Vladimir E. Oslovsky

Chemical modification of the plant isoprenoid cytokinin N6-isopentenyladenosine yields a selective inhibitor of human enterovirus 71 replication

In this study, we demonstrate that N(6)-isopentenyladenosine, which essentially is a plant cytokinin-like compound, exerts a potent and selective antiviral effect on the replication of human enterovirus 71 with an EC50 of 1.0 ± 0.2 μM and a selectivity index (SI) of 5.7. The synthesis of analogs with modification of the N(6)-position did not result in a lower EC50 value. However, in particular with the synthesis of N(6)-(5-hexene-2-yne-1-yl)adenosine (EC50 = 4.3 ± 1.5 μM), the selectivity index was significantly increased: because of a reduction in the adverse effect of this compound on the host cells, an SI > 101 could be calculated. With this study, we for the first time provide proof that a compound class that is based on the plant cytokinin skeleton offers an interesting starting point for the development of novel antivirals against mammalian viruses, in the present context in particular against enterovirus 71.

Cytokinin Nucleosides - Natural Compounds with a Unique Spectrum of Biological Activities.

Cytokinin nucleosides exhibit antitumor, antiviral, antiprotozoal, blood pressure reducing, anti-inflammatory, and antipsychotic activity. These compounds also influence platelet aggregation and exhibit some other biological activities. Cytokinins are N6-substituted adenines and represent an important group of phytohormones with diverse biochemical functions in plants, stimulating cell division and plant growth. The main structural feature of cytokinin nucleosides is the presence of a hydrophobic hydrocarbon moiety at the N6-position of adenosine. This moiety is responsible for a difference in physicochemical and biological properties as compared to adenosine. 1-N-Tuberculosinyladenosine and N6-tuberculosinyladenosine are specifically produced by Mycobacterium tuberculosis as components of the plasmatic membrane, thus making them attractive targets for clinical test development. Structurally related compounds were found in marine organisms. It has been shown also that tRNA contains N6-isoprenyladenosine and some other related compounds. This review summarizes the structural features, biological activity, and the synthesis of cytokinin nucleosides and some of their closely related derivatives such as cytokinins and terpene derivatives of adenine.

Fluorination of Naturally Occurring N6-Benzyladenosine Remarkably Increased Its Antiviral Activity and Selectivity

Recently, we demonstrated that the natural cytokinin nucleosides N6-isopentenyladenosine (iPR) and N6-benzyladenosine (BAPR) exert a potent and selective antiviral effect on the replication of human enterovirus 71. In order to further characterize the antiviral profile of this class of compounds, we generated a series of fluorinated derivatives of BAPR and evaluated their activity on the replication of human enterovirus 71 in a cytopathic effect (CPE) reduction assay. The monofluorination of the BAPR-phenyl group changed the selectivity index (SI) slightly because of the concomitant high cell toxicity. Interestingly, the incorporation of a second fluorine atom resulted in a dramatic improvement of selectivity. Moreover, N6-trifluoromethylbenzyladenosine derivatives (9–11) exhibited also a very interesting profile, with low cytotoxicity observed. In particular, the analogue N6-(3-trifluoromethylbenzyl)-adenosine (10) with a four-fold gain in potency as compared to BAPR and the best SI in the class represents a promising candidate for further development.

Synthesis of N6‐Substituted Adenosines as Cytokinin Nucleosides

This unit describes preparation of N6‐substituted adenosines (cytokinin nucleosides), a unique class of compounds with a wide spectrum of biological activities. Regioselective alkylation of N6‐acetyl‐2′,3′,5′‐tri‐O‐acetyladenosine with alkyl halides under basic conditions or alcohols under Mitsunobu conditions followed by deprotection are the methods of choice for the preparation of the cytokinin nucleosides. The attractive feature of this strategy is the possibility of using a broad library of commercially available alkyl halides and alcohols under mild reaction conditions.

Regioselective 1-N-Alkylation and Rearrangement of Adenosine Derivatives.

GRAPHICAL ABSTRACT Several methods for the preparation of some N6-substituted adenosines based on selective 1-N-alkylation with subsequent Dimroth rearrangement were developed. The proposed methods seem to be effective for the preparation of natural N6-isopentenyl- and N6-benzyladenosines, which are known to possess pronounced biological activities. Direct 1-N-alkylation of 2′,3′,5′-tri-O-acetyladenosine and 3′,5′-di-O-acetyl-2′-deoxyadenosine with alkyl halides in N,N-dimethylformamide (DMF) in the presence of BaCO3 and KI gave 1-N-substituted derivatives with quantitative yields, whereas 1-N-alkylation of adenosine was accompanied by significant O-alkylation. Moreover, the reaction of trimethylsilyl derivatives of N6-acetyl-2′,3′,5′-tri-O-acetyladenosine and N6-acetyl-3′,5′-di-O-acetyl-2′-deoxyadenosine with alkyl halides leads to the formation of the stable 1-N-substituted adenosines. Dimroth rearrangement of 1-N-substituted adenosines in aqueous ammonia yields pure N6-substituted adenosines.

Novel group of tyrosyl-DNA-phosphodiesterase 1 inhibitors based on disaccharide nucleosides as drug prototypes for anti-cancer therapy

Abstract A new class of tyrosyl-DNA phosphodiesterase 1 (TDP1) inhibitors based on disaccharide nucleosides was identified. TDP1 plays an essential role in the resistance of cancer cells to currently used antitumour drugs based on Top1 inhibitors such as topotecan and irinotecan. The most effective inhibitors investigated in this study have IC50 values (half-maximal inhibitory concentration) in 0.4–18.5 µM range and demonstrate relatively low own cytotoxicity along with significant synergistic effect in combination with anti-cancer drug topotecan. Moreover, kinetic parameters of the enzymatic reaction and fluorescence anisotropy were measured using different types of DNA-biosensors to give a sufficient insight into the mechanism of inhibitor’s action.

Synthesis of Cytokinins via Enzymatic Arsenolysis of Purine Nucleosides

This unit describes an effective method for the preparation of natural cytokinins and their synthetic derivatives based on enzymatic cleavage of the N‐glycosidic bond of N6‐substituted adenosine or O6‐substituted inosine derivatives in the presence of purine nucleoside phosphorylase (PNP) and Na2HAsO4. The arsenolysis reaction is irreversible due to the hydrolysis of the resulting α‐D‐ribose‐1‐arsenate. As a result, the desired products are formed in near‐quantitative yields, as indicated by high‐performance liquid chromatography (HPLC) analysis, and can easily be isolated. In the strategy used here, the ribose residue acts as a protective group.