Targeting the terminase: An important step forward in the treatment and prophylaxis of human cytomegalovirus infections

A key step in the replication of human cytomegalovirus (HCMV) in the host cell is the generation and packaging of unit-length genomes into preformed capsids. Enzymes required for this process are so-called terminases, first described for double-stranded DNA bacteriophages. The HCMV terminase consists of the two subunits, the ATPase pUL56 and the nuclease pUL89, and a potential third component pUL51. The terminase subunits are essential for virus replication and are highly conserved throughout the Herpesviridae family. Together with the portal protein pUL104 they form a powerful biological nanomotor. It has been shown for tailed dsDNA bacteriophages that DNA translocation into preformed capsid needs an extraordinary amount of energy. The HCMV terminase subunit pUL56 provides the required ATP hydrolyzing activity. The necessary nuclease activity to cleave the concatemers into unit-length genomes is mediated by the terminase subunit pUL89. Whether this cleavage is mediated by site-specific duplex nicking has not been demonstrated, however, it is required for packaging. Binding to the portal is a prerequisite for DNA translocation. To date, it is a common view that during translocation the terminase moves along some domains of the DNA by a binding and release mechanism. These critical structures have proven to be outstanding targets for drugs to treat HCMV infections because corresponding structures do not exist in mammalian cells. Herein we examine the HCMV terminase as a target for drugs and review several inhibitors discovered by both lead-directed medicinal chemistry and by target-specific design. In addition to producing clinically active compounds the research also has furthered the understanding of the role and function of the terminase itself.

(Z)- and (E)-2-(Hydroxymethylcyclopropylidene)-Methylpurines and Pyrimidines as Antiviral Agents

Several Z- and E-methylenecyclopropane nucleoside analogues were synthesized and evaluated for antiviral activity. Reaction of the Z- and E-2-amino-6-chloropurine methylenecyclopropanes with ammonia or cyclopropylamine gave 2,6-diamino or 2-amino-6-cyclopropylamino analogues. Alkylation elimination of N4-acetylcytosine with ethyl Z- and E-2-bromo-2-bromomethylcyclopropane-1-carboxylates gave a mixture of the Z-and E-methylenecyclopropane derivatives of cytosine. Reduction furnished a mixture of syncytol and the E isomer. Benzoylation led to the respective N4-benzoyl derivatives which were separated by chromatography. Debenzoylation afforded pure syncytol and the E isomer. Alkylation of 2,4-bis-O-trimethylsilylthymine with ethyl Z- and E-2-bromo-2-bromomethylcyclopropane-1-carboxylates gave the corresponding Z- and E-1-bromo-cyclopropylmethylderivatives of thymine. Base-catalysed elimination of HBr gave Z- and E-methylenecyclopropane carboxylic esters. Reduction furnished, after chromatographic separation, synthymol and the E isomer. The Z/E isomeric assignment of the obtained products followed from 1H NMR spectroscopy. The methylenecyclopropane analogues were tested for antiviral activity in vitro against human and murine cytomegalovirus (HCMV, MCMV), Epstein–Barr virus (EBV), varicella zoster virus (VZV), hepatitis B virus (HBV), herpes simplex virus types 1 and 2 (HSV-1, HSV-2), human herpesvirus 6 (HHV-6) and human immunodeficiency virus type 1 (HIV-1). The Z-2-amino-6-cyclopropylaminopurine analogue was the most effective agent against HCMV (EC50 or EC90 0.4–2 μM) followed by syncytol and the Z-2,6-diaminopurine analogues (EC50 or EC90 3.4–29 and 11–24 μM, respectively). The latter compound was also a strong inhibitor of MCMV (EC50 0.6 μM). Syncytol was the most potent against EBV (EC50 <0.41 and 2.5 μM) followed by the Z-2,6-diaminopurine (EC50 1.5 and 6.9 μM) and the Z-2-amino-6-cyclopropylaminopurine derivative (EC50 11.8 μM). Syncytol was also most effective against VZV (EC50 3.6 μM). Activity against HSV-1, HSV-2 and HHV-6 was generally lower; synthymol had an EC50 of 2 μM against HSV-1 (ELISA) and 1.3 μM against EBV in Daudi cells but was inactive in other assays. The 2-amino-6-cyclopropylamino analogue displayed EC50 values between 215 and >74 μM in HSV-1 and HSV-2 assays. 2-Amino-6-cyclopropylaminopurine and 2,6-diaminopurine derivatives were effective against HBV (EC50 2 and 10 μM, respectively), whereas none of the analogues inhibited HIV-1 at a higher virus load. Syncytol and the E isomer were equipotent against EBV in Daudi cells but the E isomer was much less effective in DNA hybridization assays. The E-2,6-diaminopurine analogue and E isomer of synthymol were devoid of antiviral activity.

Synthesis and antiviral activity of 6-deoxycyclopropavir, a new prodrug of cyclopropavir

Synthesis of 6-deoxycyclopropavir (10), a prodrug of cyclopropavir (1) and its in vitro and in vivo antiviral activity is described. 2-Amino-6-chloropurine methylenecyclopropane 13 was transformed to its 6-iodo derivative 14 which was reduced to prodrug 10. It is converted to cyclopropavir (1) by the action of xanthine oxidase and this reaction can also occur in vivo. Compound 10 lacked significant in vitro activity against human cytomegalovirus (HCMV), human herpes virus 1 and 2 (HSV-1 and HSV-2), human immunodeficiency virus type 1 (HIV-1), human hepatitis B virus (HBV), Epstein-Barr virus (EBV), vaccinia virus and cowpox virus. In contrast, prodrug 10 given orally was as active as cyclopropavir (1) reported previously [Kern, E. R.; Bidanset, D. J.; Hartline, C. B.; Yan, Z.; Zemlicka, J.; Quenelle, D. C. et al. Antimicrob. Agents Chemother. 2004, 48, 4745] against murine cytomegalovirus (MCMV) infection in mice and against HCMV in severe combined immunodeficient (SCID) mice.

Tyrosine-based 1-(S)-[3-hydroxy-2-(phosphonomethoxy)propyl]cytosine and -adenine ((S)-HPMPC and (S)-HPMPA) prodrugs: synthesis, stability, antiviral activity, and in vivo transport studies

Eight novel single amino acid (6-11) and dipeptide (12, 13) tyrosine P-O esters of cyclic cidofovir ((S)-cHPMPC, 4) and its cyclic adenine analogue ((S)-cHPMPA, 3) were synthesized and evaluated as prodrugs. In vitro IC(50) values for the prodrugs (<0.1-50 μM) vs vaccinia, cowpox, human cytomegalovirus, and herpes simplex type 1 virus were compared to those for the parent drugs ((S)-HPMPC, 2; (S)-HPMPA, 1; IC(50) 0.3-35 μM); there was no cytoxicity with KB or HFF cells at ≤100 μM. The prodrugs exhibited a wide range of half-lives in rat intestinal homogenate at pH 6.5 (<30-1732 min) with differences of 3-10× between phostonate diastereomers. The tyrosine alkylamide derivatives of 3 and 4 were the most stable. (l)-Tyr-NH-i-Bu cHPMPA (11) was converted in rat or mouse plasma solely to two active metabolites and had significantly enhanced oral bioavailability vs parent drug 1 in a mouse model (39% vs <5%).

Phosphorylation of antiviral and endogenous nucleotides to di- and triphosphates by guanosine monophosphate kinase

Many fraudulent nucleosides including the antivirals acyclovir (ACV) and ganciclovir (GCV) must be metabolized to triphosphates to be active. Cyclopropavir (CPV) is a newer, related guanosine nucleoside analog that is active against human cytomegalovirus (HCMV) in vitro and in vivo. We have previously demonstrated that CPV is phosphorylated to its monophosphate (CPV-MP) by the HCMV pUL97 kinase. Consequently, like other nucleoside analogs phosphorylated by viral kinases, CPV most likely must be converted to a triphosphate (CPV-TP) in order to elicit antiviral activity. Once formed by pUL97, we hypothesized that guanosine monophosphate kinase (GMPK) is the enzyme responsible for the conversion of CPV-MP to CPV-DP. Incubation of CPV-MP with GMPK resulted in the formation of CPV-DP and, surprisingly, CPV-TP. When CPV-DP was incubated with GMPK, a time-dependent increase in CPV-TP occurred corresponding to a decrease in CPV-DP thereby demonstrating that CPV-DP is a substrate for GMPK. Substrate specificity experiments revealed that GMP, dGMP, GDP, and dGDP are substrates for GMPK. In contrast, GMPK recognized only acyclovir and ganciclovir monophosphates as substrates, not their diphosphates. Kinetic studies demonstrated that CPV-DP has a K(M) value of 45±15μM. We were, however, unable to determine the K(M) value for CPV-MP directly, but a mathematical model of experimental data gave a theoretical K(M) value for CPV-MP of 332±60μM. We conclude that unlike many other antivirals, cyclopropavir can be converted to its active triphosphate by a single cellular enzyme once the monophosphate is formed by a virally encoded kinase.

Synthesis and enantioselectivity of cyclopropavir phosphates for cellular GMP kinase

Enantiomeric cyclopropavir phosphates (+)-9 and (-)-9 were synthesized and investigated as substrates for GMP kinase. N(2)-Isobutyryl-di-O-acetylcyclopropavir (11) was converted to (+)-monoacetate 12 using hydrolysis catalyzed by porcine liver esterase. Phosphorylation via phosphite 13 gave after deacylation, phosphate (+)-9. Acid-catalyzed tetrahydropyranylation of (+)-monoacetate 12 gave, after deacylation, tetrahydropyranyl derivative 14. Phosphorylation via phosphite 15 furnished, after deprotection, enantiomeric phosphate (-)-9. Racemic diphosphate 16 was also synthesized. The phosphate (+)-9 is a relatively good substrate for GMP kinase with a K(M) value of 57 microM that is similar to that of the natural substrates GMP (61 microM) and dGMP (82 microM). In contrast, the enantiomer (-)-9 is not a good substrate (K(M) 1200 microM) indicating a significant enantioselectivity for the GMP kinase catalyzed reaction of monophosphate to diphosphate.

L-valine ester of cyclopropavir: a new antiviral prodrug

BACKGROUND

Following the example of L-valine prodrugs of antiviral nucleoside analogues, L-valine ester of cyclopropavir (valcyclopropavir) was synthesized.

METHODS

The known tetrahydropyranylcyclopropavir was transformed to N-(tert-butoxycarbonyl)-L-valine ester, which was deprotected to valcyclopropavir.

RESULTS

Stability of valcyclopropavir towards hydrolysis at pH 7.0 roughly corresponded to that of valganciclovir. Valcyclopropavir inhibited replication of human cytomegalovirus (HCMV, Towne and AD169 strains) to approximately the same extent as the parent drug cyclopropavir. Pharmacokinetic studies in mice established that the oral bioavailability of valcyclopropavir was 95%.

CONCLUSIONS

The prodrug valcyclopropavir offers some improved therapeutic parameters over the parent compound cyclopropavir.

(Z)- and (E)-2-(1,2-dihydroxyethyl)methylenecyclopropane analogues of 2'-deoxyadenosine and 2'-deoxyguanosine. Synthesis of all stereoisomers, absolute configuration, and antiviral activity

Chiral Z- and E-stereoisomers of (1,2-dihydroxyethyl)methylenecyclopropane analogues of 2'-deoxyadenosine and 2'-deoxyguanosine were synthesized, and their antiviral activity was investigated. (S)-Methylenecyclopropylcarbinol (16) was converted in seven steps to reagents 26 and 27, which were used for alkylation-elimination of adenine and 2-amino-6-chloropurine to get ultimately analogues 12a, 12b, 13a, 13b, 14a, 14b, 15a, and 15b. The enantiomeric series ent-12a, ent-12b, ent-13a, ent-13b, ent-14a, ent-14b, ent-15a, and ent-15b was obtained by similar procedures starting from (R)-methylenecyclopropylcarbinol (ent-16). The Z-isomer ent-12b was an inhibitor of two strains of human cytomegalovirus (HCMV) with EC(50) of 6.8 and 7.5 microM and of murine cytomegalovirus (MCMV) with EC(50) of 11.3 microM. It was less active against HCMV with mutated gene UL97. It inhibited Epstein-Barr virus (EBV) with EC(50) of 8 microM. The E-isomers ent-15a, ent-13a, and 15b were less effective. All adenine analogues with the exception of the Z-isomers ent-12a and ent-14a were moderate substrates for adenosine deaminase.

Phosphonate analogues of cyclopropavir phosphates and their E-isomers. Synthesis and antiviral activity

Z- and E-Phosphonate analogues 12 and 13 derived from cyclopropavir and the corresponding cyclic phosphonates 14 and 15 were synthesized and their antiviral activity was investigated. The 2,2-bis(hydroxymethylmethylenecyclopropane acetate (17) was transformed to tetrahydropyranyl acetate 18. Deacetylation gave intermediate 19 which was converted to bromide 20. Alkylation with diisopropyl methylphosphonate afforded after protecting group exchange (21 to 22) acetylated phosphonate intermediate 22. Addition of bromine gave the dibromo derivative 16 which was used in the alkylation-elimination procedure with 2-amino-6-chloropurine to give Z- and E-isomers 23 and 24. Hydrolytic dechlorination coupled with removal of all protecting groups gave the guanine phosphonates 12 and 13. Cyclization afforded the cyclic phosphonates 14 and 15. Z-Phosphonate 12 was a potent and non-cytotoxic inhibitor of human and murine cytomegalovirus (HCMV and MCMV) with EC(50) 2.2-2.7 and 0.13 microM, respectively. It was also an effective agent against Epstein-Barr virus (EBV, EC(50) 3.1 microM). The cyclic phosphonate 14 inhibited HCMV (EC(50) 2.4-11.5 microM) and MCMV (EC(50) 0.4 microM) but it was ineffective against EBV. Both phosphonates 12 and 14 were as active against two HCMV Towne strains with mutations in UL97 as they were against wild-type HCMV thereby circumventing resistance due to such mutations. Z-Phosphonate 12 was a moderate inhibitor of replication of herpes simplex virus types 1 and 2 (HSV-1 and HSV-2) but it was a potent agent against varicella zoster virus (VZV, EC(50) 2.9 microM). The cyclic phosphonate 14 lacked significant potency against these viruses. E-isomers 13 and 15 were devoid of antiviral activity.

Design and synthesis of vidarabine prodrugs as antiviral agents

5'-O-D- and L-amino acid derivatives and 5'-O-(D- and L-amino acid methyl ester phosphoramidate) derivatives of vidarabine (ara-A) were synthesized as vidarabine prodrugs. Some compounds were equi- or more potent in vitro than vidarabine against two pox viruses and their uptake by cultured cells was improved compared to the parent drug.

Serine peptide phosphoester prodrugs of cyclic cidofovir: synthesis, transport, and antiviral activity

Cidofovir (HPMPC, 1), a broad-spectrum antiviral agent, is currently used to treat AIDS-related human cytomegalovirus (HCMV) retinitis and has recognized therapeutic potential for orthopox virus infections, but is limited by its low oral bioavailability. Cyclic cidofovir (2) displays decreased nephrotoxicity compared to 1, while also exhibiting potent antiviral activity. Here we describe in detail the synthesis and evaluation as prodrugs of four cHPMPC dipeptide conjugates in which the free POH of 2 is esterified by the Ser side chain alcohol group of an X-L-Ser(OMe) dipeptide: 3 (X=L-Ala), 4 (X=L-Val), 5 (X=L-Leu), and 6 (X=L-Phe). Perfusion studies in the rat establish that the mesenteric permeability to 4 is more than 20-fold greater than to 1, and the bioavailability of 4 is increased 6-fold relative to 1 in an in vivo murine model. In gastrointestinal and liver homogenates, the cHPMPC prodrugs are rapidly hydrolyzed to 2. Prodrugs 3, 4, and 5 are nontoxic at 100 microM in HFF and KB cells and in cell-based plaque reduction assays had IC 50 values of 0.1-0.5 microM for HCMV and 10 microM for two orthopox viruses (vaccinia and cowpox). The enhanced transport properties of 3-6, conferred by incorporation of a biologically benign dipeptide moiety, and the facile cleavage of the Ser-O-P linkage suggest that these prodrugs represent a promising new approach to enhancing the bioavailability of 2.

Design and synthesis of 1-(beta-D-ribofuranosyl)imidazo[4,5-c]pyrazoles as 5:5 bicyclic analogs of purine nucleosides

5-Alkylaminopyrazole nucleosides underwent nitrosation to give the corresponding N1-ribosylated 5-alkyl-amino-4-nitrosopyrazoles. The intramolecular cyclo-dehydration reactions of these 5-alkylamino-4-nitrosopyrazoles were carried out in pyridine at reflux temperature to afford the ring-closure N-1 ribosylated imidazo[4,5-c]pyrazoles in good yields.

Fluorinated methylenecyclopropane analogues of nucleosides. Synthesis and antiviral activity of (Z)- and (E)-9-{[(2-fluoromethyl-2-hydroxymethyl)-cyclopropylidene]methyl}adenine and -guanine

Synthesis and antiviral activity of the title fluoromethylenecyclopropane analogues 15a, 15b, 16a, and 16b is described. Methylenecyclopropane carboxylate was first transformed to 2,2-bis-hydroxymethylmethylenecyclopropane. Selective monoacetylation followed by introduction of fluorine gave 2-acetoxymethyl-2-fluoromethylmethylenecyclopropane as the key intermediate. The synthesis of analogues 15a, 15b, 16a, and 16b then followed alkylation-elimination procedure as described previously for other methylenecyclopropane analogues [corrected] Compounds 15a, 15b, 16a and 16b were not active against Epstein-Barr virus (EBV) [corrected] Analogue 15a inhibited hepatitis C virus by virtue of its cytotoxicity and it moderately inhibited replication of the Towne strain of human cytomegalovirus (HCMV). The E-isomer 16a was a substrate for adenosine deaminase, whereas the Z-isomer 15a was not deaminated.

Identification of acetylated, tetrahalogenated benzimidazole D-ribonucleosides with enhanced activity against human cytomegalovirus

DNA packaging is the key step in viral maturation and involves binding and cleavage of viral DNA containing specific DNA-packaging motifs. This process is mediated by a group of specific enzymes called terminases. We previously demonstrated that the human cytomegalovirus (HCMV) terminase is composed of the large subunit pUL56 and the small subunit pUL89. While the large subunit mediates sequence-specific DNA binding and ATP hydrolysis, pUL89 is required only for duplex nicking. An excellent inhibitor targeting HCMV terminase is 2-bromo-5,6-dichloro-1-(beta-d-ribofuranosyl)benzimidazole (BDCRB), but it was not developed as an antiviral drug due to its metabolic cleavage in experimental animals. We now have tested several new benzimidazole d-ribonucleosides in order to determine whether these compounds represent new, potent inhibitors. Analysis by bioluminometric ATPase activity assays identified two of the new compounds with a high inhibitory effect, 2-bromo-4,5,6-trichloro-1-(2,3,5-tri-O-acetyl-beta-D-ribofuranosyl) benzimidazole (BTCRB) and 2,4,5,6-tetrachloro-1-(2,3,5-tri-O-acetyl-beta-D-ribofuranosyl benzimidazole (Cl(4)RB). By using viral plaque formation, viral yield, and viral growth kinetics, we demonstrated that the two compounds BTCRB and Cl(4)RB had antiviral activities similar to that of BDCRB. Interestingly, BTCRB retained its inhibitory activity after preincubation with HFF cells. By use of electron microscopy, we observed an increase of B capsids and a lack of cytoplasmic capsids in the presence of the compounds that correlated with the virus yield. Furthermore, cleavage of concatenated DNA was inhibited by both compounds, and inhibition by BTCRB was shown to be dose dependent. These results demonstrate that the new compounds are highly active against HCMV and act by mechanisms similar but not identical to those of BDCRB.

Fluoroanalogues of anti-cytomegalovirus agent cyclopropavir: synthesis and antiviral activity of (E)- and (Z)-9-{[2,2-bis(hydroxymethyl)-3-fluorocyclopropylidene]methyl}-adenines and guanines

Synthesis of fluorinated cyclopropavir analogues 13a, 13b, 14a, and 14b is described starting from alkene 15. Addition of carbene derived from dibromofluoromethane gave bromofluoro cyclopropane 16. Reduction (compound 17) followed by desilylation gave intermediate 18, which was transformed to 2-nitrophenylselenenyl derivative 19. Oxidation to selenoxide 20 was followed by beta-elimination to afford methylenecyclopropane 21. Addition of bromine provided compound 22 for alkylation-elimination of adenine and 2-amino-6-chloropurine. The resultant E,Z isomeric mixtures of methylenecyclopropanes 23a + 24a and 23c + 24c were resolved and the individual isomers were deprotected to give adenine analogues 13a and 14a as well as compounds 13c and 14c. Hydrolytic dechlorination of 13c and 14c furnished guanine analogues 13b and 14b. The only significant antiviral effects were observed with analogue 13a against HCMV and 14a against VZV in cytopathic inhibition assays.

Synthesis and biological activation of an ethylene glycol-linked amino acid conjugate of cyclic cidofovir

Cidofovir (HPMPC) is a broad-spectrum anti-viral agent whose potential, particularly in biodefense scenarios, is limited by its low oral bioavailability. Two prodrugs (3 and 4) created by conjugating ethylene glycol-linked amino acids (L-Val, L-Phe) with the cyclic form of cidofovir (cHPMPC) via a P-O ester bond were synthesized and their pH-dependent stability (3 and 4), potential for in vivo reconversion to drug (3), and oral bioavailability (3) were evaluated. The prodrugs were stable in buffer between pH 3 and 5, but underwent rapid hydrolysis in liver (t(1/2) = 3.7 min), intestinal (t(1/2) = 12.5 min), and Caco-2 cell homogenates (t(1/2) = 20.2 min). In vivo (rat), prodrug 3 was >90% reconverted to cHPMPC. The prodrug was 4x more active than ganciclovir (IC50 value, 0.68 microM vs 3.0 microM) in a HCMV plaque reduction assay. However, its oral bioavailability in a rat model was similar to the parent drug. The contrast between the promising activation properties and unenhanced transport of the prodrug is briefly discussed.

9-{[3-fluoro-2-(hydroxymethyl)cyclopropylidene]methyl}adenines and -guanines. Synthesis and antiviral activity of all stereoisomers1

All stereoisomers of adenine and guanine methylene-3-fluoromethylenecyclopropane analogues of nucleosides 9a, 9b, 10a, 10b, 11a, 11b, 12a, and 12b were synthesized and their antiviral activities were evaluated. A highly convergent approach permitted the synthesis of all these analogues using a single intermediate 15. Reaction of aldehyde 13 with fluorotrichloromethane and tri-n-butylphosphine gave fluoroalkenes 14a+14b (83:17). Addition of carbene derived from ethyl diazoacetate gave cyclopropane 15 as the major product. Reduction (19), bromination (20), and phenylselenenylation (21), followed by Se oxidation and beta-elimination gave cis-methylenecyclopropane 22. Addition of bromine provided the reagent 23 for alkylation-elimination. Reaction of 23 with adenine led to an isomeric mixture 25a+26a that after deprotection afforded analogues 9a and 10a. The 2-amino-6-chloropurine furnished 25e+26e and after deblocking (9e and 10e) and hydrolysis gave targets 9b and 10b. Intermediate 15 provided, after debenzylation (27), 2-nitrophenylselenenylation (28), reduction (29), benzylation (30), and oxidation-elimination trans-methylenecyclopropane 31. Addition of bromine gave reagent 32. Further transformations followed the sequence outlined for analogues 9a, 9b, 10a, and 10b. Analogue 9b was effective against human cytomegalovirus (HCMV; Towne) with EC50 2.9 microM. The trans-isomer 10b inhibited AD169 strain of HCMV (EC50 15 microM) and the murine virus MCMV (EC50 2.5 microM). Compound 12a was effective against Epstein-Barr virus (EC50<0.03 microM). Analogue 9a inhibited varicella zoster virus (EC50 5.9 microM) and human immunodeficiency virus type 1 (EC50 5.2 microM). Analogues 9a, 10a, and 11a are moderate substrates for adenosine deaminase. The structure-activity relationships will be discussed in context with other methylenecyclopropane analogues.

Vanadium Complex of 2-(2‘-Pyridyl)-4,5-dicyanoimidazole Showing Spermicidal and Cytotoxic Properties

Two complexes having the formulas VO(DCIPy)2(H2O).1.5H2O and VO(DCIPy)2(H2O).2MeOH have been synthesized and characterized (DCIPy = 2-(2'-pyridyl)-4,5-dicyanoimidazolato). The methanol solvated species has been studied by X-ray diffraction, and single crystals form in the space group P2(1)/n. The hydrated species was studied by electron paramagnetic resonance spectroscopy in both the solid state and in a frozen solution, and the values of A( parallel) examined using the additivity relationship. The hydrated species was shown to exhibit both spermicidal and cytoxic properties.

Human cytomegalovirus UL27 is not required for viral replication in human tissue implanted in SCID mice

Inhibition of the human cytomegalovirus UL97 kinase by maribavir is thought to be responsible for the antiviral activity of this compound. Some mutations that confer resistance to maribavir map to UL97, however additional mutations that also confer resistance to the drug were mapped to UL27. These open reading frames share a low level of homology, yet the function of pUL27 remains unknown. A recombinant virus with a deletion in the UL27 open reading frame was reported previously to exhibit a slight replication deficit, but a more important function in vivo was hypothesized given its homology to the UL97 kinase. The potential for an important function in vivo was investigated by determining if these knockout viruses could replicate in human tissue implanted in SCID mice. None of the AD169 derived viruses replicated well in the implanted thymus/liver tissue, and is consistent with previous observations, although all of the viruses replicated to some degree in retinal tissue implants. Replication of the parent viruses was observed at 7 days post inoculation, whereas no replication was detected with any of the recombinant viruses with deletions in UL27. By day 14, replication was detected in two of the three knockout viruses and in all of the viruses by day 42. These data are consistent with minimal defects observed in cell culture, but are not consistent with an important role for UL27 in vivo. We conclude that UL27 is not required for viral replication in vivo.

Synthesis and antiviral activity of some 2-substituted 3-formyl- and 3-cyano-5,6-dichloroindole nucleosides

A series of dichlorinated indole nucleosides has been synthesized and tested for activity against human cytomegalovirus (HCMV) and herpes simplex virus type-1 (HSV-1) and for cytotoxicity. The isopropylidene-protected analogs of the previously reported 3-formyl-2,5,6-trichloro-1-(beta-Dribofuranosyl)indole (FTCRI) and 3-cyano-2,5, 6-trichloro-1-(beta-D-ribofuranosyl)indole (CTCRI) were modified by nucleophilic displacement of the 2-chloro substituent using secondary amines. Deprotection of the intermediates provided 2-substituted analogs of FTCRI and CTCRI in good yield. There was a significant difference in reactivity between the isopropylidene-protected and the fully deprotected FTCRI and CTCRI with respect to nucleophilic displacement of the 2-chloro substituent using dialkylamines. This difference in reactivity was not observed with monoalkylamines or with alkoxides, and the corresponding 2-alkylamino- and 2-methoxy substituted analogs were synthesized from FITCRI and CTCRI directly. None of the synthesized analogs demonstrated potent antiviral activity without some corresponding cytotoxicity.

Synthesis of 3-aminoimidazo[4,5-c]pyrazole nucleoside via the N-N bond formation strategy as a [5:5] fused analog of adenosine

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

Design, synthesis, and antiviral evaluation of some polyhalogenated indole C-nucleosides

2,5, 6-Trichloro-1-(beta-D-ribofuranosyl)benzimidazole (TCRB), 2-bromo-5, 6-dichloro-1-(beta-D-ribofuranosyl)benzimidazole (BDCRB) and 2-benzylthio-5,6-dichloro-1-(beta-D-ribofuranosyl)benzimidazole (BTDCRB) are benzimidazole nucleosides that exhibit strong and selective anti-HCMV activity. Polyhalogenated indole C-nucleosides were prepared as 1-deaza analogs of the benzimidazole nucleosides TCRB and BDCRB. A mild Knoevenagel coupling reaction between an indol-2-thione and a ribofuranose derivative was developed for the synthesis of 2-benzylthio-5, 6-dichloro-3-(beta-D-ribofuranosyl)indole (12). 3-(beta-D-ribofuranosyl)-2,5,6-trichloroindole (16) was prepared from 12 in 4 steps. A Lewis acid-mediated glycosylation method was then developed to prepare the targeted 2-haloindole C-nucleoside 16 stereoselectively in four steps from the corresponding 2-haloindole aglycons. Only 12 was active against HCMV but it also was somewhat cytotoxic.

N-methylpurine DNA glycosylase and 8-oxoguanine dna glycosylase metabolize the antiviral nucleoside 2-bromo-5,6-dichloro-1-(beta-D-ribofuranosyl)benzimidazole

The rapid in vivo degradation of the potent human cytomegalovirus inhibitor 2-bromo-5,6-dichloro-1-(beta-D-ribofuranosyl)benzimidazole (BDCRB) compared with a structural L-analog, maribavir (5,6-dichloro-2-(isopropylamino)-1-beta-L-ribofuranosyl-1H-benzimidazole), has been attributed to selective glycosidic bond cleavage. An enzyme responsible for this selective BDCRB degradation, however, has not been identified. Here, we report the identification of two enzymes, 8-oxoguanine DNA glycosylase (OGG1) and N-methylpurine DNA glycosylase (MPG), that catalyze N-glycosidic bond cleavage of BDCRB and its 2-chloro homolog, 2,5,6-trichloro-1-(beta-D-ribofuranosyl)benzimidazole, but not maribavir. To our knowledge, this is the first demonstration that free nucleosides are substrates of OGG1 and MPG. To understand how these enzymes might process BDCRB, docking and molecular dynamics simulations were performed with the native human OGG1 crystal coordinates. These studies showed that OGG1 was not able to bind a negative control, guanosine, yet BDCRB and maribavir were stabilized through interactions with various binding site residues, including Phe319, His270, Ser320, and Asn149. Only BDCRB, however, achieved orientations whereby its anomeric carbon, C1', could undergo nucleophilic attack by the putative catalytic residue, Lys249. Thus, in silico observations were in perfect agreement with experimental observations. These findings implicate DNA glycosylases in drug metabolism.

Phosphoralaninate pronucleotides of pyrimidine methylenecyclopropane analogues of nucleosides: synthesis and antiviral activity

The Z- and E-thymine and cytosine pronucleotides 3d, 4d, 3e, and 4e of methylenecyclopropane nucleosides analogues were synthesized, evaluated for their antiviral activity against human cytomegalovirus (HCMV), herpes simplex virus 1 and 2 (HSV-1 and HSV-2), varicella zoster virus (VZV), Epstein-Barr virus (EBV), human immunodeficiency virus type 1 (HSV-1), and hepatitis B virus (HBV) and their potency was compared with the parent compounds 1d, 2d, 1e, and 2e. Prodrugs 3d and 4d were obtained by phosphorylation of parent analogues 1d or 2d with reagent 8. A similar phosphorylation of N4-benzoylcytosine methylenecyclopropanes 9a and 9b gave intermediates 11a and 11b. Deprotection with hydrazine in pyridine-acetic acid gave pronucleotides 3e and 4e. The Z-cytosine analogue 3e was active against HCMV and EBV The cytosine E-isomer 4e was moderately effective against EBV.

Interaction of the putative human cytomegalovirus portal protein pUL104 with the large terminase subunit pUL56 and its inhibition by benzimidazole-D-ribonucleosides

Herpesvirus DNA replication leads to unit length genomes that are translocated into preformed procapsids through a unique portal vertex. The translocation is performed by the terminase that cleaves the DNA and powers the insertion by its ATPase activity. Recently, we demonstrated that the putative human cytomegalovirus (HCMV) portal protein, pUL104, also forms high-molecular-weight complexes. Analyses now have been performed to determine the intracellular localization and identification of interaction partners of pUL104. In infected cells, HCMV pUL104 was found to be predominantly localized throughout the nucleus as well as in cytoplasmic clusters at late times of infection. The latter localization was abolished by phosphonoacetic acid, an inhibitor of viral DNA replication. Immunofluorescence revealed that pUL104 colocalized with pUL56, the large subunit of the HCMV terminase. Specific association of in vitro translated pUL104 with the carboxy-terminal half of GST-UL56C was detected. By using coimmunoprecipitations a direct interaction with pUL56 was confirmed. In addition, this interaction was no longer detected when the benzimidazole-D-nucleosides BDCRB or Cl4RB were added, thus indicating that these HCMV inhibitors block the insertion of the DNA into the capsid by preventing a necessary interaction of pUL56 with the portal. Electron microscopy revealed that in the presence of Cl4RB DNA is not packaged into capsids and these capsids failed to egress from the nucleus. Furthermore, pulsed-field gel electrophoresis showed that DNA concatemers synthesized in the presence of the compound failed to be processed.

Synthesis, antiviral, and antitumor activity of 2-substituted purine methylenecyclopropane analogues of nucleosides

The Z- and E-2-fluoro- and 2-chloropurine methylenecyclopropanes 9a,b and 10a,b as well as enantiomeric Z-isoguanine methylenecyclopropanes 11a,b and their phenyl phosphoralaninate pronucleotides 11c,d were synthesized and their antiviral activity against several viruses was evaluated. Fluoro analogues 9a and 10a were active against human cytomegalovirus but they were cytotoxic at approximately the same concentrations. Chloro derivatives 9b and 10b were non-cytotoxic and effective against Epstein-Barr virus in Daudi cells. Isoguanine analogues 11a-d lacked antiviral activity but pronucleotides 11c,d were substrates for porcine liver esterase. From the group of 9a,b and 10a,b, the fluoro analogues 9a and 10a exhibited antitumor activity but only the Z-isomer 9a had a selective effect.

Amino acid ester prodrugs of 2-bromo-5,6-dichloro-1-(beta-D-ribofuranosyl)benzimidazole enhance metabolic stability in vitro and in vivo

2-Bromo-5,6-dichloro-1-(beta-d-ribofuranosyl)benzimidazole (BDCRB) is a potent and selective inhibitor of human cytomegalovirus (HCMV), but it lacks clinical utility due to rapid in vivo metabolism. We hypothesized that amino acid ester prodrugs of BDCRB may enhance both in vitro potency and systemic exposure of BDCRB through evasion of BDCRB-metabolizing enzymes. To this end, eight different amino acid prodrugs of BDCRB were tested for N-glycosidic bond stability, ester bond stability, Caco-2 cell uptake, antiviral activity, and cytotoxicity. The prodrugs were resistant to metabolism by BDCRB-metabolizing enzymes, and ester bond cleavage was rate-limiting in metabolite formation from prodrug. Thus, BDCRB metabolism could be controlled by the selection of promoiety. In HCMV plaque-formation assays, l-Asp-BDCRB exhibited 3-fold greater selectivity than BDCRB for inhibition of HCMV replication. This potent and selective antiviral activity in addition to favorable stability profile made l-Asp-BDCRB an excellent candidate for in vivo assessment and pharmacokinetic comparison with BDCRB. In addition to rapid absorption and sufficient prodrug activation after oral administration to mice, l-Asp-BDCRB exhibited a 5-fold greater half-life than BDCRB. Furthermore, the sum of area under the concentration-time profile (AUC)(BDCRB) and AUC(prodrug) after l-Asp-BDCRB administration was roughly 3-fold greater than AUC(BDCRB) after BDCRB administration, suggesting that a reservoir of prodrug was delivered in addition to parent drug. Overall, these findings demonstrate that amino acid prodrugs of BDCRB exhibit evasion of metabolizing enzymes (i.e., bioevasion) in vitro and provide a modular approach for translating this in vitro stability into enhanced in vivo delivery of BDCRB.

Design, Synthesis and Antiviral Activity of Novel 4,5-Disubstituted 7-(β-d-Ribofuranosyl)pyrrolo[2,3-d][1,2,3]triazines and the Novel 3-Amino-5-methyl-1-(β-d-ribofuranosyl)- and 3-Amino-5-methyl-1-(2-deoxy-β-d-ribofuranosyl)-1,5-dihydro-1,4,5,6,7,8-hexaazaacenaphthylene as Analogues of Triciribine

The synthesis of several heterocyclic analogues of the biologically important nucleoside antibiotic toyocamycin and the tricyclic nucleoside triciribine (TCN) were prepared along with their 2'-deoxy counterparts. Coupling of 2-nitropyrrole-3,4-dicarboxamide (15) under a variety of conditions with alpha-chloro-2-deoxy-3,4-di-O-toluoyl-D-ribofuranose (16a) gave mixtures of the alpha and beta anomers. A coupling of 15 with 1-chloro-2,3,5-tri-O-benzoyl-D-ribofuranose (18) gave exclusively the beta anomer. Individually, the two pyrrole nucleosides were treated with Pd/C, H2 to reduce the nitro groups and cyclized with nitrous acid, and the corresponding 4-position was functionalized as a triazoyl derivative. Nucleophillic displacement was carried out with ammonia to give a mixture of 4-amino-1-(2,3,5-tri-O-benzoyl-beta-D-ribofuranosyl)pyrrolo[2,3-d][1,2,3]triazine-5-carbonitrile (26) and 2-amino-1-(2,3,5-tri-O-benzoyl-beta-D-ribofuranosyl)pyrrole-3,4-dicarbonitrile (27), the latter being formed via a retro-Diels-Alder reaction. The subsequent addition of hydrogen sulfide, water, methanol, hydroxylamine, cyanamide, hydrazine and methylhydrazine to the 5-cyano group was carried out to give the corresponding analogues. In the case of methyl hydrazine, subsequent treatment with NaOMe in methanol gave the title hexaazaacenaphthylenes. Biological evaluation of the compounds established that the pyrrole (17beta, 19-21) and most of the pyrrolotriazine (22, 24, 28, 32-34) nucleosides were inactive or weakly active against human cytomegalovirus (HCMV) and herpes simplex virus type 1 (HSV-1). In contrast 29 and 31 were active against one or both of these viruses but activity was poorly separated from cytotoxicity. In contrast, the 2-aza analogue of sangivamycin (30) was active against HCMV and HSV-1 but this apparent activity was most likely due to its high cytotoxicity. The tricyclic nucleoside 12, was active against its target virus, human immunodeficiency virus type 1 (HIV-1), but this activity was not well separated from cytotoxicity.

Amino acid ester prodrugs of the antiviral agent 2-bromo-5,6-dichloro-1-(beta-D-ribofuranosyl)benzimidazole as potential substrates of hPEPT1 transporter

Amino acid ester prodrugs of 2-bromo-5,6-dichloro-1-(beta-d-ribofuranosyl)benzimidazole (BDCRB) were synthesized and evaluated for their affinity for hPEPT1, an intestinal oligopeptide transporter. Assays of competitive inhibition of [(3)H]glycylsarcosine (Gly-Sar) uptake in HeLa/hPEPT1 cells by the amino acid ester prodrugs of BDCRB suggested their 2- to 4-fold higher affinity for hPEPT1 compared to BDCRB. Further, promoieties with hydrophobic side chains and l-configuration were preferred by the hPEPT1 transporter.

Nucleotides and pronucleotides of 2,2-bis(hydroxymethyl)methylenecyclopropane analogues of purine nucleosides: synthesis and antiviral activity

Phenylmethylphosphor-L-alaninate pronucleotides 7a, 7b, 8a, and 8b, cyclic phosphates 10a and 10b, and phosphates 11a and 11b derived from 2,2-bis(hydroxymethyl)methylenecyclopropane analogues 1a, 1b, 2a, and 2b were synthesized and evaluated for their antiviral activity. An improved protocol for the synthesis of analogues 1a, 1b, 2a, and 2b is also described. Phosphate 11a was the most effective agent against human and murine cytomegalovirus (EC(50) 0.25-1.1 microM). The Z-pronucleotides 7a and 7b had EC(50) 3.6-25.2 and 3-18.4 microM, respectively. The EC(50) of cyclic phosphate 10a was 6.0-20 microM. The activity against Epstein-Barr (EBV) was assay-dependent. Pronucleotides 7a and 7b and phosphate 11a had EC(50) 2.3-3.4 microM against EBV/H-1, but 7b was cytotoxic (CC(50) 3.8 microM). Cyclic phosphate 10a was the only compound effective against EBV/Daudi (EC(50) 0.96 microM), but it was inactive in H-1 cells. Pronucleotide 7a was active against varicella zoster virus with EC(50) 6.3 and 7.3 microM, respectively, and hepatitis B virus (HBV, EC(50) 4.1 microM). Cyclic phosphate 10a was the most effective analogue against HBV (EC(50) 0.8 microM).

(Z)- and (E)-[2-Fluoro-2-(hydroxymethyl)cyclopropylidene]methylpurines and -pyrimidines, a new class of methylenecyclopropane analogues of nucleosides: synthesis and antiviral activity

The Z- and E-isomers of fluoromethylenecyclopropane analogues 11a-d and 12a-d were synthesized, and their antiviral activities were evaluated. The purine (Z,E)-methylenecyclopropane carboxylates 13 and 24 were selectively fluorinated using lithium diisopropylamide, LiCl, and N-fluorobenzenesulfonimide to give (Z,E)-fluoroesters 22 and 25. Reduction with LiBH(4) or diisobutylaluminum hydride gave after chromatographic separation Z-isomers 11a and 11e and E-isomers 12a and 12e. The O-demethylation of 11e and 12e afforded guanine analogues 11b and 12b. Fluorination of (Z,E)-cytosine and thymine esters 15 and 16 afforded (Z,E)-fluoroesters 26 and 27, which were resolved before the reduction to analogues 11c and 11d and 12c and 12d. Adenine Z-isomer 11a was the most effective against Towne and AD169 strains of human cytomegalovirus (HCMV, EC(50) 3.6 and 6.0 microM, respectively), but it was less effective against murine virus (MCMV, EC(50) 69 microM). Thymine Z-isomer 11d was effective against HSV-1 in BSC-1 cells (ELISA, EC(50) 2.5 microM) but inactive against HSV-1 or HSV-2 in Vero or HFF cells. All of the analogues with the exception of 12d were effective at least in one of the assays against Epstein-Barr virus (EBV) in Daudi or H-1 cells in a micromolar or submicromolar range. Cytosine and thymine Z-isomers 11c and 11d were active against varicella zoster virus (VZV) with EC(50) 0.62 microM. Adenine Z- and E-isomers 11a and 12a were effective against HIV-1 in MT-2 or MT-4 cells with EC(50) 12-22 and 2.3-7.6 microM, respectively, whereas only 12a was effective against hepatitis B virus (HBV) with EC(50) 15 microM. Analogues 11a and 12a were weak substrates for adenosine deaminase.

Synthesis and antiviral evaluation of some novel tricyclic pyrazolo[3,4-b]indole nucleosides

Novel pyrazolo[3,4-b]indole nucleoside analogs were synthesized from the corresponding 3-formyl-2-chloroindole and 3-cyano-2-chloroindole nucleosides by treatment with hydrazine. Very few examples of pyrazolo[3,4-b]indole heterocycles have been published in the literature and this is the first synthesis of nucleoside analogs containing this heterocycle. These new pyrazolo[3,4-b]indole nucleosides were active against human cytomegalovirus and herpes simplex virus type 1, but this activity was not well separated from cytotoxicity.

Inhibition of human cytomegalovirus replication by benzimidazole nucleosides involves three distinct mechanisms

The benzimidazole nucleosides 2-bromo-5,6-dichloro-1-(beta-d-ribofuranosyl)benzimidazole (BDCRB) and 2-isopropylamino-5,6-dichloro-1-(beta-l-ribofuranosyl)benzimidazole (1263W94, or maribavir) are potent and selective inhibitors of human cytomegalovirus (HCMV) replication. These inhibitors act by two different mechanisms: BDCRB blocks the processing and maturation of viral DNA, whereas maribavir prevents viral DNA synthesis and capsid nuclear egress. In order to determine by which of these two mechanisms other benzimidazole nucleosides acted, we performed time-of-addition studies and other experiments with selected new analogs. We found that the erythrofuranosyl analog and the alpha-lyxofuranosyl analog acted late in the viral replication cycle, similar to BDCRB. In marked contrast, the alpha-5'-deoxylyxofuranosyl analog of 2,5,6-trichloro-1-(beta-d-ribofuranosyl)benzimidazole (compound UMJD1311) acted early in the replication cycle, too early to be consistent with either mechanism. Similar to other reports on early acting inhibitors of herpesviruses, compound 1311 was multiplicity of infection dependent, an observation that could not be reproduced with UV-inactivated virus. HCMV isolates resistant to BDCRB and maribavir were sensitive to compound 1311, as were viruses resistant to ganciclovir, cidofovir, and foscarnet. The preincubation of host cells with compound 1311 and removal prior to the addition of HCMV did not produce an antiviral cellular response. We conclude that this newly discovered early mode of action occurs at a stage of viral replication after entry to cells but prior to viral DNA synthesis, thereby strongly suggesting that the trisubstituted benzimidazole nucleoside series possesses three distinct biochemical modes of action for inhibition of HCMV replication.

Synthesis and Antiviral Evaluation of Polyhalogenated Imidazole Nucleosides: Dimensional Analogues of 2,5,6-Trichloro-1-(β-d-ribofuranosyl)benzimidazole

A series of polyhalogenated imidazole nucleosides were designed and synthesized as ring-contracted analogues of 2,5,6-trichloro-1-(beta-D-ribofuranosyl)benzimidazole (TCRB) and its 2-bromo analogue (BDCRB) in an effort to explore the spatial limitation of the active pocket(s) in the target protein(s). 2,4,5-Trichloro-, 2-bromo-4,5-dichloro-, and 2,4,5-tribromoimidazole nucleosides were prepared by a condensation of the preformed heterocycles with the appropriate sugar precursors. The ribofuranosyl and xylofuranosyl analogues were prepared by a direct glycosylation using the Vorbruggen's silylation method and provided exclusively the beta-anomers. The arabinofuranosyl analogues were prepared by the sodium salt method to give both the alpha- and beta-anomers. The absolute configurations were established by 1H NMR spectroscopy. Alkylation of the polyhalogenated imidazoles with the appropriate bromomethyl ethers gave the acyclic acyclovir and ganciclovir analogues. In general, the parent polyhalogenated imidazoles showed some activity against human cytomegalovirus (HCMV) (IC50 approximately 35 microM). However, with the exception of two tribromo analogues (7c, 13c-beta), most of their nucleoside derivatives were inactive against both HCMV and herpes simplex virus type-1 (HSV-1) and were not cytotoxic. The results suggest that the ring-contracted nucleoside analogues of TCRB and BDCRB interacted weakly or not at all with viral and cellular targets.

Design, Synthesis, and Antiviral Activity of Certain 3-Substituted 2,5,6-Trichloroindole Nucleosides

A series of trichlorinated indole nucleosides has been synthesized and tested for activity against human cytomegalovirus (HCMV) and herpes simplex virus type-1 (HSV-1) and for cytotoxicity. Modifications of the previously reported 2,5,6-trichloro-1-(beta-d-ribofuranosyl)indole at the 3-position of the heterocycle were designed in part to test our hypothesis that hydrogen bonding is required at that position for antiviral activity. Analogues were synthesized using electrophilic addition at the 3-position or by synthesis of modified indole heterocycles followed by glycosylation and modification of the sugar. Among the modifications at the 3-position, only those analogues with hydrogen-bond-accepting character were active against HCMV (e.g., 3-formyl-2,5,6-trichloro-1-(beta-D-ribofuranosyl)indole, FTCRI, IC50 = 0.23 microM). Conversely, analogues with non-hydrogen-bonding substituents at the 3-position (e.g., 3-methyl-2,5,6-trichloro-1-(beta-D-ribofuranosyl)indole) were much less active (IC50 = 32 microM) than those with the requisite hydrogen-bonding capacity. The 5'-O-acyl analogue of FTCRI was obtained as an intermediate and also found to be a potent inhibitor of HCMV (IC50 < 0.1 microM). The synthesis of some additional 5'-O-acylated analogues did not provide a compound with increased antiviral activity. None of the indole nucleosides had significant activity against HSV-1, and none were cytotoxic to uninfected cells in their antiviral dose range. Results obtained from the antiviral evaluations have validated our hypothesis that hydrogen bonding at the 3-position is required for antiviral activity in this series of chlorinated indole nucleosides.

Synthesis, Antiviral Activity, and Mode of Action of Some 3-Substituted 2,5,6-Trichloroindole 2‘- and 5‘-Deoxyribonucleosides

A series of chlorinated indole nucleosides has been synthesized and tested for activity against human cytomegalovirus (HCMV) and herpes simplex virus type-1 (HSV-1) and for cytotoxicity. The 2'- and 5'-deoxy derivatives of the reported 3-formyl-2,5,6-trichloro-1-(beta-D-ribofuranosyl)indole (FTCRI) and 3-cyano-2,5,6-trichloro-1-(beta-D-ribofuranosyl)indole (CTCRI) were synthesized by either a modification of the appropriate 3-unsubstituted sugar-modified nucleoside analogues or by a glycosylation of 3-substituted heterocycles with a protected alpha-chlorosugar. The modifications were guided in part by structural similarity to the corresponding series of chlorinated benzimidazole ribonucleosides and the fact that 5'-deoxy analogues of 2,5,6-trichloro-1-(beta-D-ribofuranosyl)benzimidazole (TCRB) are very active against HCMV. The 5'-deoxy analogues of FTCRI and CTCRI were nearly as active as FTCRI and CTCRI, suggesting that the chlorinated benzimidazole nucleosides and the chlorinated indole nucleosides act in a similar manner. This hypothesis was supported by time-of-addition studies using FTCRI and by the resistance of TCRB-resistant strains of HCMV to four different 3-substituted indole ribonucleosides. The 2'-deoxy analogues of the trichlorinated indole nucleosides also had potent antiviral activity, in contrast to decreased activity and selectivity observed for 2'-deoxy TCRB compared to TCRB. In addition, 3-acetyl-2,5,6-trichloro-1-(2-deoxy-beta-d-ribofuranosyl)indole was also active and much less cytotoxic (HCMV IC50 = 0.30 microM, HFF CC50 >100 microM) than previous analogues. None of the analogues had significant activity against HSV-1.

Synthesis and Antiviral Activity of 3-Formyl- and 3-Cyano-2,5,6-trichloroindole Nucleoside Derivatives

A series of trichlorinated indole nucleosides has been synthesized and tested for activity against human cytomegalovirus (HCMV) and herpes simplex virus type-1 (HSV-1) and for cytotoxicity. The previously reported 3-formyl-2,5,6-trichloro-1-(beta-D-ribofuranosyl)indole (FTCRI) and its 3-cyano homologue (CTCRI) were chemically modified at the 3-position. The formation of hydrazones and oximes of FTCRI was accomplished by a dehydrative addition of the appropriate hydrazine or hydroxylamine derivatives, respectively. A carboxamide oxime and imidate were synthesized from CTCRI by the addition of hydroxylamine or methanol, respectively, to the 3-nitrile substituent. Analogues synthesized from FTCRI generally had less antiviral activity than either FTCRI or CTCRI. However, the derivatives of CTCRI were potent and selective inhibitors of HCMV in vitro. The analogue 2,5,6-trichloro-1-(beta-D-ribofuranosyl)indole-3-carboxamide oxime was especially selective (HCMV IC50 = 0.30 microM, CC50 > 100 microM). None of the analogues had significant activity against HSV-1.

Rhesus cytomegalovirus is similar to human cytomegalovirus in susceptibility to benzimidazole nucleosides

Rhesus and human cytomegalovirus (RhCMV and HCMV, respectively) exhibit comparable inhibition by benzimidazole nucleosides, including 2,5,6-trichloro-(1-beta-d-ribofuranosyl)benzimidazole (TCRB), and pyrrolo[2,3-d]pyrimidines. The two HCMV protein targets of TCRB, UL89 and UL56, are highly conserved with their RhCMV homologues. These data indicate that infection of rhesus macaques with RhCMV represents a useful model to test novel anti-HCMV drugs.