SAR studies of 9-norbornylpurines as Coxsackievirus B3 inhibitors

9-Norbornyl-6-chloropurine (NCP) induces cell death through GSH depletion-associated ER stress and mitochondrial dysfunction

9-Norbornyl-6-chloropurine (NCP) is a representative of a series of antienteroviral bicycle derivatives with selective cytotoxicity towards leukemia cell lines. In this work we explored the mechanism of the antileukemic activity of NCP in T-cell lymphoblast cells (CCRF-CEM). Specifically, we searched for a potential link between its ability to induce cell death on the one hand and to modulate intracellular glutathione (GSH) that is necessary to its metabolic transformation via glutathione-S-transferase on the other hand. We have observed that GSH levels decreased rapidly in NCP-treated cells. Despite a complete regeneration following 24h of incubation with NCP, this profound drop in cellular GSH content triggered ER stress, ROS production and lipid peroxidation leading to the loss of mitochondrial membrane potential (MMP). These events induced concentration-dependent cell cycle arrest in G2/M phase and apoptosis. Both MMP loss and apoptosis were reversed by sulfhydryl-containing compounds (GSH, N-acetyl-l-cysteine). Furthermore, we have also shown that NCP-induced GSH decrease activated the Nrf2 pathway and its downstream targets

NAD(P)H

quinone oxidoreductase (NQO-1) and glutamate cysteine ligase modifier subunit (GCLm), thus explaining the fast restoration of GSH pool and ROS decrease. Importantly, we confirmed that the cell death-inducing properties of the compounds were co-dependent on their ability to diminish cellular GSH level by analyzing the relationships between the GSH-depleting potency and cytotoxicity in a series of other norbornylpurine analogs. Altogether, the results demonstrated that in CCRF-CEM cells NCP triggered apoptosis through GSH depletion-associated oxidative and ER stress and mitochondrial depolarization.

New carbocyclic N(6)-substituted adenine and pyrimidine nucleoside analogues with a bicyclo[2.2.1]heptane fragment as sugar moiety; synthesis, antiviral, anticancer activity and X-ray crystallography

New nucleoside analogues with an optically active bicyclo[2.2.1]heptane skeleton as sugar moiety and 6-substituted adenine were synthesized by alkylation of 6-chloropurine intermediate. Thymine and uracil analogs were synthesized by building the pyrimidine ring on amine 1. X-ray crystallography confirmed an exo-coupling of the thymine to the ring and an L configuration of the nucleoside analogue. The library of compounds was tested for their inhibitory activity against influenza virus A∖California/07/09 (H1N1)pdm09 and coxsackievirus B4 in cell culture. Compounds 13a and 13d are the most promising for their antiviral activity against influenza, and compound 3c against coxsackievirus B4. Compounds 3b and 3g were tested for anticancer activity.

Norbornane-based nucleoside and nucleotide analogues locked in North conformation

We report on the synthesis of novel conformationally locked nucleoside and nucleotide derivatives, which are structurally closely related to clinically used antivirals such as didanosine and abacavir. As a suitable conformationally rigid substitute of the sugar/pseudosugar ring allowing a permanent stabilization of the nucleoside in North conformation we employed bicyclo[2.2.1]heptane (norbornane) substituted in the bridgehead position with a hydroxymethyl group and in the C-3 position with a nucleobase. Prepared nucleoside derivatives were also converted into appropriate phosphoramidate prodrugs (ProTides) in order to increase delivery of the compounds in the cells. All target compounds were evaluated in a broad antiviral and cytostatic assay panel.

From norbornane-based nucleotide analogs locked in South conformation to novel inhibitors of feline herpes virus

A synthetic route toward a series of unique cyclic nucleoside phosphonates locked in South conformation is described. The desired conformation is stabilized by a substitution of the sugar moiety by bicyclo[2.2.1]heptane (norbornane) bearing a purine or pyrimidine nucleobase in the bridgehead position. Although the final phosphonate derivatives are devoid of any significant antiviral activity probably due to the unfavorable conformational properties, several intermediates and their analogs exhibit surprising activity against feline herpes virus. Since these compounds do not possess an appropriate hydroxymethyl function allowing phosphorylation and subsequent incorporation into the polynucleotide chain, it seems to be likely that these compounds act by a novel unknown mechanism of action and may represent a new possible alternative for nucleoside and nucleotide therapeutics of this widely spread feline infection. A number of derivatives exerted also a significant antiviral activity against Coxsackievirus B3 and B4.

C6-substituted purine derivatives: an experimental and theoretical 1H, 13C and 15N NMR study

We measured the (1)H, (13)C and (15)N chemical shifts for a series of purine derivatives bearing a norbornane substituent in position 9 and various substituents in position 6. The experimental data were complemented with density functional theory (DFT) calculations. The comparison of the calculated and experimental chemical shifts provided us with information about the tautomer and conformational equilibria of the studied compounds.