Synthesis and antiviral activity of 2,4-diamino-5-cyano-6-[2-(phosphonomethoxy)ethoxy]pyrimidine and related compounds

N-Heterocycles as Promising Antiviral Agents: A Comprehensive Overview

Viruses are a real threat to every organism at any stage of life leading to extensive infections and casualties. N-heterocycles can affect the viral life cycle at many points, including viral entrance into host cells, viral genome replication, and the production of novel viral species. Certain N-heterocycles can also stimulate the host's immune system, producing antiviral cytokines and chemokines that can stop the reproduction of viruses. This review focused on recent five- or six-membered synthetic N-heterocyclic molecules showing antiviral activity through SAR analyses. The review will assist in identifying robust scaffolds that might be utilized to create effective antiviral drugs with either no or few side effects.

Design, Microwave-Assisted Synthesis and In Silico Prediction Study of Novel Isoxazole Linked Pyranopyrimidinone Conjugates as New Targets for Searching Potential Anti-SARS-CoV-2 Agents

A series of novel naphthopyrano[2,3-d]pyrimidin-11(12H)-one containing isoxazole nucleus 4 was synthesized under microwave irradiation and classical conditions in moderate to excellent yields upon 1,3-dipolar cycloaddition reaction using various arylnitrile oxides under copper(I) catalyst. A one-pot, three-component reaction, N-propargylation and Dimroth rearrangement were used as the key steps for the preparation of the dipolarophiles3. The structures of the synthesized compounds were established by ¹H NMR, ¹³C NMR and HRMS-ES means. The present study aims to also predict the theoretical assembly of the COVID-19 protease (SARS-CoV-2 M^pro) and to discover in advance whether this protein can be targeted by the compounds 4a–1 and thus be synthesized. The docking scores of these compounds were compared to those of the co-crystallized native ligand inhibitor (N3) which was used as a reference standard. The results showed that all the synthesized compounds (4a–l) gave interesting binding scores compared to those of N3 inhibitor. It was found that compounds 4a, 4e and 4i achieved greatly similar binding scores and modes of interaction than N3, indicating promising affinity towards SARS-CoV-2 M^pro. On the other hand, the derivatives 4k, 4h and 4j showed binding energy scores (−8.9, −8.5 and −8.4 kcal/mol, respectively) higher than the M^pro N3 inhibitor (−7.0 kcal/mol), revealing, in their turn, a strong interaction with the target protease, although their interactions were not entirely comparable to that of the reference N3.

A Review on Synthesis, Anticancer and Antiviral Potentials of Pyrimidine Derivatives

Background:

Pyrimidine is the six membered heterocyclic aromatic compound similar to benzene and pyridine containing two nitrogen atoms at 1st and 3rd positions. Pyrimidine is present throughout nature in various forms and is the building blocks of numerous natural compounds from antibiotics to vitamins and liposacharides. The most commonly recognized pyrimidines are the bases of RNA and DNA, the most abundant being cytosine, thymine or uracil.

Results:

Pyrimidine is a core structure in a wide variety of compounds that exhibits significant biological activity and also plays an important role in the drug discovery process. Various synthetic aspects indicated that pyrimidine derivatives are easy to synthesize and has diverse biological and chemical applications. The present review article aims to review the work reported on synthesis, anticancer and antiviral potentials of pyrimidine derivatives during new millennium.

Conclusion:

It may be concluded that the fused pyrimidine derivatives enhanced the anticancer potential against different human cancer cell lines and antiviral potential against different human immunodeficiency virus (HIV), herpes simplex virus (HSV-1) etc, which created interest among the medicinal chemists in the pyrimidine skeleton in medicinal chemistry. Thus, a tremendous scope for research is present in this direction for investigating pyrimidine derivatives as lead molecules.

Experimental (FT-IR, Laser-Raman and NMR) and theoretical comparative study on 2-benzylsulfanyl-4-pentyl-6-(phenylsulfanyl)pyrimidine-5-carbonitrile, a potential bioactive agent

In this paper, the experimental and theoretical vibrational frequencies of a potential bioactive pyrimidine derivative molecule named 2-benzylsulfanyl-4-pentyl-6-(phenylsulfanyl)pyrimidine-5-carbonitrile has been investigated. The experimental FT-IR and Laser-Raman spectra of the studied molecule are in the region (4000–400[Formula: see text]cm[Formula: see text] and (4000–100[Formula: see text]cm[Formula: see text], respectively, in gas phase. The vibrational modes and optimized ideal structure parameters(bond lengths, bond angles and selected dihedral angles) were calculated by using DFT/B3LYP, DFT/BHandHLYP and DFT/PBE1PBE methods with 6-311[Formula: see text]G(d,p) basis set. The theoretical mode assignments have been obtained by using potential energy distribution (PED) with the VEDA4 software program. Additionally, infrared and Raman intensities, the highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbital (LUMO) energies and their clouds, and other related molecular properties were calculated and evaluated. The proton (1H) and carbon-13 ([Formula: see text]C) nuclear magnetic resonance (NMR) chemical shifts have been investigated for the title molecule, both experimentally (in DMSO-d[Formula: see text] and theoretically (in vacuum and DMSO). The thermodynamic properties of the tile compound have been investigated using the mentioned theoretical computational methods. The results revealed that there isgood agreement between experimental and theoretical results and these results have supported the related literature.

Crystal structures and Hirshfeld surface analyses of 2-[(4,6-di-amino-pyrimidin-2-yl)sulfan-yl]-N-(pyridin-2-yl)acetamide and 2-[(4,6-di-amino-pyrimidin-2-yl)sulfan-yl]-N-(pyrazin-2-yl)acetamide

In the title compounds, C11H12N6OS (I) and C10H11N7OS (II), the di-amino-pyrimidine ring makes dihedral angles of 71.10 (9)° with the pyridine ring in (I) and 62.93 (15)° with the pyrazine ring in (II). The ethanamine group, -CH2-C(=O)-NH- lies in the plane of the pyridine and pyrazine rings in compounds (I) and (II), respectively. In both compounds, there is an intra-molecular N-H⋯N hydrogen bond forming an S(7) ring motif and a short C-H⋯O inter-action forming an S(6) loop. In the crystals of both compounds, mol-ecules are linked by pairs of N-H⋯N hydrogen bonds, forming inversion dimers with R22(8) ring motifs. In (I), the dimers are linked by N-H⋯O and N-H⋯N hydrogen bonds, forming layers parallel to (1[Formula: see text] [Formula: see text]). The layers are linked by offset π-π inter-actions [inter-centroid distance = 3.777 (1) Å], forming a three-dimensional supra-molecular structure. In (II), the dimers are linked by N-H⋯O, N-H⋯N and C-H⋯O hydrogen bonds, also forming a three-dimensional supra-molecular structure.

2-[(4,6-Diaminopyrimidin-2-yl)sulfanyl]-N-(4-methoxyphenyl)acetamide

In the title compound, C13H15N5O2S, the acetamide N—C(=O)—C plane makes dihedral angles of 30.51 (11) and 51.93 (11)°, respectively, with the benzene ring and the pyrimidine ring. The dihedral angle between the benzene and pyrimidine rings is 43.40 (6)°. There is an intramolecular N—H...N hydrogen bond with an S(7) ring motif. In the crystal, molecules are linked by pairs of intermolecular N—H...N hydrogen bonds, forming inversion dimers with an R 2 2(8) ring motif. The molecules are further linked by intermolecular N—H...O hydrogen bonds, forming a C(9) chain along [100]. Intermolecular C—H...π and N—H...π interactions are also observed.

Therapeutic potential of heterocyclic pyrimidine scaffolds

Heterocyclic compounds offer a high degree of structural diversity and have proven to be broadly and economically useful as therapeutic agents. Comprehensive research on diverse therapeutic potentials of heterocycles compounds has confirmed their immense significance in the pathophysiology of diseases. Heterocyclic pyrimidine nucleus, which is an essential base component of the genetic material of deoxyribonucleic acid, demonstrated various biological activities. The present review article aims to review the work reported on therapeutic potentials of pyrimidine scaffolds which are valuable for medical applications during new generation.

Crystal structures of 2-[(4,6-di-amino-pyrimidin-2-yl)sulfan-yl]-N-(2,4-di-methyl-phen-yl)acetamide and 2-[(4,6-di-amino-pyrimidin-2-yl)sulfan-yl]-N-(3-meth-oxy-phen-yl)acetamide

In the title compounds, C14H17N5OS (I) and C13H15N5O2S (II), the dihedral angle between the pyrimidine and benzene rings is 58.64 (8)° in (I) and 78.33 (9)° in (II). In both compounds, there is an intra-molecular C-H⋯O hydrogen bond, and in (II) there is also an intra-molecular N-H⋯N hydrogen bond present. In the crystals of both compounds, a pair of N-H⋯N hydrogen bonds links the individual mol-ecules to form inversion dimers with R22(8) ring motifs. In (I), the dimers are linked by N-H⋯O and C-H⋯O hydrogen bonds, enclosing R21(14), R21(11) and R21(7) ring motifs, forming layers parallel to the (100) plane. There is also an N-H⋯π inter-action present within the layer. In (II), the inversion dimers are linked by N-H⋯O hydrogen bonds enclosing an R44(18) ring motif. The presence of N-H⋯O and C-H⋯O hydrogen bonds generate an R21(6) ring motif. The combination of these various hydrogen bonds results in the formation of layers parallel to the (1-11) plane.

Crystal structures of N-(4-chloro-phen-yl)-2-[(4,6-di-amino-pyrimidin-2-yl)sulfan-yl]acetamide and N-(3-chloro-phen-yl)-2-[(4,6-di-amino-pyrimidin-2-yl)sulfan-yl]acetamide

The title compounds, C12H12ClN5OS, (I), and C12H12ClN5OS, (II), are 2-[(di-amino-pyrimidin-2-yl)sulfan-yl]acetamides. Compound (II), crystallizes with two independent mol-ecules (A and B) in the asymmetric unit. In each of the mol-ecules, in both (I) and (II), an intra-molecular N-H⋯N hydrogen bond forms an S(7) ring motif. The pyrimidine ring is inclined to the benzene ring by 42.25 (14)° in (I), and by 59.70 (16) and 62.18 (15)° in mol-ecules A and B, respectively, of compound (II). In the crystal of (I), mol-ecules are linked by pairs of N-H⋯N hydrogen bonds, forming inversion dimers with an R22(8) ring motif. The dimers are linked via bifurcated N-H⋯O and C-H⋯O hydrogen bonds, forming corrugated layers parallel to the ac plane. In the crystal of (II), the A mol-ecules are linked through N-H⋯O and N-H⋯Cl hydrogen bonds, forming layers parallel to (100). The B mol-ecules are also linked by N-H⋯O and N-H⋯Cl hydrogen bonds, also forming layers parallel to (100). The parallel layers of A and B mol-ecules are linked via N-H⋯N hydrogen bonds, forming a three-dimensional structure.

Crystal structures of 2-[(4,6-di-amino-pyrimidin-2-yl)sulfan-yl]-N-(naphthalen-1-yl)acetamide and 2-[(4,6-di-amino-pyrimidin-2-yl)sulfan-yl]-N-(4-fluoro-phen-yl)acetamide

The title compounds, C16H15N5OS, (I), and C12H12FN5OS, (II), are [(di-amino-pyrimidine)-sulfan-yl]acetamide derivatives. In (I), the pyrimidine ring is inclined to the naphthalene ring system by 55.5 (1)°, while in (II), the pyrimidine ring is inclined to the benzene ring by 58.93 (8)°. In (II), there is an intra-molecular N-H⋯N hydrogen bond and a short C-H⋯O contact. In the crystals of (I) and (II), mol-ecules are linked by pairs of N-H⋯N hydrogen bonds, forming inversion dimers with R22(8) ring motifs. In the crystal of (I), the dimers are linked by bifurcated N-H⋯(O,O) and C-H⋯O hydrogen bonds, forming layers parallel to (100). In the crystal of (II), the dimers are linked by N-H⋯O hydrogen bonds, also forming layers parallel to (100). The layers are linked by C-H⋯F hydrogen bonds, forming a three-dimensional architecture.

Crystal structures of 2-[(4,6-di-amino-pyrimidin-2-yl)sulfan-yl]-N-(3-nitro-phen-yl)acetamide monohydrate and N-(2-chloro-phen-yl)-2-[(4,6-di-amino-pyrimidin-2-yl)sulfan-yl]acetamide

The title compounds, C12H12N6O3S·H2O, (I), and C12H12ClN5OS, (II), are 2-[(4,6-di-amino-pyrimidin-2-yl)sulfan-yl]acetamides. Compound (I) crystallized as a monohydrate. In both compounds, the mol-ecules have a folded conformation, with the pyrimidine ring being inclined to the benzene ring by 56.18 (6)° in (I) and by 67.84 (6)° in (II). In both mol-ecules, there is an intra-molecular N-H⋯N hydrogen bond stabilizing the folded conformation. In (I), there is also a C-H⋯O intra-molecular short contact, and in (II) an intra-molecular N-H⋯Cl hydrogen bond is present. In the crystal of (I), mol-ecules are linked by a series of N-H⋯O, O-H⋯O and O-H⋯N hydrogen bonds, forming undulating sheets parallel to the (100). The sheets are linked via an N-H⋯Owater hydrogen bond, forming a three-dimensional network. In the crystal of (II), mol-ecules are linked by a series of N-H⋯O, N-H⋯N and C-H⋯O hydrogen bonds, forming slabs parallel to (001).

Curious discoveries in antiviral drug development: the role of serendipity

Antiviral drug development has often followed a curious meandrous route, guided by serendipity rather than rationality. This will be illustrated by ten examples. The polyanionic compounds (i) polyethylene alanine (PEA) and (ii) suramin were designed as an antiviral agent (PEA) or known as an antitrypanosomal agent (suramin), before they emerged as, respectively, a depilatory agent, or reverse transcriptase inhibitor. The 2',3'-dideoxynucleosides (ddNs analogues) (iii) have been (and are still) used in the "Sanger" DNA sequencing technique, although they are now commercialized as nucleoside reverse transcriptase inhibitors (NRTIs) in the treatment of HIV infections. (E)-5-(2-Bromovinyl)-2'-deoxyuridine (iv) was discovered as a selective anti-herpes simplex virus compound and is now primarily used for the treatment of varicella-zoster virus infections. The prototype of the acyclic nucleoside phosphonates (ANPs), (S)-9-(3-hydroxy-2-phosphonylmethoxypropyl)adenine [(S)-HPMPA], (v) was never commercialized, although it gave rise to several marketed products (cidofovir, adefovir, and tenofovir). 1-[2-(Hydroxyethoxy)methyl]-6-(phenylthio)thymine (vi) and TIBO (tetrahydroimidazo[4,5,1-jk][1,4-benzodiazepin-2(1H)]-one and -thione) (vii) paved the way to a number of compounds (i.e., nevirapine, delavirdine, etravirine, and rilpivirine), which are now collectively called non-NRTIs. The bicyclam AMD3100 (viii) was originally described as an anti-HIV agent before it became later marketed as a stem cell mobilizer. The S-adenosylhomocysteine hydrolase inhibitors (ix), while active against a broad range of (-)RNA viruses and poxviruses may be particularly effective against Ebola virus, and for (x) the O-ANP derivatives, the potential application range encompasses virtually all DNA viruses.

2-[(4,6-Diaminopyrimidin-2-yl)sulfanyl]-N-(2-methylphenyl)acetamide

In the title compound, C₁₃H₁₅NOS, the plane of the pyrimidine ring makes a dihedral angle of 54.73 (9)° with that of the o-tolyl ring. The mol­ecule adopts an extended conformation, which is evident from the C—C(=O)—N—C_ar (ar = aromatic) torsion angle of 178.42 (15)°. In the crystal, mol­ecules are linked via pairs of N—H⋯N hydrogen bonds, forming inversion dimers with an R²₂(8) ring motif. The dimers are linked by N—H⋯O and C—H⋯O hydrogen bonds, with the O atom accepting three such interactions, forming sheets parallel to (100).

5-Substituted 2-amino-4,6-dihydroxypyrimidines and 2-amino-4,6-dichloropyrimidines: synthesis and inhibitory effects on immune-activated nitric oxide production

A series of 5-substituted 2-amino-4,6-dihydroxypyrimidines were prepared by a modified condensation of the corresponding monosubstituted malonic acid diesters with guanidine in an excess of sodium ethoxide. The optimized procedure using Vilsmeier-Haack-Arnold reagent, followed by immediate deprotection of the (dimethylamino)methylene protecting groups, has been developed to convert the 2-amino-4,6-dihydroxypyrimidine analogs to novel 5-substituted 2-amino-4,6-dichloropyrimidines in high yields. Pilot screening for biological properties of the prepared compounds was done in mouse peritoneal cells using the in vitro nitric oxide (NO) assay. Irrespective of the substituent at the 5 position, 2-amino-4,6-dichloropyrimidines inhibited immune-activated NO production. The most effective was 5-fluoro-2-amino-4,6-dichloropyrimidine with an IC 50 of 2 µM (higher activity than the most potent reference compound) while the IC 50s of other derivatives were within the range of 9-36 µM. The 2-amino-4,6-dihydroxypyrimidine counterparts were devoid of any NO-inhibitory activity. The compounds had no suppressive effects on the viability of cells. The Mechanism of action remains to be elucidated.

Significance and biological importance of pyrimidine in the microbial world

Microbes are unique creatures that adapt to varying lifestyles and environment resistance in extreme or adverse conditions. The genetic architecture of microbe may bear a significant signature not only in the sequences position, but also in the lifestyle to which it is adapted. It becomes a challenge for the society to find new chemical entities which can treat microbial infections. The present review aims to focus on account of important chemical moiety, that is, pyrimidine and its various derivatives as antimicrobial agents. In the current studies we represent more than 200 pyrimidines as antimicrobial agents with different mono-, di-, tri-, and tetrasubstituted classes along with in vitro antimicrobial activities of pyrimidines derivatives which can facilitate the development of more potent and effective antimicrobial agents.

Design, Synthesis, and In Vitro Antimicrobial Evaluation of Fused Pyrano[3,2-e]tetrazolo[1,5-c]pyrimidines and Diazepines

A series of novel pyranochromene-containing tetrazoles fused with pyrimidinethiones, pyrimidines, and diazepines 3a-f, 4a-f, and 5a-f were synthesized by condensation of the corresponding tetrazoles 2a-f with carbon disulfide, benzaldehyde, and 4-methoxy phenacyl bromide, respectively. The compound 2a-f was obtained by reaction of pyrano[3,2-c]chromenes 1a-f with sodium azide. The structures of the newly synthesized compounds 2a-f to 5a-f were established on the basis of their elemental analyses, IR, (1)H NMR, (13)C NMR, and mass spectral data. All of the title compounds were subjected to in vitro antibacterial testing against four pathogenic strains and antifungal screening against two fungi. Preliminary results indicate that some of them exhibited promising activities and that they deserve more consideration as potential antimicrobials.

Phthalocyanines with phosphonate moiety viaC-nucleophilic substitution in phthalonitriles

Interaction of isomeric 4-nitro- or 3-nitrophthalonitrile with triethyl phosphonoacetate, diethyl cyanomethylphosphonate or tetraethyl methylenediphosphonate in basic conditions resulted in regioselective C -nucleophilic oxidative substitution of hydrogen ortho-located to nitro group, new phthalonitriles with diethoxyphosphorylmethyl or bis(diethoxyphosphoryl)methyl group were isolated in modest yields. In the same conditions one chlorine atom of tetrachlorophthalonitrile was regioselectively substituted with triethyl phosphonoacetate. In basic conditions, both parent phthalonitriles and corresponding zinc phthalocyanines with ortho-located nitro and diethoxyphosphoryl substituted methyl groups are involved in reversible acid-base interaction accompanied with large bathochromic shift of their long wavelength absorption maxima in visible or NIR region, correspondingly. Formation of tetraazachlorin- and tetraaza(iso)bacteriochlorin-like anions is proposed for explanation of this unprecedent bathochromic shift for phthalocyanines.

Convenient Synthesis and Antibacterial Activity of Tricyclic Azine Derivatives

1,4-Phenylenediamine reacted readily with 2 mol of ethyl acetoacetate to give diethyl ( 2Z,2′Z)-3,3′-[(1,4-phenylene)-bisimino]dibut-2-enoate, which reacted with dimethylformamide dimethylacetal, activated methylene nitriles, ylidenemalononitriles and phenyl and benzoyl isothiocyanate to give, respectively, a 4,7-phenanthroline-2,9-dicarb-oxylate-1,10-diol, and tricyclic bispyridine and bispyrimidine derivatives. Two compounds showed strong antibacterial activity against several microorganisms, while six others showed high to moderate activity.

Advances in the treatment of varicella-zoster virus infections

Varicella-zoster virus (VZV) causes two distinct diseases, varicella (chickenpox) and shingles (herpes zoster). Chickenpox occurs subsequent to primary infection, while herpes zoster (usually associated with aging and immunosuppression) appears as a consequence of reactivation of latent virus. The major complication of shingles is postherpetic neuralgia. Vaccination strategies to prevent varicella or shingles and the current status of antivirals against VZV will be discussed in this chapter. Varivax®, a live-attenuated vaccine, is available for pediatric varicella. Zostavax® is used to boost VZV-specific cell-mediated immunity in adults older than 50 years, which results in a decrease in the burden of herpes zoster and pain related to postherpetic neuralgia. Regardless of the availability of a vaccine, new antiviral agents are necessary for treatment of VZV infections. Current drugs approved for therapy of VZV infections include nucleoside analogues that target the viral DNA polymerase and depend on the viral thymidine kinase for their activation. Novel anti-VZV drugs have recently been evaluated in clinical trials, including the bicyclic nucleoside analogue FV-100, the helicase-primase inhibitor ASP2151, and valomaciclovir (prodrug of the acyclic guanosine derivative H2G). Different candidate VZV drugs have been described in recent years. New anti-VZV drugs should be as safe as and more effective than current gold standards for the treatment of VZV, that is, acyclovir and its prodrug valacyclovir.

Ten paths to the discovery of antivirally active nucleoside and nucleotide analogues

Nucleoside and nucleotide analogues have proven to be an effective approach toward the development of antiviral compounds. This approach has so far yielded a number of clinically useful antiviral drugs, such as BVDU (brivudin), (val)aciclovir, cidofovir, adefovir dipivoxil, and tenofovir disoproxil fumarate, and current perspectives justify the further development of other nucleoside analogues, such as FV-100, and that of the DAPy-based nucleotide analogues, the 5-aza analogue of cidofovir, and prodrug derivatives thereof.

A novel type of acyclic nucleoside phosphonates derived from 2-(phosphonomethoxy)propanoic acid

A convenient and efficient synthesis of a novel class of acyclic nucleoside phosphonates derived from 2-(phosphonomethoxy)propanoic acid has been developed. The key step of the synthesis is the optimized oxidation of the 3-hydroxy-2-(phosphonomethoxy)propyl (HPMP) analogues to the corresponding 2'-carboxy-PME (CPME) derivatives using the TEMPO/NaClO₂/NaClO oxidizing system. Although (S)-3-(adenin-9-yl)-2-(phosphonomethoxy)propanoic acid ((S)-CPMEA) has been designed as a compound with potential anti-HIV activity, none of the newly prepared CPME analogues exhibited any antiviral activity.

An efficient microwave-assisted synthesis and biological properties of polysubstituted pyrimidinyl- and 1,3,5-triazinylphosphonic acids

Polysubstituted pyrimidinylphosphonic and 1,3,5-triazinylphosphonic acids with potential biological properties were prepared in high yields by the microwave-assisted Michaelis-Arbuzov reaction of trialkyl phosphite with the corresponding halopyrimidines and halo-1,3,5-triazines, respectively, followed by the standard deprotection of the phosphonate group using TMSBr in acetonitrile. 4,6-Diamino-5-chloropyrimidin-2-ylphosphonic acid (7a) was found to exhibit a weak to moderate anti-influenza activity (28-50 μM) and may represent a novel hit for further SAR studies and antiviral improvement.

Emerging drugs for varicella-zoster virus infections

INTRODUCTION

Varicella-zoster virus (VZV) is the etiological agent of two distinct diseases, varicella (chickenpox) and shingles (herpes zoster). Chickenpox occurs following primary infection, while herpes zoster (usually associated with ageing and immunosuppression) is the consequence of reactivation of the latent virus. Post-herpetic neuralgia is the major complication of shingles.

AREAS COVERED

This review will discuss vaccination strategies and the current status of antivirals against VZV. A live attenuated vaccine, Varivax, is available for pediatric varicella while Zostavax was developed to boost VZV-specific cell-mediated immunity in adults older than 60 years and, via this mechanism, to decrease the burden of herpes zoster and pain associated with post-herpetic neuralgia. Despite the availability of a vaccine, there is a need for new antiviral agents. Current drugs approved for the treatment of VZV infections include nucleoside analogs that target the viral DNA polymerase and depend on the viral thymidine kinase. Novel anti-VZV drugs have recently been evaluated in clinical trials, including the bicyclic nucleoside analog FV-100, the helicase-primase inhibitor ASP2151 and valomaciclovir (prodrug of the acyclic guanosine derivative H2G).

EXPERT OPINION

New anti-VZV drugs should be as safe as and more effective than acyclovir and its prodrug valacyclovir (current gold standard for the treatment of VZV).

Acyclic nucleoside phosphonates: An unfinished story

While cidofovir, adefovir and tenofovir are the three acyclic nucleoside phosphonates (ANPs) that have been licensed for clinical use (the latter as a single-, double- and triple-drug combination), there are many more ANPs that await their application for medical or veterinary use: (S)-HPMPA, (S)-HPMPDAP, cPrPMEDAP, (R)-HPMPO-DAPy, PMEO-DAPy, 5-X-PMEO-DAPy, (R)-PMPO-DAPy, (S)-HPMP-5-azaC, and cyclic (S)-HPMP-5-azaC, and alkoxyalkyl prodrugs thereof.

Cidofovir Activity against Poxvirus Infections

Cidofovir [(S)-1-(3-hydroxy-2-phosphonylmethoxypropyl)cytosine, HPMPC] is an acyclic nucleoside analog approved since 1996 for clinical use in the treatment of cytomegalovirus (CMV) retinitis in AIDS patients. Cidofovir (CDV) has broad-spectrum activity against DNA viruses, including herpes-, adeno-, polyoma-, papilloma- and poxviruses. Among poxviruses, cidofovir has shown in vitro activity against orthopox [vaccinia, variola (smallpox), cowpox, monkeypox, camelpox, ectromelia], molluscipox [molluscum contagiosum] and parapox [orf] viruses. The anti-poxvirus activity of cidofovir in vivo has been shown in different models of infection when the compound was administered either intraperitoneal, intranasal (aerosolized) or topically. In humans, cidofovir has been successfully used for the treatment of recalcitrant molluscum contagiosum virus and orf virus in immunocompromised patients. CDV remains a reference compound against poxviruses and holds potential for the therapy and short-term prophylaxis of not only orthopox- but also parapox- and molluscipoxvirus infections.

Nucleotide HIV reverse transcriptase inhibitors: tenofovir and beyond

PURPOSE OF REVIEW

This review describes the class of nucleotide HIV reverse transcriptase inhibitors and summarises recent findings related to tenofovir and its oral prodrug tenofovir disoproxil fumarate, currently the only nucleotide approved for the treatment of HIV infection. In addition, novel strategies in the design of anti-HIV nucleotides and their prodrugs are discussed.

RECENT FINDINGS

A number of studies have demonstrated a potent and durable clinical efficacy of tenofovir disoproxil fumarate in combination with other antiretrovirals, particularly lamivudine or emtricitabine and efavirenz. The prophylactic antiretroviral effect of tenofovir and tenofovir disoproxil fumarate has been characterized in various animal models and is currently being evaluated in controlled clinical studies. In addition, efficacy of tenofovir disoproxil fumarate against hepatitis B virus has been established and is currently being explored in phase III trials. The identification of GS-7340, an alternative prodrug of tenofovir has raised the possibility of using phosphonoamidates as novel prodrugs allowing for an effective intracellular delivery of nucleotides.

SUMMARY

The concept of nucleotides as a novel class of antiretroviral therapeutics has been successfully validated through tenofovir disoproxil fumarate, a nucleotide prodrug that exhibits potent and durable clinical efficacy and favourable safety profile both in treatment-naïve and experienced HIV-infected patients. Several novel nucleotide reverse transcriptase inhibitors such as GS-9148, PMDTA, and PMEO have recently emerged from continuing preclinical drug discovery efforts.

Acyclic nucleoside bisphosphonates: synthesis and properties of chiral 2-amino-4,6-bis[(phosphonomethoxy)alkoxy]pyrimidines

2-Amino-4,6-bis[(phosphonomethoxy)alkoxy]pyrimidines bearing two equal or different achiral or chiral phosphonoalkoxy chains have been prepared either by aromatic nucleophilic substitution of 2-amino-4,6-dichloropyrimidine or by alkylation of 4,6-dihydroxy-2-(methylsulfanyl)pyrimidine with appropriate phosphonate-bearing building block. Alkylation of 4,6-dihydroxy-2-(methylsulfanyl)pyrimidine proved to be the method of choice for efficient preparation of variety of bisphosphonates. The enantiomeric purity of selected compounds was determined by capillary electrophoresis. Antiviral activity of bisphosphonates is discussed.

Activities of several classes of acyclic nucleoside phosphonates against camelpox virus replication in different cell culture models

Camelpox virus (CMLV) is the closest known virus to variola virus. Here we report on the anti-CMLV activities of several acyclic nucleoside phosphonates (ANPs) related to cidofovir [(S)-1-(3-hydroxy-2-phosphonomethoxypropyl)cytosine (HPMPC; Vistide)] against two CMLV strains, CML1 and CML14. Cytopathic effect (CPE) reduction assays performed with human embryonic lung fibroblast monolayers revealed the selectivities of the first two classes of ANPs (cHPMPA, HPMPDAP, and HPMPO-DAPy) and of the hexadecyloxyethyl ester of 1-{[(5S)-2-hydroxy-2-oxido-1,4,2-dioxaphosphinan-5-yl]methyl}-5-azacytosine (HDE-cHPMP-5-azaC), belonging to the newly synthesized ANPs, which are HPMP derivatives containing a 5-azacytosine moiety. The inhibitory activities of ANPs against both strains were also confirmed with primary human keratinocyte (PHK) monolayers, despite the higher toxicity of those molecules on growing PHKs. Virus yield assays confirmed the anti-CML1 and anti-CML14 efficacies of the compounds selected for the highest potencies in CPE reduction experiments. Ex vivo studies were performed with a 3-dimensional model of human skin, i.e., organotypic epithelial raft cultures of PHKs. It was ascertained by histological evaluation, as well as by virus yield assays, that CMLV replicated in the human skin equivalent. HPMPC and the newly synthesized ANPs proved to be effective at protecting the epithelial cells against CMLV-induced CPE. Moreover, in contrast to the toxicity on PHK monolayers, signs of toxicity in the differentiated epithelium were seen only at high ANP concentrations. Our results demonstrate that compounds belonging to the newly synthesized ANPs, in addition to cidofovir, represent promising candidates for the treatment of poxvirus infections.

Selective inhibition of porcine endogenous retrovirus replication in human cells by acyclic nucleoside phosphonates

Several anti-human immunodeficiency virus type 1 reverse transcriptase inhibitors were evaluated for their antiviral activities against porcine endogenous retrovirus in human cells. Among the test compounds, zidovudine was found to be the most active. The order of potency was zidovudine > phosphonylmethoxyethoxydiaminopyrimidine = phosphonylmethoxypropyldiaminopurine > tenofovir > or = adefovir > stavudine.

Inhibitory activities of three classes of acyclic nucleoside phosphonates against murine polyomavirus and primate simian virus 40 strains

Murine polyomavirus and simian virus 40 were used to evaluate the potencies of the compounds of three classes of acyclic nucleoside phosphonates: (i) the original HPMP (3-hydroxy-2-phosphonomethoxypropyl) and PME (2-phosphonomethoxyethyl) derivatives, (ii) the 6-[2-(phosphonomethoxy)alkoxy]-2,4-diaminopyrimidine (DAPy) derivatives, and (iii) a new class of HPMP derivatives containing a 5-azacytosine moiety. The last class showed the highest activities and selectivities against both polyomaviruses.

Syntheses and anti-cancer activities of 2-[1-(indol-3-yl-/pyrimidin-5-yl-/pyridine-2-yl-/quinolin-2-yl)-but-3-enylamino]-2-phenyl-ethanols

Schiff bases prepared by the reactions of substituted amines with indole-/, pyrimidine-/, pyridine-/, and quinoline-aldehydes are made to undergo indium mediated allylation whereby a (substituted amine, allyl)methyl group has been introduced at C-3 of indole, C-5 of pyrimidine, and C-2 of pyridine and quinoline. Amongst the 16 compounds investigated for anti-cancer activities at 59 human tumor cell lines 3, 9-12, and 14 show appreciable activities. The structure-activity relationship studies point that the contribution of phenylglycinol moiety as a part of side chain at C-3 of indole and C-5 of pyrimidine seems to be crucial for exhibiting anti-cancer activities.

Bifunctional Acyclic Nucleoside Phosphonates: 2. Symmetrical 2-{[Bis(phosphono)methoxy]methyl}ethyl Derivatives of Purines and Pyrimidines

Novel bisphosphonate alkylating agent, tetraisopropyl {2-[(mesyloxy)methyl]propane-1,3-diyl}bis(oxymethylene)bisphosphonate 19, was synthesized from diethyl 2,2-bis(hydroxymethyl)malonate. Decarbethoxylation of the diethyl 2,2-dimethyl-1,3-dioxane-5,5-dicarboxylate was followed by chloromethylation of 2-[(benzyloxy)methyl]propane-1,3-diol and Arbuzov reaction with triisopropyl phosphite. Bisphosphonate building block 19 was used in the alkylation of various nucleobases (2-amino-6-chloropurine, adenine, 2-amino-6-(cyclopropyl)aminopurine, cytosine, uracil and 4-methoxy-5-methylpyrimidin-2(1H)-one). N9-Substituted purines and N1-substituted pyrimidines were converted to appropriate free bisphosphonic acids. No antiviral or cytostatic activity was detected.

Antiviral potential of a new generation of acyclic nucleoside phosphonates, the 6-[2-(phosphonomethoxy)alkoxy]-2,4-diaminopyrimidines

Three acyclic nucleoside phosphonates (ANPs) have been formally approved for clinical use in the treatment of 1) cytomegalovirus retinitis in AIDS patients (cidofovir, by the intravenous route), 2) chronic hepatitis B virus (HBV) infections (adefovir dipivoxil, by the oral route), and 3) human immunodeficiency virus (HIV) infections (tenofovir disoproxil fumarate, by the oral route). The activity spectrum of cidofovir {(S)- 1-[3-hydroxy-2-(phosphonomethoxy)propyl]cytosine [(S)-HPMPC)]}, like that of (S)-HPMPA [(S)-9-[3-hydroxy-2-(phosphonomethoxy)propyl]adenine) and (S)-HPMPDAP [(S)-9-[3-hydroxy-2-(phosphonomethoxy)propyl]-2, 6-diaminopurine), encompasses a broad spectrum of DNA viruses, including polyoma-, papilloma-, adeno-, herpes-, and poxviruses. Adefovir {9-[2-(phosphonomethoxy)ethyl]adenine (PMEA)} and tenofovir [(R)-9-[2-(phosphonomethoxy) propyl]adenine [(R)-PMPA)]} are particularly active against retroviruses (ie., HIV) and hepadnaviruses (ie., HBV); additionally, PMEA also shows activity against herpes- and poxviruses. We have recently identified a new class of ANPs, namely 6-[2-(phosphonomethoxy)alkoxy]-2,4-diaminopyrimidines, named, in analogy with their alkylpurine counterparts, HPMPO-DAPy, PMEO-DAPy, and (R)-PMPO-DAPy. These compounds exhibit an antiviral activity spectrum and potency that is similar to that of (S)-HPMPDAP, PMEA, and (R)-PMPA, respectively. Thus, PMEO-DAPy and (R)-PMPO-DAPy, akin to PMEA and (R)-PMPA, proved particularly active against HIV- 1, HIV-2, and the murine retrovirus Moloney sarcoma virus (MSV). PMEO-DAPy and (R)-PMPO-DAPy also showed potent activity against both wild-type and lamivudine-resistant strains of HBV. HPMPO-DAPy was found to inhibit different poxviruses (ie., vaccinia, cowpox, and orf) at a similar potency as cidofovir. HPMPO-DAPy also proved active against adenoviruses. In vivo, HPMPO-DAPy proved equipotent to cidofovir in suppressing vaccinia virus infection (tail lesion formation) in immunocompetent mice and promoting healing of disseminated vaccinia lesions in athymic-nude mice. The 6-[2-(phosphonomethoxy)alkoxy]-2,4-diaminopyrimidines offer substantial potential for the treatment of a broad range of retro-, hepadna-, herpes-, adeno-, and poxvirus infections.

Novel acyclic nucleoside phosphonate analogues with potent anti-hepatitis B virus activities

Novel acyclic nucleoside phosphonates with a pyrimidine base preferentially containing an amino group at C-2 and C-4 and a 2-(phosphonomethoxy)ethoxy or (R)-2-(phosphonomethoxy)propoxy group at C-6 selectively inhibit the replication of wild-type and lamivudine-resistant hepatitis B viruses. The activity of the most potent compounds was comparable to that of adefovir.