5-(Dimethoxymethyl)-2'-deoxyuridine: a novel gem diether nucleoside with anti-orthopoxvirus activity

An Overview of Antivirals against Monkeypox Virus and Other Orthopoxviruses

The current monkeypox outbreaks during the COVID-19 pandemic have reignited interest in orthopoxvirus antivirals. Monkeypox belongs to the Orthopoxvirus genus of the Poxviridae family, which also includes the variola virus, vaccinia virus, and cowpox virus. Two orally bioavailable drugs, tecovirimat and brincidofovir, have been approved for treating smallpox infections. Given their human safety profiles and in vivo antiviral efficacy in animal models, both drugs have also been recommended to treat monkeypox infection. To facilitate the development of additional orthopoxvirus antivirals, we summarize the antiviral activity, mechanism of action, and mechanism of resistance of orthopoxvirus antivirals. This perspective covers both direct-acting and host-targeting antivirals with an emphasis on drug candidates showing in vivo antiviral efficacy in animal models. We hope to speed the orthopoxvirus antiviral drug discovery by providing medicinal chemists with insights into prioritizing proper drug targets and hits for further development.

Drug Development against Smallpox: Present and Future

Forty years after the last endemic smallpox case, variola virus (VARV) is still considered a major threat to humans due to its possible use as a bioterrorism agent. For many years, the risk of disease reemergence was thought to solely be through deliberate misuse of VARV strains kept in clandestine laboratories. However, recent experiments using synthetic biology have proven the feasibility of recreating a poxvirus de novo, implying that VARV could, in theory, be resurrected. Because of this new perspective, the WHO Advisory Committee on VARV Research released new recommendations concerning research on poxviruses that strongly encourages pursuing the development of new antiviral drugs against orthopoxviruses. In 2018, the U.S. FDA advised in favor of two molecules for smallpox treatment, tecovirimat and brincidofovir. This review highlights the difficulties to develop new drugs targeting an eradicated disease, especially as it requires working under the FDA "animal efficacy rule" with the few, and imperfect, animal models available.

5-substituted pyrimidine L-2'-deoxyribonucleosides: synthetic, quantum chemical, and NMR studies

As a part of an ongoing medicinal chemistry, we report here the synthesis and structure evaluation of 1-(2-deoxy-3,5-di-O-acetylpentofuranosyl)-5-[(3-methyl-5-oxo-1-phenyl-4,5-dihydro-4H-pyrazol-4-ylidene) pyrimidine-2,4(1H,3H)-dione 5 and 5-[bis(3-methyl-5-oxo-1-phenyl-4,5-dihydro-4H-pyrazol-4-yl)methyl-1-(2-deoxy-3,5-di-O-acetylpentofuranosyl)pyrimidine-2,4(1H,3H)-dione 6 derived from 3',5'-di-O-acetyl-5-formyl-2'-deoxy-β-L-uridine 1. Base hydrolysis of compounds 1 and 6 furnished their deacetylated analogues in good yields, whereas hydrolysis of 5 was troublesome. Structural features of these molecules are discussed by NMR spectra analyses and density functional theory quantum chemical calculations. The newly synthesized L-analogues show no significant activity against vaccinia and cowpox viruses.

[(2R,3S,5R)-3-Acet-oxy-5-(5-formyl-2,4-dioxo-1,2,3,4-tetra-hydro-pyrimidin-1-yl)-2,3,4,5-tetra-hydro-furan-2-yl]methyl acetate

In the two independent but very similar mol-ecules (A and B) of the title compound, C(14)H(16)N(2)O(8), both six-membered pyrimidine rings are nearly planar [maximum deviations = 0.010 (3) Å in A and 0.028 (3) Å in B]. The five-membered furan-ose ring in mol-ecule A adopts an envelope conformation, while the same ring in mol-ecule B has a twisted conformation. In the crystal, the A mol-ecules are linked via a pair of inter-molecular N-H⋯O hydrogen bonds, forming dimers. Each A mol-ecule is further linked to a B mol-ecule via a second N-H⋯O hydrogen bond. There are also a number of C-H⋯·O inter-actions present, leading to the formation of a three-dimensional network.

Solvent-free synthesis of pyrimidine nucleoside-aminophosphonate hybrids and their biological activity evaluation

A novel and highly efficient one-pot three-component synthesis of alpha-aminophosphonates under neat condition was developed. By employing this method, hybrid compounds of aminophosphonate with pyrimidine nucleosides were synthesized in good to excellent yields starting from 5-formyl-2'-deoxyuridine, aniline and dimethyl phosphite. The antiviral and antileishmanial activities of these novel hybrid compounds were also studied but none were found to be active.

Antiviral Activity of 4'-thioIDU and Thymidine Analogs against Orthopoxviruses

The search for effective therapies for orthopoxvirus infections has identified diverse classes of molecules with antiviral activity. Pyrimidine analogs, such as 5-iodo-2'-deoxyuridine (idoxuridine, IDU) were among the first compounds identified with antiviral activity against a number of orthopoxviruses and have been reported to be active both in vitro and in animal models of infection. More recently, additional analogs have been reported to have improved antiviral activity against orthopoxviruses including several derivatives of deoxyuridine with large substituents in the 5 position, as well as analogs with modifications in the deoxyribose moiety including (north)-methanocarbathymidine, and 5-iodo-4'-thio-2'-deoxyuridine (4'-thioIDU). The latter molecule has proven to have good antiviral activity against the orthopoxviruses both in vitro and in vivo and has the potential to be an effective therapy in humans.

Ionic liquid mediated and promoted eco-friendly preparation of thiazolidinone and pyrimidine nucleoside-thiazolidinone hybrids and their antiparasitic activities

Without any catalyst, 2,3-disubstituted-1,3-thiazolidin-4-one derivatives were synthesized efficiently via the three-component reaction of aldehyde, amine and mercaptoacetic acid in [bmim][PF(6)]. The whole procedure is simple and straightforward and no aqueous work-up is needed. By employing this protocol, a series of novel pyrimidine nucleoside-thiazolidin-4-one hybrids were prepared and their preliminary antiparasitic activities were also studied and reported.

Ionic liquid promoted and mediated green preparation of arylbispyranylmethane and pyran derivatives and their hybrid with a pyrimidine nucleoside

The utilisation of an ionic liquid-[bmim][BF4] as both reaction medium and promoter for the reaction between aldehyde and 4-hydroxy-6-methylpyran-2-one is described. Without any added catalyst, this reaction was realised efficiently to give arylbispyranylmethane derivatives in high yields. Alternatively, when this reaction was carried out in the presence of acetic anhydride, fused pyran derivatives were obtained. These two novel procedures have advantages such as an environmentally benign nature, high efficiency, simple operation process and mild reaction conditions. As an application, these procedures were used in the preparation of novel 5-substituted pyrimidine nucleoside derivatives with potential antiviral activities.

Ionic liquid promoted preparation of 4H-thiopyran and pyrimidine nucleoside-thiopyran hybrids through one-pot multi-component reaction of thioamide

One-pot multi-component reactions of aldehydes, cyanothioacetamide and malononitrile promoted by ionic liquid proved to be an efficient way for the synthesis of thiopyran derivatives. Without any added catalyst, both aromatic and aliphatic aldehydes participated in this reaction smoothly. As an application of this method, a pyrimidine nucleoside-thiopyran chimera with potential biological activities was obtained in high yield from 5-formyl-2'-deoxyuridine. In addition, the ionic liquid used can be easily recovered and effectively reused for at least 5 times.

Biophysical characterization of vaccinia virus thymidine kinase substrate utilization

To provide information for the development of new antiviral compounds that inhibit orthopoxviruses, further characterization of the kinetics and thermodynamics that underlie substrate utilization reactions of vaccinia virus thymidine kinase (VVTK) has been undertaken. The kinetics of 2'deoxythymidine phosphorylation by VVTK and the thermodynamics of complex formation between VVTK and the substrate 2' deoxythymidine were determined using spectroscopic and calorimetric techniques. These studies demonstrated that kinetic parameters for 2' deoxythymidine phosphorylation by VVTK were 25 microM and 0.2s(-1) for K(m) and k(cat), respectively. The enthalpy change, Delta H, for the enzyme catalyzed reaction is -18.1 kcal/mol. Thermodynamic studies for the formation of the enzyme substrate complex demonstrated a binding affinity (K(a)) of 4 x 10(4)M(-1), an enthalpy change for binding (Delta H) of -17.4 kcal/mol, and a reaction stoichiometry of two molecules of substrate binding to each enzyme tetramer. Kinetic and thermodynamic data were in agreement (K(a) approximately 1/K(m)) and showed similarities to literature values reported for herpes simplex virus thymidine kinase (HSV-TK) and human thymidine kinase 1 (hTK1) with respect to k(cat) but not with respect to K(m). The K(m) value found for VVTK in this study is nearly two orders of magnitude larger than the values reported for the hTK1 and the HSV TK enzymes.

Selective phosphorylation of antiviral drugs by vaccinia virus thymidine kinase

The antiviral activity of a new series of thymidine analogs was determined against vaccinia virus (VV), cowpox virus (CV), herpes simplex virus, and varicella-zoster virus. Several compounds were identified that had good activity against each of the viruses, including a set of novel 5-substituted deoxyuridine analogs. To investigate the possibility that these drugs might be phosphorylated preferentially by the viral thymidine kinase (TK) homologs, the antiviral activities of these compounds were also assessed using TK-deficient strains of some of these viruses. Some of these compounds were shown to be much less effective in the absence of a functional TK gene in CV, which was unexpected given the high degree of amino acid identity between this enzyme and its cellular homolog. This unanticipated result suggested that the CV TK was important in the mechanism of action of these compounds and also that it might phosphorylate a wider variety of substrates than other type II enzymes. To confirm these data, we expressed the VV TK and human TK1 in bacteria and isolated the purified enzymes. Enzymatic assays demonstrated that the viral TK could efficiently phosphorylate many of these compounds, whereas most of the compounds were very poor substrates for the cellular kinase, TK1. Thus, the specific phosphorylation of these compounds by the viral kinase may be sufficient to explain the TK dependence. This unexpected result suggests that selective phosphorylation by the viral kinase may be a promising new approach in the discovery of highly selective inhibitors of orthopoxvirus replication.

Status Presens of Antiviral Drugs And Strategies: Part I: DNA Viruses and Retroviruses

More than 40 compounds have been formally licensed for clinical use as antiviral drugs, and half of these are used for the treatment of HIV infections. The others have been approved for the therapy of herpesvirus (HSV, VZV, CMV), hepadnavirus (HBV), hepacivirus (HCV) and myxovirus (influenza, RSV) infections. New compounds are in clinical development or under preclinical evaluation, and, again, half of these are targeting HIV infections. Yet, quite a number of important viral pathogens (i.e. HPV, HCV, hemorrhagic fever viruses) remain in need of effective and/or improved antiviral therapies.

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.

Structurally diverse 5-substituted pyrimidine nucleosides as inhibitors of Leishmania donovani promastigotes in vitro

The following structurally diverse 5-substituted-2'-deoxyuridine nucleosides displayed potent in vitro antileishmanial activity: 5-formyl, 5-(2,2,-dicyanovinyl)-, 5-(2-cyano-2-ethoxycarbonylvinyl), 5-(2-cyano-2-methoxycarbonylvinyl)-, 5-(2-amino-3-cyano-5-oxo-5,6,7,8-tetrahydro-4H-chromen-4-yl)- and related congeners, and the 5-(3-methyl-5-oxo-1-phenyl-4,5-dihydro-4H-pyrazol-4-ylidene) group.

The Ugi reaction in the generation of new nucleosides as potential antiviral and antileishmanial agents

5-Formyl-2'-deoxyuridine-3',5'-diacetate was converted to a small library of 5-substituted pyrimidine nucleoside N-acylamino acid amides by means of a Ugi multicomponent reaction. The reaction allowed introduction of various substituents at the acyl moiety, at the amino acid alpha-amide group, and at the amino acid carboxyl function. Evaluation of these novel 5-substituted nucleosides against vaccinia virus and cowpox virus provided one compound with discernable activity against cowpox virus but five- to eightfold less active than the Cidofovir standard. More promising activity was seen for the inhibition of Leishmania donovani promastigotes. Several synthetic products showed antileishmanial activity in the 10(-5)M range. When compared to earlier studies demonstrating anti-orthopoxviral and antileishmanial activity of 5-substituted pyrimidine nucleosides, these results imply that the 5-(N-acylamino acid amide)-derivatized pyrimidine nucleosides may possess more steric bulk, greater hydrophobicity, and more flexibility than is compatible with these particular biological activities.

Toward orthopoxvirus countermeasures: a novel heteromorphic nucleoside of unusual structure

Two privileged drug scaffolds have been hybridized to create the novel heteromorphic nucleoside 5-(2-amino-3-cyano-5-oxo-5,6,7,8-tetrahydro-4H-chromen-4-yl)-1-(2-deoxypentofuranosyl)pyrimidine-2,4(1H,3H)-dione (2). Compound 2 inhibited the replication of two orthopoxviruses, vaccinia virus (VV) (EC(50) = 4.6 +/- 2.0 microM), and cowpox virus (CV) (EC(50) = 2.0 +/- 0.3 microM). Compound 2 exhibited reduced activity against a thymidine kinase (TK) negative strain of CV, implying a requirement for 5'-monophosphorylation for antiorthopoxvirus activity. Compound 2 was efficiently phosphorylated by VV TK, establishing that VV TK is more promiscuous than previously believed.