Triazole-Modified Nucleic Acids for the Application in Bioorganic and Medicinal Chemistry.

This review covers studies which exploit triazole-modified nucleic acids in the range of chemistry and biology to medicine. The 1,2,3-triazole unit, which is obtained via click chemistry approach, shows valuable and unique properties. For example, it does not occur in nature, constitutes an additional pharmacophore with attractive properties being resistant to hydrolysis and other reactions at physiological pH, exhibits biological activity (i.e., antibacterial, antitumor, and antiviral), and can be considered as a rigid mimetic of amide linkage. Herein, it is presented a whole area of useful artificial compounds, from the clickable monomers and dimers to modified oligonucleotides, in the field of nucleic acids sciences. Such modifications of internucleotide linkages are designed to increase the hybridization binding affinity toward native DNA or RNA, to enhance resistance to nucleases, and to improve ability to penetrate cell membranes. The insertion of an artificial backbone is used for understanding effects of chemically modified oligonucleotides, and their potential usefulness in therapeutic applications. We describe the state-of-the-art knowledge on their implications for synthetic genes and other large modified DNA and RNA constructs including non-coding RNAs.

Nucleoside dimers analogs containing floxuridine and thymidine with unnatural linker groups: synthesis and cancer line studies. Part III.

Two series of novel fluorinated nucleosides dimers with an unnatural 1,2,3-triazole linkage were synthesized. The obtained molecules were prepared using "click" chemistry approach based on copper(I) catalyzed Huisgen azide-alkyne cycloaddition. It was performed between 3'- and 5'-azido-nucleosides as the azide components, and the 3'-O- and 5'-O-propargyl-nucleosides as the alkyne components. Based on analysis of the 3 JHH, 3 JH1'C2 and 3 JH1'C6 we estimated conformational preferences of sugar part and orientation around glycosidic bond. All described nucleosides dimers analogs were characterized by spectroscopic methods and evaluated for their in vitro cytotoxicity in three human cancer cell lines: cervical (HeLa), oral (KB) and breast (MCF-7).

Nucleoside dimers analogues with a 1,2,3-triazole linkage: conjugation of floxuridine and thymidine provides novel tools for cancer treatment. Part II.

The fluorinated nucleoside dimers with a 1,2,3-triazole linkage are novel compounds within the field of bioorganic chemistry. We report on the synthesis and properties of two groups of nucleoside dimers analogs possessing a different arrangement of the 1,4-disubstituted 1,2,3-triazole linkage. Based on analysis of the 3JHH, 3JH1'C2, and 3JH1'C6 we estimated conformational preferences of sugar part and orientation around glycosidic bond. These compounds show moderate anticancer activity, with cytostatic studies in three different cancer cell lines.

Aryl H-phosphonates. 19. New anti-HIV pronucleotide phosphoramidate diesters containing amino- and hydroxypyridine auxiliaries.

We have designed a new type of AZT and ddU phosphoramidate diesters containing various combinations of 2-, 3-, 4-aminopyridine and 2-, 3-, 4-hydroxypyridine moieties attached to the phosphorus center, as potential anti-HIV pronucleotides. Depending on the pKa values of the aminopyridines and the hydroxypyridines used, alternative synthetic strategies based on H-phosphonate chemistry were developed for their preparation. Synthetic aspects of these transformations and the biological activity of the synthesized compounds are discussed.

Synthesis and biological assay of new 2'-deoxyuridine dimers containing a 1,2,3-triazole linker. Part I.

We describe a simple method for the synthesis of modified dinucleosides containing pyrimidine nucleoside analogues (2'-deoxyuridine, thymidine and 5-fluoro-2'-deoxyuridine). Six different dimers with a 1,2,3-triazole linkage were obtained by azide-alkyne 1,3-dipolar cycloaddition (click reaction), starting from propargylated 2'-deoxyuridine and 5'-azido-nucleoside derivatives. Their cytotoxic activity was tested in five human cancer cell lines: cervical (HeLa), high grade gliomas (U-118 MG, U-87 MG, T98G), liver (HepG2), and normal human fibroblast cell line (MRC-5) using the sulforhodamine B (SRB) assay. The experiment showed that the obtained dimers with a 1,2,3-triazole moiety were very stable compounds, also in the physiological-like media, and had no anticancer activity.

Thermodynamic, structural and fluorescent characteristics of DNA hairpins containing functionalized pyrrolo-2'-deoxycytidines.

Herein, we present comprehensive physicochemical and structural analysis of various DNA hairpins modified with pyrrolo-2'-deoxycytidine (Py-dC) derivatives. The introduction of modified Py-dC in most cases causes minor decrease of hairpin thermodynamic stability. The energetically unfavorable effect is more pronounced when modified residue is present within hairpin loop. Our studies indicate that thermodynamic effects induced by all Py-dC derivatives are net results of increased stacking interactions caused by larger surface of pyrrolo-2'-deoxycytidine aromatic ring and unfavorable effect implied by the presence of additional side chains. The CD spectra of all modified hairpins are similar to unmodified hairpin indicating that the presence of Py-dC derivatives does not disrupt the secondary structure of DNA. Interestingly, the presence of various side chains can increase fluorescent discrimination of paired and unpaired regions of DNA. The fluorescence observed for hairpins modified within loop is significantly quenched when Py-dC derivative is present in the stem region.

Searching for anti-glioma activity. Ribonucleoside analogues with modifications in nucleobase and sugar moieties.

Several ribonucleoside analogues with modifications in the nucleobase and sugar moiety have been screened for anti-glioma activity in the T98G glioma cell line using cervical (HeLa) cell line as reference human malignant cells, and lung fibroblast (MCR-5) cell line as non-cancerous reference cells. Among the investigated compounds, ribonucleosides containing 6-chloropurine (3), 7-guanine (5) and a pyrrolopyrimidine (18) as nucleobases, show promising anti-glioma activity with good selectivity indices, and can be considered as lead structures for further anti-cancer studies.

Regioselective Mitsunobu Reaction of Partially Protected Uridine.

Mitsunobu reaction of partially acylated uridine proceeds with high regioselectivity for intramolecular SN2 anhydro linkage closuring. Under the reaction conditions, an isomeric mixture of diacyl uridine derivatives with either free 2'- or 3'-hydroxyl group was transformed into a single cyclonucleosidic product, 2,2'-anhydro-3',5'-di-O-acyluridine. This paper presents a possible mechanism of the reactions, the explanation of observed phenomenon based on semiempirical and density functional theory (DFT) calculations and possible utility of this synthetic pathway.

Base-Modified Nucleosides: Etheno Derivatives.

This review presents synthesis and chemistry of nucleoside analogs, possessing an additional fused, heterocyclic ring of the "etheno" type, such as 1,N(6)-ethenoadenosine, 1,N(4)-ethenocytidine, 1,N(2)-ethenoguanosine, and other related derivatives. Formation of ethenonucleosides, in the presence of α-halocarbonyl reagents and their mechanism, stability, and degradation, reactions of substitution and transglycosylation, as well as their application in the nucleoside synthesis, have been described. Some of the discussed compounds may be applied as chemotherapeutic agents in antiviral and anticancer treatment, acting as pro-nucleosides of already known, biologically active nucleoside analogs.

New 3'-O-aromatic acyl-5-fluoro-2'-deoxyuridine derivatives as potential anticancer agents.

New aromatic and aliphatic 3'-O-acyl-5-fluoro-2'-deoxyuridine derivatives were synthesized and evaluated as candidates for prodrugs against various cancer cell lines. As the most promising candidate for antimalignant therapeutics was found a dual-acting acyl derivative 7h, which apparently released not only the known anticancer nucleoside, 5-fluoro-2'-deoxyuridine (FdU), but also an additional active metabolite, acetylsalicylic acid, reinforcing thus therapeutic effect of FdU. Promising therapeutic indices showed also some aromatic dicarboxylic acids derivatives decorated with FdU esters (11 and 12).

3'-O- and 5'-O-Propargyl Derivatives of 5-Fluoro-2'-Deoxyuridine: Synthesis, Cytotoxic Evaluation and Conformational Analysis.

A series of new 3'-O- and 5'-O-propargyl derivatives of 5-fluoro-2'-deoxyuridine (1-4) was synthesized by means of propargyl reaction of properly blocked nucleosides (2,4), followed by the deprotection reaction with ammonium fluoride. The synthesized propargylated 5-fluoro-2'-deoxyuridine analogues (1-4) were evaluated for their cytotoxic activity in three human cancer cell lines: cervical (HeLa), oral (KB) and breast (MCF-7), using the sulforhodamine B (SRB) assay. The highest activity and the best SI coefficient in all of the investigated cancer cells were displayed by 3'-O-propargyl-5-fluoro-2'-deoxyuridine (1), and its activity was higher than that of the parent nucleoside. The other new compounds exhibited moderate activity in all of the used cell lines.

Aryl H-Phosphonates 18. Synthesis, properties, and biological activity of 2',3'-dideoxynucleoside (N-heteroaryl)phosphoramidates of increased lipophilicity.

Recently, AZT (N-pyridyl)phosphoramidates were reported as a new type of potential anti-HIV therapeutics. In continuation of that work, here we present new (N-heteroaryl)phosphoramidate derivatives of antiviral 2',3'-dideoxynucleosides containing other types of N-heteroaryl moieties, particularly those with higher lipophilicity. The present studies comprise mechanistic investigations using (31)P NMR correlation analysis, which permitted improvements in the synthetic procedures. The obtained compounds were tested in biological systems to establish their cytotoxicity and anti-HIV activity. The results were analyzed with respect to possible correlations between biological and physico-chemical properties of the phosphoramidates studied, to get some insight into their antiviral mode of action.

Bioactive fused heterocycles: Nucleoside analogs with an additional ring.

The following mini-review summarizes the basic literature data regarding synthesis, biological activity, structure-activity relationship, and discussion of the mechanisms of action of two major classes of nucleoside analogs with fused heterocyclic rings: (i) the ethenonucleosides and their related derivatives of the 5,9-dihydro-3-glycosyl-6-alkyl-9-oxo-5H-imidazo[1,2-a]purine type; (ii) the bicyclic nucleosides of 6-alkyl-2,3-dihydrofurano[2,3-d]-pyrimidin-2(3H)-one and 6-alkyl-2,3-dihydropyrrolo[2,3-d]-pyrimidin-2(3H,7H)-one.

Aryl H-phosphonates 17: (N-aryl)phosphoramidates of pyrimidine nucleoside analogues and their synthesis, selected properties, and anti-HIV activity.

New synthetic protocol for the preparation of nucleoside 5'-(N-aryl)phosphoramidate monoesters 4 was developed. It consisted of a condensation of the corresponding nucleoside 5'-H-phosphonates with aromatic- or heteroaromatic amines promoted by diphenyl phosphorochloridate, followed by oxidation of the produced H-phosphonamidates with iodine/water. 5'-(N-Aryl)phosphoramidate monoesters derived from 3'-azido-3'-deoxythymidine (AZT) or 2',3'-dideoxyuridine (ddU) nucleosides and various aromatic and heteroaromatic amines were evaluated as potential anti-HIV drugs. It was found that these compounds act most likely as pronucleotides and that some of them have therapeutic indices superior to those of the reference AZT.

A fluorescence correlation spectroscopy study of ligand interaction with cytokinin-specific binding protein from mung bean.

Cytokinins are essential plant hormones that regulate numerous physiological processes. Recently, a protein was identified in mung bean (Vigna radiata) and characterized as a cytokinin-specific binding protein (VrCSBP). Fluorescence correlation spectroscopy was used to investigate the interaction between VrCSBP and its ligands. The synthetic cytokinin, N-phenyl-N'-(4-pyridyl) urea, was labeled with two fluorophores, 7-nitro-2,1,3-benzoxadiazole and rhodamine B. Protein-ligand binding was analyzed in an equilibrium saturation binding experiment and confirmed by the competition assay. Surprisingly, it was found that VrCSBP binds not only to cytokinins, but also to gibberellins. In addition, in the presence of natural cytokinins and gibberellins, two populations of VrCSBP that differ in their diffusion coefficients were detected. The diffusion coefficients of these two populations could be related to mono- and dimeric states, which suggests a new mode of operation in ligand binding by VrCSBP, in which dimerization induced by natural ligands enhances the ligand binding capacity of the protein.

Aryl nucleoside H-phosphonates. Part 16: synthesis and anti-HIV-1 activity of di-aryl nucleoside phosphotriesters.

Di-aryl nucleoside phosphotriesters have been explored as a new type of pronucleotides for the purpose of anti-HIV-1 therapy and efficient synthetic protocols, based on H-phosphonate chemistry, have been developed for the preparation of this class of compounds. It was found that anti-HIV-1 activity of the phosphotriesters bearing an antiviral nucleoside moiety (AZT, ddA) and also ddU was due, at least partially, to intracellular conversion into the corresponding nucleoside 5'-monophosphates, and their efficiency correlated well with the pK(a) values of the aryloxy groups present.

Synthesis and antiviral evaluation of 2'-C-methyl analogues of 5-alkynyl- and 6-alkylfurano- and pyrrolo[2,3-d]pyrimidine ribonucleosides.

A series of novel 2'-C-methylribonucleosides, involving 5-iodo and 5-alkynyl uridine analogues as well as related bicyclic furano- and pyrrolo[2,3-d]pyrimidinone compounds, has been synthesized and evaluated for their inhibitory effect on replication of the hepatitis C virus (HCV). The new nucleoside analogues did not show meaningful anti-HCV activity.

Synthesis and antiviral activity of novel derivatives of 2'-beta-C-methylcytidine.

A series of novel derivatives of 2'-C-beta-methylcytidine, involving nucleosides modified in the "upper part" of the pyrimidine base (N(4)- and/or 5-position), has been synthesized and evaluated for their inhibitory effect on in vitro replication of the hepatitis C virus and the yellow fever virus (both Flaviviridae).

Synthetic analogs of natural glycosides in drug discovery and development.

Secondary metabolites, which have vital environmental and allelopathic functions for a host, and long tradition of ethnopharmacological applications preceding modern medicinal use, often occur in their native state as glycosides. The role of sugar moiety looks completely different from plant physiology point of view and from drug discovery and development perspective. Based on a short survey of cases, in which structural modification of natural glycone (saccharide part of a low molecular weight secondary metabolite) resulted in advantageous pharmacological changes, we postulate that glycosides of natural origin can be quite promising as drug leads, based on general rules of drug design. In particular, polyfunctional sugar moieties offer ample opportunities for almost continuous changes in shape, electron density and polarity. By the same token, glycosylation of other biologically active natural products, which are not natively glycosylated, can be viewed as a tool for tune up of their activity in direction of higher efficacy and better selectivity. Despite of considerable advances towards turning enzymatic glycosylations into biotechnological processes, chemical transformations still remain more practical, particularly for synthesis of modified glycosides, both: in research laboratory and in industry.

New analogs of acyclovir substituted at the side chain.

A series of novel analogs of acyclovir, substituted with an alkyl (methyl, ethyl, n-butyl) or phenyl group at the positions 1', 4', and/or 5', has been obtained in a direct one-pot coupling reaction of guanosine and the respective 1,3-dioxolanes. The new acyclonucleosides were essentially inactive in antiviral (HSV, VV, VSV, HBV) evaluation in vitro.