Enantiomeric 3-deaza-1′,6′-isoneplanocin and its 3-bromo analogue: Synthesis by the Ullmann reaction and their antiviral properties

2- and 3-Fluoro-3-deaza-1',6'-isoneplanocin: Synthesis and antiviral properties (including Ebola and Marburg)

To extend the antiviral properties of 2- and 3-fluoro-3-deazaneplanocins into the evolving 3-deaza-1',6'-isoneplanocin library, 2- (11) and 3-fluoro-1',6'-iso-3-deazaneplanocin A (12) have been explored. The requisite synthesis began with an Ullmann reaction by coupling of a protected cyclopentenyl iodide with either 2-fluoro- or 3-fluoro-3-deazaadenine. Target 12 displayed significant activity towards 5 viruses (μM): H1N1 (EC₅₀ < 0.36, CC₅₀ > 357, SI > 1000), hepatitis B virus (EC₅₀ 1.28, CC₅₀ > 357, SI > 279), norovirus (EC₅₀ 0.64, CC₅₀ > 357, SI > 558), Ebola (EC₅₀ < 0.1, CC₅₀ > 100, SI > 1000), and Marburg (EC₅₀ < 0.1, CC₅₀ > 100, SI > 1000). On the other hand, while 11 showed limited antiviral effects, its toxicity was significant, precluding any further usefulness.

Advances in Therapeutic L-Nucleosides and L-Nucleic Acids with Unusual Handedness

Nucleic-acid-based small molecule and oligonucleotide therapies are attractive topics due to their potential for effective target of disease-related modules and specific control of disease gene expression. As the non-naturally occurring biomolecules, modified DNA/RNA nucleoside and oligonucleotide analogues composed of L-(deoxy)riboses, have been designed and applied as innovative therapeutics with superior plasma stability, weakened cytotoxicity, and inexistent immunogenicity. Although all the chiral centers in the backbone are mirror converted from the natural D-nucleic acids, L-nucleic acids are equipped with the same nucleobases (A, G, C and U or T), which are critical to maintain the programmability and form adaptable tertiary structures for target binding. The types of L-nucleic acid drugs are increasingly varied, from chemically modified nucleoside analogues that interact with pathogenic polymerases to nanoparticles containing hundreds of repeating L-nucleotides that circulate durably in vivo. This article mainly reviews three different aspects of L-nucleic acid therapies, including pharmacological L-nucleosides, Spiegelmers as specific target-binding aptamers, and L-nanostructures as effective drug-delivery devices.

Enantiomeric 4'-truncated 6'-fluoro-3-deazaneplanocin and its 3-bromo derivative: Synthesis and antiviral properties, including Ebola and Marburg

In seeking to increase the library of fluorine containing adenine-derived carbocyclic nucleoside antiviral candidates, d-like and l-like 6'-fluoro-3-deazaneplanocin and its 3-bromo derivative lacking the 4'-hydroxylmethylene substituent (2/3 and 4/5, respectively) are presented. Their synthesis was accomplished from d-ribose by developing a more facile precursor route than suggested by the literature. The 2/4d-like pair displayed significant anti-filo virial properties while the enantiomeric l-like congeners 3/5 were inactive. Target compounds 2/4 also were active towards measles and norovirus. The effect of 2/4 is further evidence of the role fluoro-derived adenine carbocyclic nucleoside can play in antiviral drug discovery. Furthermore, the simplicity of their synthesis lends them to more efficacious analogs and to scale-up optimization. There were no other relevant antiviral properties for 2/3 and 4/5 (except BK polyomavirus for 3/5).

Mechanisms of anti-vesicular stomatitis virus activity of deazaneplanocin and its 3-brominated analogs

3-deazaneplanocin A (DzNep) and its 3-brominated analogs inhibit replication of several RNA viruses. This antiviral activity is attributed to inhibition of S-adenosyl homocysteine hydrolase (SAHase) and consequently inhibition of viral methyltransferases, impairing translation of viral transcripts. The L-enantiomers of some derivatives retain antiviral activity despite dramatically reduced inhibition of SAHase in vitro. To better understand the mechanisms by which these compounds exert their antiviral effects, we compared DzNep, its 3-bromo-derivative, CL123, and the related enantiomers, CL4033 and CL4053, for their activities towards the model negative-sense RNA virus vesicular stomatitis virus (VSV). In cell culture, DzNep, CL123 and CL4033 each exhibited 50 percent inhibitory concentrations (IC50s) in the nanomolar range whereas the IC50 for the L-form, CL4053, was 34-85 times higher. When a CL123-resistant mutant (VSV^R) was selected, it exhibited cross-resistance to each of the neplanocin analogs, but retained sensitivity to the adenosine analog BCX4430, an RNA chain terminator. Sequencing of VSV^R identified a mutation in the C-terminal domain (CTD) of the viral large (L) protein, a domain implicated in regulation of L protein methyltransferase activity. CL123 inhibited VSV viral mRNA 5' cap methylation, impaired viral protein synthesis and decreased association of viral mRNAs with polysomes. Modest impacts on viral transcription were also demonstrated. VSV^R exhibited partial resistance in each of these assays but its replication was impaired, relative to the parent VSV, in the absence of the inhibitors. These data suggest that DzNep, CL123 and CL4033 inhibit VSV through impairment of viral mRNA cap methylation and that the L-form, CL4053, based on the cross-resistance of VSV^R, may act by a similar mechanism.

5'-Nor-3-Deaza-1',6'-Isoneplanocin, the Synthesis and Antiviral Study

The arbocyclic nucleosides aristeromycin and neplanocin have been studied as a source for new antiviral agents. A convenient synthesis of C-5'-truncated 3-deaza-1',6'-isoneplanocin, which combines the features of antiviral candidates 5'-noraristeromycin and 3-deaza-1',6'-isoneplanocin is reported from (-)-cyclopentenone to give the two C-4' epimers of 5'-nor-3-deaza isoneplanocin. Antiviral assays showed activity against the JC virus (EC₅₀ = 1.12 µM for (4'R)-8; EC₅₀ = 59.14 µM for (4'S)-7) and inactivity of both compounds against several DNA and RNA viruses. Both compounds lacked cytotoxicity.

Enantiomeric 4'-Truncated 3-deaza-1',6'-isoneplanocins: Synthesis and antiviral properties including Ebola

Enantiomeric 3-deaza-1',6'-isoneplanocins (C-3 unsubstituted 7a/7b and C-3 with a bromine 8a/8b) lacking the 4'-hydroxymethyl as mechanistically designed anti-viral targets have been prepared by utilizing the Ullmann reaction. Anti-Ebola properties were found for the D-like 7a and 8a and L-like 8b. All four products showed effects against human cytomegalovirus while D-like 7a/8a affected measles; 7a was effective versus norovirus and 8a inhibited Pichinde. Both 7a and 8a produced SAHase inhibitory effects. However, the anti-EBOV activity of 7a and 8a cannot be readily correlated with this observation due with their contrasting IC₅₀ values (8a > 7a). It is to be noted that 7b showed no effects on this enzyme and 8b was minimally inhibitory. These results offer preliminary insight into the differing mechanisms of action of D- and L- like structures and enlighten structural features to guide additional antiviral agent pursuit in the isoneplanocin series.

Synthesis of D-like and L-like 5'-fluoro-5'-deoxy-1',6'-isoneplanocins and their antiviral activity including Ebola

In exploring the 1',6'-isoneplanocin structural framework for antiviral compound development, both the D-like and L-like 5'-fluoro-5'-deoxy analogs have been synthesized from readily available cyclopentenyl iodides and adenine in five steps. Antiviral evaluation found D-like 5'-fluoro-5'-deoxy-1',6'-isoneplanocin to display less broad-spectrum antiviral effects than the parent D-like including weaker activity against Ebola and norovirus. The L-like enantiomer was devoid of any activity, contrary to the parent L-like compound.

l-like 3-deazaneplanocin analogues: Synthesis and antiviral properties

The potent antiviral properties of 3-deazaneplanocin, 3-deaza-isoneplanocins (1) and recently discovered l-like carbocyclic nucleosides (2, 3 and 4) prompted us to pursue rationally conceived l-like 3-deazaneplanocin analogues. The synthesis of those analogues including l-like 3-deazaneplanocin (5), l-like 3-bromo-3-deazaneplanocin (6), and l-like 5'-fluoro-5'-deoxy-3-deazaneplanocin (7), was accomplished from a common intermediate, (-)-cyclopentenone (8). Antiviral analysis found 5 and 6 to display favorable activity against the Ebola virus, as expected for 3-deazaadenine carbocyclic nucleosides. Compound 5 also showed activity against arenaviruses, including Pinchinde and Tacaribe.

Current status of small molecule drug development for Ebola virus and other filoviruses

The filovirus family includes some of the deadliest viruses known, including Ebola virus and Marburg virus. These viruses cause periodic outbreaks of severe disease that can be spread from person to person, making the filoviruses important public health threats. There remains a need for approved drugs that target all or most members of this virus family. Small molecule inhibitors that target conserved functions hold promise as pan-filovirus therapeutics. To date, compounds that effectively target virus entry, genome replication, gene expression, and virus egress have been described. The most advanced inhibitors are nucleoside analogs that target viral RNA synthesis reactions.

Both enantiomers of 6'-Isoneplanocin

Both enantiomers of the isomer of neplanocin where the C-4' hydroxymethyl has been displaced to the 6'-position (that is, 6'-isoneplanocin) have been prepared in 5 steps from known, protected iodocyclopentenones. Both products were evaluated against a number of DNA and RNA viruses and found to be inactive. This observation is suggested to be due to the displacement of the C-4' hydroxymethyl of neplanocin (in the D-like form) away from the lysine⁴²⁵ of S-adenosylhomocysteine hydrolase, which is important for inhibition by neplanocin and, in turn, its antiviral activity.

Tuning Cross-Coupling Approaches to C3 Modification of 3-Deazapurines

A general approach to C3 modification of purine scaffold through various types of cross-coupling reactions has been established. Tuning substrate electronics and reaction conditions resulted in the development of highly efficient sp²-sp, sp²-sp², and sp²-sp³ cross-coupling conditions for modification of 3-deazaadenine to access C3-modified adenine and hypoxanthine scaffolds. The optimized methodologies to access the corresponding 3-deazaadenosine phosphoramidites for solid-phase DNA synthesis have been demonstrated.

Synthesis, conformational study and antiviral activity of l-like neplanocin derivatives

The l-like enantiomer of 9-(trans-2', trans-3'-dihydroxycyclopent-4'-enyl)-3-deazaadenine (DHCDA) (1), its 3-deaza-3-bromo derivative (3), and the conformational restricted methanocarba (MC) nucleoside analogues (2 and 4) were synthesized. X-ray crystal structures showed the L isomer MC analogue 4 adopts a similar North-like locked conformation as conventional D-MC nucleosides, while the DHCDA analogue 3 preferred south-like conformer. Compounds 1 and 4 showed potent antiviral activity against norovirus, while compound 2 and 3 were less potent or inactive. The conformational behavior of "sugar" puckering (north/south) and nucleobase orientation (syn /anti) may contribute to the antiviral activity differences. For compound 3, antiviral activity was also found against Ebola virus.