Antiviral enantiomeric preference for 5'-noraristeromycin

A mini-review on synthesis and antiviral activity of natural product oxetanocin A derivatives

Oxetanocin A (Oxt-A), a novel oxetanosyl N-glycoside nucleoside, was isolated from Bacillus megaterium in 1986. It carries an oxetane ring on the sugar moiety of the nucleoside scaffold, which contributes to differences in its structure from those of common tetrahydrofuranyl-based nucleosides. In view of the unique 3D-spatial framework, the complete synthesis of Oxt-A has been achieved by multiple research groups. The pharmacological properties of this natural product have also been broadly investigated by pharmacists and chemists since its discovery. Notably, the potential antiviral effect of Oxt-A has captured attention of researchers in the field of antiviral agent development. Furthermore, epidemic outbreaks caused by viruses have been stimulating the preparation and modification of various Oxt-A analogs over the past few decades. However, none of the studies have overviewed the antiviral efficacies of this naturally occurring scaffold yet. Thus, the present review summarizes the synthesis, structural modification, and antiviral activities of Oxt-A and its derivatives. We believe that these comprehensive descriptions will provide a novel perspective for the discovery of antivirus drugs with well-improved performance and pave newer paths for combating sudden public health issues triggered by viruses in the future.

Analogues of Pyrimidine Nucleosides as Mycobacteria Growth Inhibitors

Tuberculosis (TB) is the oldest human infection disease. Mortality from TB significantly decreased in the 20th century, because of vaccination and the widespread use of antibiotics. However, about a third of the world’s population is currently infected with Mycobacterium tuberculosis (Mtb) and the death rate from TB is about 1.4–2 million people per year. In the second half of the 20th century, new extensively multidrug-resistant strains of Mtb were identified, which are steadily increasing among TB patients. Therefore, there is an urgent need to develop new anti-TB drugs, which remains one of the priorities of pharmacology and medicinal chemistry. The antimycobacterial activity of nucleoside derivatives and analogues was revealed not so long ago, and a lot of studies on their antibacterial properties have been published. Despite the fact that there are no clinically used drugs based on nucleoside analogues, some progress has been made in this area. This review summarizes current research in the field of the design and study of inhibitors of mycobacteria, primarily Mtb.

Uracil-Containing Heterodimers of a New Type: Synthesis and Study of Their Anti-Viral Properties

Widespread latent herpes viral infections within a population can lead to the development of co-infections in HIV-infected patients. These infections are not particularly dangerous for healthy individuals and often occur with minimal symptoms, but for those who are immunocompromised, these infections can accelerate the acute phase of HIV infection and AIDS. Thus, the idea of designing compounds that could combine activity against HIV and co-infections would seem promising. In that regard, eleven compounds were synthesized that represent conjugates of non-nucleoside HIV reverse transcriptase inhibitors and nucleoside inhibitors of the herpes family viruses with the hope that these novel heterodimers will result in dual activity against HIV and concomitant herpes virus infections.

l-like 3-deazaneplanocin analogues: Synthesis and antiviral properties

The potent antiviral properties of 3-deazaneplanocin, 3-deaza-isoneplanocins (1) and recently discovered l-like carbocyclic nucleosides (2, 3 and 4) prompted us to pursue rationally conceived l-like 3-deazaneplanocin analogues. The synthesis of those analogues including l-like 3-deazaneplanocin (5), l-like 3-bromo-3-deazaneplanocin (6), and l-like 5'-fluoro-5'-deoxy-3-deazaneplanocin (7), was accomplished from a common intermediate, (-)-cyclopentenone (8). Antiviral analysis found 5 and 6 to display favorable activity against the Ebola virus, as expected for 3-deazaadenine carbocyclic nucleosides. Compound 5 also showed activity against arenaviruses, including Pinchinde and Tacaribe.

Unnatural verticilide enantiomer inhibits type 2 ryanodine receptor-mediated calcium leak and is antiarrhythmic

Ca²⁺ leak via ryanodine receptor type 2 (RyR2) can cause potentially fatal arrhythmias in a variety of heart diseases and has also been implicated in neurodegenerative and seizure disorders, making RyR2 an attractive therapeutic target for drug development. Here we synthesized and investigated the fungal natural product and known insect RyR antagonist (-)-verticilide and several congeners to determine their activity against mammalian RyR2. Although the cyclooligomeric depsipeptide natural product (-)-verticilide had no effect, its nonnatural enantiomer [ent-(+)-verticilide] significantly reduced RyR2-mediated spontaneous Ca²⁺ leak both in cardiomyocytes from wild-type mouse and from a gene-targeted mouse model of Ca²⁺ leak-induced arrhythmias (Casq2^-/-). ent-(+)-verticilide selectively inhibited RyR2-mediated Ca²⁺ leak and exhibited higher potency and a distinct mechanism of action compared with the pan-RyR inhibitors dantrolene and tetracaine and the antiarrhythmic drug flecainide. ent-(+)-verticilide prevented arrhythmogenic membrane depolarizations in cardiomyocytes without significant effects on the cardiac action potential and attenuated ventricular arrhythmia in catecholamine-challenged Casq2^-/- mice. These findings indicate that ent-(+)-verticilide is a potent and selective inhibitor of RyR2-mediated diastolic Ca²⁺ leak, making it a molecular tool to investigate the therapeutic potential of targeting RyR2 hyperactivity in heart and brain pathologies. The enantiomer-specific activity and straightforward chemical synthesis of (unnatural) ent-(+)-verticilide provides a compelling argument to prioritize ent-natural product synthesis. Despite their general absence in nature, the enantiomers of natural products may harbor unprecedented activity, thereby leading to new scaffolds for probe and therapeutic development.

Novel 5'-Norcarbocyclic Pyrimidine Derivatives as Antibacterial Agents

A series of novel 5'-norcarbocyclic derivatives of 5-alkoxymethyl or 5-alkyltriazolyl-methyl uracil were synthesized and the activity of the compounds evaluated against both Gram-positive and Gram-negative bacteria. The growth of Mycobacterium smegmatis was completely inhibited by the most active compounds at a MIC99 of 67 μg/mL (mc²155) and a MIC99 of 6.7⁻67 μg/mL (VKPM Ac 1339). Several compounds also showed the ability to inhibit the growth of attenuated strains of Mycobacterium tuberculosis ATCC 25177 (MIC99 28⁻61 μg/mL) and Mycobacterium bovis ATCC 35737 (MIC99 50⁻60 μg/mL), as well as two virulent strains of M. tuberculosis; a laboratory strain H37Rv (MIC99 20⁻50 μg/mL) and a clinical strain with multiple drug resistance MS-115 (MIC99 20⁻50 μg/mL). Transmission electron microscopy (TEM) evaluation of M. tuberculosis H37Rv bacterial cells treated with one of the compounds demonstrated destruction of the bacterial cell wall, suggesting that the mechanism of action for these compounds may be related to their interactions with bacteria cell walls.

5′-Norcarbocyclic analogues of furano[2,3-d]pyrimidine nucleosides

5′-Norcarbocyclic analogues of furano[2,3-d]pyrimidine nucleosides as well as 5-bromo and 5-iodouracil derivatives were synthesized to evaluate their potential antitumor activity. The halogenated derivatives display no cytotoxicity with respect to all tested cells: KB-3-1 (human epidermoid carcinoma), HeLa (human cervical epithelioid carcinoma), HuTu-80 (human duodenal cancer), B16 (mouse melanoma), and MDCK (normal epithelial). The cytotoxicity of the non-halogenated furano[2,3-d]pyrimidine derivatives increases with the lengthening of the alkyl chain of the substituent from 45 to 60 μm for octyl to from 3 to 10 μm for dodecyl.

The 5'-nor aristeromycin analogues of 5'-deoxy-5'-methylthioadenosine and 5'-deoxy-5'-thiophenyladenosine

To extend the potential of 5'-noraristeromycin (and its enantiomer) as potential antiviral candidates, the enantiomers of the carbocyclic 5'-nor derivatives of 5'-methylthio-5'-deoxyadenosine and 5'-phenylthio-5'-deoxyadenosine have been synthesized and evaluated. None of the compounds showed meaningful antiviral activity.

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).

A new synthesis and an antiviral assessment of the 4'-fluoro derivative of 4'-deoxy-5'-noraristeromycin

A synthetic route to (1S,2S,3R,5S)-3-(6-amino-9H-purin-9-yl)-5-fluorocyclopentane-1,2-diol (that is, the 4'-fluoro derivative of 4'-deoxy-5'-noraristeromycin, 3) is described via a fluorinated cyclopentanol, which is in contrast to existing schemes where fluorination occurred once the purine ring was present. Compound 3 was assayed versus a number of viruses. A favorable response was observed towards measles (IC(50) of 1.2 microg/mL in the neutral red assay and 14 microg/mL by the visual assay) but this was accompanied by cytotoxicity in the CV-1 host cells (21-36 microg/mL). Among the viruses unaffected by 3 were human cytomegalovirus and the poxviruses (vaccinia and cowpox), which are three viruses that were inhibited by the 4',4'-difluoro analog of 3 (that is, 2).

Carbocyclic 4'-Epiformycin

Formycin is a naturally occurring biologically responsive C-nucleoside. In pursuing the design and syntheses of novel C-nucleosides, convenient access to carbocyclic C-nucleosides based on the formycin framework was a goal. One such target was carbocyclic 4'-epiformycin (4). This compound is reported via a procedure based on an asymmetric aldol/ring closure methathesis strategy. To provide a preliminary glimpse into the biological characterization of 4 an antiviral assay was conducted. Target 4 was found to be inactive and to lack cytotoxicity to the host cells.

5'-Fluoro-5'-deoxyaristeromycin

5′-Fluoro-5′-deoxyaristeromycin (2) has been prepared via a Mitsunobu coupling of (1S,2S,3R,4S)-2,3-(cyclopentylidenedioxy)-4-fluoromethylcyclopentan-1-ol with N⁶-bis-boc protected adenine. This procedure is adaptable to preparing a number of 5′-fluoro-5′-deoxycarbocyclic nucleoside analogs with diversity in the heterocyclic base. Antiviral analysis found promising activity for 2 toward measles but no other viruses. No cytotoxicity was observed for 2.

Substrate-dependent dihydroxylation of substituted cyclopentenes: toward the syntheses of carbocyclic sinefungin and noraristeromycin

Carbocyclic nucleosides are of considerable interest for the development of new therapeutic agents. A key reaction in the preparation of many such nucleoside analogues is dihydroxylation of appropriately substituted cyclopentenes. Although often considered a routine reaction, in this paper, we report the dramatic influence of substituents on the facial selectivity of dihydroxylations. The substituted cyclopentene substrates are derived from acylnitroso cycloaddition reactions of cyclopentadiene, followed by N-O reduction and efficient enzymatic resolution. The results are directly utilized in a very efficient asymmetric synthesis of an antiviral carbocyclic nucleoside, noraristeromycin 5. Extensions toward the synthesis of carbocyclic sinefungin 7 document the importance of realizing the substituent dependence of the dihydroxylation reaction.

Syntheses and anti-HIV activities of (+/-)-norcarbovir and (+/-)-norabacavir

Norcarbovir (1) and norabacavir (2), the desmethylene derivatives of anti-HIV agents carbovir and abacavir, were efficiently synthesized from a common intermediate . Their antitumor and antiviral activities were evaluated and the results indicate norabacavir showed comparable anti-HIV activity to that of abacavir.

S-Adenosyl-L-homocysteine Hydrolase as an Attractive Target for Antimicrobial Drugs

S-Adenosyl-L-homocysteine (SAH) hydrolase catalyzes breakdown of SAH, which arises after S-adenosylmethionine-dependent methylation, into adenosine and homocysteine. The enzyme activity is required for both metabolic pathway of sulfur-containing amino acids and a variety of biological methylations. Because of the essential roles of SAH hydrolase for living cells, inhibitors of SAH hydrolase are expected to be antimicrobial drugs, especially for viruses and malaria parasite. Our research focused on the development of new antimalarials based on the SAH hydrolase inhibition. Malaria parasite employs SAH hydrolase of itself for coping with the toxicity of SAH, so that the target offers opportunities for chemotherapy if structural differences are exploited between the parasite and human enzymes. In vitro screens of nucleoside analogs resulted in moderate but selective inhibition for recombinant SAH hydrolase of malaria parasite, Plasmodium falciparum, by 2-position substituted adenosine analogs. Similar selectivity was observed in the growth inhibition assay of cultured cells. Following crystal structure analysis of the parasite SAH hydrolase discovered an additional space, which is located near the 2-position of the adenine-ring, in the substrate binding pocket. Mutagenic analysis of the amino acid residue forming the additional space confirmed that the inhibition selectivity is due to the difference of only one amino acid residue, between Cys59 in P. falciparum and Thr60 in human. For developing antimalarial drugs, it might be suitable to select target from pathways that are present in the parasite but absent from humans; nevertheless, even if the target was common in parasite and host, slight structural difference such as single amino acid variation is likely to be available for improving inhibitor selectivity.

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.

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.

Synthesis and Anti-HCMV Activity of Novel 5′-Norcarboacyclic Nucleosides

A very simple route for synthesizing a novel carboacyclic version of 5 cent-noraristeromycin is described. Condensation of the mesylates 9 and 23 with the natural nucleosidic bases (A, U, T, C) under standard nucleophilic substitution (K(2)CO(3), 18-Crown-6, DMF) and deblocking conditions, afforded the target nucleosides 14, 15, 16, 17, 28, 29, 30, and 31. In addition, these compounds were evaluated for their antiviral properties against various viruses.

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.

Amino substituted derivatives of 5′-amino-5′-deoxy-5′-noraristeromycin

The potent antiviral potential of 5'-amino-5'-deoxy-5'-noraristeromycin (2) is limited by associated toxicity. To seek derivatives of 2 that circumvent this undesirable property, three amino substituted derivatives (acetyl, 3; formyl, 4; and methyl, 5) of 2 have been prepared in 4-7 steps from the same intermediate, (1S,4R)-4-(6-chloropurin-9-yl)cyclopent-2-en-1-ol (6). Key steps involved an improved Pd(0)-catalyzed allylic azidation and a novel Pd(0)-catalyzed allylic amidation. The three target compounds were evaluated against a large number of viruses and found to be inactive except for a very weak effect of 5 on human cytomegalovirus, varicella zoster virus, and Epstein-Barr virus. There was also no noteworthy cytotoxicity associated with the new derivatives. Thus, these results indicate variation of the cyclopentyl amine of 2 does not offer a means to improve upon its antiviral potential.

5′-Homoaristeromycin. Synthesis and antiviral activity against orthopox viruses

An efficient synthesis of 5'-homoaristeromycin has been developed. This permitted an extensive antiviral analysis, which found potent activity toward vaccinia, cowpox, and monkeypox viruses. For comparative purposes, 5'-homoadenosine was made available by a newly designed route and found to be inactive.

L-deaza-5'-noraisteromycin

(+/-)-1-Deazaaristeromycin (4) has been reported to be an inactivator of S-adenosylhomocysteine (AdoHcy) hydrolase and, as a consequence, to affect S-adenosylmethionine (AdoMet) mediated macromolecular biomethylations. To extend this to our program focused on 5'-noraristeromycin derivatives as inhibitors of the same hydrolase enzyme as potential antiviral agents, both enantiomers of 1-deaza-5'-noraristeromycin (5 and 20) have been prepared. Compounds 5 and 20 were evaluated against the following viruses: vaccinia, cowpox, monkeypox, Ebola, herpes simplex type 1 and 2, human cytomegalovirus, Epstein Barr, varicella zoster, hepatitis B, hepatitis C, HIV-1 and HIV-2, adenovirus type 1, measles, Pichinde, parainfluenza type 3, influenza A (H1N1 and H3N2), influenza B, Venezuelan equine encephalitis, rhinovirus type 2, respiratory syncytial, yellow fever, and West Nile. No activity was found nor was there any cytotoxicity to the viral host cells.

5′-Amino-5′-deoxyaristeromycin and its antiviral properties

An efficient, three-step synthesis of 5'-amino-5'-deoxyaristeromycin (5), from a protected form of aristeromycin (6), is described. Compound 5 was evaluated against a large number of viruses. It showed weak activity towards vaccinia, herpes simplex virus 2, and cytomegalovirus. No other activity was observed. Compound 5 displayed some cytotoxicity towards the host cell lines human foreskin fibroblast, Daudi, and human T-lymphocyte (CEM).

9-deaza-5'-noraristeromycin

9-deaza-5'-noraristeromycin (2) has been prepared in 10 steps from the readily available (+)-(1R,4S)-4-t-butyldimethylsilyloxycyclopent-2-en-1-yl acetate. Compound 2 was evaluated against a large number of viruses. No activity was found nor did 2 display cyctotoxicity towards the viral host cells.

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.

The enantiomers of carbocyclic 5'-norguanosine: activity towards Epstein-Barr virus

(-)-5'-noraristeromycin (1) has shown antiviral activity towards, particularly cytomegalovirus, vaccinia virus and measles while its (+)-enantiomer (2) is effective towards hepatitis B virus. To determine if the antiviral characteristics of 1 and 2 extended to the guanine analogues (3 and 4), these enantiomers were prepared and evaluated against herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2), cytomegalovirus (CMV), varicella zoster virus (VZV), Epstein-Barr virus (EBV), human herpes virus type 6 (HHV-6), human herpes virus type 8 (HHV-8), vaccinia virus (VV), cowpox virus (CV), vesicular stomatitis virus (VSV), respiratory syncytial virus (RSV), hepatitis B virus (HBV), and human immunodeficiency virus type 1 (HIV-1) and type 2 (HIV-2). The only activity found for 3 was for Epstein-Barr virus in VCA Elisa (EC50 0.78 microg/mL), immunofluorescence assay for VCA or gp 350/250 (1.8-4.0 microg/mL) and DNA hybridization (EC50 0.82 microg/mL) assays with no accompanying toxicity seen in the host Daudi cells. No activity was noted for 4.

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.

Inhibition of measles virus replication by 5'-nor carbocyclic adenosine analogues

Despite intense efforts to increase vaccine coverage, measles virus (MV) still causes significant morbidity and mortality in the world, sometimes as the result of severe, chronic, lethal disease. In an effort to develop therapies to supplement immunization strategies, a number of 5'-nor carbocyclic adenosine analogues were evaluated for anti-MV activity in CV-1 monkey kidney cells. Of those compounds tested, those either unsubstituted at C4 or possessing a hydroxyl, azido or amino substituent at that position were the most active, with particularly significant inhibition of MV, strain Chicago-1. The EC50 values against this strain ranged from <0.1 to 1 mg/ml, as determined by cytopathic effect reduction assay, and confirmed by neutral red uptake. By virus yield reduction assay (+)-(1S,25,3R,4S)-4-(6'-amino-9'H-purin-9'-yl)cyclopentane-1,2,3-triol (2) (-)-(1R,2S,3R)-1-(6'-amino-9'H-purin-9'-yl)-2,3-dihydoxycyclopent-4-ene (3) (-)-(1R,2S,3R)-1-(6'-amino-9'H-purin-9'-yl)cyclopentane-2,3-dihydoxycyclopentane (5) and (-)-(1R,2R,3R,4S)-4-amino-1-(6'-amino-9'H-purin-9'-yl)cyclopentane-2,3-diol (8) were the most potent compounds tested, all with EC90 values of < or =0.4 mg/ml. Compounds 3 and 5 were also tested against other MV strains, and similarly inhibited those strains except for four designated as Bil, Edmonston, SA and X-1108. Compound 8 did not potently inhibit these other MV strains. In addition, 3, 5 and 8 demonstrated synergistic (additive) inhibition of MV replication in combination with ribavirin at several concentrations. Compounds 3, 5 and 8 were also potent MV inhibitors even when added to infected cells 24 h after virus exposure. None of these three compounds was virucidal at concentrations that inhibited viral replication as determined by virus yield reduction assay. Most compounds tested were also not toxic at concentrations >100 mg/ml in actively growing and stationary-phase cells. Results suggest that these compounds may be clinically useful anti-MV virus agents.

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.

5'-Nor carbocyclic 5'-deoxy-5'-(isobutylthio)adenosine and a 2',3'-dideoxy-2',3'-didehydro derivative

The inhibition of biochemical processes requiring S-adenosylmethionine as a co-factor have led to many nucleoside-based medicinal agents. Included in this group are 5'-deoxy-5'-(isobutylthio)adenosine (SIBA), a nucleoside with antiparasitic, antiviral and antiproliferative effects, and 5'-noraristeromycin, a carbocyclic-derived nucleoside with potent antiviral properties. This report brings together the structural components of these two compounds by describing both enantiomers of carbocyclic 5-nor SIBA (3 and 4). Owing to the recent interest in 2',3'-dideoxy-2',3'-didehydro nucleosides as antiviral agents, this derivative of 3 (5) is also described. All three compounds were screened against a variety of viruses and were found to be inactive at high concentrations or at limiting concentrations for the screening methods. The viruses subjected to 3-5 were herpes simplex virus types 1 and 2, human cytomegalovirus, vaccinia virus, vesicular stomatitis virus, respiratory syncytial virus, varicelIa zoster virus, coxsackie virus, parainfluenza-3 virus, sindbis virus, punta toro virus, reovirus-1, human immunodeficiency virus, influenza virus types A and B, adenovirus type 1 and measles virus. These results suggest that the C-5' methylene of the C-5' thio-based carbocyclic nucleosides is important for their antiviral properties.

Carbocyclic 5'-noruridine

A convenient preparation of (1'R,2'S,3'R,4'S)-1-(2',3',4'-trihydroxycyclopent-1'-yl)-1H-uracil (carbocyclic 5'-noruridine, 1) is described in 2 steps from the palladium complex of (+)-(1R,4S)-4-hydroxy-2-cyclopenten-1-yl acetate (3) and the sodium salt of uracil (2). Compound 1 was sought as a previously unknown member of the series of carbocyclic 5'-nor nucleosides needed as moieties for new oligomers. With 1 available, its antiviral properties and those of its enantiomer (5) are reported with 5 showing promising activity towards Epstein-Barr virus.

Interactions of (-)-ilimaquinone with methylation enzymes: implications for vesicular-mediated secretion

BACKGROUND

The marine sponge metabolite (-)-ilimaquinone has antimicrobial, anti-HIV, anti-inflammatory and antimitotic activities, inhibits the cytotoxicity of ricin and diptheria toxin, and selectively fragments the Golgi apparatus. The range of activities demonstrated by this natural product provides a unique opportunity for studying these cellular processes.

RESULTS

Affinity chromatography experiments show that (-)-ilimaquinone interacts with enzymes of the activated methyl cycle: S-adenosylmethionine synthetase, S-adenosylhomocysteinase and methyl transferases. Known inhibitors of these enzymes were found to block vesicle-mediated secretion in a manner similar to (-)-ilimaquinone. Moreover, the antisecretory effects of (-)-ilimaquinone and inhibitors of methylation chemistry, but not brefeldin A, could be reversed in the presence of the cellular methylating agent S-adenosylmethionine. Of the enzymes examined in the activated methyl cycle, S-adenosylhomocysteinase was specifically inhibited by (-)-ilimaquinone. Consistent with these observations, (-)-ilimaquinone was shown to obstruct new methylation events in adrenocorticotrophic hormone (ACTH)-secreting pituitary cells.

CONCLUSIONS

(-)-ilimaquinone inhibits cellular methylations through its interactions with S-adenosylhomocysteinase. Furthermore, these studies indicate that the inhibition of secretion by ilimaquinone is the result of the natural product's antimethylation activity. It is likely that the ability to fragment the Golgi apparatus, as well as other activities, are also related to ilimaquinone's influence on methylation chemistry.

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.