phosphonomethoxy)propyl]adenine with Potent Anti-Herpesvirus Activity

A series of amidate prodrugs of cyclic 9-[3-hydroxy-2-(phosphonomethoxy)­propyl]­adenine (cHPMPA) featuring different amino acid motifs were synthesized. All phosphonamidates derived from (<i>S</i>)-cHPMPA displayed a broad spectrum activity against herpesviruses with EC₅₀ values in the low nanomolar range. A phosphonobisamidate prodrug of (<i>S</i>)-HPMPA also exhibited a remarkably potent antiviral activity. In addition, the leucine ester prodrug of (<i>S</i>)-cHPMPA and phosphonobisamidate valine ester prodrug of (<i>S</i>)-HPMPA proved stable in human plasma. These data warrant further development of cHPMPA prodrugs, especially against human cytomegalovirus (HCMV), for which there is a high need for treatment in transplant recipients

Amidate Prodrugs of Deoxythreosyl Nucleoside Phosphonates as Dual Inhibitors of HIV and HBV Replication

The synthesis of four l-2′-deoxy-threose nucleoside phosphonates with the natural nucleobases adenine, thymine, cytosine, and guanosine has been performed. Especially the adenine containing analogue (PMDTA) was endowed with potent antiviral activity displaying an EC₅₀ of 4.69 μM against HIV-1 and an EC₅₀ value of 0.5 μM against HBV, whereas completely lacking cytotoxicity. The synthesis of a number of phosphonomonoamidate and phosphonobisamidate prodrugs of PMDTA led to a boost in antiviral potency. The most potent congeners were a l-aspartic acid diisoamyl ester phenoxy prodrug and a l-phenylalanine propyl ester phosphonobisamidate prodrug that both display anti-HIV and anti-HBV activities in the low nanomolar range and selectivity indexes of more than 300

Imidazopyridine- and Purine-Thioacetamide Derivatives: Potent Inhibitors of Nucleotide Pyrophosphatase/Phosphodiesterase 1 (NPP1)

Nucleotide pyrophosphatase/phosphodiesterase 1 (NPP1) belongs to the family of ecto-nucleotidases, which control extracellular nucleotide, nucleoside, and (di)­phosphate levels. To study the (patho)­physiological roles of NPP1 potent and selective inhibitors with drug-like properties are required. Therefore, a compound library was screened for NPP1 inhibitors using a colorimetric assay with <i>p</i>-nitrophenyl 5′-thymidine monophosphate (<i>p</i>-Nph-5′-TMP) as an artificial substrate. This led to the discovery of 2-(3<i>H</i>-imidazo­[4,5-<i>b</i>]­pyridin-2-ylthio)-<i>N</i>-(3,4-dimethoxyphenyl)­acetamide (<b>5a</b>) as a hit compound with a <i>K</i>_i value of 217 nM. Subsequent structure–activity relationship studies led to the development of purine and imidazo­[4,5-<i>b</i>]­pyridine analogues with high inhibitory potency (<i>K</i>_i values of 5.00 nM and 29.6 nM, respectively) when assayed with <i>p</i>-Nph-5′-TMP as a substrate. Surprisingly, the compounds were significantly less potent when tested versus ATP as a substrate, with <i>K</i>_i values in the low micromolar range. A prototypic inhibitor was investigated for its mechanism of inhibition and found to be competitive versus both substrates

Amidate Prodrugs of Deoxythreosyl Nucleoside Phosphonates as Dual Inhibitors of HIV and HBV Replication

The synthesis of four l-2′-deoxy-threose nucleoside phosphonates with the natural nucleobases adenine, thymine, cytosine, and guanosine has been performed. Especially the adenine containing analogue (PMDTA) was endowed with potent antiviral activity displaying an EC₅₀ of 4.69 μM against HIV-1 and an EC₅₀ value of 0.5 μM against HBV, whereas completely lacking cytotoxicity. The synthesis of a number of phosphonomonoamidate and phosphonobisamidate prodrugs of PMDTA led to a boost in antiviral potency. The most potent congeners were a l-aspartic acid diisoamyl ester phenoxy prodrug and a l-phenylalanine propyl ester phosphonobisamidate prodrug that both display anti-HIV and anti-HBV activities in the low nanomolar range and selectivity indexes of more than 300

Selective Inhibitors of Cyclin G Associated Kinase (GAK) as Anti-Hepatitis C Agents

Cyclin G associated kinase (GAK) emerged as a promising drug target for the treatment of viral infections. However, no potent and selective GAK inhibitors have been reported in the literature to date. This paper describes the discovery of isothiazolo­[5,4-<i>b</i>]­pyridines as selective GAK inhibitors, with the most potent congeners displaying low nanomolar binding affinity for GAK. Cocrystallization experiments revealed that these compounds behaved as classic type I ATP-competitive kinase inhibitors. In addition, we have demonstrated that these compounds exhibit a potent activity against hepatitis C virus (HCV) by inhibiting two temporally distinct steps in the HCV life cycle (i.e., viral entry and assembly). Hence, these GAK inhibitors represent chemical probes to study GAK function in different disease areas where GAK has been implicated (including viral infection, cancer, and Parkinson’s disease)

Optimization of Isothiazolo[4,3‑<i>b</i>]­pyridine-Based Inhibitors of Cyclin G Associated Kinase (GAK) with Broad-Spectrum Antiviral Activity

There is an urgent need for strategies to combat dengue and other emerging viral infections. We reported that cyclin G-associated kinase (GAK), a cellular regulator of the clathrin-associated host adaptor proteins AP-1 and AP-2, regulates intracellular trafficking of multiple unrelated RNA viruses during early and late stages of the viral lifecycle. We also reported the discovery of potent, selective GAK inhibitors based on an isothiazolo­[4,3-<i>b</i>]­pyridine scaffold, albeit with moderate antiviral activity. Here, we describe our efforts leading to the discovery of novel isothiazolo­[4,3-<i>b</i>]­pyridines that maintain high GAK affinity and selectivity. These compounds demonstrate improved in vitro activity against dengue virus, including in human primary dendritic cells, and efficacy against the unrelated Ebola and chikungunya viruses. Moreover, inhibition of GAK activity was validated as an important mechanism of antiviral action of these compounds. These findings demonstrate the potential utility of a GAK-targeted broad-spectrum approach for combating currently untreatable emerging viral infections