Nucleoside Phosphonate Antiviral Strategies

Nucleoside phosphonates constitute a class of antiviral agents in which a non‐hydrolysable carbon–phosphorus bond replaces the labile phosphate linkage, thereby yielding stable mimics of natural nucleotides. Many of these molecules, exemplified by adefovir and tenofovir, act as chain terminators of viral polymerases once converted into their active phosphate forms. However, the intrinsic negative charge of the phosphonate group limits membrane permeability and oral bioavailability. To overcome this, chemists have devised prodrug approaches that mask the phosphonate moiety with bioreversible ester or phosphoramidate groups, facilitating cellular uptake and unmasking by enzymatic cleavage. Recent advances span the development of lipophilic masking units at γ- or β-phosphate positions, diastereoselective phosphoramidate syntheses (“ProTides”), and peptidomimetic esters, together improving pharmacokinetics, target selectivity and resistance profiles. Structural studies of viral and protozoan enzymes guide the rational design of inhibitors with tailored binding modes. Collectively, these strategies have yielded clinically approved drugs, promising candidates against HIV, hepatitis B virus and emerging pathogens, and illustrate the power of merging enzymology, structural biology and prodrug chemistry in antiviral research.

Research from Nature Portfolio

Building upon the challenge of inefficient phosphorylation, one foundational study demonstrated a series of triphosphate prodrugs bearing two lipophilic masking units at the γ-phosphate of nucleoside analogues. These compounds showed efficient enzyme‐triggered release of active triphosphates in lymphocyte extracts, yielding submicromolar inhibition of HIV-1 and HIV-2 even in thymidine kinase-deficient cells. In parallel, high‐resolution crystal structures of the Trypanosoma brucei hypoxanthine–guanine phosphoribosyltransferase in complex with acyclic nucleoside phosphonates revealed key conformational changes upon inhibitor binding and identified substituents that confer nanomolar affinity and selectivity over the human enzyme. These insights underpin the design of selective antiparasitic agents harnessing phosphonate motifs.

Nucleoside Phosphonate Antiviral Strategies publication trend

The graph below shows the total number of articles in nucleoside phosphonate antiviral strategies across all publications each year (not limited to Nature Index journals).

Technical terms

Nucleoside phosphonate: A nucleoside analogue in which the phosphate is replaced by a non‐hydrolysable phosphonate (P–C bond), conferring enzymatic stability.

Prodrug: A pharmacologically inactive derivative that undergoes in vivo transformation to release the active drug.

ProTide: A phosphoramidate prodrug design that uses amino acid esters to mask phosphate or phosphonate groups and enhance cellular uptake.

Lipophilicity: A measure of a compound’s affinity for lipid environments, often increased to improve membrane permeability.

Reverse transcriptase: A viral enzyme that synthesises DNA from an RNA template, commonly targeted by nucleoside analogues.

References

1. Lipophilic Nucleoside Triphosphate Prodrugs of Anti‐HIV Active Nucleoside Analogs as Potential Antiviral Compounds. Advanced Science (2023).
2. Potent Anti‐HIV Activity of Alkyl‐Modified DiPPro‐Nucleotides. Small Structures (2023).
3. Lipophilic prodrugs of nucleoside triphosphates as biochemical probes and potential antivirals. Nature Communications (2015).
4. Phosphonates and Phosphonate Prodrugs in Medicinal Chemistry: Past Successes and Future Prospects. Frontiers in Chemistry (2022).
5. Diastereoselective synthesis of P -chirogenic phosphoramidate prodrugs of nucleoside analogues (ProTides) via copper catalysed reaction. Chemical Communications (2015).
6. Overview of Biologically Active Nucleoside Phosphonates. Frontiers in Chemistry (2021).
7. Crystal structures and inhibition of Trypanosoma brucei hypoxanthine–guanine phosphoribosyltransferase. Scientific Reports (2016).