Potent and Selective Inhibitors of Human Immunodeficiency Virus Protease Structurally Related to L-694,746

A series of human immunodeficiency virus (HIV) protease inhibitors, which are analogues of N-[2( R)-hydroxy-1( S)-indanyl]-5( S)-[( tert-butyloxycarbonyl)amino]-4( S)-hydroxy-6-phenyl-2-( R)-[[4-(carboxymethoxy)phenyl]methyl]hexanamide (L-694,746), a metabolite of the anti-HIV agent L-689,502, were synthesized. In these compounds, the acetic group linked to the para position of the P1′ phenyl in the reference inhibitor was replaced either by the bioisosteric phosphonomethoxy group and its diisopropyl/dibenzyl derivatives, or the 1H-tetrazol-5-yl-methoxy group and its 1-benzyl derivative. In enzyme assays, phosphonomethoxy and tetrazolmethoxy analogues proved to be potent inhibitors of the HIV-1 protease, with IC50 values as low as 0.04 nM. When tested for anti-HIV-1 activity in cell-based assays, most of the new derivatives proved active, with benzyl derivatives being more active than their highly polar, unsubstituted counterparts. The dibenzylphosphonomethoxy analogue was the most active compound, with an EC50 value of 10 nM and a selectivity index of 20 000. When compounds were examined for their capability to reduce p24 levels in both acutely and chronically infected MT-4 and H9/IIIB cells, all of them were found to be active at concentrations close to those capable of preventing HIV-1-induced cytopathic effect.

Synthesis and Antiviral Activity of New 3,4-Dihydro-2-Alkoxy-6-Benzyl-4-Oxopyrimidines (DABOs), Specific Inhibitors of Human Immunodeficiency Virus Type 1

3,4-Dihydro-2-alkoxy-6-benzyl-4-oxopyrimidines (DABOs) have emerged as non-nucleoside inhibitors of human immunodeficiency virus type 1 [Artico et al. (1993), Antiviral Chem Chemother 4: 361-368]. With a view to increasing their potency, a new series of DABO derivatives, differently substituted at positions C-2 and/or C-5 of the pyrimidine ring and 3′ or 3′,5′ of the benzyl moiety, have been synthesized. DABOs were prepared by reacting O-methylisourea with the appropriate methyl 2-alkyl-4-phenylacetylacetate, with formation of 3,4-dihydro-2-methoxy-6-arylmethyl-4-oxopyrimidines. Subsequent displacement of the methoxy group linked at the 2-position of the pyrimidine ring by treatment with alkoxy and cycloalkoxy potassium salts led to the required derivatives. In vitro, the most potent compounds were 12e and 12p, which had an EC50 of 0.8 μM and a selective index of 400.

4'-C-methyl-beta-D-ribofuranosyl purine and pyrimidine nucleosides revisited

In order to evaluate their antiviral properties, a series of 4'-C-methyl-beta-D-ribofuranosyl purine and pyrimidine nucleosides has been prepared. Unfortunately, none of these 4'-branched nucleosides showed any antiviral activity or cytotoxcity when tested against HIV, HBV, and Yellow Fever virus.

Antiviral beta-L-nucleosides specific for hepatitis B virus infection

Three simple, related nucleosides, beta-L-2'-deoxycytidine (LdC), beta-Lthymidine (LdT), and beta-L-2'-deoxyadenosine (LdA), have been discovered to be potent, specific and selective inhibitors of the replication hepatitis B virus (HBV), as well as the closely related duck and woodchuck hepatitis viruses (WHV). Structure-activity relationship analysis indicates that the 3'-OH group of the beta-L-2'-deoxyribose of the beta-L-2'-deoxynucleoside confers specific anti-hepadnavirus activity. The simple nucleosides had no effect on the replication of 15 other RNA and DNA viruses, and did not inhibit human DNA polymerases (alpha, beta and gamma) or compromise mitochondrial function. The nucleosides are efficiently converted intracellularly into active triphosphate metabolites that have a long half-life. Once-daily oral administration of these compounds in the woodchuck efficacy model of chronic HBV infection reduced viral load by as much as 10(8) genome equivalents/ml serum and there was no drug-related toxicity. In addition, a decline in WHV surface antigen (WHsAg) paralleled the decrease in viral load. This class of nucleosides displays an excellent overall safety profile. The first compound, LdT, has already entered clinical trials and LdC, currently being developed as a prodrug, is expected to enter the clinic in the near future. These compounds have the potential for use in combination therapy with the goal of achieving superior viral suppression and diminishing the onset of resistance.

DABOs as candidates to prevent mucosal HIV transmission

Worldwide, the heterosexual route is the prevalent mode of transmission of AIDS; therefore, demands have been raised for measures that block sexual spreading of the HIV infection. Development of microbicides for topical use may represent an efficacious alternative to condoms. Several approaches are being investigated. Besides surfactants, which directly act on the virus particle, and measures that enhance natural defence mechanisms, promising new candidates appear to be drugs that block the early steps of HIV multiplication. We describe herein a long-term assay which enables the establishment of whether the above drugs reversibly (virustatic action) or irreversibly (virucidal action) inhibit HIV-1 multiplication, thus allowing screening for effective and potent microbicides. We validated our assay with nucleoside (NRTIs) and non-nucleoside reverse transcriptase inhibitors (NNRTIs). Following a chronic treatment, the NRTIs tested (didanosine, zalcitabine, stavudine and lamivudine) simply delayed the viral breakthrough with respect to infected, untreated controls. Under the same experimental conditions, non-nucleoside reveres transcriptase inhibitors (NNRTIs), such as MKC-442, alphaAPA, nevirapine, efavirenz and 3,4-dihydro-2-alkoxy-6-benzyl-4-oxopyrimidines (DABOs) MC 1047 and MC 1220 suppressed HIV-1 replication for the entire experimental period (40 days). When cell culture samples were evaluated for the presence of infectious virus, p24 antigen and viral DNA sequences, none of them was detected up to day 40 post-infection (p.i.). Identical results were obtained after a treatment with the above NNRTIs limited to the first 4 days p.i. Under more selective experimental conditions, that is drug treatments limited to the first 4 h p.i., nevirapine and efavirenz proved to be virustatic; in fact, viral breakthrough ensued shortly after their removal from the culture medium. Conversely, DABO MC 1220 was endowed with potent virucidal activity; in fact, at 3.5 microM it was able to suppress HIV-1 multiplication in cultures acutely infected with a very high multiplicity of infection (5 CCID50/cell), thus allowing exponential cell multiplication as in uninfected cultures for the next 40 days.

Targeting HIV: old and new players

Despite the unprecedented successes in the therapy of HIV infection, AIDS remains a major world health problem being the first cause of death in Africa and the fourth leading cause of death worldwide. Rapid emergence of drug-resistant HIV variants and severe side effects limit the efficacy of existing therapies. The intrinsic high variability of HIV calls for combining different drugs with distinct mode of action to achieve synergistic antiviral activity. Efforts are being made to develop agents addressing new steps in HIV replication and to optimize both antiviral activity and pharmacokinetic of the current drugs targeting reverse transcriptase and protease. The class of viral entry inhibitors is undergoing evaluation for both systemic and topical administration, and compounds targeting the fusion step may be the first to reach the market. Identification of compounds unambiguously affecting HIV replication by targeting integrase supports the potential of this crucial viral enzyme as a drug target. Targeting HIV gene regulation, which could also lead to cellular toxicity, may also become an important discovery strategy, provided that inhibitors with sufficient specificity are identified. In this review we will summarize the current understanding of the key steps in HIV life cycle in the context of representative inhibitors based on their modes of action. We then present a summary of compounds under clinical development, with the aim of providing a picture of the current potential for targeting HIV.

Anti-HBV specific beta-L-2'-deoxynucleosides

A unique series of simple unnatural L-nucleosides that specifically inhibit hepatitis B virus (HBV) replication has been discovered. These molecules have in common a hydroxyl group in the 3'-position (3'-OH) of the beta-L-2'-deoxyribose sugar that confers antiviral activity specifically against hepadnaviruses. Replacement of the 3'-OH broadens activity to other viruses. Substitution in the base decreases antiviral potency and selectivity. Human DNA polymerases and mitochondrial function are not effected. Plasma viremia is reduced up to 8 logs in a woodchuck model of chronic HBV infection. These investigational drugs, used alone or in combination, are expected to offer new therapeutic options for patients with chronic HBV infection.

Antiviral activity and intracellular metabolism of bis(tButylSATE) phosphotriester of beta-L-2',3'dideoxyadenosine, a potent inhibitor of HIV and HBV replication

The beta-L-nucleoside analogue beta-L-2',3'-dideoxy adenosine (beta-L-ddA) has been shown to exhibit limited antiviral activities. This was attributed to its rapid catabolism through cleavage of the glycosidic bond and poor phosphorylation to the nucleotide beta-L-2',3'-dideoxyadenosine-5'-mono phosphate (beta-L-ddAMP) (Placidi et al., 2000). However, the nucleotide beta-L-2',3'-dideoxyadenosine-5'-triphosphate (beta-L-ddATP) inhibited the activity of both HIV-1 reverse transcriptase (RT) and viral DNA polymerase isolated from woodchuck hepatitis virus-infected serum (a model of hepatitis B) with an inhibitory concentration (IC50) of 2.0 microM without inhibiting human DNA polymerases alpha, beta, or gamma up to a concentration of 100 microM. These results suggested that prodrugs of beta-L-ddAMP may bypass the poor metabolic activation of beta-L-ddA and lead to more potent and selective antiviral activity. Therefore, the mononucleoside phosphotriester derivative of beta-L-ddAMP incorporating the S-pivaloyl-2-thioethyl (tButylSATE) groups, beta-L-ddAMP-bis(tButylSATE) was synthesized. Beta-L-ddAMP-bis(tButylSATE) inhibited HIV replication in human peripheral blood mononuclear cells (PBMCs) and HBV replication in 2.2.15 cells with effective concentrations (EC50s) of 2 and 80 nM, respectively. Intracellular metabolism of beta-L-ddAMP-bis(tButylSATE) demonstrated that beta-L-ddATP was the predominant intracellular metabolite in PBMC and liver cells. The intracellular half-life of beta-L-ddATP was 5.4 and 9.2 h in HepG2 and PBMCs, respectively. The intracellular concentrations of beta-L-ddATP were maintained above the EC50 for the inhibition of HIV RT and hepatitis B virus (HBV) for as long as 24 h after removal of the drug.

Antiviral L-nucleosides specific for hepatitis B virus infection

A unique series of simple "unnatural" nucleosides has been discovered to inhibit hepatitis B virus (HBV) replication. Through structure-activity analysis it was found that the 3'-OH group of the beta-L-2'-deoxyribose of the beta-L-2'-deoxynucleoside confers specific antihepadnavirus activity. The unsubstituted nucleosides beta-L-2'-deoxycytidine, beta-L-thymidine, and beta-L-2'-deoxyadenosine had the most potent, selective, and specific antiviral activity against HBV replication. Human DNA polymerases (alpha, beta, and gamma) and mitochondrial function were not affected. In the woodchuck model of chronic HBV infection, viral load was reduced by as much as 10(8) genome equivalents/ml of serum and there was no drug-related toxicity. In addition, the decline in woodchuck hepatitis virus surface antigen paralleled the decrease in viral load. These investigational drugs, used alone or in combination, are expected to offer new therapeutic options for patients with chronic HBV infection.

Computer-assisted design, synthesis and biological evaluation of novel pyrrolyl heteroaryl sulfones targeted at HIV-1 reverse transcriptase as non-nucleoside inhibitors

Three pyrrolyl heteroaryl sulfones (ethyl 1-[(1H-benzimidazol-2(3H)one-5-yl)sulfonyl]-1H-pyrrole-2-carboxyla te, ethyl 1-[(1H-benzimidazol-5(6)-yl)sulfonyl]-1H-pyrrole-2-carboxylate and ethyl 1-[(1H-benzotriazol-5(6)-yl)sulfonyl]-1H-pyrrole-2-carboxylate) were designed as novel HIV-1 reverse transcriptase non-nucleoside inhibitors using structure-based computational methods. Although these compounds were inactive in the cell-based assay, they inhibited the target enzyme with micromolar potency (IC50s = 2 microM, 3 microM and 9 microM, respectively).

Structure-based design, synthesis, and biological evaluation of novel pyrrolyl aryl sulfones: HIV-1 non-nucleoside reverse transcriptase inhibitors active at nanomolar concentrations

Pyrrolyl aryl sulfones (PASs) have been recently reported as a new class of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) inhibitors acting at the non-nucleoside binding site of this enzyme (Artico, M.; et al. J. Med. Chem. 1996, 39, 522-530). Compound 3, the most potent inhibitor within the series (EC(50) = 0.14 microM, IC(50) = 0.4 microM, and SI > 1429), was then selected as a lead compound for a synthetic project based on molecular modeling studies. Using the three-dimensional structure of RT cocrystallized with the alpha-APA derivative R95845, we derived a model of the RT/3 complex by taking into account previously developed structure-activity relationships. Inspection of this model and docking calculations on virtual compounds prompted the design of novel PAS derivatives and related analogues. Our computational approach proved to be effective in making qualitative predictions, that is in discriminating active versus inactive compounds. Among the compounds synthesized and tested, 20 was the most active one, with EC(50) = 0.045 microM, IC(50) = 0.05 microM, and SI = 5333. Compared with the lead 3, these values represent a 3- and 8-fold improvement in the cell-based and enzyme assays, respectively, together with the highest selectivity achieved so far in the PAS series.

Synthesis and antiviral evaluation of some beta-L-2', 3'-dideoxy-5-chloropyrimidine nucleosides and pronucleotides

The synthesis and in vitro anti human immunodeficiency virus (HIV) and anti-hepatitis B virus (HBV) activities of some unnatural beta-L-nucleoside enantiomers related to the anti-HIV compound 2', 3'-dideoxy-3'-fluoro-5-chlorouridine (beta-D-3'Fdd5ClU) are reported. In contrast to beta-D-3'Fdd5ClU, beta-L-3'Fdd5ClU and the other L-congeners were devoid of significant anti-HIV effects, but beta-L-2',3'-dideoxy-5-chlorocytidine (beta-L-dd5ClC) and beta-L-2', 3'-dideoxy-3'-fluoro-cytidine (beta-L-3'FddC) showed a distinct anti-HBV activity. Three mononucleoside phosphotriester derivatives with S-pivaloyl-2-thioethyl (t-BuSATE) groups as biolabile phosphate protective groups were also synthesized. The bis(t-BuSATE) derivative of beta-D-3'Fdd5ClU retained anti-HIV activity in thymidine kinase deficient (TK(-)) CEM cells.

In vitro and in vivo metabolism and pharmacokinetics of bis [(t-butyl)-S-acyl-2-thioethyl]-beta-L-2',3'-dideoxy-5-fluorocytidine monophosphate

Exposure to 10 &M L-FddCMP-bisSATE led to formation of intracellular L-FddCTP levels of 410.1(+/-) +/- 46.2 and 242.1 +/- 13.2 pmol/10(6) cells in unstimulated and PHAstimulated PBM cells, respectively; whereas, exposure of cells to the parent nucleoside, L-FddC, generated 5-10-fold less L-FddCTP. In Hep-G2 cells and EGF/HGF stimulated and unstimulated primary cultured hepatocytes, the active metabolite reached 113 +/- 29, 23.9 +/- 15.6, and 20.6 +/- 10.5 pmol/10(6) cells. Three other metabolites, L-FddCMP-monoSATE, L-FddCMP-SH, and M I, were detected intracellularly and extracellularly in all cell types examined. Intravenous administered dose of 3 mg/kg L-FddCMP-bisSATE to rhesus monkeys resulted in plasma concentration levels of 2.06 +/- 1.00 and 0.39 +/- 0.15 &M of L-FddCMP-monoSATE and L-FddC, respectively, while the prodrug was completely cleared metabolically within 15 min. Following oral administration of an equivalent dose, the absolute oral bioavailability of L-FddC derived from L-FddCMP-bisSATE administration was 65%.

Comparison of anti-HBV activity of beta-D- and beta-L-DDA-5'monophosphate prodrugs and effectiveness in combination with lamivudine

We have investigated the effects of several beta-D-ddA 5'-monophospate (beta-D-ddAMP), and their corresponding beta-L-enantiomers prodrugs against HBV replication. All ddAMP prodrugs inhibited HBV replication in a dose-dependent manner.

Effect of acyclic nucleoside phosphonates on the HIV-1 integrase in vitro

Integrase (IN) is an essential enzyme in the human immunodeficiency virus type-1 (HIV-1) replication cycle and, thus, a potential target for chemotherapeutic agents. Because various nucleotide analogues have been reported to inhibit IN in vitro, we investigated the effect of acyclic nucleoside phosphonates. Both unphosphorylated and diphosphorylated derivatives were inhibitory to IN at concentrations ranging between 60 and 800 microM, with diphosphorylated derivatives being 5- to 8-fold more potent than unphosphorylated counterparts.

5-Alkyl-2-(alkylthio)-6-(2,6-dihalophenylmethyl)-3, 4-dihydropyrimidin-4(3H)-ones: novel potent and selective dihydro-alkoxy-benzyl-oxopyrimidine derivatives

Molecular modeling analysis of compounds belonging to the recently published series of dihydro-alkoxy-benzyl-oxopyrimidines (DABOs), such as S-DABOs and DATNOs, gave support to the design of new 2, 6-disubstituted benzyl-DABO derivatives as highly potent and specific inhibitors of the HIV-1 reverse transcriptase (RT). To follow up on the novel DABO derivatives, we decided to investigate the effect of electron-withdrawing substituents in the benzyl unit of the S-DABO skeleton versus their anti-HIV-1 activity. Such chemical modifications impacted the inhibitory activity, especially when two halogen units were introduced at positions 2 and 6 in the phenyl portion of the benzyl group bound to C-6 of the pyrimidine ring. Various 5-alkyl-2-(alkyl(or cycloalkyl)thio)-6-(2, 6-dichloro(or 2,6-difluoro)phenylmethyl)-3, 4-dihydropyrimidin-4(3H)-ones were then synthesized and tested as anti-HIV-1 agents in both cell-based and enzyme (recombinant reverse transcriptase, rRT) assays. Among the various mono- and disubstituted phenyl derivatives, the most potent were those containing a 6-(2,6-difluorophenylmethyl) substituent (F-DABOs), which showed EC50's ranging between 40 and 90 nM and selectivity indexes up to >/=5000. An excellent correlation was found between EC50 and IC50 values which confirmed that these compounds act as inhibitors of the HIV-1 RT. The structure-activity relationships of the newly synthesized pyrimidinones are presented herein.

Potent and selective inhibitors of human immunodeficiency virus protease structurally related to L-694,746

A series of human immunodeficiency virus (HIV) protease inhibitors, which are analogues of N-[2(R)-hydroxy-1(S)- indanyl]-5(S)-[(tert-butyloxycarbonyl)amino]-4(S)-hydroxy-6-phenyl-2-(R) - [[4-(carboxymethoxy)phenyl]methyl]hexanamide (L-694,746), a metabolite of the anti-HIV agent L-689,502, were synthesized. In these compounds, the acetic group linked to the para position of the P1' phenyl in the reference inhibitor was replaced either by the bioisosteric phosphonomethoxy group and its diisopropyl/dibenzyl derivatives, or the 1H-tetrazol-5-yl-methoxy group and its 1-benzyl derivative. In enzyme assays, phosphonomethoxy and tetrazolmethoxy analogues proved to be potent inhibitors of the HIV-1 protease, with IC50 values as low as 0.04 nM. When tested for anti-HIV-1 activity in cell-based assays, most of the new derivatives proved active, with benzyl derivatives being more active than their highly polar, unsubstituted counterparts. The dibenzylphosphonomethoxy analogue was the most active compound, with an EC50 value of 10 nM and a selectivity index of 20,000. When compounds were examined for their capability to reduce p24 levels in both acutely and chronically infected MT-4 and H9/IIIB cells, all of them were found to be active at concentrations close to those capable of preventing HIV-1-induced cytopathic effect.

1,2,5-Benzothiadiazepine and pyrrolo[2,1-d]-[1,2,5]benzothiadiazepine derivatives with specific anti-human immunodeficiency virus type 1 activity

We synthesized and tested as novel inhibitors of human immunodeficiency virus type 1 (HIV-1) bi- and tricyclic thiadiazine ring homologues of 7-chloro-2-ethyl-2H-1,2,4-benzothiadiazin-3-(4H)-one 1,1-dioxide, which is a compound endowed with anti-HIV-1 activity at low micromolar concentrations. Benzothiadiazepine derivatives were obtained by alkylation of 8-chloro-2,3-dihydro-3-methyl-1,2,5-benzothiadiazepin-4(5H)-one 1,1-dioxide, which was obtained by intramolecular cyclization of 2-(2-amino-5-chloro-benzenesulphonamido) propanoic acid. Pyrrolobenzothiadiazepines were synthesized from N-substituted 5-chloro-2-(1H-pyrrol-1-yl)benzene-sulphonamides by treating with triphosgene. N6-substituted pyrrolo[2,1-d][1,2,5]benzothiazepin-7(6H)-one 5,5-dioxides were active, though not very potent. Both a chlorine atom and an unsaturated alkyl chain were found to be determinants of anti-HIV-1 activity. The highest potency was shown by a derivative with a TIBO-related 3,3-dimethylallyl chain. 2,3-Dihydro-1,2,5-benzothiadiazepin-4(5H)-one 1,1-dioxides were scarcely active in HIV-1-infected MT-4 cell assays; however, the introduction of the dimethylallyl chain into 7-chloro-1,2,5-benzothiadiazepine moiety led to a bicyclic derivative which was more potent and less cytotoxic than the tricyclic pyrrole-containing counterpart.

Glycosidopyrroles. Part 1. Acyclic derivatives: 1-(2-hydroxyethoxy)methylpyrroles as potential anti-viral agents

Acyclic glycosidopyrroles of type 1, synthesized in good overall yields, were evaluated for anti-viral activity. Compound 10i was found to inhibit the HIV-1 replication at concentrations that were very close to those cytotoxic for MT-4 cells. Compounds 10a,f,i inhibited both strains HSV-1 and HSV-2 at concentrations slightly below those cytotoxic for Vero cells. However for this series of glycosidopyrroles some relationship between calculated log P values and the observed cytotoxicity was found.

Synthesis, structure, and antiproliferative activity of selenophenfurin, an inosine 5'-monophosphate dehydrogenase inhibitor analogue of selenazofurin

The synthesis and biological activity of selenophenfurin (5-beta-D-ribofuranosylselenophene-3-carboxamide, 1), the selenophene analogue of selenazofurin, are described. Glycosylation of ethyl selenophene-3-carboxylate (6) under stannic chloride-catalyzed conditions gave 2- and 5-glycosylated regioisomers, as a mixture of alpha- and beta-anomers, and the beta-2,5-diglycosylated derivative. Deprotected ethyl 5-beta-D-ribofuranosylselenophene-3-carboxylate (12 beta) was converted into selenophenfurin by ammonolysis. The structure of 12 beta was determined by 1H- and 13C-NMR, crystallographic, and computational studies. Selenophenfurin proved to be antiproliferative against a number of leukemia, lymphoma, and solid tumor cell lines at concentrations similar to those of selenazofurin but was more potent than the thiophene and thiazole analogues thiophenfurin and tiazofurin. Incubation of K562 cells with selenophenfurin resulted in inhibition of IMP dehydrogenase (IMPDH) (76%) and an increase in IMP pools (14.5-fold) with a concurrent decrease in GTP levels (58%). The results obtained confirm the hypothesis that the presence of heteroatoms such as S or Se in the heterocycle in position 2 with respect to the glycosidic bond is essential for both cytotoxicity and IMP dehydrogenase inhibitory activity in this type of C-nucleosides.

Dihydro(alkylthio)(naphthylmethyl)oxopyrimidines: novel non-nucleoside reverse transcriptase inhibitors of the S-DABO series

Novel compounds related to 2-(cyclohexylthio)-3,4-dihydro-5-methyl-6-(3-methylbenzyl)-4-ox opyrimidine (3c, MC 639) have been synthesized and tested as inhibitors of human immunodeficiency virus type-1 (HIV-1). Reaction of thiourea with ethyl arylmethylacetoacetates furnished 5-alkyl-6-(arylmethyl)-3,4-dihydro-2-mercapto-4-oxopyrimidines which were then alkylated at the sulfur atom to afford the required 2-alkylthio or 2-cycloalkylthio derivatives (S-DABOs). Chemical modifications at N-3, C-4, and C-6 of the pyrimidine ring were attempted with the aim of improving antiretroviral activity. In particular, replacement of the benzyl group with the 1-naphthylmethyl moiety enhanced the activity of S-DABOs, whereas N-3 alkylation and C=O transformation into C=S at position 4 of the pyrimidine ring led to compounds devoid of anti-HIV-1 activity. Lower activity was generally observed when 1-naphthylmethyl was replaced by the isomeric 2-naphthylmethyl moiety. The most active compounds showed activity in the low micromolar range with EC50 values comparable to that of nevirapine.

Acyclic glycosidopyrroles analogues of ganciclovir: synthesis and biological activity

Acyclic glycosidopyrroles of type 3 were synthetized in good overall yields, according to the Scheme. When evaluated for antiviral activity against DNA and RNA viruses, only compound in which R1 = R2 = Ph, R3 = NH2 was found to inhibit the HIV-1 replication at concentrations that were not cytotoxic for MT-4 cells.

Native oligodeoxynucleotides specifically active against human immunodeficiency virus type 1 in vitro: a G-quartet-driven effect?

Among a series of unmodified phosphodiester (PO)-oligodeoxynucleotides (PO-ODNs) complementary to some of the human immunodeficiency virus type 1 (HIV-1) regulatory genes, several PO-ODN sequences complementary to the vpr gene (PO-ODNs-a-vpr, where a-vpr is the antisense vpr sequence) emerged as potent inhibitors (at concentrations of 0.8 to 3.3 microM) of HIV-1 multiplication in de novo infected MT-4 cells, while they showed no cytotoxicity for uninfected cells at concentrations up to 100 microM. Unlike phosphorothioate counterparts, PO-ODN-a-vpr sequences were not inhibitory to HIV-2 multiplication in de novo infected C8166 cells and neither prevented the fusion between chronically infected and bystander CD4+ cells nor inhibited the activity of the HIV-1 reverse transcriptase in enzyme assays. Moreover, they were not inhibitory to HIV-1 multiplication in chronically infected cells. Delayed addition experiments showed that PO-ODNs-a-vpr inhibit an event in the HIV-1 replication cycle following adsorption to the host cell, but preceding reverse transcription. Structure-activity relationship studies indicated that the antiviral activity of the test PO-ODN-a-vpr sequences is not related to an antisense mechanism but to the presence, within the active sequences, of contiguous guanine residues. Physical characterization of the test PO-ODNs suggested that the active structure is a tetramer stabilized by G quartets (i.e., four G residues connected by eight hydrogen bonds).

5H-pyrrolo[1,2-b] [1,2,5]benzothiadiazepines (PBTDs): a novel class of non-nucleoside reverse transcriptase inhibitors

With the aim of developing novel inhibitors of human immunodeficiency virus, various derivatives (10-17) related to 5H-pyrrolo[1,2-b] [1,2,5]benzothiadiazepine (PBTD) were prepared and tested in vitro. The title tricyclic derivatives were obtained by intramolecular cyclization of the open-chain intermediate arylpyrrylsulfones, followed by N-alkylation at position 10. Among test derivatives some 10-alkyl-5H-pyrrolo[1,2-b] [1,2,5]benzothiadiazepin-11(10H)-one-5,5-dioxides were found to exert potent and specific activity against HIV-1. In particular, 7-chloro derivatives 11i and j showed a potency comparable to that of nevirapine. However, when the chloro atom was shifted to the 8 position, the related products were scarcely active or totally inactive. Replacement of the pyrrole with pyrrolidine led to inactive products and the reduction of SO2 to S strongly diminished the antiviral potency. PBTD derivatives active in cell cultures were also inhibitory to the recombinant HIV-1 RT in enzyme assays, thus allowing the conclusion that PBTDs are a new class of non-nucleoside reverse transcriptase inhibitors (NNRTIs).

Synthesis and anti-HIV activity of 10,11-dihydropyrrolo [1,2-b][1,2,5]benzothiadiazepine-11-acetic acid 5,5-dioxide derivatives and related compounds

The synthesis and the in vitro anti-HIV-1 activity of novel pyrrolo annulated benzothiadiazepine acetic acids and some related derivatives are reported. The new compounds share chemical features with pyrrolo[1,2-d][1,4]benzodiazepin-6-one 1 and Ro 5-3335 pyrrylbenzodiazepinone 4, two inhibitors of HIV-replication at the level of reverse transcriptase (RT) and transcriptional transactivation by Tat, respectively. Two derivatives, namely methyl 10,11-dihydropyrrolo[1,2-b][1,2,5]benzothiadiazepine-11-acetic-5,5 -dioxide (5a) and 1,12b-dihydro-2H-azeto[2,1-d]pyrrolo[1,2-b][1,2,5]benzoth iadiazepin-2-one 8,8-dioxide (7a), were found to exhibit a significant, although not very potent, activity against human immunodeficiency virus Type 1 (HIV-1).

Decomposition pathways and in vitro HIV inhibitory effects of isoddA pronucleotides: toward a rational approach for intracellular delivery of nucleoside 5'-monophosphates

The decomposition pathways and kinetics in various biological media and the in vitro anti-HIV-1 and anti-HIV-2 activities of four derivatives of the 5'-mononucleotide of isoddA incorporating carboxylate esterase-labile transient phosphate protecting groups are reported and compared: namely, two mononucleoside aryl phosphoramidate derivatives 1a,b and two mononucleoside phosphotriester derivatives incorporating two S-acyl-2-thioethyl groups 2a,b. All four compounds show better antiviral activity, compared to the parent nucleoside analog isoddA. The results highlight that both types of compounds act as pronucleotides, i.e. they exert their antiviral effect via intracellular delivery of the 5'-mononucleotide of isoddA. The results may give insights for the design of new more efficient pronucleotides.

2-Sulfonyl-4-chloroanilino moiety: a potent pharmacophore for the anti-human immunodeficiency virus type 1 activity of pyrrolyl aryl sulfones

The synthesis and the evaluation of cytotoxicity and anti-HIV-1 activity of new aryl pyrrolyl (8) and aryl indolyl (9) sulfones are reported. Preparation of above sulfones was achieved by reacting arylsulfonyl chlorides with substituted pyrroles and indoles or by condensing sulfonamides with 2,5-dimethoxytetrahydrofuran in glacial acetic acid according to the Clauson-Kaas method. Chemical requisites relevant to the anti-HIV-1 activity of these compounds are both a 2-sulfonyl-4-chloroanilino moiety and an alkoxycarbonyl group at position 2 of the pyrrole ring. The best activity and selectivity were obtained with ethoxycarbonyl and isopropoxycarbonyl substituents. Substitutions at the amino group of the pharmacophore moiety led to inactive products (alkylation) or weakened (acylation) anti-HIV-1 activity. Among test derivatives, 16 compounds showed EC50 values ranging between 10 and 1 microM, and five (8b',d',f',h'j') showed EC50S in the sub-micromolar range. The compounds were active against HIV-1, both wild type and AZT-resistant strains, but not against HIV-2. Moreover, in enzyme assays they potently inhibited the HIV-1 recombinant reverse transcriptase, were 10 times less active against enzymes from nevirapine- and TIBO-resistant strains, and were totally inactive against the HIV-2 recombinant enzyme. Interestingly, some compounds (8r'-y') were inactive against the recombinant reverse transcriptase while being active in tissue culture.

Synthesis and antiviral activity of 8-aza analogs of chiral [2-(phosphonomethoxy) propyl]guanines

(R)- And (S)-8-aza-9(-)[2-(phosphonomethoxy)propyl]guanine [(R)-and (S)-8-aza-PMPG] were synthesized and tested in vitro for anti-human immunodeficiency virus (HIV) activity. The synthesis of the above compounds and of (R)-9(-)[2-(phosphonomethoxy)propyl]guanine [(R)-PMPG] was carried out through the alkylation of 8-azaguanine or guanine with (R)- and (S)-2-O(-)[(diisopropylphosphono)methyl]-1-O-(tolylsulfonyl) -1,2-propanediol followed by deprotection of the phosphonic moiety. A different, even more convenient synthesis of (R)-8-aza-PMPG starting from 2-amino-6-chloro-5-nitro-4(3H)-pyrimidinone and (R)(-)[2(-)[(diisopropylphosphono)-methoxy]propyl]amine is also reported. Both (R)-8-aza-PMPG and (R)-PMPG demonstrated anti-HIV activity in the MTT assay with EC50 values of 12 and 4.5 microM, respectively. The corresponding S enantiomers were found to be less potent. When evaluated in combination with AZT, ddI, or DABO 603, (R)-8-aza-PMPG gave additive, additive, and synergistic anti-HIV-1 effects, respectively.

Synthesis and anti-HIV-1 activity of thio analogues of dihydroalkoxybenzyloxopyrimidines

Various thio analogues of dihydroalkoxybenzyloxopyrimidines (DABOs), a new class of non-nucleoside reverse transcriptase inhibitors, were found to selectively inhibit the HIV-1 multiplication in vitro. Among the C-5 H-substituted 6-benzyl-3,4-dihydro-4-oxopyrimidines, the introduction of alkylthio or cycloalkylthio substituents at C-2 of the pyrimidine ring led to derivatives (S-DABOs) which were up to 10-fold more potent than the alkyloxy or cycloalkyloxy counterparts. The further introduction of a methyl group at the 3'-position of the benzyl portion of 2-(alkylthio)-6-benzyluracils reduced the cytotoxicity leading to more selective compounds. Among C-5 methyl-substituted S-DABOs, numerous derivatives showed EC50 values as low as 0.6 microM and lacked cytotoxicity at doses as high as 300 microM. In the C-5 double methyl-substituted series, a more pronounced cytotoxicity was observed and the further introduction of a methyl at the 3'-position in the benzylidene group resulted in total loss of antiviral activity. S-DABOs, namely 2-(alkylthio)-6-benzyl-3,4-dihydro-4-oxopyrimidines, were synthesized by reacting proper methyl (phenylacetyl)acetates or their 2-methyl compounds with thiourea to afford 6-benzyl-4-oxo-1,2,3,4-tetrahydro-2-thiaoxopyrimidines or the related 5-methyl derivatives. Treatment of the latter derivatives with alkyl or cycloalkyl halides in alkaline medium gave the required title compounds.

[[[(Thienylcarbonyl)alkyl]oxy]phenyl]- and [[[(pyrrylcarbonyl)alkyl]oxy]phenyl]oxazoline derivatives with potent and selective antihuman rhinovirus activity

As an approach to more extensive structural modifications of [(oxazolylphenoxy)alkyl]isoxazoles, we synthesized new compounds characterized by the replacement of the isoxazole nucleus with furan, pyrrole, and thiophene rings and by the presence of a ketocarbonyl group in the aliphatic chain connecting these pentatomic heterocycles to the 4-(4,5-dihydro-2-oxazolyl)phenoxy, 4-(ethoxycarbonyl)phenoxy, and 4-carboxyphenoxy moieties. Some pentamethylene derivatives were also prepared, and their antirhinovirus activity was compared to that of the corresponding ketomethylene derivatives. Syntheses were carried out by Friedel-Crafts acylation of the above pentatomic heterocycles and subsequent reaction of chloroalkyl ketones with the proper 4-substituted phenol. Reduction of the ketone function afforded the related polymethylene derivatives. The new compounds were tested for antirhinovirus activity and cytotoxicity in comparison with WIN 51711, used as reference drug. Inspection of the structure-activity relationships revealed that the thiophene ring and the carbonyl group are the structural components which to a large extent contribute to the positive biological profile in terms of both wideness of spectrum and low cytotoxicity. Among the various derivatives, compounds 8e,d showed in vitro the same potency of WIN 51711 but a cytotoxicity at least 10 times lower.

Synthesis and evaluation of the anti-HIV activity of aza and deaza analogues of isoddA and their phosphates as prodrugs

Some aza and deaza analogues of the anti-HIV agent 2',3'-dideoxy-3'-oxoadenosine (isoddA) (8-aza-, 8-aza-1-deaza, 8-aza-3-deaza-, 1-deaza-, and 3-deaza-isoddA) were synthesized and found inactive against HIV in vitro. The hypothesis that the inactivity of these isonucleosides might be due to their poor affinity for cellular nucleoside kinases was checked by the synthesis of a series of 5'-[bis(2,2,2-trichloroethyl) phosphate] triesters and 5'-phenyl phosphoramidate derivatives which, acting as membrane soluble prodrugs, could release the free phosphate form inside the cell. The 5'-(phenylmethoxy)alaninyl phosphate derived from 8-aza-isoddA was found active against HIV-1 and HIV-2 with a potency similar to that of isoddA, while the anti-HIV potency of 5'-(phenylmethoxy)alaninyl phosphate of isoddA proved remarkably higher than that of isoddA, in particular against HIV-2, being similar to that of AZT. Further evidence that 8-aza-isoddA could behave as anti-HIV agent, provided that it is activated as phosphate, was obtained by the synthesis of its 5'-triphosphate derivative, which proved to be an active inhibitor of HIV-1 recombinant reverse transcriptase.

Characterization of the anti-HIV-1 activity of 3,4-dihydro-2-alkoxy-6-benzyl-4-oxopyrimidines (DABOs), new non-nucleoside reverse transcriptase inhibitors

Novel 3,4-dihydro-6-benzyl-4-oxopyrimidines (DABOs), variously substituted at both the C-2 and C-5 positions of the pyrimidine ring, proved to be specific inhibitors of the human immunodeficiency virus type 1 (HIV-1) in vitro. Some compounds showed potency at micromolar doses, no cytotoxicity at the maximum testable doses and selectivity indexes comparable to that of 2'-3'-dideoxyinosine (ddI). Mode of action studies suggested that DABOs interfered with a step of the virus multiplication cycle following adsorption and preceding integration. Enzyme assays indicated that DABOs targeted HIV-1 reverse transcriptase: they inhibited the RNA-dependent DNA polymerase activity in a template-dependent manner and, to a lesser extent, the DNA-dependent DNA polymerase activity. No inhibition of the RNase-H associated activity was observed. When DABOs were assayed in combination with 3'-azido-3'-dideoxythymidine (AZT) or ddI against HIV-1 in cell cultures, a slightly synergistic inhibitory effect was observed. The combination of DABO 546 and AZTTP in enzyme assays showed that the two compounds were kinetically mutually exclusive.