2'-Fluoro-4'-thio-2',3'-unsaturated nucleosides: anti-HIV activity, resistance profile, and molecular modeling studies

Both D- and L-2'-fluoro-4'-thio-2',3'-unsaturated nucleosides were synthesized and their anti-HIV activity against the drug sensitive virus and lamivudine-resistant mutant (M184V) were evaluated. In vitro antiviral evaluation indicated that the L-isomers are more potent than the D-isomers, but unfortunately all were cross-resistant with 3TC. Molecular modeling studies revealed that the unnatural sugar moiety of the L-nucleosides as well as 4'-sulfur atom of the D-isomer has a steric conflict with the bulky side chain of valine 184, resulting in cross-resistance.     

Synthesis and antiviral activity of D- and L-2'-azido-2',3'-dideoxy-4'-thiopyrimidine and purine nucleosides

Novel D- and L-2'-azido-2',3'-dideoxy-4'-thionucleosides were synthesized starting from L- and D-xylose via D- and L-4-thioarabitol derivative as key intermediates and evaluated for antiviral activity, respectively. When the final nucleosides were tested against HIV-1, HSV-1, HSV-2, and HCMV, they were found to be only active against HCMV without cytotoxicity up to 100 micrograms/ml.     

Structural basis for activation of the therapeutic L-nucleoside analogs 3TC and troxacitabine by human deoxycytidine kinase

L-nucleoside analogs represent an important class of small molecules for treating both viral infections and cancers. These pro-drugs achieve pharmacological activity only after enzyme-catalyzed conversion to their tri-phosphorylated forms. Herein, we report the crystal structures of human deoxycytidine kinase (dCK) in complex with the L-nucleosides (-)-beta-2',3'-dideoxy-3'-thiacytidine (3TC)--an approved anti-human immunodeficiency virus (HIV) agent--and troxacitabine (TRO)--an experimental anti-neoplastic agent. The first step in activating these agents is catalyzed by dCK. Our studies reveal how dCK, which normally catalyzes phosphorylation of the natural D-nucleosides, can efficiently phosphorylate substrates with non-physiologic chirality. The capability of dCK to phosphorylate both D- and L-nucleosides and nucleoside analogs derives from structural properties of both the enzyme and the substrates themselves. First, the nucleoside-binding site tolerates substrates with different chiral configurations by maintaining virtually all of the protein-ligand interactions responsible for productive substrate positioning. Second, the pseudo-symmetry of nucleosides and nucleoside analogs in combination with their conformational flexibility allows the L- and D-enantiomeric forms to adopt similar shapes when bound to the enzyme. This is the first analysis of the structural basis for activation of L-nucleoside analogs, providing further impetus for discovery and clinical development of new agents in this molecular class.     

New classes of fluorinated L-nucleosides; synthesis and antiviral activity.

The synthesis of 3'-fluorinated apionucleosides 7 and 2'-fluoro-2',3'-unsaturated L-nucleosides 8 via common synthon, 2-fluoro-butenolide 2, has been described. Among the newly synthesized nucleosides, L-2'-F-d4C, L-2'-F-d4FC and L-2'-F-d4A exhibit significant anti-HIV and anti-HBV activities.     

Phosphoramidate protides of carbocyclic 2',3'-dideoxy-2',3'-didehydro-7-deazaadenosine with potent activity against HIV and HBV

Synthesis of phosphoramidate protides of carbocyclic D- and L-2',3'-dideoxy-2',3'-didehydro-7-deazaadenosine by treatment of the nucleoside with phosphorochloridates in the presence of pyridine and t-BuMgCl is described. Several of these protides showed significantly improved antiviral potency over the parent nucleosides against both HIV and HBV.     

Synthesis of Novel 4′-Trifluoromethyl-5′-Norcarbocyclic C-Nucleoside Phosphonic Acids as Potent Anti-Leukemic Agents

The syntheses of novel C-nucleoside phosphonic acids as potential antiviral agents are described. The sugar moiety that served as the nucleoside skeleton was produced starting from commercially available 1,3-dihydroxy cyclopentane. The key C-C bond formation from sugar to base precursor was performed using the Knoevenagel-type condensation. The synthesized compounds exhibited anti-HIV activity and cytotoxicity. Also, the synthesized compounds were screened in vitro for tumor growth inhibitory activity against mouse leukemia cell lines (L-1210, P-815).     

Synthesis of neplanocin F analogues as potential antiviral agents

Neplanocin F is a natural carbocyclic nucleoside. Herein, we describe the synthesis and antiviral activity of (±)-5′-deoxy-neplanocin F analogues. The key intermediate 4, synthesized from the commercially available (±)-2-azabicyclo[2.2.1]-hept-5-en-3-one (ABH), was utilized to prepare the target nucleosides. Among the target compounds, 5′-deoxyneplanocin F adenine exhibited moderate anti-HIV activity in human lymphocytes without any marked cytotoxicity.     

Synthesis and antiviral activities of new acyclic and "double-headed" nucleoside analogues

To develop an understanding of the structure-activity relationships for the inhibition of orthopoxviruses by nucleoside analogues, a variety of novel chemical entities were synthesized. These included a series of pyrimidine 5-hypermodified acyclic nucleoside analogues based upon recently discovered new leads, and some previously unknown "double-headed" or "abbreviated" nucleosides. None of the synthetic products possessed significant activity against two representative orthopoxviruses; namely, vaccinia virus and cowpox virus. They were also devoid of significant activity against a battery of other DNA and RNA viruses. So far as the results with the orthopoxviruses and herpes viruses, the results may point to the necessity for nucleoside analogues 5'-phosphorylation for antiviral efficacy.     

Synthesis and biological evaluation of 2',4'- and 3',4'-bridged nucleoside analogues

Most nucleosides in solution typically exist in equilibrium between two major sugar pucker forms, N-type and S-type, but bridged nucleosides can be locked into one of these conformations depending on their specific structure. While many groups have researched these bridged nucleosides for the purpose of determining their binding affinity for antisense applications, we opted to look into the potential for biological activity within these conformationally-locked structures. A small library of 2',4'- and 3',4'-bridged nucleoside analogues was synthesized, including a novel 3',4'-carbocyclic bridged system. The synthesized compounds were tested for antibacterial, antitumor, and antiviral activities, leading to the identification of nucleosides possessing such biological activities. To the best of our knowledge, these biologically active compounds represent the first example of 2',4'-bridged nucleosides to demonstrate such properties. The most potent compound, nucleoside 33, exhibited significant antiviral activity against pseudoviruses SF162 (IC(50)=7.0 μM) and HxB2 (IC(50)=2.4 μM). These findings render bridged nucleosides as credible leads for drug discovery in the anti-HIV area of research.     

Antimicrobial and cytotoxic arylazoenamines. Part III: antiviral activity of selected classes of arylazoenamines

Eighty-five arylazoenamines, characterized by different types of aryl and basic moieties, have been synthesized and evaluated in cell-based assays for cytotoxicity and antiviral activity against a panel of ten RNA and DNA viruses. The most commonly affected viruses were, in decreasing order, CVB-2, RSV, BVDV, YFV, and Sb-1; the remaining viruses were either not affected (HIV-1, VSV, and VV) or susceptible only to a very few compounds (Reo-1 and HSV-1). Thirty-five compounds exhibited high activity, with EC(50) in the range 0.8-10 microM, and other 28 compounds had EC(50) between 11 and 30 microM, thus indicating that the arylazoenamine molecular pattern is an interesting novel pharmacophore for antiviral agents against ssRNA viruses. Moreover, some compounds (as 28, 32, 42, and 53) appear of high interest, being devoid of toxicity on the human MT-4 cells (CC(50)>100 microM). A ligand-based computational approach was employed to identify highly predictive pharmacophore models for the most frequently affected viruses CVB-2, RSV, and BVDV. These models should allow the design of second generation of more potent inhibitors of these human and veterinary pathogens.     

New Classes of Fluorinated L-Nucleosides; Synthesis and Antiviral Activity

Abstract

The synthesis of 3′-fluorinated apionucleosides 7 and 2′-fluoro-2′, 3′-unsaturated L-nucleosides 8 via common synthon, 2-fluoro-butenolide 2, has been described. Among the newly synthesized nucleosides, L-2′-F-d4C, L-2′-F-d4FC and L-2′-F-d4A exhibit significant anti-HIV and anti-HBV activities.     

Synthesis and biological evaluation of pyrimidine nucleosides fused with 3',4'-tetrahydrofuran ring

Pyrimidine nucleosides fused with 3',4'-tetrahydrofuran ring were synthesized, starting from 1,2;5,6-di-O-isopropylidene-D-glucose and assayed for antiviral activities. Thymine analogue 1 and its corresponding 2'-deoxy analogue 3 exhibited high cytotoxicity instead of giving antiviral activities.     

Synthesis and antiviral evaluation of novel open-chain analogues of neplanocin A

Novel acyclic nucleoside analogues were designed and synthesized as open-chain analogues of neplanocin A. The coupling of the allylic bromide with purine bases using cesium carbonate afforded a series of novel acyclic nucleosides. The synthesized compounds Ia-II were evaluated for their antiviral activity against various viruses such as HIV HSV-1, HSV-2, and ECMV.     

Concise synthesis and antiviral activity of novel unsaturated acyclic pyrimidine nucleosides

Novel acyclic nucleoside analogues were designed and synthesized as open-chain analogues of neplanocin A. The coupling of the allylic bromide with pyrimidine bases using cesium carbonate afforded a series of novel acyclic nucleosides. The synthesized compounds 15-22 were evaluated for their antiviral activity against various viruses such as HIV, HSV-1, HSV-2, and HCMV.     

Selective synthesis and application to the synthesis of (E)-fluorovinyl nucleosides

A selective method for synthesizing (E)-fluorovinyl was developed. Novel acyclic (E)-fluorovinyl versions of neplanocin A were designed and selectively synthesized as potential antiviral agents. The condensation of the bromide 7 with the nucleosidic bases (5-FU, C, A, G) and the deprotection afforded the desired acyclic fluorovinyl nucleosides. The synthesized compounds 11, 12, 13, and 16 were evaluated for their antiviral activity. The guanine derivative 16 showed toxicity-dependent anti-HIV-1 activity in MT-4 cells.     

Synthesis and biological evaluation of thymine nucleosides fused with 3',4'-tetrahydrofuran ring

The pyrimidine nucleosides fused with 3',4'-tetrahydrofuran ring were successfully synthesized, starting from 1,2;5,6-di-O-isopropylidene-D-glucose and assayed for antiviral activities against HIV-1, HIV-2, EMCV, Cox. B3 and VSV. Thymine analogue (5) and its corresponding 2'-deoxy analogue (6) exhibited high cytotoxicity instead of giving antiviral activities.     

Design and Synthesis of Novel 1′,3′-Dioxolane 5′-Deoxyphosphonic Acid Purine Analogues as Potent Antiviral Agents

Electronic parameters of 1′,3 ′-oxygen play significant roles in steering the conformation of nucleoside phosphonic acid analogues. To investigate the relationship of two oxygen atoms with antiviral enhancement, novel 1′,3 ′-dioxolane 5 ′-deoxyphosphonic acid purine analogues were synthesized via de novo acyclic stereoselective route from acrolein and glycolic acid. The synthesized nucleoside phosphonic acid analogues 14 and 19 were subjected to antiviral screening against several viruses, such as HIV-1, HSV-1, HSV-2, and HCMV. The guanine analogue 19 exhibits in vitro anti-HIV-1 activity similar to that of 9-[2-(phosphonomethoxy)ethyl]adenine (PMEA) in MT-4 cells.     

Synthesis and Potent Anti-HCMV Activity of 2′,5′,5′-trifluoro-3′-hydroxy-apiosyl Nucleoside Phosphonic Acid Analogues

As antiviral nucleosides containing a fluorine atom at 2′-position are endowed with increased stabilization of glycosyl bond, it was of interest to investigate the influence of three fluorine atoms at 2′- and 5′-positions of apiosyl nucleoside phosphonate analogues. Various pyrimidine and purine 2′,5′,5′-trifluoro-3′-hydroxy-apiose nucleoside phosphonic acid analogues were synthesized from 1,3-dihydroxyacetone. Electrophilic fluorination of lactone was performed using N-fluorodibenzenesulfonimide. Difluorophosphonation was performed by direct displacement of triflate intermediate with diethyl(lithiodifluoromethyl) phosphonate to give the corresponding (α,α-difluoroalkyl) phosphonate. Condensation successfully proceeded from a glycosyl donor with persilylated bases to yield nucleoside phosphonate analogues. Deprotection of diethyl phosphonates provided the final phosphonic acid sodium salts. The synthesized nucleoside analogues were subjected to antiviral screening against various viruses.