Elena A. Shirokova

Modified triphosphates of carbocyclic nucleoside analogues: Synthesis, stability towards alkaline phosphatase and substrate properties for some DNA polymerases

Abstract New triphosphate derivatives of carbocyclic nucleoside analogues have been synthesized and shown to be potent substrates for terminal deoxynucleotidyltransferase and/or HIV reverse trascriptase; the compounds are stable to dephosphorylation with human placental alkaline phosphatase.

Anti-HIV therapy with AZT prodrugs: AZT phosphonate derivatives, current state and prospects

Importance of the field: AIDS, a disease caused by human immunodeficiency virus, was called ‘plague of the twentieth century’. 3′-Azido-3′-deoxythymidine (AZT), the first compound approved for the treatment of HIV, is still a mandatory component of treatment schemes. However, its toxicity stimulated a search for new agents. Areas covered in this review: This review presents the history and current state of the design of AZT prodrugs based on its phosphonate derivatives. What the reader will gain: Although every effort was made to include as many AZT structures bearing phosphonate residues and demonstrate the variety they offer, we also concentrated on the studies performed in our laboratory. Special attention was also paid to AZT 5′-H-phosphonate (phosphazide, Nikavir®) approved in the Russian Federation as a drug for the prevention and treatment of HIV infection. Take home message: The prodrug strategy applied to AZT phosphonate derivatives enriched chemistry, biology and medicine not only with new knowledge, methods and structures, but also with a new anti-HIV drug Nikavir. Currently, study of another phosphonate, AZT 5′-aminocarbonylphosphonate, is underway. Slow release of AZT following oral administration and penetration into cells, decreased toxicity and the lack of cumulative properties make the compounds of this group promising as extended-release forms of AZT.

5′-Aminocarbonyl Phosphonates as New Zidovudine Depot Forms: Antiviral Properties, Intracellular Transformations, and Pharmacokinetic Parameters

The main disadvantages of 3′-azido-3′-deoxythymidine (zidovudine, AZT), the most common anti-HIV drug, are toxicity and a short half-life in the organism. The introduction of an H-phosphonate group into the AZT 5′ position resulted in significant improvement of its therapeutic properties and allowed a new anti-HIV drug, Nikavir (AZT H-phosphonate). In this work, we described a new group of AZT derivatives, namely, AZT 5′-aminocarbonylphosphonates. The synthesized compounds displayed antiviral properties in cell cultures infected with HIV-1 and the capacity to release the active nucleoside in animals (rabbits and dogs) in a dose-dependent manner. The compounds were less toxic in MT-4 and HL-60 cell cultures and experimental animals compared with AZT. Major metabolites found in MT-4 cells after their incubation with AZT 5′-aminocarbonylphosphonate 1 were AZT and AZT 5′-phosphate (25 and 55%, respectively). Among the tested compounds, phosphonate 1 was the most effective AZT donor, and its longest t1/2 and Tmax values in the line phosphonate 1 - AZT H-phosphonate - AZT imply that compound 1 is an extended depot form of AZT. Although bioavailability of AZT after oral administration of phosphonate 1 was lower than those of AZT H-phosphonate and AZT (8 against 14 and 49%), we expect that this reduction would not cause essential decrease of antiviral activity but noticeably decrease toxicity as a result of gradual accumulation of AZT in blood and the absence of sharp difference between Cmax and Cmin. Such a combination of properties makes the compounds of this group promising for further studies as extended-release forms of AZT.

dNTP modified at triphosphate residues: substrate properties towards DNA polymerases and stability in human serum.

Substrate and terminating substrate properties of dNTP with phosphate groups replaced by phosphonates at alpha-, gamma-, beta, gamma-, and alpha, beta, gamma-positions towards different human DNA polymerases and retroviral reverse transcriptases are reviewed. Substitution of the phosphate group by the phosphonate at any of the three phosphate positions of dNTP increased their stability towards dephosphorylating enzymes of human blood. In some cases hydrophobicity of these compounds was markedly enhanced.

New modified nucleoside 5′-triphosphates: synthesis, properties towards DNA polymerases, stability in blood serum and antiviral activity

A series of new nucleoside 5′-triphosphate mimetics, 2, 3, 5, 6, 8–10, modified at the glycone and all three phosphate residues, have been synthesised and studied. These compounds only bear the enzymatically labile anhydride bond between the α and β phosphorus atoms. The preparative chemistry involved the preparation of phosphonic salts 30, 31 and 32 and coupling of these species to the morpholidate 33. The mechanism of formation of some of the intermediates ‘en route’ to 27 and 28 is discussed. All of the target compounds demonstrated high stability in human blood serum with half lives towards hydrolysis of up to 4.5 days. Some of these nucleoside triphosphonates have been shown to be selective inhibitors of DNA synthesis catalysed by retroviral reverse transcriptases and terminal deoxynucleotidyl transferases. They inhibited replication of the artificial virus containing Moloney murine leukemia virus reverse transcriptase in infected cell culture, probably due to the inhibition of a reverse transcription step of a genomic RNA. Compared to the triphosphonates, the corresponding monophosphonates demonstrated decreased antiviral activity by 1–2 orders of magnitude. This implies that the triphosphonates inhibit virus replication directly, rather than by a two-step mechanism based on their hydrolysis to the monophosphonates and subsequent intracellular diphosphorylation. Being totally independent of the enzymatic phosphorylation pathways of the host cell, the compounds under study may also be able to inhibit retrovirus reproduction both in kinase deficient cell lines and in the intercellular blood media.