H-phosphonate Monoesters Research Articles

Synthesis of Nucleoside Selenophosphoramidates via H-Phosphonate Intermediates.

Two synthetic routes for the preparation of nucleoside selenophosphoramidates have been developed by using H-phosphonate derivatives as key substrates. The first method is a one-pot synthesis, which involves the condensation of an amine with H-phosphonate monoesters, mediated by a coupling agent, followed by oxidation with elemental selenium (A). The second approach makes use of the oxidative condensation reaction of H-phosphonoselenoate monoesters with amines promoted by iodine as an oxidizing agent (B). Both methods are efficient and experimentally simple, but the second method (B) seems to be more suited for the synthesis of selenophosphoramidates with bulky or sterically hindered amine residues. It has been shown that both methods also provide a convenient way to produce sulfurized counterparts, i.e., the corresponding thiophosphoramidate derivatives.

Preparative Synthesis of an R P-Guanosine-3',5'-Cyclic Phosphorothioate Analogue, a Drug Candidate for the Treatment of Retinal Degenerations.

Cyclic guanosine monophosphorothioate analogue 1a is currently showing potential as a drug for the treatment of inherited retinal neurodegenerations. To support ongoing preclinical and clinical work, we have developed a diastereoselective synthesis via cyclization and sulfurization of the nucleoside 5′-H-phosphonate monoester, which affords the desired RP-3′,5′-cyclic phosphorothioate in 9:1 ratio to the undesired SP-diastereomer. This route was made viable as a result of the silyl protection sequence used, which achieved >80% selectivity for 2′,5′-hydroxyls over 3′,5′-hydroxyls. Finally, the chromatography-free process allowed for a scale-up, as intermediates and the final product were isolated by crystallization to give 125 g of 1a (13.8% total yield) with over 99.9% HPLC purity.

A practical synthesis of nucleoside 5′-diphosphates from nucleoside 5′-H-phosphonate monoesters

A simple and convenient synthetic protocols based on H-phosphonate chemistry have been developed for the preparation of nucleoside 5′-diphosphates. It consists of oxidation of the silylated H-phosphonate monoesters in pyridine with iodine to produce the corresponding N-pyridiniumphosphonate intermediates, followed by their reactions with orthophosphoric acid used as a nucleophile. The added value of the method is that substrates for the reaction, H-phosphonate monoesters, can be prepared in situ from the corresponding nucleosides and used for the next step without isolation. The procedure is simple and applicable to the preparation of various diphosphates of ribo- and deoxyribonucleosides, and their analogues.

Efficient Synthesis of Pyrimidine-Nucleoside Monophosphates from <i>H</i>-Phosphonates

Two natural pyrimidine-nucleoside 5′-monophosphates have been synthesized from the corresponding nucleoside 5′-H-phosphonate monoesters via a one-pot reaction in high yields.31P NMR tracing experiments revealed that after H2O was added, iodophosphate intermediates were hydrolyzed immediately to generate nucleoside 5′-monophosphates almost quantitatively. Unlike the reaction in pyridine, the iodine oxidation reaction in DMF followed by immediate hydrolysis formed only a very small amount of dinucleoside diphosphate self-condensation byproduct.

A Novel <i>H</i>-Phosphonate Method for the Synthesis of D-Mannose-1-Phosphate

A novel and efficient method for the preparation of α-D-mannose-1-phosphate has been developed. Phosphitylation of tetraacetylated D-mannose, hydrolysis yielded H-phosphonate monoester. Silylation of H-phosphonate, followed by oxidative coupling and hydrolysis gave protected D-mannose-1-phosphate. Finally, deprotection of tetraacetylated D-mannose-1-phosphate afforded D-mannose-1-phosphate in excellent yield.

Novel method of synthesis of 5''-phosphate 2'-O-ribosyl-ribonucleosides and their 3'-phosphoramidites.

Synthesis of 5''-phosphate 2'-O-ribosylribonucleosides [Nr(p)] of four common ribonucleosides, and 3'-phosphoramidites of 5''-phosphate 2'-O-ribosyladenosine and 2'-O-ribosylguanosine using the H-phosphonate chemistry is described. An additional ring protected by benzoyl groups was incorporated into the main ribosyl ring in the reaction with 1-O-acetyl-2,3,5-tri-O-benzoyl-β-d-ribofuranose in the presence of SnCl4. The obtained 2'-O-ribosylribonucleosides (Nr) were applied in the subsequent transformations with selective deprotection. Ethanolamine was applied as a very convenient reagent for selective removal of benzoyl groups. Additionally, the tetraisopropyldisiloxane-1,3-diyl (TIPDSi) group was found to be stable under these deprotection conditions. Thus, the selectively deprotected 5''-hydroxyl group of Nr was transformed into an H-phosphonate monoester which was found to be stable under the following conditions: the removal of the TIPDSi group with triethylammonium fluoride and the dimethoxytritylation of the 5''-hydroxyl function. The 5''-H-phosphonate of Nr precursors was easily transformed to the corresponding dicyanoethyl 5''-O-phosphotriesters before phosphitylation, which gave 3'-phosphoramidite units of Nr(p) in high yield. The derived phosphoramidite units were used in an automated oligonucleotide synthesizer to produce dimer Ar(p)T via the phosphoramidite approach. The obtained products were fully deprotected under standard deprotection conditions giving dimers with a 5''-phosphate monoester function. Application of an alkaline phosphatase to prove the presence of an additional phosphate group was described.

An H-phosphonate strategy for the synthesis of 2′,3′-dideoxynucleoside triphosphates and homodinucleotides

The triphosphates and homodinucleotides of AZT and d4T have been efficiently synthesized from the corresponding nucleoside 5′-H-phosphonate monoesters via the reactive pyridinium phosphoramidate intermediates.

One-Pot Synthesis of <i>P</i><sup>1</sup>,<i>P</i><sup>2</sup>-Diaciclovir-5'-Diphosphate from Aciclovir 5'-<i>H</i>-Phosphonate

P1,P2-Diaciclovir-5'-diphosphate has been synthesized efficiently from aciclovir 5'-H-phosphonate monoester via a one-pot reaction. This method features easily accessibleH-phosphonate starting material, short reaction time, and good isolated yield.

Solid‐Phase Chemical Synthesis of 5′‐Triphosphate DNA, RNA, and Chemically Modified Oligonucleotides

A chemical method for the solid-phase synthesis of 5'-triphosphate oligonucleotides is described. The full-length oligonucleotides are first constructed using standard solid-phase DNA/RNA synthesis, and then efficient implementation of a sequential 4-steps synthetic procedure, executed either manually or in a fully automated fashion, affords the corresponding solid-supported 5'-triphosphate oligonucleotides. Using this synthetic procedure, the full-length 5'-hydroxyl oligonucleotides are initially transformed into the corresponding 5'-H-phosphonate mono esters, subsequently oxidized in the presence of imidazole to the activated 5'-phosphorimidazolidates, and finally reacted with pyrophosphate on the solid support. The method uses safe, stable, and inexpensive reagents, and the process is scalable and readily applicable to automated synthesis compatible with the current commercially available DNA/RNA synthesizers. After cleavage from the solid support and deprotection, a range of DNA, RNA, and chemically modified 5'-triphosphate oligonucleotides are obtained in a convenient and efficient manner and isolated in good yields after HPLC purification.

A New, Efficient Entry to Non-Lipophilic H-Phosphonate Monoesters – Preparation of Anti-HIV Nucleotide Analogues

Crystalline ammonium (9H-fluoren-9-yl)methyl H-phosphonate was prepared by a new, simple method and it was used as the reagent of choice for the introduction of an H-phosphonate monoester functionality into non-lipophilic anti-HIV nucleoside analogues.

Palladium(0)-Catalyzed Benzylation of H-Phosphonate Diesters: An Efficient Entry to Benzylphosphonates

This thesis focuses on chemical transformations of H-phosphonate and H-phosphonothioate and can be divided in two parts. The first part, is devoted to the development of the palladium-catalyzed P-C bond formation. Both mechanistic and synthetic studies of the transformations have been performed. The stereochemical aspects of palladium catalyzed arylation and benzylation of DNA analogs containing H-phosphonate and H-phosphonothioate have been studied. In chapter 5 the condensation using Mitsunobu reaction of H-phosphonate function and nucleoside has been studied. Efficient protocols for the synthesis of nucleoside H-phosphonate monoester were developed. The last chapter deals with development of silylation-mediated transesterfication of phenyl H-phosphonothioate as a thiophosphonylating agent. The methodology was used to prepare nucleoside H-phosphonothioate monomeric building blocks in good yields.

Synthetic studies on nucleoside 5'-H-phosphonate monoesters under Mitsunobu reaction conditions

Synthetic studies on nucleoside 5'-H-phosphonate monoesters under Mitsunobu reaction conditions

The Case for the Intermediacy of Monomeric Metaphosphate Analogues during Oxidation of H-Phosphonothioate, H-Phosphonodithioate, and H-Phosphonoselenoate Monoesters: Mechanistic and Synthetic Studies

Studies on the reaction of H-phosphonothioate, H-phosphonodithioate, and H-phosphonoselenoate monoesters with iodine in the presence of a base led to identification of a unique oxidation pathway, which consists of the initial oxidation of the sulfur or selenium atom in these compounds, followed by oxidative elimination of hydrogen iodide to generate the corresponding metaphosphate analogues. The intermediacy of the latter species during oxidation of the investigated H-phosphonate monoester derivatives with iodine was supported by various diagnostic experiments. The scope and limitation of these oxidative transformations for the purpose of the synthesis of nucleoside phosphorothioate, nucleoside phosphorodithioate, and nucleoside phosphoroselenoate diesters was also investigated.

One-pot synthesis of nucleoside 5'-triphosphates from nucleoside 5'-H-phosphonates.

Nucleoside 5'-triphosphates (NTPs) play key roles in biology and medicine. However, these compounds are notoriously difficult to synthesize. We describe a one-pot method to prepare NTPs from nucleoside 5'-H-phosphonate monoesters via pyridinium phosphoramidates, and we used this approach to synthesize ATP, UTP, GTP, CTP, ribavirin-TP, and 6-methylpurine ribonucleoside-TP (6MePTP). Poliovirus RNA-dependent RNA polymerase efficiently employed 6MePTP as a substrate, suggesting that the cognate nucleoside, a poorly understood antiviral agent, may damage viral RNA.

New access to H-phosphonates via metal-catalyzed phosphorus–oxygen bond formation

A novel approach to H-phosphonates from hypophosphorous acid using a transfer hydrogenation process was developed. This method is atom-economical, environmentally friendly, catalytic, and efficient, leading easily to H-phosphonate monoesters or ammonium salt in moderate to good yields.

Synthesis of Amino Acid Phosphoramidate Monoesters via H‐Phosphonate Intermediates

Diphenyl phosphite and bis(N,N-diisopropylamino)chlorophosphine are used as phosphitylating reagents to generate H-phosphonate monoesters. These H-phosphonate intermediates are subsequently oxidized with iodine to generate the 5'-nucleoside amino acid phosphoramidates.

Microwave Assisted “Click” Chemistry for the Synthesis of Multiple Labeled-Carbohydrate Oligonucleotides on Solid Support

A versatile approach has been developed for the multiple labeling of oligonucleotides. First, three linkers as a H-phosphonate monoester derivative were condensed on a solid-supported T12 to introduce H-phosphonate diester linkages which were oxidized in the presence of propargylamine. Second, three galactosyl azide derivatives were conjugated to the solid-supported three-alkyne-modified T12 by a 1,3-cycloaddition so-called "click chemistry" in the presence of Cu(I) assisted by microwaves.

A novel method for the synthesis of DNA using 2′-deoxyribonucleoside 5′-phosphites as monomer units

We propose a new method for the synthesis of DNA analogs completely different from the conventional methods (Scheme 1). Base-unprotected 2'-deoxyribo-nucleoside 5'-phosphites were employed as monomer units in this method. The 3'-OH of the monomer unit is condensed with the H-phosphonate monoester group at the 5'-terminus of the oligomer. The removal of the phosphite protecting groups gave the corresponding H-phosphonate monoester, which was allowed to condense with the 3'-OH of the monomer unit again. The synthesis of the monomer units by a simple one-step reaction from base-unprotected 2'-deoxyribo-nucleosides, and mild reaction conditions for the quantitative and rapid conversion of phosphites into H-phosphonate monoesters are described.

Synthesis of Oligodeoxyribo‐ and Oligoribonucleotides According to the H‐Phosphonate Method

Oligonucleotides can be synthesized by condensing a protected nucleoside H-phosphonate monoester with a second nucleoside in the presence of a coupling agent to produce a dinucleoside H-phosphonate diester. This can then be converted to a dinucleoside phosphate or to a backbone-modified analog such as a phosphorothioate or phosphoramidite. This unit discusses four alternative methods for synthesizing nucleoside H-phosphonate monoesters. The methods are efficient and experimentally simple, and use readily available reagents. The unit describes the activation of the monoesters, as well as competing acylation and other potential side reactions.

Highly chemo- and regioselective phosphitylation of 2'-deoxyribonucleosides.

We developed a novel method for the highly chemo- and regioselective phosphitylation of the 5'-hydroxy group of 2'-deoxyribonuleosides with bis(O-tert-butyl) N,N-diethylphosphoramidite. The tert-butyl groups introduced in the thymidine 5'-O-phosphite and 2'-deoxycytidine 5'-O-phosphite were simultaneously removed within 5 min by treatment with trimethylsilyl triflate in acetonitrile to give the corresponding H-phosphonate monoesters without any side reactions.