An epimer of 5'-noraristeromycin and its antiviral properties

3-Deazaneplanocin A and neplanocin A analogues and their effects on apoptotic cell death

3-Deazaneplanocin A (DzNep) is a potential epigenetic drug for the treatment of various cancers. DzNep has been reported to deplete histone methylations, including oncogenic EZH2 complex, giving rise to epigenetic modifications that reactivate many silenced tumor suppressors in cancer cells. Despite its promise as an anticancer drug, little is known about the structure-activity relationships of DzNep in the context of epigenetic modifications and apoptosis induction. In this study, a number of analogues of DzNep were examined for DzNep-like ability to induce synergistic apoptosis in cancer cells in combination with trichostatin A, a known histone deacetylase (HDAC) inhibitor. The structure-activity relationship data thus obtained provide valuable information on the structural requirements for biological activity. The studies identified three compounds that show similar activities to DzNep. Two of these compounds show good pharmacokinetics and safety profiles. Attempts to correlate the observed synergistic apoptotic activities with measured S-adenosylhomocysteine hydrolase (SAHH) inhibitory activities suggest that the apoptotic activity of DzNep might not be directly due to its inhibition of SAHH.

Historical perspectives in the development of antiviral agents against poxviruses

The poxvirus vaccinia virus (VV) served as the model virus for which the first antivirals, the thiosemicarbazones, were identified. This dates back to 1950; and, although there is at present no single antiviral drug specifically licensed for the chemotherapy or -prophylaxis of poxvirus infections, numerous candidate compounds have been described over the past 50 years. These compounds include interferon and inducers thereof (i.e., polyacrylic acid), 5-substituted 2’-deoxyuridines (i.e., idoxuridine), IMP dehydrogenase inhibitors, S-adenosylhomocysteine hydrolase inhibitors, acyclic nucleoside phosphonates (such as cidofovir) and alkoxyalkyl prodrugs thereof (such as CMX001), viral egress inhibitors (such as tecovirimat), and cellular kinase inhibitors (such as imatinib).

Inhibition of human immunodeficiency virus type 1 replication in human cells by Debio-025, a novel cyclophilin binding agent

Debio-025 is a synthetic cyclosporine with no immunosuppressive capacity but a high inhibitory potency against cyclophilin A (CypA)-associated cis-trans prolyl isomerase (PPIase) activity. A lack of immunosuppressive effects compared to that of cyclosporine was demonstrated both in vitro and in vivo. For three cyclosporines, the inhibitory potential against PPIase activity was quantitatively correlated with that against human immunodeficiency virus type 1 (HIV-1) replication. Debio-025 selectively inhibited the replication of HIV-1 in a CD4+ cell line and in peripheral blood mononuclear cells: potent activity was demonstrated against clinical isolates of various HIV-1 subtypes, including isolates with multidrug resistance to reverse transcriptase and protease inhibitors. Simian immunodeficiency virus and HIV-2 strains were generally resistant to inhibition by Debio-025; however, some notable exceptions of sensitive HIV-2 clinical isolates were detected. In two-drug combination studies, additive inhibitory effects were found between Debio-025 and 19 clinically used drugs of different classes. Clinical HIV-1 isolates that are naturally resistant to Debio-025 and that do not depend on CypA for infection were identified. Comparison of the amino acid sequences of the CypA binding domain of the capsid (CA) protein from Debio-025-sensitive and -resistant HIV-1 isolates indicated that resistance was mostly associated with an H87Q/P exchange. Mechanistically, cyclosporines competitively inhibit the binding of CypA to the HIV-1 CA protein, which is an essential interaction required for early steps in HIV-1 replication. By real-time PCR we demonstrated that early reverse transcription is reduced in the presence of Debio-025 and that late reverse transcription is almost completely blocked. Thus, Debio-025 seems to interfere with the function of CypA during the progression/completion of HIV-1 reverse transcription.

Synthesis and antiviral evaluation of novel 5'-norcarboacyclic phosphonic acid nucleosides

This article describes a very simple route for synthesizing a novel 5'-norcarboacyclic nucleotides. The condensation of the mesylates 17 and 18 with the natural nucleosidic bases (A,U,T,C) under standard nucleophilic substitution (K2CO3, 18-Crown-6, DMF) and deprotection afforded the target nucleotide analogues 27-34. In addition, these compounds were evaluated for their antiviral properties against various viruses.

4′-Fluorinated carbocyclic nucleosides: Synthesis and inhibitory activity against S-adenosyl-l-homocysteine hydrolase

4'-Fluorinated analogue of 9-[(1'R,2'S,3'R)-2',3'-dihydroxy-cyclopentan-1'-yl]adenine (DHCaA) and their related analogues were systematically synthesized under the Mitsunobu and palladium(0) coupling conditions followed by fluorination with inversion of the configuration by using diethylaminosulfur trifluoride, respectively. 4'-beta-Fluoro DHCaA and 2-amino-4'-alpha-fluoro DHCaA demonstrated slight inhibitory activity against human and Plasmodium falciparum S-adenosyl-L-homocysteine hydrolase, respectively.

John Montgomery's legacy: carbocyclic adenosine analogues as SAH hydrolase inhibitors with broad-spectrum antiviral activity

Ever since the S-adenosylhomocysteine (AdoHcy, SAH) hydrolase was recognized as a pharmacological target for antiviral agents (J. A. Montgomery et al., J. Med. Chem. 25:626-629, 1982), an increasing number of adenosine, acyclic adenosine, and carbocyclic adenosine analogues have been described as potent SAH hydrolase inhibitors endowed with broad-spectrum antiviral activity. The antiviral activity spectrum of the SAH hydrolase inhibitors include pox-, rhabdo-, filo-, arena-, paramyxo-, reo-, and retroviruses. Among the most potent SAH hydrolase inhibitors and antiviral agents rank carbocyclic 3-deazaadenosine (C-c3 Ado), neplanocin A, 3-deazaneplanocin A, the 5'-nor derivatives of carbocyclic adenosine (C-Ado, aristeromycin), and the 2-halo (i.e., 2-fluoro) and 6'-R-alkyl (i.e., 6'-R-methyl) derivatives of neplanocin A. These compounds are particularly active against poxviruses (i.e., vaccinia virus), and rhabdoviruses (i.e., vesicular stomatitis virus). The in vivo efficacy of C-c3 Ado and 3-deazaneplanocin A has been established in mouse models for vaccinia virus, vesicular stomatitis virus, and Ebola virus. SAH hydrolase inhibitors such as C-c3Ado and 3-deazaneplanocin A should in thefirst place be considered for therapeutic (or prophylactic) use against poxvirus infections, including smallpox, and hemorrhagic fever virus infections such as Ebola.

A survey of antiviral drugs for bioweapons

Smallpox (variola major), and the haemorrhagic fever viruses (filoviruses and arenaviruses) are classified as Category A biowarfare agents by the Centers for Disease Control. Category A agents pose a significant risk to public health and national security because they can be easily disseminated by aerosol, although with the exception of variola, they are not easily transmitted from person to person. An attack with these viruses would result in high morbidity and mortality and cause widespread panic. With the exception of smallpox and Argentine haemorrhagic fever virus, there are no vaccines or approved treatments to protect against these diseases. In this review we focus on promising prophylactic, therapeutic and disease modulating drugs (see Figure 1 for select chemical structures).

Adenosine N1-Oxide Analogues as Inhibitors of Orthopox Virus Replication

Several new types of adenosineN1-oxide (ANO) derivatives includingN1-alkoxy andN6-alkyl as well as the analogues with a trihydroxycyclopentane ring in place of the ribose residue were synthesized and their antiviral properties were evaluated in Vero and LLC-MK2 cell cultures infected with vaccinia, mousepox, monkeypox, cowpox, and different isolates of smallpox viruses. The antiviral activity of ANO and its derivatives significantly depended on the virus type and cell cultures. Mousepox and monkeypox viruses were the most sensitive to these compounds, while vaccinia and cowpox viruses were inhibited at the concentrations 1-1.5 orders of magnitude higher. The toxicity of the synthesized compounds was much lower than that of ANO. Modifications of the ANON6-position did not offer any advantages over the parent compound. The synthesizedN1-oxide derivatives of noraristeromycin retained the activity comparable with noraristeromycin and displayed a decreased toxicity. No direct correlation between antiviral activity and stability of the compounds was found.

The 4',4'-difluoro analog of 5'-noraristeromycin: a new structural prototype for possible antiviral drug development toward orthopoxvirus and cytomegalovirus

As a surrogate for 4'-hydroxy-5'-noraristeromycin and related carbocyclic nucleosides, an efficient, enantiodivergent synthetic route to both enantiomers of 5-(6-amino-9H-purin-9-yl)-3,3-difluorocyclopentane-1,2-diol (6 and ent-6) has been developed from a common starting material ((+)-(1R,4S)-4-hydroxy-2-cyclopenten-1-yl acetate, 10). Both compounds were assayed versus a series of viruses. The only response found was for compound 6 toward vaccinia and cowpox (EC50 of 143 and 94 microM, respectively) and human cytomegalovirus (EC50 of 6.2 microM). Both compounds were non-cytotoxic. While not as active as cidofovir toward the orthopox viruses and ganciclovir toward cytomegalovirus, compound 6 offers a new structural prototype upon which to build for uncovering new agents effective against these viral types.

Therapy and short-term prophylaxis of poxvirus infections: historical background and perspectives

The era of antiviral chemotherapy started more than 50 years with the findings by Domagk and his colleagues that thiosemicarbazones showed activity against vaccinia virus. One of the derivatives, methisazone, was even investigated in the prophylaxis of smallpox. With the successful implementation of the smallpox vaccine, the use of methisazone was not further pursued. Should there be a threat of smallpox or other poxvirus infections, that could not be immediately controlled by vaccination, a therapeutic intervention could be envisaged based on several therapeutic strategies targeted at such cellular enzymes as IMP dehydrogenase, SAH hydrolase, OMP decarboxylase and CTP synthetase, as well as viral enzymes such as the DNA polymerase. Most advanced as a therapeutic or early prophylactic modality to tackle poxvirus infection is cidofovir, which was found active (i) in vitro against all poxviruses studied so far; (ii) in vivo, against vaccinia and cowpox virus infections in experimental animal models; as well as (iii) some human poxvirus infections, such as molluscum contagiosum. In case of an inadvertent poxvirus epidemic, antiviral therapy (i.e. with cidofovir) will offer the possibility to provide short-term prophylaxis, or therapy. Cidofovir should also allow to treat severe complications of vaccination as may happen in for example immunosuppressed patients.

A mercapto analogue of 5'-noraristeromycin

5'-Noraristeromycin and its enantiomer have been found to possess a wide range of antiviral effects. In the search for analogues of and with improved activity, the synthesis of both enantiomers of 5'-mercapto-5'-deoxy-5'-noraristeromycin ( and ) has been accomplished. While (+)-7 was inactive, (-)- did show marginal activity against vaccinia virus, but not any other virus.

Vaccinia virus inhibitors as a paradigm for the chemotherapy of poxvirus infections

Poxviruses continue to pose a major threat to human health. Monkeypox is endemic in central Africa, and the discontinuation of the vaccination (with vaccinia virus) has rendered most humans vulnerable to variola virus, the etiologic agent of smallpox, should this virus be used in biological warfare or terrorism. However, a large variety of compounds have been described that are potent inhibitors of vaccinia virus replication and could be expected to be active against other poxviruses as well. These compounds could be grouped in different classes: (i) IMP dehydrogenase inhibitors (e.g., EICAR); (ii) SAH hydrolase inhibitors (e.g., 5'-noraristeromycin, 3-deazaneplanocin A, and various neplanocin A derivatives); (iii) OMP decarboxylase inhibitors (e.g., pyrazofurin) and CTP synthetase inhibitors (e.g., cyclopentenyl cytosine); (iv) thymidylate synthase inhibitors (e.g., 5-substituted 2'-deoxyuridines); (v) nucleoside analogues that are targeted at viral DNA synthesis (e.g., Ara-A); (vi) acyclic nucleoside phosphonates [e.g., (S)-HPMPA and (S)-HPMPC (cidofovir)]; and (vii) polyanionic substances (e.g., polyacrylic acid). All these compounds could be considered potential candidate drugs for the therapy and prophylaxis of poxvirus infections at large. Some of these compounds, in particular polyacrylic acid and cidofovir, were found to generate, on single-dose administration, a long-lasting protective efficacy against vaccinia virus infection in vivo. Cidofovir, which has been approved for the treatment of cytomegalovirus retinitis in immunocompromised patients, was also found to protect mice, again when given as a single dose, against a lethal aerosolized or intranasal cowpox virus challenge. In a biological warfare scenario, it would be advantageous to be able to use a single treatment for an individual exposed to an aerosolized poxvirus. Cidofovir thus holds great promise for treating human smallpox, monkeypox, and other poxvirus infections. Anecdotal experience points to the efficacy of cidofovir in the treatment of the poxvirus infections molluscum contagiosum and orf (ecthyma contagiosum) in immunosuppressed patients.

Chemotherapy of respiratory viruses: prospects and challenges

Billions of people are infected with respiratory viruses annually. Infants and young children, the elderly, immunocompromised individuals and those debilitated by other diseases or nutritional deficiencies are most at risk for serious disease. There are few vaccines available for use against these viruses, and even where there are (influenza, measles and adenovirus), infections remain common. The continued prevalence of respiratory virus infections has lead to renewed efforts to find safe agents effective against the most medically important respiratory viruses: influenza, respiratory syncytial, parainfluenza, measles, rhino- and adenovirus. Copyright 1999 Harcourt Publishers Ltd.

Respiratory syncytial virus (RSV) disease and prospects for its control

Respiratory syncytial virus (RSV) is a major virus pathogen of infants and young children, an important cause of disease in adults and is responsible for a significant amount of excess morbidity and mortality in the elderly. It also can be devastating in immunosuppressed populations. Vaccines are being developed, but none are currently licensed. Moreover, even if one or more are approved, they may not be suitable for some populations vulnerable to RSV (e.g. very young infants and the immunosuppressed). Ribavirin and immunoglobulin preparations with high titers of RSV-specific neutralizing antibodies are currently approved for use to treat and prevent RSV infection. However, neither of these is cost-effective or simple to administer. New agents are needed to reduce the impact of RSV. This review is concerned with the means currently available for controlling RSV, the search for new agents effective against this virus, and future prospects for preventing and treating RSV infections.

Synthesis of Aminocyclitols by Intramolecular Reductive Coupling of Carbohydrate Derived delta- and epsilon-Functionalized Oxime Ethers Promoted by Tributyltin Hydride or Samarium Diiodide

The intramolecular reductive coupling of a series of simple or polyoxygenated oxime ethers delta- or epsilon-functionalized with bromide, alpha,beta-unsaturated ester, aldehyde, or ketone groups is reported. The cyclization of a nitrile-tethered aldehyde is also studied. These reductive couplings are promoted by tributyltin hydride or samarium diiodide. The reactions proceed under mild conditions, in good chemical yield, and with high stereoselectivity. When applied to highly functionalized substrates derived from carbohydrates, this approach provides a selective entry to enantiomerically pure aminocyclitols of varying regio- and stereochemistry. In particular, the reductive coupling reaction of carbonyl-tethered oxime ethers promoted by samarium diiodide can be performed in a one-pot sequence, following a Swern oxidation step, allowing the direct transformation of hydroxyl-tethered oxime ethers into the corresponding aminocyclitols. Moreover, the resultant O-benzylhydroxylamine products of these cyclizations can be further reduced in situ with excess samarium diiodide, in the presence of water, to the corresponding amino alcohols in excellent yields. Some transformations of these compounds are discussed.