Diastereoselective synthesis of aryloxy phosphoramidate prodrugs of 3'-deoxy-2',3'-didehydrothymidine monophosphate

Prodrugs of Nucleoside 5'-Monophosphate Analogues: Overview of the Recent Literature Concerning their Synthesis and Applications

Nucleoside analogues are widely used as anti-infectious and antitumoral agents. However, their clinical use may face limitations associated with their physicochemical properties, pharmacokinetic parameters, and/or their peculiar mechanisms of action. Indeed, once inside the cells, nucleoside analogues require to be metabolized into their corresponding (poly-)phosphorylated derivatives, mediated by cellular and/or viral kinases, in order to interfere with nucleic acid biosynthesis. Within this activation process, the first-phosphorylation step is often the limiting one and to overcome this limitation, numerous prodrug approaches have been proposed. Herein, we will focus on recent literature data (from 2015 and onwards) related to new prodrug strategies, the development of original synthetic approaches and novel applications of nucleotide prodrugs (namely pronucleotides) leading to the intracellular delivery of 5'-monophosphate nucleoside analogues.

Recent advances in the synthesis and applications of phosphoramides

Phosphoramide, as an important framework of many biologically active molecules, has attracted widespread attention in recent decades. It is not only widely used in pharmaceuticals because of its excellent biological activities, but it also shows good performance in organic dyes, flame retardants and extractors. Thus, it is of great significance to develop effective and convenient methods for the synthesis of phosphoramides. In this review, the recent advancements made in the synthesis routes and applications of phosphoramides are discussed. The synthetic strategies of phosphoramides can be separated into five categories: phosphorus halides as the substrate, phosphates as the substrate, phosphorus hydrogen as the substrate, azides as the substrate and other methods. The latest examples of these methods are provided and some representative mechanisms are also described.

Single Diastereomers of the Clinical Anticancer ProTide Agents NUC-1031 and NUC-3373 Preferentially Target Cancer Stem Cells In Vitro

A 3'-protected route toward the synthesis of the diastereomers of clinically active ProTides, NUC-1031 and NUC-3373, is described. The in vitro cytotoxic activities of the individual diastereomers were found to be similar to their diastereomeric mixtures. In the KG1a cell line, NUC-1031 and NUC-3373 have preferential cytotoxic effects on leukemic stem cells (LSCs). These effects were not diastereomer-specific and were not observed with the parental nucleoside analogues gemcitabine and FUDR, respectively. In addition, NUC-1031 preferentially targeted LSCs in primary AML samples and cancer stem cells in the prostate cancer cell line, LNCaP. Although the mechanism for this remains incompletely resolved, NUC-1031-treated cells showed increased levels of triphosphate in both LSC and bulk tumor fractions. As ProTides are not dependent on nucleoside transporters, it seems possible that the LSC targeting observed with ProTides may be caused, at least in part, by preferential accumulation of metabolized nucleos(t)ide analogues.

An overview of ProTide technology and its implications to drug discovery

Introduction: The ProTide technology is a phosphate (or phosphonate) prodrug method devised to deliver nucleoside monophosphate (or monophosphonate) intracellularly bypassing the key challenges of antiviral and anticancer nucleoside analogs. Three new antiviral drugs, exploiting this technology, have been approved by the FDA while others are in clinical studies as anticancer agents.Areas covered: The authors describe the origin and development of this technology and its incredible success in transforming the drug discovery of antiviral and anticancer nucleoside analogues. As evidence, discussion on the antiviral ProTides on the market, and those currently in clinical development are included. The authors focus on how the proven capacity of this technology to generate new drug candidates has stimulated its application to non-nucleoside-based molecules.Expert opinion: The ProTide approach has been extremely successful in delivering blockbuster antiviral medicines and it seems highly promising in oncology. Its application to non-nucleoside-based small molecules is recently emerging and proving effective in other therapeutic areas. However, investigations to explain the lack of activity of certain ProTide series and comprehensive structure activity relationship studies to identify the appropriate phosphoramidate motifs depending on the parent molecule are in our opinion mandatory for the future development of these compounds.

Phosphorus-containing amino acids with a P–C bond in the side chain or a P–O, P–S or P–N bond: from synthesis to applications

Strategies for the preparation of phosphorus-containing amino acids and their utility in the organic chemistry, physico-chemistry, agrochemistry, and pharmacology fields are reported.

Enantiomeric impurities in chiral catalysts, auxiliaries, and synthons used in enantioselective syntheses. Part 5

The enantiomeric excess of chiral starting materials is one of the important factors determining the enantiopurity of products in asymmetric synthesis. Fifty-one commercially available chiral reagents used as building blocks, catalysts, and auxiliaries in various enantioselective syntheses were assayed for their enantiomeric purity. The test results were classified within five impurities level (ie, <0.01%, 0.01%-0.1%, 0.1%-1%, 1%-10%, >10%). Previously from 1998 to 2013, several reports have been published on the enantiomeric composition of more than 300 chiral reagents. This series of papers is necessitated by the fact that new reagents are forthcoming and that the enantiomeric purity of the same reagent can vary from batch to batch and/or from supplier to supplier. This report presents chiral liquid chromatography (LC) and gas chromatography (GC) methods to separate enantiomers of chiral compounds and evaluate their enantiomeric purities. The accurate and efficient LC analysis was done using newly introduced superficially porous particle (SPP 2.7 μm) based chiral stationary phases (TeicoShell, VancoShell, LarihcShell-P, and NicoShell).

Synthesis and Evaluation of Biological Activity of New Arylphosphoramidates

The synthesis of new substituted arylphosphoramidates is performed in two steps through phosphorylation of the corresponding alcohols followed by aminolysis. The formation of the desired phosphoramidates depends on the subsequent addition of the two alcohols with the amine being added at the last step. The products were obtained in 58-95% yields. They were characterized mainly by multinuclear (¹H, ¹³C, ³¹P, and ¹⁹F) NMR and IR spectroscopy. In addition, the antimicrobial and antiacetylcholinesterase activities were evaluated. The results showed acetylcholinesterase activity by some compounds, whilst no significant inhibitory effect against the tested bacterial strains has been recorded.

Phosphoramidates and phosphonamidates (ProTides) with antiviral activity

Following the first report on the nucleoside phosphoramidate (ProTide) prodrug approach in 1990 by Chris McGuigan, the extensive investigation of ProTide technology has begun in many laboratories. Designed with aim to overcome limitations and the key resistance mechanisms associated with nucleoside analogues used in the clinic (poor cellular uptake, poor conversion to the 5'-monophosphate form), the ProTide approach has been successfully applied to a vast number of nucleoside analogues with antiviral and anticancer activity. ProTides consist of a 5'-nucleoside monophosphate in which the two hydroxyl groups are masked with an amino acid ester and an aryloxy component which once in the cell is enzymatically metabolized to deliver free 5'-monophosphate, which is further transformed to the active 5'-triphosphate form of the nucleoside analogue. In this review, the seminal contribution of Chris McGuigan's research to this field is presented. His technology proved to be extremely successful in drug discovery and has led to two Food and Drug Administration-approved antiviral agents.

Diastereoselective synthesis of P-chirogenic phosphoramidate prodrugs of nucleoside analogues (ProTides) via copper catalysed reaction

The first example of transition metal assisted diastereoselective synthesis of phosphoramidate of nucleoside analogues is presented.

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.

Stereoselective synthesis and antiviral activity of methyl-substituted cycloSal-pronucleotides

Methyl-substituted cycloSal-pronucleotides of d4TMP were synthesized with high diastereoselectivities in satisfying chemical yields. The individual diastereomers were tested against HIV-1 and HIV-2 infected wild-type CEM/0 and HIV-2 infected thymidine kinase deficient CEM cells. All diastereomers tested showed significant antiviral activity in CEM/0 and strong activity in CEM/TK(-) cell cultures. The antiviral activities were strongly dependent on the chirality at the phosphate group and the position of the methyl-group(s) in the cycloSal moiety. In CEM/TK(-) cell cultures the difference in antiviral potency was found to be 7- to 20-fold. The stability of each diastereomer was studied in aqueous phosphate buffer and in CEM/0 cell extracts. Large differences in the half-lives were found. A comparison of the relative lipophilicity of the methyl-substituted cycloSal triesters was performed based on the retention times obtained by reversed phase HPLC. The results obtained clearly confirm the importance of a diastereoselective synthesis of cycloSal-pronucleotides.

Synthesis of diastereomerically pure nucleotide phosphoramidates

Prodrugs of therapeutic nucleoside monophosphates masked as phosphoramidate derivatives have become an increasingly important class of antiviral drugs in pharmaceutical research for delivering nucleotides in vitro and in vivo. Conventionally, phosphoramidate derivatives are prepared as a mixture of two diastereomers. We report a class of stable phosphoramidating reagents containing an amino acid ester and two phenolic groups, one unsubstituted and the other with electron-withdrawing substituents. The reagents can be isolated as single diastereomers and reacted with the 5'-hydroxyl group of nucleosides through selective nucleophilic displacement of the substituted phenol to prepare single diastereomer phosphoramidate products. This method has been used to prepare the HCV clinical candidate PSI-7977 in high yield and high diastereomeric purity.

Diastereoselective synthesis of cyclosaligenyl-nucleosyl-phosphotriesters

A diastereoselective synthesis of cycloSal-phosphotriesters (cycloSal=cycloSaligenyl) based on chiral auxiliaries has been developed that allows the synthesis of single diastereomers of the cycloSal-pronucleotides. In previously described synthesis routes, the cycloSal-compounds were always obtained as 1:1 diastereomeric mixtures that could be separated in only rare cases. However, it was shown that the diastereomers have different antiviral activity, toxicity, and hydrolysis stabilities. Here, first a chiral thiazoline derivative was used to prepare nonsubstituted and 5-methyl-cycloSal-phosphotriesters in 48 and ≥95% de (de=diastereomeric excess). However, this approach failed to give the important group of 3-substituted cycloSal-nucleotides. Therefore, two other chiral groups were discovered that allowed the synthesis of (R(P))- and (S(P))-3-methyl-cycloSal-phosphotriesters as well. The antiviral activity was found to be five- to 20-fold different between the two individual diastereomers, which proved the importance of this approach.