S-acyl-2-thioethyl aryl phosphotriester derivatives of AZT: synthesis, antiviral activity, and stability study

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.

Solid-Phase Synthesis, Hybridizing Ability, Uptake, and Nuclease Resistant Profiles of Position-Selective Cationic and Hydrophobic Phosphotriester Oligonucleotides

Analogues of oligonucleotides and mononucleotides with hydrophobic and/or cationic phophotriester functionalities often generate an improvement in target affinity and cellular uptake. Here we report the synthesis of phosphotriester oligodeoxyribonucleotides (ODNs) that are stable to the conditions used for their preparation. The method has been demonstrated by introducing phosphoramidite synthons where N-benzyloxycarbonyl (Z) protected amino alcohols replace the cyanoethyl group. After synthesis these ODNs were found to be stable to the condition required to remove base labile protecting groups and the ODNs from the solid support. Moreover the use of 1-(4,4-dimethyl-2, 6-dioxocyclohex-1-ylidene) ethyl (Dde) in place of Z protection on the amino alcohol has allowed us to introduce cationic aminoethyl phosphotriester modifications into ODNs. Melting temperatures of duplexes containing cationic or hydrophobic Z modified ODNs indicate that the backbone-phosphotriester modifications minimally affect duplex stability. Nuclease stability assays demonstrate that these phosphotriesters are resistant toward 5'- and 3'-exonucleases. Fluorescently labeled 23-mer ODNs modified with four cationic or hydrophobic Z phosphotriester linkages show efficient cellular uptake during passive transfection in HeLa and Jurkat cells.

Diastereoisomeric resolution of a pronucleotide using solid phase extraction and high performance liquid chromatography: Application to a stereoselective decomposition kinetic in cell extracts

A stereospecific HPLC methodology has been developed for the diastereoisomeric resolution of a mononucleotide prodrug in cell extracts. This method involves the use of solid phase extraction on a C18 cartridge. Diastereoisomers and internal standard resolutions were performed on a cellulose based chiral column (Chiralcel OD-H) used in the normal phase mode. The method was validated in terms of specificity, recovery, linearity (diasteroisomers mixture concentration: 3-60 micromol L(-1)), precision and accuracy and detection limit (1.67 and 1.33 micromol L(-1) for first and second eluted diastereoisomer). This method was applied to the determination of the apparent rate constants of disappearance and half-lives of each stereoisomers. This permits to conclude to the stereoselectivity of the enzymatic activity involved in the decomposition pathway of 2.

Separation of 3′-azido-2′,3′-dideoxythymidine pronucleotide diastereoisomers in biological samples by CZE with cyclodextrin addition

The possibility of using capillary electrophoresis as an alternative technique to HPLC for the separation of pronucleotide diastereoisomers of AZT was investigated. In the pH range 6.2-7.2 where the analytes are stable, a chiral additive, carboxymethyl-beta-CD, was found appropriate to enable the separation of the uncharged diastereoisomers. An experimental design strategy was used to study the influence of several parameters (CD and phosphate buffer concentration, methanol content of the electrolyte, injected volume, capillary length, electric field and separation temperature) on the separation and find suitable analytical conditions for monitoring the prodrugs in cell extracts. The diastereoisomers of the three tBuSATE phenylphosphotriester derivatives of AZT studied could be fully resolved within short analysis time (less than 10 min). Method validation results showed satisfactory results for linearity, accuracy and repeatability.

Column selection and method development for the separation of nucleoside phosphotriester diastereoisomers, new potential anti-viral drugs. Application to cellular extract analysis

Analytical HPLC methods using derivatized cellulose and amylose chiral stationary phases used in normal and reversed-phase modes were developed for the diastereoisomeric separation of mononucleotide prodrugs (pronucleotides) of 3'-azido-2',3'-dideoxythymidine (AZT). The resolutions were performed with two silica-based celluloses using normal and reversed-phase methodologies: Tris-3,5-dimethylphenylcarbamate (Chiralcel OD-H and Chiracel OD-RH) and Tris-methylbenzoate (Chiralcel OJ and OJ-R). Two amyloses phases, Tris-3,5-dimethylphenylcarbamate (Chiralpak AD) and Tris-(S)-1-phenylethylcarbamate (Chiralpak AS), were used in normal-phase mode. Additionally, we developed separation using two stationary phases with immobilized cyclodextrins in reversed-phase and polar-organic modes. The mobile phase and the chiral stationary phase were varied to achieve the best resolution. Different types and concentration of aliphatic alcohols, acetonitrile or water in the mobile phase were also tested for the different separation modes. An optimal baseline separation (Rs > 1.5) was readily obtained with all silica-based celluloses and amyloses using a normal-phase methodology. The different columns gave complementary results in term of resolution. Limits of detection and quantification were 0.12-0.20 and 0.40-0.67 microm, respectively. This analytical method was applied in a preliminary study for the pronucleotide 2 quantification in cellular extract.

Synthesis and evaluation of double-prodrugs against HIV. Conjugation of D4T with 6-benzyl-1-(ethoxymethyl)-5-isopropyluracil (MKC-442, emivirine)-type reverse transcriptase inhibitors via the SATE prodrug approach

This paper reports the synthesis and the antiviral activities of new double-prodrugs against HIV based on the known mixed SATE (S-acyl-2-thioethyl) prodrug approach. The monophosphate of the nucleoside reverse transcriptase inhibitor (NRTI) d4T was masked with one SATE group and one aromatic group through which a nonnucleoside reverse transcriptase inhibitor (NNRTI) was linked. Double-prodrug 1 was a hybrid between d4T monophosphate and the known NNRTI MKC-442, which were linked through a labile p-hydroxybenzoyl protection group in the N-3 position of MKC-442. Double-prodrugs 2 and 3 were conjugates between d4T monophosphate and the new NNRTIs 15 and 19 linked through a stable phenolic linker that was a part of the N-1 substituents of the NNRTIs. The double-prodrugs 1, 2, and 3 all had good activities against wild-type HIV-1, Y181C mutant, and also against a HIV-2 strain that was resistant to NNRTIs.