Lipophilic phosphoramidates as antiviral pronucleotides

Allenyl Thianthrenium Salt: A Bench-Stable C3 Synthon for Annulation and Cross-Coupling Reactions

Herein, we report the first bench-stable and nonhygroscopic monosubstituted allenyl sulfonium salt (ATT) synthesized from thianthrene and propargyl alcohol. We demonstrate its use in annulation chemistry to synthesize heterocycles, such as 2-hydroxy morpholine, 2-methyl quinoxalines, and benzodioxepinone derivatives, with an exocyclic double bond. The reagent is the first allenyl sulfonium salt that can undergo palladium-catalyzed cross-coupling reactions to form a C(sp2)-C(sp2) bond via Suzuki coupling and a C(sp3)-C(sp2) bond formation via reductive coupling.

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.

Palladium-Catalyzed (3+3) Annulation of Allenylethylene Carbonates with Nitrile Oxides

In this paper, we designed and synthesized a new type of cyclic carbonates, allenylethylene carbonates (AECs). With AECs as reactive precursors, we developed palladium-catalyzed (3+3) annulation of AECs with nitrile oxides. Various AECs worked well in this reaction under mild reaction conditions. A variety of 5,6-dihydro-1,4,2-dioxazine derivatives with allenyl quaternary stereocenters can be accessed in a facile manner in high yields (≤98%).

Deciphering the Chameleonic Chemistry of Allenols: Breaking the Taboo of a Onetime Esoteric Functionality

The allene functionality has participated in one of the most exciting voyages in organic chemistry, from chemical curiosities to a recurring building block in modern organic chemistry. In the last decades, a special kind of allene, namely, allenol, has emerged. Allenols, formed by an allene moiety and a hydroxyl functional group with diverse connectivity, have become common building blocks for the synthesis of a wide range of structures and frequent motif in naturally occurring systems. The synergistic effect of the allene and hydroxyl functional groups enables allenols to be considered as a unique and sole functionality exhibiting a special reactivity. This Review summarizes the most significant contributions to the chemistry of allenols that appeared during the past decade, with emphasis on their synthesis, reactivity, and occurrence in natural products.

N-Acyl-phosphoramidates as potential novel form of gemcitabine prodrugs

Gemcitabine (dFdC) is a cytidine analog remarkably active against a wide range of solid tumors. Inside a cell, gemcitabine is phosphorylated by deoxycytidine kinase to yield gemcitabine monophosphate, further converted to gemcitabine di- and triphosphate. The most frequent form of acquired resistance to gemcitabine in vitro is the deoxycytidine kinase deficiency. Thus, proper prodrugs carrying the 5'-pdFdC moiety may help to overcome this problem. A series of new derivatives of gemcitabine possessing N-acyl(thio)phosphoramidate moieties were prepared and their cytotoxic properties were determined. N-Acyl-phosphoramidate derivatives of gemcitabine have similar cytotoxicity as gemcitabine itself, and have been found accessible to the cellular enzymes. The nicotinic carboxamide derivative of gemcitabine 5'-O-phosphorothioate occurred to be the best inhibitor of bacterial DNA polymerase I and human DNA polymerase α.

Ester prodrugs of acyclic nucleoside thiophosphonates compared to phosphonates: synthesis, antiviral activity and decomposition study

9-[2-(Thiophosphonomethoxy)ethyl]adenine [S-PMEA, 8] and (R)-9-[2-(Thiophosphonomethoxy)propyl]adenine [S-PMPA, 9] are acyclic nucleoside thiophosphonates we described recently that display the same antiviral spectrum (DNA viruses) as approved and potent phosphonates PMEA and (R)-PMPA. Here, we describe the synthesis, antiviral activities in infected cell cultures and decomposition study of bis(pivaloyloxymethoxy)-S-PMEA [Bis-POM-S-PMEA, 13] and bis(isopropyloxymethylcarbonyl)-S-PMPA [Bis-POC-S-PMPA, 14] as orally bioavailable prodrugs of the S-PMEA 8 and S-PMPA 9, in comparison to the equivalent "non-thio" derivatives [Bis-POM-PMEA, 11] and [Bis-POC-PMPA, 12]. Compounds 11, 12, 13 and 14 were evaluated for their in vitro antiviral activity against HIV-1-, HIV-2-, HBV- and a broad panel of DNA viruses, and found to exhibit moderate to potent antiviral activity. In order to determine the decomposition pathway of the prodrugs 11, 12, 13 and 14 into parent compounds PMEA, PMPA, 8 and 9, kinetic data and decomposition pathways in several media are presented. As expected, bis-POM-S-PMEA 13 and bis-POC-S-PMPA 14 behaved as prodrugs of S-PMEA 8 and S-PMPA 9. However, thiophosphonates 8 and 9 were released very smoothly in cell extracts, in contrast to the release of PMEA and PMPA from "non-thio" prodrugs 11 and 12.

Progress in the development of anti-hepatitis C virus nucleoside and nucleotide prodrugs

The search for new anti-hepatitis C virus (HCV) therapeutics continues as the current treatment, consisting of PEGylated IFN-α and ribavirin, is of limited efficacy, nonspecific and can cause significant side effects. Modified nucleoside analogues with improved efficacy and selectivity, may become the backbone of the future standard of care for anti-HCV therapies. Several families of modified nucleoside are known to inhibit HCV RNA-dependent RNA polymerase, a vital enzyme for viral replication. Ongoing efforts are focused on improvement of potency, selectivity and delivery of antiviral nucleoside analogues, with several recent promising advances into clinical trials. This review summarizes the current progress in the development of new anti-HCV nucleoside and nucleotide prodrugs.

Histidine triad nucleotide-binding protein 1 (HINT-1) phosphoramidase transforms nucleoside 5'-O-phosphorothioates to nucleoside 5'-O-phosphates

Nucleoside 5'-O-phosphorothioates are formed in vivo as primary products of hydrolysis of oligo(nucleoside phosphorothioate)s (PS-oligos) that are applied as antisense therapeutic molecules. The biodistribution of PS-oligos and their pharmacokinetics have been widely reported, but little is known about their subsequent decay inside the organism. We suggest that the enzyme responsible for nucleoside 5'-O-monophosphorothioate ((d)NMPS) metabolism could be histidine triad nucleotide-binding protein 1 (Hint-1), a phosphoramidase belonging to the histidine triad (HIT) superfamily that is present in all forms of life. An additional, but usually ignored, activity of Hint-1 is its ability to catalyze the conversion of adenosine 5'-O-monophosphorothioate (AMPS) to 5'-O-monophosphate (AMP). By mutagenetic and biochemical studies, we defined the active site of Hint-1 and the kinetic parameters of the desulfuration reaction (P-S bond cleavage). Additionally, crystallographic analysis (resolution from 1.08 to 1.37 Å) of three engineered cysteine mutants showed the high similarity of their structures, which were not very different from the structure of WT Hint-1. Moreover, we found that not only AMPS but also other ribonucleoside and 2'-deoxyribonucleoside phosphorothioates are desulfurated by Hint-1 at the following relative rates: GMPS > AMPS > dGMPS ≥ CMPS > UMPS > dAMPS ≫ dCMPS > TMPS, and during the reaction, hydrogen sulfide, which is thought to be the third gaseous mediator, was released.

Aryloxy phosphoramidate triesters: a technology for delivering monophosphorylated nucleosides and sugars into cells

Prodrug technologies aimed at delivering nucleoside monophosphates into cells (protides) have proved to be effective in improving the therapeutic potential of antiviral and anticancer nucleosides. In these cases, the nucleoside monophosphates are delivered into the cell, where they may then be further converted (phosphorylated) to their active species. Herein, we describe one of these technologies developed in our laboratories, known as the phosphoramidate protide method. In this approach, the charges of the phosphate group are fully masked to provide efficient passive cell-membrane penetration. Upon entering the cell, the masking groups are enzymatically cleaved to release the phosphorylated biomolecule. The application of this technology to various therapeutic nucleosides has resulted in improved antiviral and anticancer activities, and in some cases it has transformed inactive nucleosides to active ones. Additionally, the phosphoramidate technology has also been applied to numerous antiviral nucleoside phosphonates, and has resulted in at least three phosphoramidate-based nucleotides progressing to clinical investigations. Furthermore, the phosphoramidate technology has been recently applied to sugars (mainly glucosamine) in order to improve their therapeutic potential. The development of the phosphoramidate technology, mechanism of action and the application of the technology to various monophosphorylated nucleosides and sugars will be reviewed.

Overview of the synthesis of nucleoside phosphates and polyphosphates

This overview summarizes methodology used for the synthesis of nucleoside mono-, di-, and triphosphates. Selected techniques such as the Mitsunobu reaction, displacement reactions involving nucleoside 5'-tosylates, "anion-exchange" techniques, and phosphoramidite and phosphoramidate methodologies are highlighted. The chemistry of phosphorylation is detailed with respect to advantages and limitations under various conditions. Applicability of the methods toward the synthesis of analogs such as imidophosphates, phosphorothioates, and radiolabeled nucleotides is also addressed.

Stereochemistry of rHint1 hydrolase assisted cleavage of P–N bond in nucleoside 5′-O-phosphoramidothioates

The Hint-1 hydrolase assisted cleavage of the P-N bond in adenosine-5'-O-[N-(tryptophanylamide)]phosphoramidothioate proceeds with retention of configuration at the phosphorus atom which is consistent with the formation of a covalent enzyme-substrate complex.

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.

Phosphoralaninate pronucleotides of pyrimidine methylenecyclopropane analogues of nucleosides: synthesis and antiviral activity

The Z- and E-thymine and cytosine pronucleotides 3d, 4d, 3e, and 4e of methylenecyclopropane nucleosides analogues were synthesized, evaluated for their antiviral activity against human cytomegalovirus (HCMV), herpes simplex virus 1 and 2 (HSV-1 and HSV-2), varicella zoster virus (VZV), Epstein-Barr virus (EBV), human immunodeficiency virus type 1 (HSV-1), and hepatitis B virus (HBV) and their potency was compared with the parent compounds 1d, 2d, 1e, and 2e. Prodrugs 3d and 4d were obtained by phosphorylation of parent analogues 1d or 2d with reagent 8. A similar phosphorylation of N4-benzoylcytosine methylenecyclopropanes 9a and 9b gave intermediates 11a and 11b. Deprotection with hydrazine in pyridine-acetic acid gave pronucleotides 3e and 4e. The Z-cytosine analogue 3e was active against HCMV and EBV The cytosine E-isomer 4e was moderately effective against EBV.

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, antiviral, and antitumor activity of 2-substituted purine methylenecyclopropane analogues of nucleosides

The Z- and E-2-fluoro- and 2-chloropurine methylenecyclopropanes 9a,b and 10a,b as well as enantiomeric Z-isoguanine methylenecyclopropanes 11a,b and their phenyl phosphoralaninate pronucleotides 11c,d were synthesized and their antiviral activity against several viruses was evaluated. Fluoro analogues 9a and 10a were active against human cytomegalovirus but they were cytotoxic at approximately the same concentrations. Chloro derivatives 9b and 10b were non-cytotoxic and effective against Epstein-Barr virus in Daudi cells. Isoguanine analogues 11a-d lacked antiviral activity but pronucleotides 11c,d were substrates for porcine liver esterase. From the group of 9a,b and 10a,b, the fluoro analogues 9a and 10a exhibited antitumor activity but only the Z-isomer 9a had a selective effect.

Synthesis and biological evaluation of phosphonated carbocyclic 2'-oxa-3'-aza-nucleosides

The synthesis of carbocyclic 2'-oxa-3'-aza-nucleosides has been described, based on the 1,3-dipolar cycloaddition of a new phosphonated nitrone with vinyl acetate followed by coupling with silylated nucleobases. The obtained compounds have been evaluated for their ability to inhibit the reverse transcriptase of avian myeloblastosis retrovirus: no significant activity has been observed.

A novel rearrangement in electrospray ionization multistage tandem mass spectrometry of amino acid ester cyclohexyl phosphoramidates of AZT

Several amino acid ester cyclohexyl phosphoramidates of AZT as anti-HIV prodrugs were synthesized and investigated by electrospray ionization tandem mass spectrometry (ESI-MS(n)). A novel methoxy group migration from the carbonyl group to the phosphoryl group was observed in ESI-MS2. This migration is believed to be a general pathway for ions with a methyl ester moiety at the gamma-position to a phosphoric acid moiety, which is assisted with metal ions such as Li(+), Na(+) and K(+). Coordination between metal ions with both the carbonyl oxygen and phosphoryl oxygen might be a key factor responsible for this migration.

Intracellular metabolism and pharmacokinetics of 5'-hydrogenphosphonate of 3'-azido-2',3'-dideoxythymidine, a prodrug of 3'-azido-2',3'-dideoxythymidine

5'-Hydrogenphosphonate of 3'-azido-2',3'-dideoxythymidine (HpAZT), a novel anti-HIV drug approved for the treatment of HIV-infected patients in Russia, displays some clinical advantages over azidothymidine (AZT). Metabolism in the HL-60 cell culture and pharmacokinetics in mice of [6-3H]-HpAZT (in comparison with [6-3H-AZT) were studied to elucidate the metabolic basis of its lower clinical toxicity. Accumulation of [6-3H]-HpAZT-derived products in cells with time, distribution of its radioactive metabolites among blood and different mouse organs and dependence of drug accumulation on the route of administration were investigated. The rate of accumulation of [3H]-HpAZT metabolites in cells was slower than the rate of accumulation of [3H]-AZT metabolites. [3H]-AZTMP was the dominating metabolite at all time points, achieving the level of 15 +/- 3 pmol/10(6) cells after 25 h incubation. After oral or intravenous administrations of [3H]-HpAZT, the (radioactive) metabolites were rapidly distributed among blood, stomach, intestine and liver and were not found in brain, muscles and spleen. [3H]-HpAZT underwent rapid and extensive metabolism, [3H]-AZT being the dominating product at all time points. Administration of 180 nmol of [3H]-HpAZT resulted in an AZT concentration in blood of 1-3 microM after 5 min, which remained practically constant during the next 25 min and did not depend on the route of administration.

HPLC and mass spectrometry analysis of the enzymatic hydrolysis of anti-HIV pronucleotide diastereomers

In one current strategy to develop membrane-soluble pronucleotides, the phosphoramidate derivatives of the approved anti-HIV nucleosides 2',3'-didehydro-3'-deoxythymidine (d4T), 3'-azido-3'-deoxythymidine (AZT), (-)-beta-L-2',3'-dideoxy-3'- thiacytidine (3TC), and 2',3'-dideoxyadenosine (ddA) exhibit promising antiviral activity. However, the non-stereoselective synthetic route results in a mixture of diastereoisomers, which differ in the configuration of the phosphorus chiral center. Since it is believed that enzymatic ester hydrolysis is the first step in the intracellular activation of these prodrugs and that this process could be dependent on the stereochemistry at the phosphorus center, analytical methods must be developed. In the present work, in vitro evaluation of the selectivity of pig liver esterase (PLE) towards each diastereomer of d4T, AZT, 3TC, and ddA prodrugs has been investigated, applying our recently published HPLC-MS procedure using a polysaccharide-type chiral stationary phase. This method has been used to analyze the products of the PLE-catalyzed hydrolysis of the pronucleotides. It was found that both diastereomers of the four prodrugs were substrates for PLE.

Synthesis of methylenecyclobutane analogues of nucleosides with axial chirality and their phosphoralaninates: a new pronucleotide effective against Epstein-Barr virus

Methylenecyclobutane analogues of 2'-deoxyadenosine, 2'-deoxyguanosine and 2'-deoxycytidine, and the corresponding phosphoralaninate pronucleotides comprising adenine and guanine bases, were synthesized as potential antiviral agents. Phosphoralaninate of adenine methylenecyclobutane was a potent inhibitor of replication of Epstein-Barr virus (EBV) in Daudi cell culture. Phosphoralaninate of guanine analogue was inactive but both pronucleotides were substrates for porcine liver esterase. Adenine methylenecyclobutane analogue was deaminated by adenosine deaminase.