The clinical potential of the acyclic (and cyclic) nucleoside phosphonates. The magic of the phosphonate bond

Synthesis of Novel 4'-Trifluoromethyl-5'-Norcarbocyclic C-Nucleoside Phosphonic Acids as Potent Anti-Leukemic Agents

The syntheses of novel C-nucleoside phosphonic acids as potential antiviral agents are described. The sugar moiety that served as the nucleoside skeleton was produced starting from commercially available 1,3-dihydroxy cyclopentane. The key C-C bond formation from sugar to base precursor was performed using the Knoevenagel-type condensation. The synthesized compounds exhibited anti-HIV activity and cytotoxicity. Also, the synthesized compounds were screened in vitro for tumor growth inhibitory activity against mouse leukemia cell lines (L-1210, P-815).

Synthesis and potent anti-leukemic activity of novel 5'-deoxycarbocyclic C-nucleoside phosphonic acids

The first synthetic route to 5'-deoxycarbocyclic C-nucleoside [9-deazaadenosine, (pyrrolo[3,2-d]pyrimidine)] phosphonic acids from commercially available 1,4-dihydroxy-2-butene was described. The key C-C bond formation from cyclopentanone to base precursor was performed using Knoevenagel-type condensation. Synthesized C-nucleoside phosphonic acids were tested for anti-HIV activity as well as anti-leukemic activity. They showed moderate cytotoxicity derived anti-HIV activity and anti-leukemic activity.

The first synthesis of 4'-branched 5'-deoxycarbocyclic 9-deazaadenosine and phosphonic acids as antiviral agents

The first synthetic route to 4'-trifluoromethylated 5'-deoxycarbocyclic-9-deazaadenosine analog and its phosphonic acid derivatives was described from α-trifluoromethyl-α,β-unsaturated ester. The C-C bond connection between cyclopentane and base moiety was accomplished using Knoevenagel type condensation from ketone derivative 11. Synthesized nucleoside and phosphonic acid analogs were tested for anti-HIV activity as well as cytotoxicity.

Synthesis of novel 2',3'-difluorinated 5'-deoxythreosyl phosphonic acid nucleosides as antiviral agents

A novel route for the synthesis of 2',3'-difluorinated 5'-deoxythreosyl phosphonic acid nucleosides from glyceraldehyde using the Horner-Emmons reaction in the presence of triethyl α-fluorophosphonoacetate is described. The second fluorination at the 2'-position was an electrophilic reaction performed using N-fluorodibenzenesulfonimide. Glycosylation reactions between the nucleosidic bases and glycosyl donor 9 generated nucleosides that were further phosphonated and hydrolyzed to produce the desired nucleoside analogues. The synthesized nucleoside analogues 13, 16, 20, and 23 were tested for anti- human immunodeficiency virus (HIV) activity as well as cytotoxicity. Adenine derivative 16 showed significant anti-HIV activity up to 100 μM.

Synthesis and antiviral evaluation of novel 4'-trifluoromethylated 5'-deoxyapiosyl nucleoside phosphonic acids

On the basis of the discovery that the threosyl nucleoside phosphonate PMDTA is a potent anti-HIV compound, we synthesized several 4'-trifluoromethyl-5'-deoxyapiosyl nucleoside phosphonic acids and evaluated their anti-HIV activity. An efficient synthetic route was optimized, starting from an α-trifluoromethyl-α,β-unsaturated ester. Glycosylation of the purine nucleosidic bases with a glycosyl donor yielded modified nucleoside intermediates, which were then phosphonated and hydrolyzed to provide the targeted nucleoside analogs. Once synthesized, the anti-HIV and cytotoxic activities of each analog were evaluated. None of the analogs showed significant anti-HIV activity at concentrations up to 100 μM.

Prodrugs of phosphonates and phosphates: crossing the membrane barrier

A substantial portion of metabolism involves transformation of phosphate esters, including pathways leading to nucleotides and oligonucleotides, carbohydrates, isoprenoids and steroids, and phosphorylated proteins. Because the natural substrates bear one or more negative charges, drugs that target these enzymes generally must be charged as well, but small charged molecules can have difficulty traversing the cell membrane by means other than endocytosis. The resulting dichotomy has stimulated a great deal of effort to develop effective prodrugs, compounds that carry little or no charge to enable them to transit biological membranes, but able to release the parent drug once inside the target cell. This chapter presents recent studies on advances in prodrug forms, along with representative examples of their application to marketed and developmental drugs.

KSHV targeted therapy: an update on inhibitors of viral lytic replication

Kaposi’s sarcoma-associated herpesvirus (KSHV) is the causative agent of Kaposi’s sarcoma, primary effusion lymphoma and multicentric Castleman’s disease. Since the discovery of KSHV 20 years ago, there is still no standard treatment and the management of virus-associated malignancies remains toxic and incompletely efficacious. As the majority of tumor cells are latently infected with KSHV, currently marketed antivirals that target the virus lytic cycle have shown inconsistent results in clinic. Nevertheless, lytic replication plays a major role in disease progression and virus dissemination. Case reports and retrospective studies have pointed out the benefit of antiviral therapy in the treatment and prevention of KSHV-associated diseases. As a consequence, potent and selective antivirals are needed. This review focuses on the anti-KSHV activity, mode of action and current status of antiviral drugs targeting KSHV lytic cycle. Among these drugs, different subclasses of viral DNA polymerase inhibitors and compounds that do not target the viral DNA polymerase are being discussed. We also cover molecules that target cellular kinases, as well as the potential of new drug targets and animal models for antiviral testing.

Synthesis of novel 2'-fluoro-3'-hydroxymethyl-5'-deoxythreosyl phosphonic acid nucleoside analogues as antiviral agents

A series of purine 5'-deoxyphosphonate analogues were designed and synthesized to mimic naturally occurring purine monophosphate from 1,3-dihydroxyacetone as starting material. The discovery of threosyl phosphonate nucleoside (PMDTA, EC50 = 2.53 μM) as a potent anti-HIV agent has led to the synthesis and biological evaluation of 2',3'-modified 5'-deoxyversions of the threosyl phosphonate nucleosides. The synthesized 2'-fluoro-3'-hydroxymethyl 5'-deoxythreosyl phosphonic acid nucleoside analogues 14, 18, 23, and 27 were tested for anti-HIV activity as well as cytotoxicity. The adenine analogue 18 exhibits weak in vitro anti-HIV-1 activity (EC50 = 19.2 μM).

Insights into the mechanism of action of cidofovir and other acyclic nucleoside phosphonates against polyoma- and papillomaviruses and non-viral induced neoplasia

Acyclic nucleoside phosphonates (ANPs) are well-known for their antiviral properties, three of them being approved for the treatment of human immunodeficiency virus infection (tenofovir), chronic hepatitis B (tenofovir and adefovir) or human cytomegalovirus retinitis (cidofovir). In addition, cidofovir is mostly used off-label for the treatment of infections caused by several DNA viruses other than cytomegalovirus, including papilloma- and polyomaviruses, which do not encode their own DNA polymerases. There is considerable interest in understanding why cidofovir is effective against these small DNA tumor viruses. Considering that papilloma- and polyomaviruses cause diseases associated either with productive infection (characterized by high production of infectious virus) or transformation (where only a limited number of viral proteins are expressed without synthesis of viral particles), it can be envisaged that cidofovir may act as antiviral and/or antiproliferative agent. The aim of this review is to discuss the advances in recent years in understanding the mode of action of ANPs as antiproliferative agents, given the fact that current data suggest that their use can be extended to the treatment of non-viral related malignancies.

Application of RPTEC/TERT1 cells for investigation of repeat dose nephrotoxicity: A transcriptomic study

The kidney is a major target organ for toxicity. Incidence of chronic kidney disease (CKD) is increasing at an alarming rate due to factors such as increasing population age and increased prevalence of heart disease and diabetes. There is a major effort ongoing to develop superior predictive models of renal injury and early renal biomarkers that can predict onset of CKD. In the EU FP7 funded project, Predict-IV, we investigated the human renal proximal tubule cells line, RPTEC/TERT1 for their applicability to long term nephrotoxic mechanistic studies. To this end, we used a tiered strategy to optimise dosing regimes for 9 nephrotoxins. Our final testing protocol utilised differentiated RPTEC/TERT1 cells cultured on filter inserts treated with compounds at both the apical and basolateral side, at concentrations not exceeding IC10, for 14 days in a 24 h repeat application. Transepithelial electrical resistance and supernatant lactate were measured over the duration of the experiments and genome wide transcriptomic profiles were assayed at day 1, 3 and 14. The effect of hypoxia was investigated for a subset of compounds. The transcriptomic data were analysed to investigate compound-specific effects, global responses and mechanistically informative signatures. In addition, several potential clinically useful renal injury biomarkers were identified.

Cidofovir and brincidofovir reduce the pathology caused by systemic infection with human type 5 adenovirus in immunosuppressed Syrian hamsters, while ribavirin is largely ineffective in this model

There are no drugs approved specifically to treat disseminated adenovirus (Ad) infections in humans. Cidofovir is active against Ad in cell culture, and it is used frequently in the clinic with disseminated infection in pediatric transplant patients; however, controlled clinical studies have not been conducted to prove the anti-Ad efficacy of cidofovir. Brincidofovir, a lipid-linked derivative of cidofovir, which has strong activity against Ad in cell culture and in animal models, is a promising new drug currently in clinical trials. Ribavirin, which has modest activity against some Ad types in cell culture, has been used in the clinic against disseminated Ad, but the efficacy of ribavirin is unknown. In the current study, we have examined the activity of cidofovir, brincidofovir, and ribavirin against disseminated Ad5 infection in the immunosuppressed Syrian hamster model. Hamsters are immunosuppressed by treatment with cyclophosphamide, then infected intravenously with Ad5, leading to disseminated Ad5 infection, especially in the liver. We found that cidofovir and brincidofovir have excellent activity against Ad5 pathology and replication in the liver, even when administered therapeutically starting at 3 days post-challenge with Ad5. Ribavirin did not have anti-Ad5 activity in our model. Our data support the use of cidofovir and brincidofovir in humans for the treatment of disseminated Ad infections in humans.

Enantiomerically pure phosphonated carbocyclic 2'-oxa-3'-azanucleosides: synthesis and biological evaluation

Starting from enantiomeric pure 1-[(3S,5R)- and 1-[(3R,5S)-3-(hydroxymethyl)-2-methylisoxazolidin-5-yl]-5-methylpyrimidine-2,4(1H,3H)-diones (-)7a and (+)7b, obtained by lipase-catalyzed resolution, pure diethyl{[(3S,5R)-2-methyl-5-(5-methyl-2,4-dioxo-3,4-dihydropyrimidin-1(2H)-yl)isoxazolidin-3-yl]methyl}phosphonate (-)12a and diethyl{[(3R,5S)-2-methyl-5-(5-methyl-2,4-dioxo-3,4-dihydropyrimidin-1(2H)-yl)isoxazolidin-3-yl]methyl}phosphonate (+)12b have been synthesized. The obtained compounds showed no cytotoxic activity versus the U937 cell line in comparison with AZT, and were poorly able to inhibit HIV infection in vitro.

Intramolecular indicator displacement assay for anions: supramolecular sensor for glyphosate

One of the well-known strategies for anion sensing is an indicator (dye) displacement assay. However, the disadvantage of the dye displacement assays is the low sensitivity due to the excess of the dye used. To overcome this setback, we have developed an "Intramolecular Indicator Displacement Assay (IIDA)". The IIDAs comprise a receptor and a spacer with an attached anionic chromophore in a single-molecule assembly. In the resting state, the environment-sensitive anionic chromophore is bound by the receptor, while the anionic substrate competes for binding into the receptor. The photophysical properties of the dye exhibit change in fluorescence when displaced by anions, which results in cross-reactive response. To illustrate the concept, we have prepared IID sensors 1 and 2. Here, the characterization of sensors and microtiter arrays comprising the IIDA are reported. The microtiter array including IID sensors 1 and 2 is capable of recognizing biological phosphates in water. The utility of the IIDA approach is demonstrated on sensing of a phosphonate herbicide glyphosate and other biologically important anions such as pyrophosphate in the presence of interferent sodium chloride.

Synthesis and study of (R)- and (S)-β-hydroxyphosphonate acyclonucleosides as structural analogues of (S)-HPMPC (cidofovir)

Modification of the acyclic chain highly impacts antiviral activity and recognition by human nmpks.

Synthesis and evaluation of novel 6',6'-difluoro 5'-deoxycarbocyclic phosphonic acid nucleosides as antiviral agents

The authors describe highly efficient synthetic routes for the preparation of novel 6',6'-difluoro 5'-deoxycarbocyclic phosphonic acid nucleosides from 1,4-dihydroxy-2-butene. The discovery that the 6'-fluorinated carbocyclic nucleoside (2, EC₅₀ = 0.16 μM) is a potent anti-HSV-1 agent led to the syntheses and biological evaluations of 6'-modified 5'-deoxyversions of carbocyclic phosphonate nucleosides. The synthesized nucleoside analogues 15, 18, 22, and 25 were tested for anti-HIV activity and for cytotoxicity. However, none of them showed significant anti-HIV-1 activity or cytotoxicity at concentrations up to 100 μM.

Evaluation of novel acyclic nucleoside phosphonates against human and animal gammaherpesviruses revealed an altered metabolism of cyclic prodrugs upon Epstein-Barr virus reactivation in P3HR-1 cells

Acyclic nucleoside phosphonates (ANPs), such as (S)-1-[(3-hydroxy-2-phosphonomethoxy)propyl)]cytosine (HPMPC), are an important group of broad-spectrum antiviral agents with activity against DNA viruses. In this report, we present the in vitro potencies of novel ANPs against gammaherpesviruses, including Kaposi's sarcoma-associated herpesvirus, Epstein-Barr virus (EBV), and three animal gammaherpesviruses. 1-(S)-[3-hydroxy-2-(phosphonomethoxy)propyl]-5-azacytosine (HPMP-5-azaC), (S)-9-[3-hydroxy-2-(phosphonomethoxy)propyl]-3-deazaadenine (3-deaza-HPMPA), and their cyclic derivatives have emerged as highly potent antigammaherpesvirus agents. Interestingly, cyclic prodrugs of ANPs exhibited reduced activities against EBV strain P3HR-1, but not against EBV strain Akata. Cell culture metabolism studies with HPMPC and cyclic HPMPC revealed that these differences were attributable to an altered drug metabolism in P3HR-1 cells after EBV reactivation and, more specifically, to a reduced hydrolysis of cyclic HPMPC by cyclic CMP phosphodiesterase. We did not correlate this effect with phosphodiesterase downregulation, or to functional mutations. Instead, altered cyclic AMP levels in P3HR-1 cells indicated a competitive inhibition of the phosphodiesterase by this cyclic nucleotide. Finally, both HPMPC and HPMP-5-azaC emerged as highly effective inhibitors in vivo through significant inhibition of murine gammaherpesvirus replication and dissemination. With the current need for potent antigammaherpesvirus agents, our findings underline the requirement of appropriate surrogate viruses for antiviral susceptibility testing and highlight HPMP-5-azaC as a promising compound for future clinical development.

Synthesis of new acadesine (AICA-riboside) analogues having acyclic D-ribityl or 4-hydroxybutyl chains in place of the ribose

The antiviral activity of certain acyclic nucleosides drew our attention to the fact that the replacement of the furanose ring by an alkyl group bearing hydroxyl(s) could be a useful structural modification to modulate the biological properties of those nucleosides. Herein, we report on the synthesis of some novel acadesine analogues, where the ribose moiety is mimicked by a D-ribityl or by a hydroxybutyl chain.

Interactions with selected drug renal transporters and transporter-mediated cytotoxicity in antiviral agents from the group of acyclic nucleoside phosphonates

Members of acyclic nucleoside phosphonates (ANPs) possess antiviral and antiproliferative activities. However, several clinically important ANPs may cause renal injury, most likely due to their active accumulation in the renal tubular cells. The goal of this study was to investigate in vitro relationships between the affinity of several structurally related potent ANPs to selected human transporters and their cytotoxicity. SLC (solute carrier family) transporters (hOAT1, hOCT2, hCNT2, hCNT3) and ABC (ATP-binding cassette) transporters (MDR1, BCRP), which are typically expressed in the kidney, were included in the study. The transport and toxic parameters of the tested compounds were compared to those of two clinically approved ANPs, adefovir and tenofovir. Transport studies with transiently transfected cells were used as the main method in the experiments. Most of the ANPs studied showed the potency to interact with hOAT1. GS-9191, a double prodrug of PMEG, displayed an affinity for hOAT1 comparable with that of adefovir and tenofovir. No significant interaction of the tested ANPs with hOCT2, hCNT2 and hCNT3 was observed. Only GS-9191 was found to be a strong inhibitor for both MDR1 and BCRP. PMEO-DAPy showed the potency to interact with MDR1. Most of the tested substances caused a significant decrease in cellular viability in the cells transfected with hOAT1. Only with the exclusion of GS-9191, a relatively lipophilic compound, did the in vitro cytotoxicity of the ANPs closely correspond to their potential to interact with hOAT1. The increased cytotoxicity of the studied ANPs found in OAT1 transfected cells was effectively reduced by OAT inhibitors probenecid and quercetin. The higher cytotoxicity of the compounds with affinity to hOAT1 proved in the inhibitory experiments evidences that ANPs are not only inhibitors but also substrates of hOAT1. Any clear relationship between the potency of ANPs to inhibit the studied efflux transporters and their cytotoxicity was not demonstrated. In conclusion, the study documented that among the studied transporters hOAT1 seems to be the decisive determinant for renal handling in most of the tested ANPs. This transporter may also play an important role in the mechanism of their potential cytotoxic effects. These facts are in good accordance with previous findings in the clinically used ANPs.

Antiviral drug development--success and failure: a personal perspective with a Japanese connection

At the 25th International Conference on Antiviral Research, I received a special recognition for my contribution to the International Society of Antiviral Research over a period of 25 years (from 1987 until 2012). This review follows the theme of my presentation at that event, which comprised 10 reminiscences, all with a Japanese connection concerning the success, or otherwise, in the clinical development of: double- and single-stranded polynucleotides; suramin, a polysulfonate; dextran sulfate, a polysulfate; brivudin; BVaraU; 2',3'-dideoxynucleoside analogues; HEPT; adefovir and tenofovir; CXCR4 antagonists; and elvitegravir.

Synthesis of novel 3'-hydroxymethyl 5'-deoxythreosyl phosphonic acid nucleoside analogues as potent antiviral agents

A very efficient synthetic route to novel 3'-hydroxymethyl 5'-deoxythreosyl phosphonic acid nucleosides was described. The discovery of threosyl phosphonate nucleoside (PMDTA, EC(50) = 2.53 μM) as a potent antihuman immunodeficiency virus (anti-HIV) agent has led to the synthesis and biological evaluation of 3'-modified 5'-deoxy versions of the threosyl phosphonate nucleosides. 3'-Hydroxymethyl 5 '-deoxythreosyl phosphonic acid nucleoside analogues 15, 19, 24, and 28 were synthesized from 1,3-dihydroxyacetone and tested for anti-HIV activity as well as cytotoxicity. The adenine analogue 19 exhibits moderate in vitro anti-HIV-1 activity (EC(50) = 10.2 μM).

The antiviral activity and mechanism of action of (S)-[3-hydroxy-2-(phosphonomethoxy)propyl] (HPMP) nucleosides

One class of compounds that has shown promise as antiviral agents are the (S)-[3-hydroxy-2-(phosphonomethoxy)propyl] (HPMP) nucleosides, members of the broader class of acyclic nucleoside phosphonates. These HPMP nucleosides are nucleotide analogs and have been shown to be effective inhibitors of a wide range of DNA viruses. Prodrugs of these compounds, which achieve higher levels of the active metabolites within the cell, have an expanded activity spectrum that also includes RNA viruses and retroviruses. Because they are analogs of natural nucleotide substrates, HPMP nucleosides are predicted to target polymerases (DNA polymerases, RNA polymerases and reverse transcriptases), resulting in the inhibition of viral genome replication. Previous work using the replicative enzymes of different viruses including human cytomegalovirus (HCMV) and vaccinia virus DNA polymerases and human immunodeficiency virus type 1 (HIV-1) reverse transcriptase has shown that the activated forms of these compounds are substrates for viral polymerases and that incorporation of these compounds into either the primer strand or the template strand inhibits, but does not necessarily terminate, further nucleic acid synthesis. The activity of these compounds against other viruses that do not encode their own polymerases, like polyoma viruses and papilloma viruses, suggests that host cell DNA polymerases are also targeted. This complex mechanism of action and broad activity spectrum has implications for the development of resistance and host cell genome replication, and suggests these compounds may be effective against other viruses such as influenza virus, respiratory syncytial virus and Dengue virus. This class of nucleotide analogs also points to a potential avenue for the development of newer antivirals.

5-azacytosine compounds in medicinal chemistry: current stage and future perspectives

This review summarizes the basic milestones of the research of 5-azacytosine nucleosides chronologically from their discovery and anticancer activity identification, through to subsequent unveiling of their mechanism of action based on DNA hypomethylation and tumor-suppressor gene reactivation, to the final US FDA approval of 5-azacytidine (Vidaza®) and 2´-deoxy-5-azacytidine (Dacogen®) for the treatment of myelodysplastic syndromes. 5,6-dihydro-2´-deoxy-5-azacytidine, a compound with anti-HIV activity through lethal mutagenesis, representing a unique mechanism of action among existing anti-retroviral drugs, is discussed together with quite recent discovery of its so far unexpected hypomethylation activity. Special attention is paid to 5-azacytosine acyclic nucleoside analogues and phosphonomethyl derivatives with the emphasis on the new potent anti-DNA virus agent (S)-1-[3-hydroxy-2-(phosphonomethoxy)propyl]-5-azacytosine and its prodrug forms. Considering the potential pharmaceutical applications, 5-azacytosine and 5,6-dihydro-5-azacytosine appear to be so far the most effective cytosine mimics for the design of novel antiviral and anti-tumor drug candidates.

Pre-steady state kinetic analysis of cyclobutyl derivatives of 2'-deoxyadenosine 5'-triphosphate as inhibitors of HIV-1 reverse transcriptase

Pre-steady state kinetic analysis was utilized for biochemical evaluation of a series of cyclobutyl adenosine nucleotide analogs with HIV-1 RT(WT). The phosphonyl-diphosphate form of the cyclobutyl nucleotide, 5, was the most efficiently incorporated of the series. Nucleotide 5 was fourfold more efficiently incorporated than the FDA approved TFV-DP by RT(WT). The kinetics of incorporation for 5 using the drug resistant mutant enzyme K65R was also determined. Compound 5 was threefold more efficiently incorporated compared to TFV-DP with RT(K65R). These results demonstrate cyclobutyl adenosine analogs can act as substrates for incorporation by HIV-1 RT and be a potential scaffold for HIV inhibitors.

Medicinal Chemistry of Nucleoside Phosphonate Prodrugs for Antiviral Therapy

Considerable attention has been focused on the development of phosphonate-containing drugs for application in many therapeutic areas. However, phosphonate diacids are deprotonated at physiological pH and thus phosphonate-containing drugs are not ideal for oral administration, an extremely desirable requisite for the treatment of chronic diseases. To overcome this limitation several prodrug structures of biologically active phosphonate analogues have been developed. The rationale behind the design of such agents is to achieve temporary blockade of the free phosphonic functional group until their systemic absorption and delivery, allowing the release of the active drug only once at the target. In this paper, an overview of acyclic and cyclic nucleoside phosphonate prodrugs, designed as antiviral agents, is presented.

Stereoselective synthesis of uridine-derived nucleosyl amino acids

Novel hybrid structures of 5'-deoxyuridine and glycine were conceived and synthesized. Such nucleosyl amino acids (NAAs) represent simplified analogues of the core structure of muraymycin nucleoside antibiotics, making them useful synthetic building blocks for structure-activity relationship (SAR) studies. The key step of the developed synthetic route was the efficient and highly diastereoselective asymmetric hydrogenation of didehydro amino acid precursors toward protected NAAs. It was anticipated that the synthesis of unprotected muraymycin derivatives via this route would require a suitable intermediate protecting group at the N-3 of the uracil base. After initial attempts using PMB- and BOM-N-3 protection, both of which resulted in problematic deprotection steps, an N-3 protecting group-free route was envisaged. In spite of the pronounced acidity of the uracil-3-NH, this route worked equally efficient and with identical stereoselectivities as the initial strategies involving N-3 protection. The obtained NAA building blocks were employed for the synthesis of truncated 5'-deoxymuraymycin analogues.

Synthesis of (R)- and (S)-β-hydroxyphosphonate acyclonucleosides: structural analogues of Adefovir (PMEA)

A synthetic pathway to new acyclonucleoside phosphonates, as analogues of Adefovir, is described. The reduction of an acyclonucleoside β-ketophosphonate, readily available from the nucleobase and benzylacrylate, afforded a mixture of (R)- and (S)-β-hydroxyphosphonate derivatives which was resolved. The assignment of the absolute configuration was proposed on the basis of NMR studies and was supported by molecular modelling studies.

Exploiting the nucleotide substrate specificity of repair DNA polymerases to develop novel anticancer agents

The genome is constantly exposed to mutations that can originate during replication or as a result of the action of both endogenous and/or exogenous damaging agents [such as reactive oxygen species (ROS), UV light, genotoxic environmental compounds, etc.]. Cells have developed a set of specialized mechanisms to counteract this mutational burden. Many cancer cells have defects in one or more DNA repair pathways, hence they rely on a narrower set of specialized DNA repair mechanisms than normal cells. Inhibiting one of these pathways in the context of an already DNA repair-deficient genetic background, will be more toxic to cancer cells than to normal cells, a concept recently exploited in cancer chemotherapy by the synthetic lethality approach. Essential to all DNA repair pathways are the DNA pols. Thus, these enzymes are being regarded as attractive targets for the development of specific inhibitors of DNA repair in cancer cells. In this review we examine the current state-of-the-art in the development of nucleotide analogs as inhibitors of repair DNA polymerases.