Acyclic nucleoside/nucleotide analogues with an imidazole ring skeleton

Syntheses of a few acyclic nucleoside and acyclic nucleoside phosphonate analogues containing an imidazole ring have been reported. These analogues include methyl 1-(2-hydroxyethoxymethyl)imidazole-4, 5-dicarbo-xylate (1), 4,5-dicarbamoyl-1-(2-hydroxyethoxymethyl)imidazole (2), 4,5-dicyano-1-(2-hydroxyethoxymethyl)imidazole (4), Methyl 1-(2-bromoethoxymethyl)imidazole-4,5-dicarboxylate (7), 4,5-dicyano-(2-bromoethoxymethyl)imidazole (8), and Methyl 1-(2-phosphonomethoxyethyl)imidazole (10). Also reported are a few potential prodrugs of the above compounds, including the acetyl derivatives 5 and 6 (of 1 and 4, respectively), and the diethyl phosphonate ester 9 (of 10). In addition, the corresponding benzyl-protected precursors 11 and 12 (of 1 and 4, respectively), along with their common hydrolysis product, 1-(2-benzyloxy-ethoxymethyl)-4,5-imidazoledicarboxylic acid (3), are reported. Another potential prodrug included in the list is 1-(2-acetoxyethyl)-4,5-dicyanoimidazole (15). The compounds were screened for in vitro antiviral activity against a wide variety of herpes and respiratory viruses. The most active compound was the phosphonate analogue 9 which exhibited an anti-measles virus activity with an EC50 of <2.5 microg/mL and an SI value of > 176.     

Therapeutic Potential of HPMPC (Cidofovir), PMEA (Adefovir) and Related Acyclic Nucleoside Phosphonate Analogues as Broad-Spectrum Anttviral Agents

Abstract

This article reviews the antiviral features of the acyclic nucleoside phosphonate (ANP) analogues, with a special focus on the most recent findings concerning the biochemistry and clinical efficacy of HPMPC [(S)-1-(3-hydroxy-2-phosphonylmethoxypropyl)cytosine; cidofovir; Vistide®] and PMEA [9-(2-phosphonyl-methoxyethyl)adenine; adefovir].     

An Unusual Iodine Monochloride Chlorination of an Imidazole Nucleoside

Abstract

The reaction of iodine monochloride with the imidazole nucleoside, 5-amino-1-(2,3,5-tri-0-acetyl-α-D-ribofuranosyl)imidazole-4-carboxamide, provides the 2-chloroimidazole nucleoside in good yield.     

Synthesis of 3-Aminoimidazo[4,5-c]pyrazole Nucleoside via the N-N Bond Formation Strategy as a [5:5] Fused Analog of Adenosine

3-Amino-6-(β-D-ribofuranosyl)imidazo[4,5-c]pyrazole (2) was synthesized via an N-N bond formation strategy by a mononuclear heterocyclic rearrangement (MHR). A series of 5-amino-1-(5-O-tert-butyldimethylsilyl-2,3-O-isopropylidene-β-D-ribofuranosyl-4-(1,2,4-oxadiazol-3-yl)imidaz-oles (6a-d), with different substituents at the 5-position of the 1,2,4-oxadiazole, were synthesized from 5-amino-1-(β-D-ribofuranosyl)imidazole-4-carboxamide (AICA Ribose, 3). It was found that 5-amino-1-(5-O-tert-butyldimethylsilyl-2,3-O-isopropylidene-β-D-ribofuranosyl)-4-(5-methyl-1,2,4-oxadiazol-3-yl)imidazole (6a) underwent the MHR with sodium hydride in DMF or DMSO to afford the corresponding 3-acetamidoimidazo[4,5-c]pyrazole nucleoside(s) (7b and/or 7a) in good yields. A direct removal of the acetyl group from 3-acetamidoimidazo[4,5-c]pyrazoles under numerous conditions was unsuccessful. Subsequent protecting group manipulations afforded the desired 3-amino-6-(β-D-ribofuranosyl)imidazo[4,5-c]pyrazole (2) as a 5:5 fused analog of adenosine (1).     

Synthesis and Biological Activity of Certain 4-Substituted Imidazo[4,5-d]Pyridazine Nucleosides

Abstract

Purine analogues and derivatives exhibit a broad range of pharmacological activities and are used in the chemotherapy of cancer, parasitic and viral infections, and for the suppression of immune responses. Undoubtedly, this wide range of biological activities reflect an equally wide number of biochemical sites of action, one of which is the purine de novo pathway. New agents which can either serve as inhibitors of enzymes involved in this pathway or as substrates are continually sought. The unique series of nucleosides described herein should meet these desired needs.

The synthesis of 1involved glycosylation of a suitably 4,5-disubstituted imidazole and subsequent cyclization of the imidazole nucleoside so formed to the imidazo[4,5-d]pyridazine nucleoside. Such methodology was successfully employed^1,2 in the preparation of certain 4,7-disubstituted imidazo[4,5-d]pyridazine nucleosides. Chlorination of 1furnished 4-chloro-1-(2,3,5-tri-O-acetyl-β-D-ribo-furanosyl)imidazo[4,5-dlpyridazine (2) in 80% yield. This versatile intermediate can now serve as a precursor to a variety of 4-substituted imidazo[4,5-d]pyridazine nucleosides.     

Synthesis of New PMEA Diphosphate Mimics

Abstract

We synthesized and characterized new diphosphate mimics of the acyclic nucleoside phosphonate PMEA [Adefovir, 9-(2-phosphonylmethoxyethyl)adenine].     

Synthesis and Anti-HIV Activity of Novel 2′-Deoxy-2′-β-Fluoro-Threosyl Nucleoside Phosphonic Acid Analogues

Novel 2′-deoxy-2′-β-fluoro-threose purine phosphonic acid analogues were designed and racemically synthesized from 2-propanone-1,3-diacetate. Condensation successfully proceeded from a glycosyl donor 9 under Vorbrüggen conditions. Cross-metathesis of vinyl analogues 13 and 23 with diethyl vinylphosphonate yielded the desired nucleoside phosphonate analogues 14 and 24, respectively. Ammonolysis and hydrolysis of phosphonates yielded the nucleoside phosphonic acid analogues 16, 19, 26, and 29. The synthesized nucleoside analogues were subjected to antiviral screening against human immunodeficiency virus (HIV)-1. Adenine analogue 18 exhibited weak in vitro activities against human immunodeficiency virus (HIV)-1.     

Synthesis of Unsaturated Analogues of 9-[2(Phosphono- Methoxy)Propyl]Guanine as Antiviral Agents

Abstract

The synthesis of 9-[2-(phosphonomethoxy)allyl]guanine (1) and 9-[2-(phosphonomethoxy)allyl]-8-aza-guanine (2), two new unsaturated acyclic phosphonate nucleosides analogues of the anti-HIV agents PMPG and 8-aza-PMPG, is described. Compounds 1 and 2 were evaluated for activity against human immunodeficiency virus (HIV-1 and HIV-2) and herpes simplex virus (HSV-1 and HSV-2).     

A NEW CLASS OF ACYCLIC NUCLEOSIDE PHOSPHONATES: SYNTHESIS AND BIOLOGICAL ACTIVITY OF 9-{[(PHOSPHONOMETHYL)AZIRIDIN-1-YL]METHYL}GUANINE (PMAMG) AND ANALOGUES

ABSTRACT

A new class of acyclic nucleoside phosphonates PMAMG, PMAMA, PMAMC, and PMAMT (compounds 1, 2, 3 and4) have been synthesized and tested in vitro against a wide variety of viruses, fungi and bacteria. PMAMG (1) was synthesized by the alkylation reaction of acetylguanine with the phosphonate side-chain, diisopropyl {[2-(bromomethyl)aziridin-1-yl]methyl}phosphonate (9), followed by deesterification reaction in the presence of TMSBr. In similar way, PMAMA, PMAMC, and PMAMT were prepared.     

Crystal Structure of Calf Spleen Purine Nucleoside Phosphorylase in a Complex with Multisubstrate Analogue Inhibitor with 2,6-Diaminopurine Aglycone

Abstract

The crystal structure at 2.05 Å resolution of calf spleen PNP complexed with stoichiometric concentration of acyclic nucleoside phosphonate inhibitor, 2,6-diamino-(S)-9-[2-(phosphonomethoxy)propyl]purine, in a new space group P2₁2₁2₁ which contains two full trimers in the asymmetric crystal unit is described.     

Design and Synthesis of Novel 1′,3′-Dioxolane 5′-Deoxyphosphonic Acid Purine Analogues as Potent Antiviral Agents

Electronic parameters of 1′,3 ′-oxygen play significant roles in steering the conformation of nucleoside phosphonic acid analogues. To investigate the relationship of two oxygen atoms with antiviral enhancement, novel 1′,3 ′-dioxolane 5 ′-deoxyphosphonic acid purine analogues were synthesized via de novo acyclic stereoselective route from acrolein and glycolic acid. The synthesized nucleoside phosphonic acid analogues 14 and 19 were subjected to antiviral screening against several viruses, such as HIV-1, HSV-1, HSV-2, and HCMV. The guanine analogue 19 exhibits in vitro anti-HIV-1 activity similar to that of 9-[2-(phosphonomethoxy)ethyl]adenine (PMEA) in MT-4 cells.     

Kinetic Properties of Adenine Nucleotide Analogues Against Purified 5-Phosphoribosyl-1-pyrophosphate Synthetases from E. coli,Rat Liver and Human Erythrocytes

Abstract

The nucleoside analogue 2′,3′-dideoxyadenosine (ddA), the phosphonate isostere of 2′,3′-dideoxy-2′,3′-didehydro-adenosine (d4A) 5′-monophosphate (d4API), and the acyclic nucleoside phosphonates PMEoA, PMEA, FPMPA and PMPA are potent and selective antiretroviral agents. We found that these compounds are recognized as substrates by the PRPP synthetases from E. coli, rat liver and human erythrocytes, as their monophosphate and triphosphate form in the reverse and forward reaction, respectively. In particular, ddA-5′-monophosphate (ddAMP) and ddA-5′-triphosphate proved to be excellent substrates for the enzymes. D4API was a relatively good substrate of the rat liver and human erythrocyte PRPP synthetases. The acyclic nucleoside phosphonates were rather poor substrates, as evident from their low V_max values. None of the PRPP synthetases are found to act stereospecifically: they recognized both the S- and R-enantiomers of FPMPA and PMPA in a comparably efficient manner. Our data indicate that PRPP synthetase may recognize a much broader range of adenine nucleotide analogues than previously thought.     

Acid-Catalyzed Hydrolysis of 2-Amino-9-(α-D-Ribofuranosyl)-purine and its Acyclo and 2-Methyl Analogues: Competition Between Depurination and Opening of the Imidazole Ring

Abstract

Hydrolytic decomposition of 2-amino- and 2-methyl-9-(B-D-ribofuranosyl)purines, 2-methyladenosine, 2-amino-7-and -9-(2-hydroxyethoxymethyl)purines and 9-ethoxymethyl-purine has been followed by HPLC under acidic conditions. 2-Methyladenosine undergoes depurination over the entire acidity range studied (pH 4.7 to H_o -0.7). The other compounds are depurinated only at high hydronium ion concentrations, while under mildly acidic conditions the imidazole ring is opened to give 2-substituted 4-amino-5-formamidopyrimidine. The latter compound finally undergoes competitive deformylation to 4,5-diaminopyrimidine and cyclization to 2-substituted purine. The mechanism of the imidazole ring opening is discussed on the basis of the pH-rate profiles and structural effects.     

AN IMPROVED SYNTHESIS OF 9-[2-(DIETHOXYPHOSPHONOMETHOXY)ETHYL]ADENINE AND ITS ANALOGUES WITH OTHER PURINE BASES UTILIZING THE MITSUNOBU REACTION

Abstract

Unprotected adenine, 6-chloropurine, 2.6-diaminopurine. and 2-amino-6-chluropurine have been directly coupled with 2-(diethoxyphosphonomethoxy)ethanol under Mitsunobu reaction conditions to provide acyclic phosphonate nucleotide analogues which are intermediates for antiviral agents such as PMEA.     

Synthesis and Biological Activity of 4-Amino-1-(β-D-ribofuranosyl)imidazo[4,5-d]pyridazin-7-one

Abstract

The Lewis acid catalyzed ribosylation of 5(4)-cyano-4(5)-(5-methyl-1,2,4-oxadiazol-3-yl)-1H-imidazole (2) with 1-O-acetyl-2,3,5-tri-O-benzoyl-B-D-ribose gave only 4-(5-methyl-1,2,4-oxadiazol-3-yl)-1-(2,3,5-tri-O-benzoy 1-B-D-ribofuranosyl)imidazole-5-carbonitrile (3). Treatment of 3 with methanolic ammonia gave 4-(5-methyl-1,2,4-oxadiazol-3-yl)-1-(6-D-ribofuranosyl)imidazole-5-carbonitrile (4). Treatment of 4 with hydrogen peroxide in ammonia gave -(5-methyl-1,2,4-oxadiazol-3-yl)-1-(B-D-ribofuranosyl)imidazole-5-carboxamide (5). When 5 was treated with sodium hydride in dimthyl-sulfoxide a rearrangement (mononuclear heterocyclic rearrangement, m.h.r.) occurred to give a modest 17% yield of 4-acetamido-1-(B-D ribofuranosyl)imidazo[4,5-d]pyridazin-7-one (6). Treatment of 6 with aqueous ammonia gave4-amino-l-(B-D-ribofuranosyl)imidazo[4,5-d]pyridazin-7-one (1). The synthesis of compound 1 using the m.h.r. for the preparation of a single regioisomer of the imidazo[4,5-d]pyridazin-7-one ring system, has demonstrated the potential of this methodology. Neither compound 5 nor 6 affected the growth or replication of human foreskin fibroblasts (HFF cells) or human cytomegalovirus (HCMV). In contrast, compound 1 inhibited the replication of HCMV (IC₅₀=29 μM) but produced visual cytotoxicity in uninfected HFF cells (IC₅₀=70μM). Compound 1 also inhibited the proliferation of L1210 murine leukemic cells (IC₅₀=25μM), whereas the precursors 4 and 6 did not.     

Design and Synthesis of Novel Threosyl-5′- Deoxyphosphonic Acid Purine Analogues as Potent Anti-Hiv Agents

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 5 ′-deoxyversions of threosyl phosphonate nucleosides from 1,4-dihydroxy-2-butene. The synthesized nucleoside phosphonic acid analogues 14 and 19 were tested for anti-HIV activity as well as cytotoxicity. The adenine analogue 14 exhibits moderate in vitro anti-HIV-1 activity (EC₅₀ = 12.6 μM).     

Effect of Acyclic Nucleoside Phosphonates on the HIV-1 Integrase in Vitro

Abstract

Integrase (IN) is an essential enzyme in the human immunodeficiency virus type-1 (HIV-1) replication cycle and, thus, a potential target for chemotherapeutic agents. Because various nucleotide analogues have been reported to inhibit IN in vitro, we investigated the effect of acyclic nucleoside phosphonates. Both unphosphorylated and diphosphorylated derivatives were inhibitory to IN at concentrations ranging between 60 and 800 μM, with diphosphorylated derivatives being 5- to 8-fold more potent than unphosphorylated counterparts.     

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).     

Activity of acyclic nucleoside phosphonate analogues against human immunodeficiency virus in monocyte/macrophages and peripheral blood lymphocytes

A number of acyclic nucleoside phosphonate analogues, including 9-(2-phosphonylmethoxyethyl)adenine (PMEA) and its 2,6-diaminopurine derivative PMEDAP, (R,S)-9-(3-fluoro-2-phosphonylmethoxypropyl)adenine [(R,S)-FPMPA] and its 2,6-diaminopurine derivative (R,S)-FPMPDAP were evaluated for their inhibitory effects on HIV-1 replication in two natural human cell systems, i.e. peripheral blood lymphocytes (PBL) and freshly prepared monocyte/macrophages (M/M). All compounds were potent inhibitors of HIV-1 replication in PBL [50% effective concentration (EC50): 0.94-3.9 microM] and M/M (EC50: 0.022-0.95 microM). In particular, (R,S)-FPMPA and (R,S)-FPMPDAP showed a greater antiviral selectivity than PMEA and PMEDAP due to the virtual lack of toxicity of the former compounds in these cell systems. Also, the antiviral selectivity of the acyclic nucleoside phosphonate analogues was much higher in M/M than in the human T-cell lines MT-4, ATH8 and CEM.     

Synthesis and Biological Application of a New Heterodinucleotide with Both Anti-HSV and Anti-HIV Activity

Abstract

A new antiviral drug with both anti-HSV and anti-HIV activity was synthesized by coupling Acyclovir and the acyclic nucleoside phosphonate (R)PMPA. The heterodinucleotide ACVpPMPA encapsulated into autologous erythrocytes was added to human macrophages providing an effective in vitro protection from HSV-1 and HIV-1 replication.