(Z)- and (E)-2-((hydroxymethyl)cyclopropylidene)methyladenine and -guanine. New nucleoside analogues with a broad-spectrum antiviral activity

Synthesis and antiviral activity of novelc-methyl branched cyclopropyl nucleosides

A series of novel cyclopropyl nucleosides was synthesized using the highly stereoselective Simmons-Smith reaction starting from 1,2:5,6-di-O-isopropylidene-D-mannitol. The structural assignments of these nucleosides were determined by NMR studies and X-ray crystallography. All the synthesized nucleosides were assayed against several viruses.

Inhibition of hepatitis B virus by a novel L-nucleoside, β-L-D4A and related analogues

AIM: To explore the inhibition of β-L-D4A on hepatitis B virus (HBV) in 2.2.15 cells derived from HepG2 cells transfected with HBV genome.

METHODS: 2.2.15 cells were plated at a density of 5 × 10⁴ per well in 12-well tissue culture plates, and treated with various concentrations of β-L-D4A for 6 days. In the end, 5 μl of medium was used for the estimation of HBsAg and HBeAg, the other medium was processed to obtain virions by a polyethlene glycol precipitation method. At the same time, intracellular DNA was also extracted and digested with HindIII. Both DNAs were subjected to Southern blot, hybridized with a ³²P-labeled HBV probe and autoradiographed. Intensity of the autoradiographic bands was quantitated by densitometric scans of computer and ED₅₀ was calculated. Then Hybond-N membrane was washed and rehybridized with a ³²P-labeled mtDNA-specific probe, and effect of β-L-D4A on mitochondrial DNA was studied. 2. 2.15 cells were also seeded in 24-well tissue culture plates, and cytotoxicity with different concentrations was examined by MTT method. ID₅₀ was calculated. Structure-activity relationships between D2A and D4A were also studied as above.

RESULTS: Autoradiographic bands were similar between supernatant and intracellular HBV DNA. Episomal HBV DNA was inhibited in a dose-dependent manner. ED₅₀ was 0.2 μM. HBsAg or HBeAg was not apparently decreased, and inhibition of mitochondrial DNA was not obvious. The experiment of cytotoxicity gained ID₅₀ at 200 μM.

CONCLUSION: β-L-D4A possesses potent inhibitory effects on the replication of HBV in vitro with little cytotoxicity and mitochondrial toxicity, TI value is 1000. It is expected to be developed as a new clinically anti-HBV drug.

Synthesis, structural studies, and biological evaluation of some purine substituted 1-aminocyclopropane-1-carboxylic acids and 1-amino-1-hydroxymethylcyclopropanes

The novel purine derivatives of 1-aminocyclopropane-1-carboxylic acid (8 and 9) and 1-amino-1-hydroxymethylcyclopropane (12 and 13) with methylene spacer between the base and the cyclopropane ring were prepared by multistep synthetic route involving alkylation of adenine and 6-(N-pyrrolyl)purine with 2-hydroxy-methyl-1-aminocyclopropane-1-carboxylic acid derivative 3 as a key reaction. All novel compounds were racemic. The N-9 substitution of the purine ring and the Z-configuration of the cyclopropane ring in 4-13 were deduced from their 1H and 13C NMR spectra by analyses of chemical shifts, H-H coupling constants and connectivities in two-dimensional homo- and heteronuclear correlation spectra. An unequivocal proof of the stereostructure of 1, 4 and 5 was obtained by their X-ray structure analysis. The novel compounds were evaluated on cytostatic and antiviral activities in several cell lines. The 6-(N-pyrrolyl)purine derivative of 1,2-aminocyclopropane alcohol 12 exhibited a more pronounced inhibitory activity against the proliferation of cervical carcinoma (HeLa) and human fibroblast (WI-38) cells than other types of tumor cell lines. None of the compounds showed inhibitory activities against cytomegalovirus, varicella-zoster virus or other viruses.

Synthesis of (Z)-(2,3-bis-hydroxymethyl)methylenecyclopropane analogues of purine nucleosides

Synthesis of (Z)-(2,3-bis-hydroxymethyl)methylenecyclopropane analogues of nucleosides adenosine 10a, 10b, 10c and 17 is described. Epimerization of Feist's acid (11) using acetic anhydride gave cyclic anhydride 12 which was reduced in situ to give diol 13. Acetylation (compound 14) followed by addition of bromine led to dibromo derivative 15. Alkylation-elimination of adenine with 15 afforded, after deacetylation, analogue 10a. Similar treatment of 2-amino-6-chloropurine and 2,6-diaminopurine led to diacetates 16 and 18. Deprotection then gave compounds 17 and 10c. Hydrolysis of 17 furnished guanine analogue 10b. Compounds 10a, 10b or 10c were inactive against HCMV, HSV-1, HSV-2, EBV VZV and HBV. Analogues 10a and 10b were also assayed for anti-HIV activity. Compound 10a was effective in HIV-1/MT-2 culture with EC50/CC50 33/> 100 microM but 10b was inactive. Analogue 10a was not a substrate for adenosine deaminase.

Synthesis and biological activity of 2-aminopurine methylenecyclopropane analogues of nucleosides

Synthesis and biological activity of racemic 2-aminopurine methylenecyclopropane analogues of nucleosides 4, 5, 10 and 11 is described. One-pot alkylation-elimination of 2-aminopurine (6) with dibromide 7 gave a mixture of four isomeric methylenecyclopropanes. The (E, Z)-N9 and (E, Z)-N7 isomers 8 and 9 were resolved by chromatography on silica gel. Deacetylation of 8 afforded the respective (Z)-N9 and (E)-N9 isomers 4 and 10 which were separated by chromatography on silica gel. In a similar fashion, (E, Z)-N7 mixture 9 furnished (Z)-N7 and (E)-N7 isomers 5 and 11. The S-(+)-enantiomer 4 was obtained by desulfurization of (S)-(+)-6-thiosynguanol (13) with Raney Ni. Compound 13 was obtained from (S)-(+)-2-amino-6-chloro derivative 12 and NaSH in methanol. Racemic analogues 4, 5, 10 and 11 were inactive against HCMV, HSV-1, HSV-2, EBV and VZV. Enantiomer (S)-(+)-4 inhibited replication of HSV-1 in BSC-1 cells (ELISA) with EC50 35 microM and it was non-cytotoxic in KB cells (CC50 > 100 microM). Compound (S)-(+)-4 was also moderately effective against VZV in HFF culture with EC50/CC50 (microM) 60/>460 and it was a substrate for xanthine oxidase.

Synthesis and antiviral activity of novel exomethylene cyclopropyl pyrimidine nucleosides

A series of novel exomethylene cyclopropyl nucleosides have been synthesized starting from Feist's acid. Classical nucleophilic substitution conditions (K2CO3, 18-crown-6) of the tosylate 2 as well as Mitsunobu reaction (DEAD, PPh3) of alcohol 1 with pyrimidine bases afforded a series of novel cyclopropyl nucleosides. Compound 4b displayed moderate anti-HBV activity without any cytotoxicity up to 100 microM.

Tryptophanyl phosphoramidates as prodrugs of synadenol and its E-isomer: synthesis and biological activity

Phosphorotryptophanates 2c and 3c were synthesized and investigated as prodrugs of synadenol (2a) and its E-isomer 3a. The antiviral activity of 2c corresponds to parent analogue 2a but it is lower than that of phenylphosphoralaninate 2b. This may indicate an enzymatic cleavage of phosphorotryptophanate 2c to 2a before or after entering the host cells. The E-isomer 3c was effective only against EBV with parameters suggesting intracellular delivery of the respective phosphate. Compound 2c has a moderate but selective activity against solid tumors.

Alkoxyalkyl esters of cidofovir and cyclic cidofovir exhibit multiple-log enhancement of antiviral activity against cytomegalovirus and herpesvirus replication in vitro

The incidence of cytomegalovirus (CMV) retinitis is declining in AIDS patients but remains a significant clinical problem in patients with organ transplants and bone marrow transplants. Prophylaxis with ganciclovir (GCV) or valganciclovir reduces the incidence of CMV disease but may lead to the emergence of drug-resistant virus with mutations in the UL97 or UL54 gene. It would be useful to have other types of oral therapy for CMV disease. We synthesized hexadecyloxypropyl and octadecyloxyethyl derivatives of cyclic cidofovir (cCDV) and cidofovir (CDV) and found that these novel analogs had 2.5- to 4-log increases in antiviral activity against CMV compared to the activities of unmodified CDV and cCDV. Multiple-log increases in activity were noted against laboratory CMV strains and various CMV clinical isolates including GCV-resistant strains with mutations in the UL97 and UL54 genes. Preliminary cell studies suggest that the increase in antiviral activity may be partially explained by a much greater cell penetration of the novel analogs. 1-O-Hexadecyloxypropyl-CDV, 1-O-octadecyloxyethyl-CDV, and their corresponding cCDV analogs are worthy of further preclinical evaluation for treatment and prevention of CMV and herpes simplex virus infections in humans.

Lipophilic phosphoramidates as antiviral pronucleotides

In order to overcome restrictions imposed by activation (phosphorylation) mechanism of antiviral and antitumor nucleoside analogues several prodrug approaches have been designed. Lipophilic pronucleotides are capable of intracellular delivery of monophosphates of nucleoside analogues, thus circumventing the limitations of enzymic phosphorylation. One of the successful approaches employs lipophilic amino acid ester (alanine) phenyl phosphoramidates as pronucleotides. This approach was applied to AIDS drugs such as AZT, d4T and related analogues but also to nonclassical nucleoside analogues based on allenic and methylenecyclopropane structure. Antiviral effects of the parent analogues were in many cases increased by conversion to phenyl phosphoralaninate (PPA) pronucleotides. Although cytotoxicity increase frequently accompanies antiviral effects of these pronucleotides, a favorable selectivity index can be obtained by manipulation of the parent structure as shown, e.g., for 2,6-diaminopurine methylenecyclopropane pronucleotide 15c. A lack of in vivo toxicity was demonstrated for 2-amino-6-methoxypurine methylenecyclopropane pronucleotide 15e in mice. The PPA pronucleotides can overcome deficiency of phosphorylating enzymes and offer favorable cross-resistance patterns when compared with other antiviral drugs.

Synthesis of methylenecyclobutane analogues of nucleosides with axial chirality and their phosphoralaninates: a new pronucleotide effective against Epstein-Barr virus

Methylenecyclobutane analogues of 2'-deoxyadenosine, 2'-deoxyguanosine and 2'-deoxycytidine, and the corresponding phosphoralaninate pronucleotides comprising adenine and guanine bases, were synthesized as potential antiviral agents. Phosphoralaninate of adenine methylenecyclobutane was a potent inhibitor of replication of Epstein-Barr virus (EBV) in Daudi cell culture. Phosphoralaninate of guanine analogue was inactive but both pronucleotides were substrates for porcine liver esterase. Adenine methylenecyclobutane analogue was deaminated by adenosine deaminase.

9-[(Hydroxymethyl)phenyl]adenines: new aryladenine substrates of adenosine deaminase

New phenyl adenine compounds 5-7 were synthesized as analogues of adenosine and studied for their adenosine deaminase (ADA) substrate activity. The 9-[(o-hydroxymethyl)phenyl]methyl]adenine 5 and 9-[(m-hydroxymethyl)phenyl]adenine 7 were deaminated by ADA, and 9-[(o-hydroxyethyl)phenyl]adenine 6 was not deaminated up to 7 days. The ADA substrates 5 and 7 were deaminated quantitatively to their inosine analogues in 10 and 6h, respectively.

Synthesis and antiviral activity of novel exomethylene cyclopropyl nucleosides

Novel cyclopropyl nucleosides were synthesized as potential antiviral agents. The key intermediate 5, prepared from Feist's acid 1 was condensed with purine derivatives by the SN2 type reaction. All the synthesized compounds were evaluated for antiviral activity.

Acyclic/carbocyclic guanosine analogues as anti-herpesvirus agents

Several guanosine analogues, i.e. acyclovir (and its oral prodrug valaciclovir), penciclovir (in its oral prodrug form, famciclovir) and ganciclovir, are widely used for the treatment of herpesvirus [i.e. herpes simplex virus type 1 (HSV-1), and type 2 (HSV-2), varicella-zoster virus (VZV) and/or human cytomegalovirus (HCMV)] infections. In recent years, several new guanosine analogues have been developed, including the 3-membered cyclopropylmethyl and -methenyl derivatives (A-5021 and synguanol) and the 6-membered D- and L-cyclohexenyl derivatives. The activity of the acyclic/carbocyclic guanosine analogues has been determined against a wide spectrum of viruses, including the HSV-1, HSV-2, VZV, HCMV, and also human herpesviruses type 6 (HHV-6), type 7 (HHV-7) and type 8 (HHV-8), and hepatitis B virus (HBV). The new guanosine analogues (i.e. A-5021 and D- and L-cyclohexenyl G) were found to be particularly active against those viruses (HSV-1, HSV-2, VZV) that encode for a specific thymidine kinase (TK), suggesting that their antiviral activity (at least partially) depends on phosphorylation by the virus-induced TK. Marked antiviral activity was also noted with A-5021 against HHV-6 and with D- and L-cyclohexenyl G against HCMV and HBV. The antiviral activity of the acyclic/carbocyclic nucleoside analogues could be markedly potentiated by mycophenolic acid, a potent inhibitor of inosine 5'-monophosphate (IMP) dehydrogenase. The new carbocyclic guanosine analogues (i.e. A-5021 and D- and L-cyclohexenyl G) hold great promise, not only as antiviral agents for the treatment of herpesvirus infections, but also an antitumor agents for the combined gene therapy/chemotherapy of cancer, provided that (part of) the tumor cells have been transduced by the viral (HSV-1, VZV) TK gene.

Synthesis and antiviral activity of methylenedifluorocyclopropane analogues of nucleosides

Synthesis and antiviral activity of methylenedifluorocyclopropane analogues 8a, 8b and 9a, 9b are described.

In vitro and in vivo activity of 1-O-hexadecylpropanediol-3-phospho-ganciclovir and 1-O-hexadecylpropanediol-3-phospho-penciclovir in cytomegalovirus and herpes simplex virus infections

Human cytomegalovirus (HCMV) and herpes simplex virus (HSV) can cause a wide variety of clinical manifestations in man. Ganciclovir (GCV) is effective against HCMV infection when administered by the intravenous route and may be used orally in large doses for prophylaxis of HCMV infections in organ transplantation patients and in AIDS patients. In previous studies with acyclovir (ACV), we found that covalent attachment of an alkyl glycerol phosphate moiety greatly increased oral bioavailability and increased antiviral activity against hepatitis B virus. Adducts of ACV with alkyl propanediol phosphate were more active than the alkyl glycerol phosphate analogue in vitro in 2.2.15 cells, which constitutively produce hepatitis B virus. To see if this strategy would work for two other poorly absorbed nucleoside analogues, we synthesized 1-O-hexadecylpropanediol-3-phospho-GCV (HDP-P-GCV) and 1-O-hexadecyl-propanediol-3-phospho-penciclovir (HDP-P-PCV), and evaluated the in vitro antiviral activity, selectivity and oral antiviral activity of both compounds versus GCV or PCV in mice infected with HSV-1 or HDP-P-GCV versus murine cytomegalovirus (MCMV). HDP-P-GCV is orally active in both MCMV and HSV-1 infection in mice with antiviral activity equivalent to (HSV-1) or greater than oral GCV (MCMV). Oral HDP-P-PCV was more active than PCV orally versus intranasal HSV-1 infection in mice.

Synthesis and antiviral activity of novel methylene cyclopropyl nucleosides

Novel exomethylene cyclopropyl nucleosides were synthesized as potential antiviral agents. The key intermediate 5 was synthesized in 4 steps, from Feists acid 1 and was condensed with purine derivatives by the SN2 type reaction to give some cyclopropyl nucleosides. The synthesized nucleosides did not showed any significant antiviral activity against HSV-1, HSV-2, HCMV, HIV-1, HIV-2, and HBV up to 100 microM.

Guanosine analogues as anti-herpesvirus agents

Several guanosine analogues, i.e. acyclovir (and its oral prodrug valaciclovir), penciclovir (in its oral prodrug form, famciclovir) and ganciclovir, are widely used for the treatment of herpesvirus (i.e. HSV-1, HSV-2, VZV and HCMV) infections. In recent years, several new guanosine analogues have been developed, including the 3-membered (cyclopropyl) sugar derivative A-5021 and the 6-membered D- and L-cyclohexenyl derivatives. Prominent features shared by all guanosine analogues are the following. They depend for their phosphorylation on the virus-encoded thymidine kinase (TK), which makes them particularly effective against those viruses (HSV-1, HSV-2 and VZV) that encoded for such TK. They are also active against HCMV, whether or not they are subject of phosphorylation by the HCMV-induced UL97 protein kinase. Their antiviral activity can be markedly potentiated by mycophenolic acid, an IMP dehydrogenase inhibitor, and they hold great promise, not only as antiviral agents for the treatment of herpesvirus infections, but also as antitumor agents for the combined gene therapy/chemotherapy of cancer, provided that (part of) the tumor cells have been transfected by the viral TK gene.

Dendrimers, a new class of candidate topical microbicides with activity against herpes simplex virus infection

Dendrimers are large highly branched macromolecules synthesized from a polyfunctional core. They have shown a variety of biological properties, including, in some instances, antiviral activity. In this study, five dendrimers were evaluated for in vitro activity against herpes simplex virus (HSV) types 1 and 2 by cytopathic effect (CPE) inhibition and plaque reduction (PR) assay in human foreskin fibroblast cells. All of the compounds were active against both virus types in the CPE inhibition assay, in which drug was added to the cells prior to the addition of virus. Antiviral activity was reduced or lost in the PR assays, in which the cells were incubated with the virus before the drug was added. The prophylactic efficacy suggested that the dendrimers might have potential as topical microbicides, products intended to be applied to the vaginal or rectal mucosa to protect against sexually transmitted infections. Three dendrimers were evaluated for this application against genital HSV infection in mice. Two of the compounds, BRI-2999 and BRI-6741, significantly reduced infection rates when 15 microl of a 100-mg/ml solution was administered immediately prior to intravaginal challenge, and the most effective compound, BRI-2999, provided significant protection even when applied 30 min before challenge. This is the first report of microbicidal activity by dendrimers in vivo.

Facile synthesis of N-(1-alkenyl) derivatives of 2,4-pyrimidinediones

N-(1-alkenyl) derivatives of 2,4-pyrimidinediones (6-9) were prepared in a one pot synthesis from aldehydes and the nucleobases using trimethylsilyl trifluoromethanesulfonate (TfOTMS) as coupling reagent. Presilylation of the above nucleobases, and N6-benzoyladenine, with excess N,O-bis(trimethylsilyl)acetamide (BSA) followed by addition of one mol eq. TfOTMS yielded the N-(1-trimethylsilyloxyalkyl) derivatives 1-5.

In vitro activities of methylenecyclopropane analogues of nucleosides and their phosphoralaninate prodrugs against cytomegalovirus and other herpesvirus infections

Human cytomegalovirus (HCMV) infection does not generally cause problems in the immunocompetent adult but can result in severe clinical disease in the fetus, neonate, and immunocompromised host. Ganciclovir (GCV), the agent currently used to treat most HCMV infections, has resulted in much therapeutic success; however, efficacy remains suboptimal. Therefore, there is still a need to develop new compounds for use against HCMV infections. In the present study, several Z- and E-series methylenecyclopropane analogues and their phosphoroalaninate prodrugs were tested initially for activity against HCMV, strain AD169, and murine cytomegalovirus (MCMV) in vitro. Many were found to exhibit efficacy comparable to that of GCV against HCMV in plaque assays and were active against MCMV as well. The compounds were also tested for efficacy against herpes simplex virus types 1 and 2, varicella-zoster virus, and Epstein-Barr virus, and some had levels of activity that were comparable to that of acyclovir. In addition, the compounds synguanol (QYL-438) and 2-amino-6-cyclopropylamino analogue (QYL-769) were chosen for further evaluation and were found to be effective against additional laboratory and clinical isolates of HCMV and GCV-resistant isolates. QYL-438 and QYL-769 were found to be nontoxic in human and mouse fibroblasts and were considerably less toxic than GCV in granulocyte macrophage CFUs and erythroid burst-forming units. These results provide evidence for the high activity of some of these methylenecyclopropane analogues against various herpesviruses, particularly HCMV, in tissue culture and suggest that further evaluation is warranted to determine their potential for use in future clinical studies.

Synthesis and enantioselectivity of the antiviral effects of (R,Z)-,(S,Z)-methylenecyclopropane analogues of purine nucleosides and phosphoralaninate prodrugs: influence of heterocyclic base, type of virus and host cells

A series of R and S enantiomers of 2-aminopurine methylenecyclopropane analogues of nucleosides was synthesized. Two diastereoisomeric lipophilic phosphate prodrugs derived from R and S enantiomers of 2,6-diaminopurine analogue were also prepared. Enantioselectivity (diastereoselectivity in case of prodrugs) of in vitro antiviral effects was investigated with human and murine cytomegalovirus (HCMV and MCMV, respectively), herpes simplex virus types 1 and 2 (HSV-1 and HSV-2, respectively), human immunodeficiency virus type 1 (HIV-1), hepatitis B virus (HBV), Epstein-Barr virus (EBV) and varicella zoster virus (VZV). Strong differences in enantioselectivity were found between the R and S enantiomers of adenine analogue and enantiomeric 2-aminopurine analogues. Thus, the enantiomers of adenine analogue were equipotent against HCMV but not MCMV, where the S enantiomer is strongly preferred. The same S preference was found throughout the 2-aminopurine series for both HCMV and MCMV. In contrast, R-synadenol in HIV-1 assays was the best agent, whereas the S enantiomers of moderately effective 2-amino-6-cyclopropylamino and 2-amino-6-methoxypurine analogues were preferred. Little enantiomeric preference was found for R and S enantiomers of synadenol and the corresponding enantiomers of 2,6-diaminopurine analogue against HBV. A mixed pattern of enantioselectivity was observed for EBV depending on the type of host cells and assay. Against VZV, the R and S enantiomers of adenine analogue were equipotent or almost equipotent, but throughout the series of 2-aminopurine analogues a distinct preference for the S enantiomers was found. The stereoselectivity pattern of both diastereoisomeric prodrugs mostly followed enantioselectivity of the parent analogues. The varying enantioselectivities in the series of purine methylenecyclopropane analogues are probably a consequence of differences in the mechanisms of action in different virus/host cell systems.

The latest progress in the synthesis of carbocyclic nucleosides

This review presents the latest developments in the field of carba-nucleosides (1994-1998). Special attention is paid to the synthesis of key precursors to those carba-nucleosides that possess significant biological activities or have novel structures.

Synthesis of (Z)- and (E)-9-[(2-hydroxyethylidene)cyclopropyl]adenine--new methylenecyclopropane analogues of adenosine and their substrate activity for adenosine deaminase

Synthesis of Z- and E-methylenecyclopropane analogues of adenosine 3 and 4 by alkylation of adenine with novel alkylating agent 5 is described. The E-isomer 4 is a substrate for adenosine deaminase. Compounds 3 and 4 were tested for antiviral activity against HCMV, HSV-1, HSV-2, EBV, VZV, HBV and HIV-1.

Effective treatment of murine cytomegalovirus infections with methylenecyclopropane analogues of nucleosides

A number of new nucleoside analogues with a Z- or E-methylenecyclopropane structure exhibited significant activity against human and murine cytomegaloviruses (HCMV, MCMV) in tissue culture that was generally comparable to, or greater than, 9-[(1-3-dihydroxy-2-propoxy)methyl]guanine (ganciclovir, GCV). Several of these analogues were chosen for further evaluation of therapeutic efficacy utilizing a MCMV infection. Intraperitoneal (i.p.) inoculation of 3-week-old Balb/c mice with 2.0 x 10(5) plaque forming units (pfu) of MCMV results in an acute, lethal infection with rapid virus replication in visceral and glandular tissue, thus, making it an ideal model for identifying compounds that have potential for use in humans. Synadenol (QYL-284A) and synguanol (QYL-438) were administered i.p. once daily for 5 days initiated 6, 24, or 48 h post-viral infection. Significant protection was demonstrated at 50 and 16.7 mg/kg compared to placebo, with efficacy comparable to GCV. When delivered orally once or twice daily at 100 mg/kg per day, QYL-438 was active, but less effective than GCV. In addition, 2-amino-6-methoxypurine analogue (QYL-941) was active at 60 mg/kg administered orally twice daily, comparable to GCV, while it's prodrug (QYL-972) was as effective as GCV at 40 mg/kg when delivered twice daily for 5 days. Additionally, analogue 2-amino-6-cyclopropylaminopurine (QYL-769) was found to be highly efficacious when given orally twice daily for 5 days. Mortality of 0% and 13% was observed at 60 and 20 mg/kg, respectively, which was similar to GCV. Oral treatment with QYL-769 or GCV reduced virus replication in target organs, but neither resulted in complete clearance of MCMV. These data indicate that these new analogues have activity comparable to GCV when given orally to mice and should be evaluated further to assess their potential for use in humans.

Synthesis of new nucleoside analogues comprising a geminal difluorocyclopropane moiety as potential antiviral/antitumor agents

Geminal difluorocyclopropane analogues of nucleosides 7a-7e were synthesized. Compounds 7a and 7c-7e were obtained by alkylation of nucleic acid bases or their appropriate precursors with (cis)-1-benzyloxymethyl-2-bromomethyl-3,3-difluorocyclopropane+ ++ (8). Analogue 7b was prepared by hydrolysis of 2-amino-6-chloropurine derivative 7e. Compounds 7a-7d did not exhibit any antiviral activity against HCMV, HSV-1, HSV-2, EBV, VZV, HBV and HIV-1 or antitumor effects against murine leukemia L1210, mouse tumors PO3 or C38 and human tumor H15.

In vitro induction of human immunodeficiency virus type 1 variants resistant to phosphoralaninate prodrugs of Z-methylenecyclopropane nucleoside analogues

Two methylenecyclopropane nucleoside analogues with a phenylphosphoralaninate moiety, QYL-685 and QYL-609, exert potent and specific activities against human immunodeficiency virus type 1 strain LAI (HIV-1(LAI)) and HIV-2 in vitro. In this study, we induced HIV-1 variants resistant to QYL-685 by exposing HIV-1(LAI) to increasing concentrations of QYL-685. After 16 passages, the virus (HIV-1(P16)) was less sensitive to QYL-685 (104-fold), QYL-609 (>41-fold), and (-)-beta-2',3'-dideoxy-3'-thiacytidine (3TC) (>1, 100-fold) than was HIV-1(LAI) and contained an M184I mutation. Two infectious clones, HIV-1(M184I) and HIV-1(M184V), were resistant to QYL-685, QYL-609, and 3TC, confirming that the M184I mutation was responsible for the observed resistance. Viral-fitness analyses (competitive HIV-1 replication assays) revealed that in the absence of drugs, M184I and M184V conferred a replication disadvantage on the virus compared to the replication efficiency of the wild-type infectious clone (HIV-1(wt)). However, in the presence of QYL-685 (4 microM), HIV-1(M184I) and HIV-1(M184V) showed greater fitness than HIV-1(wt). These data may provide structural and virological relevance with regard to the emergence of M184I and M184V substitutions in HIV-1.

Synthesis and antiviral activity of phosphoralaninate derivatives of methylenecyclopropane analogues of nucleosides

Phenylmethylphosphoro-L-alaninate prodrugs of antiviral Z-methylenecyclopropane nucleoside analogues and their inactive E-isomers were synthesized and evaluated for their antiviral activity against HCMV, HSV-1, HSV-2, HHV-6, EBV, VZV, HIV-1 and HBV. The adenine Z-analogue was a potent inhibitor of all these viruses but it displayed cellular toxicity. The guanine Z-derivative was active against HCMV, HBV, EBV and VZV and it was not cytotoxic. The 2,6-diaminopurine analogue was the most potent against HIV-1 and HBV and somewhat less against HHV-6, HCMV, EBV and VZV in a non-cytotoxic concentration range. The 2-amino-6-cyclopropylamino and 2-amino-6-methoxypurine prodrugs were also more active than parent analogues against several viruses but with a less favorable cytotoxicity profile. In the E-series of analogues, adenine derivative was active against HIV-1, HBV and EBV, and it was non-cytotoxic. The guanine analogue exhibited a significant effect only against HBV. The 2,6-diaminopurine E-analogue was inactive with the exception of a single EBV assay. The 2-amino-6-methoxypurine Z-methylenecyclopropane nucleoside analogue was an effective inhibitor of HCMV, MCMV and EBV. The 2,6-diaminopurine Z-prodrug seems to be the best candidate for further development.

In vitro anti-human immunodeficiency virus activities of Z- and E-methylenecyclopropane nucleoside analogues and their phosphoro-L-alaninate diesters

Nucleoside analogues with a Z- or an E-methylenecyclopropane moiety were synthesized and examined for activity against human immunodeficiency virus type 1 (HIV-1) in vitro. The addition of a methyl phenyl phosphoro-L-alaninate moiety to modestly active analogues resulted in potentiation of their anti-HIV-1 activity. Two such compounds, designated QYL-685 (with 2,6-diaminopurine) and QYL-609 (with adenine), were most potent against HIV-1 in vitro, with 50% inhibitory concentrations of 0.034 and 0.0026 microM, respectively, in MT-2 cell-based assays. Both compounds were active against zidovudine-resistant, didanosine-resistant, and multi-dideoxynucleoside-resistant infectious clones in vitro. Further development of these analogues as potential therapies for HIV-1 infection is warranted.

Methylenecyclopropane analogues of nucleosides: synthesis, absolute configuration, and enantioselectivity of antiviral effect of (R)-(-)- and (S)-(+)-synadenol

Synthesis, absolute configuration and antiviral activity of enantiomeric antiviral agents (R)-(-)- and (S)-(+)-synadenol (2 and 3a) are described.