Synthesis of 3'- and 5'-nitrooxy pyrimidine nucleoside nitrate esters: "nitric oxide donor" agents for evaluation as anticancer and antiviral agents

A group of 3'-O-nitro-2'-deoxyuridines, 3'-O-nitro-2'-deoxycytidines, and 5'-O-nitro-2'-deoxyuridines possessing a variety of substituents (H, Me, F, I) at the C-5 position were synthesized for evaluation as anticancer/antiviral agents that have the ability to concomitantly release cytotoxic nitric oxide (*NO). Although these compounds generally released a greater percent of *NO than the reference drug isosorbide dinitrate upon incubation in the presence of l-cysteine, or serum, their cytotoxicity (CC(50) = 10(-3) to 10(-6) M range) was comparable to 5-iodo-2'-deoxyuridine, but weaker than 5-fluoro-2'-deoxyuridine, against a variety of cancer cell lines. No differences in cytotoxicity against nontransfected (KBALB, 143B), and the corresponding transfected (KBALB-STK, 143B-LTK) cancer cell lines possessing the herpes simplex virus type 1 (HSV-1) thymidine kinase gene (TK(+)) were observed, indicating that expression of the viral TK enzyme did not provide a gene therapeutic effect. These nitrate esters were inactive antiviral agents except for 5-iodo-3'-O-nitro-2'-deoxyuridine that showed modest activity against HSV-1, HSV-2, and vaccinia virus.     

Antiviral activity of cyclosaligenyl prodrugs of the nucleoside analogue bromovinyldeoxyuridine against herpes viruses

A series of 42 lipophilic bromovinyldeoxyuridine monophosphates (BVDUMPs) are presented as potential prodrugs of the antiviral agent (E)-5-(2-bromovinyl)-2'-deoxyuridine (BVDU). The 5'-cycloSal-masking group technique has been applied to this cyclic nucleoside analogue to achieve delivery of the monophosphate of BVDU inside the target cells. The new substances have been tested for their antiviral activity against herpes simplex virus types 1 and 2 (HSV-1 and -2), thymidine kinase-deficient (TK(-)) HSV-1, varicella-zoster virus (VZV), human cytomegalovirus (HCMV) and Epstein-Barr virus (EBV). The XTT-based tetrazolium reduction assay EZ4U (for HSV), the plaque inhibition test (for VZV and HCMV) and a DNA hybridisation assay (for EBV) were used to assess antiviral activity. The results indicate that cycloSal-BVDUMP triesters proved to be potent and selective inhibitors of HSV-1 comparable with aciclovir. VZV replication was inhibited by very low concentrations, and two substances had a slightly better anti-VZV activity than the parent compound BVDU. No antiviral effect could be demonstrated against TK(-)-HSV-1, HSV-2 and HCMV, most likely owing to the lack of phosphorylation to BVDU diphosphate. Most remarkably, several cycloSal-BVDUMP triesters yielded promising anti-EBV activity whereas the parent compound BVDU was entirely inactive.     

Synthesis and antiviral activity of novel 5-(1-cyanamido-2-haloethyl) and 5-(1-hydroxy(or methoxy)-2-azidoethyl) analogues of uracil nucleosides

A new class of 5-(1-cyanamido-2-haloethyl)-2'-deoxyuridines (4-6) and arabinouridines (7, 8) were synthesized by the regiospecific addition of halogenocyanamides (X-NHCN) to the 5-vinyl substituent of the respective 5-vinyl-2'-deoxyuridine (2) and 2'-arabinouridine (3). Reaction of 2 with sodium azide, ceric ammonium nitrate, and acetonitrile-methanol or water afforded the 5-(1-hydroxy-2-azidoethyl)-(10) and 5-(1-methoxy-2-azidoethyl)-2'-deoxyuridines (11). In vitro antiviral activities against HSV-1-TK(+) (KOS and E-377), HSV-1-TK(-), HSV-2, VZV, HCMV, and DHBV were determined. Of the newly synthesized compounds, 5-(1-cyanamido-2-iodoethyl)-2'-deoxyuridine (6) exhibited the most potent anti-HSV-1 activity, which was equipotent to acyclovir and superior to 5-ethyl-2'-deoxyuridine (EDU). In addition, it was significantly inhibitory for thymidine kinase deficient strain of HSV-1 (EC(50) = 2.3-15.3 microM). The 5-(1-cyanamido-2-haloethyl)-2'-deoxyuridines (4-6) all were approximately equipotent against HSV-2 and were approximately 1.5- and 15-fold less inhibitory for HSV-2 than EDU and acyclovir, respectively. Compounds 4-6 were all inactive against HCMV but exhibited appreciable antiviral activity against VZV. Their anti-VZV activity was similar or higher to that of EDU and approximately 5-12-fold lower than that of acyclovir. The 5-(1-cyanamido-2-haloethyl)-(7,8) analogues of arabinouridine were moderately inhibitory for VZV and HSV-1 (strain KOS), whereas compounds 10 and 11 were inactive against herpes viruses. Compounds 5 and 6 also demonstrated modest anti-hepatitis B virus activity against DHBV (EC(50) = 19.9-23.6 microM). Interestingly, the related 5-(1-azido-2-bromoethyl)-2'-deoxyuridine (1n) analogue proved to be markedly inhibitory to DHBV replication (EC(50) = 2.6-6.6 microM). All compounds investigated exhibited low host cell toxicity to several stationary and proliferating host cell lines as well as mitogen-stimulated proliferating human T lymphocytes.     

Specific recognition of the bicyclic pyrimidine nucleoside analogs, a new class of highly potent and selective inhibitors of varicella-zoster virus (VZV), by the VZV-encoded thymidine kinase.

Recently, an entirely new class of bicyclic nucleoside analogs (BCNAs) was found to display exquisite potency and selectivity as inhibitors of varicella-zoster virus (VZV) replication in cell culture. A striking difference in their ability to convert the BCNAs to their phosphorylated derivatives was observed between the VZV-encoded thymidine kinase (TK) and the very closely related herpes simplex virus type 1 (HSV-1) TK. Whereas VZV TK efficiently phosphorylated the BCNAs, HSV-1 TK was unable to do so. In addition, the thymidylate (dTMP) kinase activity of VZV TK further converted BCNA-5'-MP to BCNA-5'-DP. The BCNAs (or their phosphorylated derivatives) were not a substrate for cytosolic TK, mitochondrial TK, or cytosolic dTMP kinase. Human erythrocyte nucleoside diphosphate (NDP) kinase was unable to phosphorylate the BCNA 5'-diphosphates to BCNA 5'-triphosphates. Under the same experimental conditions, the anti-herpetic (E)-5-(2-bromovinyl)-2'-deoxyuridine (BVDU) derivative was efficiently converted to BVDU-MP and BVDU-DP by both VZV TK and HSV-1 TK and further, into BVDU-TP, by NDP kinase. Our observations may account for the unprecedented specificity of BCNAs as anti-VZV agents.     

5-(Haloalkyl)-2'-deoxyuridines: a novel type of potent antiviral nucleoside analogue

Syntheses of 5-(2-haloethyl)-2'-deoxyuridines, 5-(3-chloropropyl)-2'-deoxyuridines, and 5-(2-chloroethyl)-2'-deoxycytidine are described. The antiviral activities of these compounds were determined in cell culture against herpes simplex virus types 1 and 2. All compounds were shown to possess significant and selective antiviral activity. The most potent derivative, 5-(2-chloroethyl)-2'-deoxyuridine (CEDU), inhibited HSV-1 at concentrations below 0.1 microgram/mL. It exerted measurable inhibitory effects on cell proliferation only at concentrations higher than 100 micrograms/mL. In vivo CEDU reduced the mortality rate of HSV-1-infected mice at concentrations lower than 5 mg/kg per day when given intraperitoneally and orally. Thus, it proved to be more effective in this in vivo model than the reference compounds (E)-5-(2-bromovinyl)-2'-deoxyuridine (BVDU) and 9-[(2-hydroxyethoxy)methyl]guanine (ACV).     

6-azapyrimidine-2'-deoxy-4'-thionucleosides: antiviral agents against TK+ and TK- HSV and VZV strains

The synthesis of a series of novel 1-(2-deoxy-4-thio-beta-D-erythro-pentofuranosyl)-(6-azapyrimidine) nucleosides is described. X-ray crystallographic data of the thymidine derivative allowed conformational analysis, which indicated a twist (3T2) sugar conformation. Hydrogen-bonded assemblies for the crystal structure were determined using PLATON software to allow further interpretation of the crystal packing and base interactions. The 6-azapyrimidine nucleosides described were evaluated against a range of viral strains. The thymidine analogue showed pronounced activity against herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2), varicella-zoster virus (VZV), and vaccinia virus. This compound lost only 5- to 10-fold of its antiviral activity against thymidine kinase (TK)-deficient HSV-1 and VZV strains. These observations suggest that the compounds may not entirely depend on viral TK-catalyzed phosphorylation for antiviral activity and/or use an alternative metabolic activation pathway, and/or display a unique mechanism of antiviral action by the unmetabolized nucleoside analogue.     

(E)-5-(2-bromovinyl)-2'-desoxyuridine--a new nucleoside analog with selective inhibitory action against herpesviruses. Studies in cell culture and animal experiments

(E)-5-(2-Bromovinyl)-2'-deoxyuridine (1; BrVUdR) inhibits the replication of herpes simplex virus type 1 (HSV-1) and of varicella-zoster virus (VZV) in vitro at concentrations of 0.01 to 0.23 mumol/l, whereas herpes simplex virus type 2 (HSV-2) is influenced only at 5.5 to 27 mumol/l. In comparison to some classical and newly developed antiherpetics, i. e. 5-iodo-2'-desoxyuridine (2; idoxuridine, IDU), 9-beta-D-arabinofuranosyladenine (4; vidarabine Ara-A), 9-(2-hydroxyethoxymethyl) guanine (5; acyclovir, ACV) and 2'-fluoro-5-iodo-1-beta-D-aracytosine (6;FIAC) the following order of decreasing activity was found:1 greater than 6 greater than 5 greater than 2 greater than 4 (against HSV-1) and 6 greater than 2 greater than 5 greater than 1 greater than 4 (against HSV-2). The high selectivity of the antiviral effect of BrVUdR towards HSV-1 and TZV is based on the fact, that proliferation of different mammalian cell lines is inhibited by 50% only at concentrations as high as 90 to 170 mumol/l, resulting in a therapeutical index of 1000 to 10,000. Successful treatment of an HSV-1 encephalitis in mice as well as an HSV-1 keratitis of rabbits confirmed the efficiency of 1 in experimental animal infections. No toxic side effects in both local and systemic applications were observed. Promising data from cell culture and animal experiments recommend 1 as a potential candidate for the local and systemic treatment of HSV-1 and VZV infections in man.     

Differential binding affinities of sugar-modified derivatives of (E)-5-(2-bromovinyl)-2'-deoxyuridine for herpes simplex virus-induced and human cellular deoxythymidine kinases

The affinity of a large number of sugar-modified derivatives of (E)-5-(2-bromovinyl)-2'-deoxyuridine (BVDU) was determined towards deoxythymidine (dThd) kinases (TK) of various origin, i.e. human cytosol and mitochondrial TK, as well as herpes simplex virus (HSV) type 1 and type 2 TK. Substitution at the 3'- and 5'-position had differential effects on the interaction of BVDU with TK from different sources. The binding affinity of the nucleoside analogs for these different TKs was also influenced by the nature of the 5-substituent (2-bromovinyl vs 2- chlorovinyl ). The 5'-azido and 5'-amino derivatives of BVDU showed affinity for HSV-1 TK only and may, therefore, be useful to differentiate HSV-1 TK from all other TKs . There was no stringent correlation between the antiviral effects of the compounds and their binding constants for viral TK, suggesting that phosphorylation by viral TK is an essential but not sufficient factor in determining the antiviral activity of these analogs.     

2'-Fluorinated arabinonucleosides of 5-(2-haloalkyl)uracil: synthesis and antiviral activity

The synthesis of 5-(2-fluoroethyl)-2'-deoxyuridine (FEDU, 4b), its 2'-fluoro analogue 1-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl)-5-(2-fluoroethyl)-1H,3H- pyrimidine-2,4-dione (FEFAU, 4k), and the 2'-fluoro analogue of the potent antiherpes virus compound 5-(2-chloroethyl)-2'-deoxyuridine (CEDU), 5-(2-chloroethyl)-1-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl)-1H,3H-pyr imidine - 2,4-dione (CEFAU, 4i), is described. The antiviral activities of these compounds were determined in cell culture against herpes simplex virus (HSV) types 1 and 2 and varicella zoster virus (VZV). All compounds were shown to possess significant and selective antiviral activity. FEDU proved less potent than CEDU against VZV replication; however, it was more active against HSV-2. CEFAU showed marked activity against HSV-1, HSV-2, and VZV. The compound containing fluorine at both positions, FEFAU, exhibited the strongest antiviral potency against HSV-1, HSV-2, and VZV. It inhibited HSV-1 at a concentration of 0.03-0.2 microgram/mL, HSV-2 at 0.1-0.3 microgram/mL, and VZV at 0.03 microgram/mL. Neither FEDU nor CEFAU or FEFAU exerted a significant inhibitory effect on cell proliferation at a concentration of 100 micrograms/mL. Thus, the cytotoxicity of these compounds is as low as that of CEDU and compares favorably to that of previously described 2'-fluoroarabinosyl nucleoside analogues.     

Synthesis of (E)-5-(3,3,3-trifluoro-1-propenyl)-2'-deoxyuridine and related analogues: potent and unusually selective antiviral activity of (E)-5-(3,3,3-trifluoro-1-propenyl)-2'-deoxyuridine against herpes simplex virus type 1

Syntheses of (E)-5-(3,3,3-trifluoro-1-propenyl)-2'-deoxyuridine (TFPe-dUrd) (1), 5-(3,3,3-trifluoro-1-propyl)-2'-deoxyuridine (11), 5-(3,3,3-trifluoro-1-methoxy-1-propyl)-2'-deoxyuridine (8), and 5-(3,3,3-trifluoro-1-hydroxy-1-propyl)-2'-deoxyuridine (10) from 5-chloromercuri-2'-deoxyuridine are described. The antiviral activity of TFPe-dUrd was determined in cell culture against herpes simplex virus type 1 (HSV-1), herpes simplex virus type 2 (HSV-2), and vaccinia virus and compared concurrently with 5-(1-propenyl)-2'-deoxyuridine, 5-(2-bromovinyl)-2'-deoxyuridine, 5-iodo-2'-deoxyuridine, and 5-(trifluoromethyl)-2'-deoxyuridine. TFPe-dUrd demonstrated a potent and unusually selective activity against HSV-1, with a 2-log reduction in virus yield at 0.03 micrograms/mL (0.09 microM); L-1210 cell growth was inhibited by 50% only at 290 micrograms/mL. Isopycnic centrifugation of 32P-labeled DNA indicated that if 0.5 or 2 microM TFPe-dUrd was present for 0-6 h postinfection, viral DNA synthesis was reduced by ca. 50 and 85%, respectively; concomitantly, a new DNA band appeared at lower density than normal cellular or viral DNA.     

Synthesis and antiviral properties of (Z)-5-(2-bromovinyl)-2'-deoxyuridine

(Z)-5-(2-Bromovinyl)uracil was obtained by photoisomerization of the E. isomer. Similarly, (E)-5-(2-bromovinyl)-2'-deoxyuridine gave the required Z isomer. (Z)-5-(2-Bromovinyl)-2'-deoxyuridine is much less active against herpes simplex virus type 1 (HSV-1) and somewhat less active against herpes simplex virus type 2 than is the E isomer. Both isomers show similar activity against vaccinia virus. Therefore, the highly potent and selective activity of (E)-5-(2-bromovinyl)-2'-deoxyuridine against HSV-1 is due to its E configuration.     

Establishment and use of a cell line expressing HSV-1 thymidine kinase to characterize viral thymidine kinase-dependent drug-resistance

To understand the mechanisms of antiviral drug resistance and to have a system to examine the cytotoxicity of herpes simplex virus type 1 (HSV-1) inhibitors that are thymidine kinase (TK)-dependent, we have constructed a plasmid pFTK1 by inserting a DNA fragment containing the TK gene of HSV-1 strain F into the eukaryotic expression vector pcDNA3.1/His A. TK-deficient 143B cells were transfected with this vector and neomycin-resistant cells were selected. Cell survival in HAT medium and TK activity of the cell lysates were examined to ascertain HSV-1 TK expression. A cell line expressing the viral TK gene, FTK143B (FTK), was established and used for characterization of two laboratory-derived TK-deficient drug-resistant HSV-1 mutants of strain F. The antiviral activities of several drugs, mostly nucleoside analogues, were compared in the Vero, 143B and FTK cell culture systems. We showed that both mutant viruses lost their resistance to acyclovir and to other HSV-1 TK-dependent compounds in FTK cells but not in Vero and 143B cells. Significantly increased cytotoxicity of ganciclovir and (E)-5-(2-bromovinyl)-2'-deoxyuridine was also observed in the FTK cells. This HSV-1 TK gene-transfected cell model is a useful tool to rapidly determine HSV-1 drug resistance at the viral TK level.     

Synthesis of 5-[1-hydroxy(or methoxy)-2-bromo(or chloro)ethyl]-2'-deoxyuridines and related halohydrin analogues with antiviral and cytotoxic activity

A series of new 5-(1-hydroxy-2-haloethyl)-2'-deoxyuridines (3, 6, 8) were synthesized in 60-70% yields by addition of HOX (X = Br, Cl, I) to the vinyl substituent of the respective 5-vinyl-2'-deoxyuridines (2, 5, 7). Treatment of 3a,b with methanolic sulfuric acid afforded the corresponding 5-(1-methoxy-2-haloethyl)-2'-(deoxyuridines (4a,b). The 5-(1-hydroxy-2-chloroethyl) (3b), 5-(1-methoxy-2-bromoethyl) (4a), 5-(1-hydroxy-2-bromo-2-(ethoxycarbonyl)ethyl) (6a), and 5-(1-hydroxy-2-iodo-2-(ethoxycarbonyl)ethyl) (6b) derivatives exhibited in vitro antiviral activity (ID50 = 0.1-1 microgram/mL range) against herpes simplex virus type 1 (HSV-1). 5-(1-Hydroxy-2-bromo-2-(ethoxycarbonyl)-ethyl)-2'-deoxyuridine (6a) was the most active cytotoxic agent in the in vitro L1210 screen exhibiting an ED50 of 11 micrograms/mL relative to melphalan (ED50 = 0.15 micrograms/mL).     

Antiviral activity of ganciclovir elaidic acid ester against herpesviruses

A fatty acid derivative of ganciclovir (GCV), elaidic acid ganciclovir (E-GCV), has been evaluated for its inhibitory activity against laboratory and clinical strains of herpes simplex type 1 (HSV-1) and type 2 (HSV-2), varicella-zoster virus (VZV) and human cytomegalovirus (HCMV) in human embryonic lung fibroblasts. GCV, cidofovir, acyclovir (ACV), brivudin (BVDU) and foscarnet (PFA) were included as reference compounds. The viruses studied were wild-type, thymidine kinase-deficient (TK(-)) and PFA-resistant (PFA(r)) HSV strains. The IC(50) values obtained for E-GCV were 5- to 30-fold lower than those observed for GCV, the IC(50) value of E-GCV for HSV-1 strain KOS being 0.07 nM. A similarly increased activity of E-GCV (as compared to GCV) was noted for TK(-) and PFA(r) HSV-1 or HSV-2 strains. However, E-GCV did not exhibit superior activity over GCV to VZV or HCMV in vitro. The antiviral efficacy of E-GCV was also evaluated in vivo against intracerebral HSV-2 infection in NMRI mice. Animals were treated intraperitoneally or perorally with E-GCV, GCV or placebo once daily for 10 days, starting the day of infection. E-GCV compared to GCV at equimolar doses, proved markedly more efficacious than GCV in terms of reduction of mortality rate and delay of mean time of death. The elaidic acid ester of GCV should therefore be considered as a novel approach towards the treatment of HSV infections.     

(E)-5-(2-bromovinyl)uridine requires phosphorylation by the herpes simplex virus (type 1)-induced thymidine kinase to express its antiviral activity

(E)-5-(2-Bromovinyl)uridine (BVUrd), the riboside counterpart of (E)-5-(2-bromovinyl)-2'-deoxyuridine (BVdUrd), effected a dose-dependent inhibition of viral progeny formation and viral DNA synthesis in herpes simplex virus type 1 (HSV-1, strain KOS)-infected human (E6SM) diploid fibroblast cells. BVUrd was directly phosphorylated in HSV-1-infected cells, presumably by the virus-encoded thymidine kinase (TK), since (i) BVUrd was not phosphorylated by extracts of cells infected with a HSV-1 strain deficient in TK expression and (ii) the phosphorylation was inhibited by a polyclonal anti-HSV-1 antibody. Within the HSV-1-infected cells, BVUrd was incorporated into the viral DNA as BVdUMP (BVdUrd 5'-monophosphate). This incorporation may account for the antiviral action of BVUrd, and implies that, following its initial phosphorylation by the viral TK, BVUrd is converted to its 2'-deoxy counterpart, most likely at the 5'-diphosphate level (BVUDP----BVdUDP).     

Synthesis and biological activities of 4-O-(difluoromethyl)-5-substituted-uracil nucleoside analogues

Various 4-O-difluoromethyl analogues of 5-substituted uridine (Urd), 2'-deoxyuridine (dUrd), and arabinofuranosyluracil (araU) nucleosides were prepared via a CF2-insertion reaction into 4-O-silylated nucleosides and evaluated for activity against herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) and cytotoxicity in human embryonic lung fibroblast (HELF) cell cultures. The introduction of the 4-substituent led to a strong reduction of antiviral activity for dUrd but not for araU analogues. Three of the 4,5-disubstituted uracil nucleoside derivatives, 4-O-(difluoromethyl)-5-bromo-araU (5c),-5-methyl-araU (5e), and -(E)-5-(2-bromovinyl)-araU (5g), displayed a high and selective inhibitory effect against HSV-1, but only 5e was effective against both HSV-1 and HSV-2 comparably with the antiherpes potential of the reference compounds 9-[(2-hydroxyethoxy)methyl]guanine (acyclovir) and 1-beta-D-arabino-furanosylthymine (araT).     

Efficacy of (E)-5-(2-bromovinyl)-2'-deoxyuridine against different herpes simplex virus strains in cell culture and against experimental herpes encephalitis in mice

(E)-5-(2-Bromovinyl-2'-deoxyuridine (BrVUdR) showed strong antiviral activity against different laboratory strains and clinical isolates of herpes simplex virus type 1 (HSV-1) on primary rabbit testes (PRT) cells with a 50% inhibition of plaque formation (ID50) at 0.01-0.02 microM. One laboratory strain (HSV-1-S), however, was completely refractory even at concentrations as high as 100 microM. In contrast, the ID50S for all herpes simplex virus type 2 (HSV-2) strains were about 10(2) - 10(3) times higher (8-25 microM) than for the HSV-1 strains. No toxicity in mice treated with 140 mg BrVUdR/kg/day for 14 days was observed, and successful treatments of herpes encephalitis in mice induced experimentally by intracerebral infection with one laboratory strain (HSV-1-Kupka) and one clinical isolate (HSV-1-64) were achieved. Treatment of encephalitis in mice induced by the strain HSV-1-S insensitive to BrVUdR in cell culture failed to be effective. Similar antibody titers against HSV-1 were found in surviving mice of the control and of the BrVUdR-treated groups.     

4-Oxo-4,7-dihydrothieno[2,3-b]pyridines as non-nucleoside inhibitors of human cytomegalovirus and related herpesvirus polymerases

A novel series of 4-oxo-4,7-dihydrothieno[2,3-b]pyridine-5-carboxamides have been identified as potential antivirals against human herpesvirus infections resulting from human cytomegalovirus (HCMV), herpes simplex virus type 1 (HSV-1), and varicella-zoster virus (VZV). Compounds 10c and 14 demonstrated broad-spectrum inhibition of the herpesvirus polymerases HCMV, HSV-1, and VZV. High specificity for the viral polymerases was observed compared to human alpha polymerase. The antiviral activity of 10c and 14, as determined by plaque reduction assay, was comparable or superior to that of existing antiherpes drugs, ganciclovir (for HCMV) and acyclovir (for HSV-1 and VZV). Drug resistance to compound 14 correlated to point mutations in conserved domain III of the herpesvirus DNA polymerase, but these mutations do not confer resistance to existing nucleoside therapy. In addition, compound 14 maintained potent antiviral activity against acyclovir-resistant HSV-1 strains. Substitution to the pyridone nitrogen (N7) was found to be critical for enhanced in vitro antiviral activity.     

Phosphonoformate and phosphonoacetate derivatives of 5-substituted 2'-deoxyuridines: synthesis and antiviral activity

The synthesis of potential "combined prodrugs" wherein phosphonoformate or phosphonoacetate was attached to the 5'-position of 2'-deoxyuridine, 2'-deoxythymidine, 5-iodo-2'-deoxyuridine (IDU), 5-(2-chloroethyl)-2'-deoxyuridine (CEDU), or 5-(2-bromovinyl)-2'-deoxyuridine (BVDU) or to the 3'-position of CEDU is described. The antiviral activities of these derivatives and of reference compounds were compared in Vero, HEp-2, and primary rabbit kidney cells against herpes simplex virus types 1 and 2 (HSV-1 and -2). The CEDU and BVDU analogues were also evaluated against systemic and intracutaneous HSV-1 infection in mice. The nature of the 5-substituent proved critical for antiviral activity, since only the 5-iodo-, 5-(2-bromovinyl)-, and 5-(2-chloroethyl)-substituted derivatives were inhibitory to the herpesviruses. Furthermore, the type specificity is determined by the nature of the 5-substituent: the IDU analogues were similarly inhibitory to HSV-1 and -2 whereas the CEDU and BVDU analogues inhibited HSV-2 replication only at considerably higher concentrations than HSV-1. In vivo, several derivatives were shown to possess significant antiviral activity; however, none surpassed its respective parent compound, CEDU or BVDU, in potency. It seems improbable, therefore, that a synergistic effect between PFA or PAA and the nucleoside analogue occurred. The extent of in vitro and in vivo activity of the CEDU and BVDU 5'-phosphonoformates and 5'-phosphonoacetates is most plausibly explained by the ease by which the "combined prodrugs" are hydrolyzed and the parent compound, CEDU and BVDU, respectively, is released.     

The mechanism of action of the anti-herpes virus compound 2,3-dimethyl-6(2-dimethylaminoethyl)-6H-indolo-(2,3-b)quinoxaline.

The compound 2,3-dimethyl-6(2-dimethylaminoethyl)6H-indolo-(2,3-b)quinoxaline (B-220) has been shown to exhibit potent antiviral activity against herpes simplex virus type 1 (HSV-1), varicella-zoster virus (VZV) and cytomegalovirus (CMV). The mechanism of antiviral action of B-220 against HSV-1 has been studied; from the results it appears that B-220 binds by intercalation into the DNA helix and then disturbs steps that are vital for viral uncoating.