Synthesis of 2′-Deoxyribonucleoside Derivatives of 1-Deazapurine

Differential reactivity of α and β 2′-deoxyribonucleosides towards protonation and metalation

The reactivity of artificial 2'-deoxyribonucleosides, designed as nucleoside surrogates in metal-mediated base pairs, towards protonation and metalation has been shown to be dependent on the choice of the anomer. The alpha nucleosides comprising the aglycones imidazole, 1,2,4-triazole, benzimidazole and imidazo[4,5-b]pyridine are more basic than the respective beta nucleosides as was shown by a combined experimental and theoretical approach. The DeltapK(a) values observed experimentally are in the range of 0.19+/-0.03 to 0.41+/-0.07 (with the error representing three times the standard deviation of the mean value). An independent confirmation of this differential reactivity was obtained from density functional theory (DFT) calculations using 1,2,4-triazole nucleoside as an example. The result of these calculations is in good agreement with the experimental data (DeltapK(a)=0.16 vs. 0.21+/-0.07). The stability of the respective metal ion complexes of the anomeric 1,2,4-triazole nucleosides follows the same trend as that of the respective protonated nucleosides: Those of the alpha nucleoside are more stable than those of the beta nucleoside (Deltalogbeta(2)=0.6+/-0.2 for the 2:1 complex with Ag(+); Deltalogbeta(1)=0.51+/-0.07 for the 1:1 complex with Hg(2+)). These slightly different reactivities will be useful for fine-tuning the metal-ion binding behavior of oligonucleotides containing metal-mediated base pairs.

Adenine and deazaadenine nucleoside and deoxynucleoside analogues: inhibition of viral replication of sheep MVV (in vitro model for HIV) and bovine BHV-1

A series of N(6)-cycloalkyl-2',3'-dideoxyadenosine derivatives has been prepared by coupling of 2,6-dichloropurine to protected 2,3-dideoxyribose, followed by reaction with appropriate cycloalkylamines. Synthesized compounds, along with other purine nucleoside analogues previously synthesized in our laboratory, have been tested for their antiviral activity against Bovine herpesvirus 1 (BHV-1) and sheep Maedi/Visna Virus (MVV), the latter being an in vitro and in vivo model of Human Immunodeficiency Virus (HIV). All compounds showed good antireplicative activity against MVV, with the N(6)-cycloheptyl-2',3'-dideoxyadenosine (5b) being the most active [effective concentration (EC(50)) causing 50% reduction of cytopatic effects (CPE)=27 nM]. All compounds showed also a from low to very low cell toxicity, resulting in a cytotoxic dose 50 (CD(50))/EC(50) ratio in some cases higher than 1000.

Structure-activity relationships of bisphosphate nucleotide derivatives as P2Y1 receptor antagonists and partial agonists

The P2Y1 receptor is present in the heart, in skeletal and various smooth muscles, and in platelets, where its activation is linked to aggregation. Adenosine 3',5'- and 2',5'-bisphosphates have been identified as selective antagonists at the P2Y1 receptor (Boyer et al. Mol. Pharmacol. 1996, 50, 1323-1329) and have been modified structurally to increase receptor affinity (Camaioni et al. J. Med. Chem. 1998, 41, 183-190). We have extended the structure-activity relationships to a new series of deoxyadenosine bisphosphates with substitutions in the adenine base, ribose moiety, and phosphate groups. The activity of each analogue at P2Y1 receptors was determined by measuring its capacity to stimulate phospholipase C in turkey erythrocyte membranes (agonist effect) and to inhibit phospholipase C stimulation elicited by 10 nM 2-(methylthio)adenosine 5'-diphosphate (antagonist effect). 2'-Deoxyadenosine bisphosphate analogues containing halo, amino, and thioether groups at the 2-position of the adenine ring were more potent P2Y1 receptor antagonists than analogues containing various heteroatom substitutions at the 8-position. An N6-methyl-2-chloro analogue, 6, was a full antagonist and displayed an IC50 of 206 nM. Similarly, N6-methyl-2-alkylthio derivatives 10, 14, and 15 were nearly full antagonists of IC50 < 0.5 microM. On the ribose moiety, 2'-hydroxy, 4'-thio, carbocyclic, and six-membered anhydrohexitol ring modifications have been prepared and resulted in enhanced agonist properties. The 1,5-anhydrohexitol analogue 36 was a pure agonist with an EC50 of 3 microM, i.e., similar in potency to ATP. 5'-Phosphate groups have been modified in the form of triphosphate, methyl phosphate, and cyclic 3',5'-diphosphate derivatives. The carbocyclic analogue had enhanced agonist efficacy, and the 5'-O-phosphonylmethyl modification was tolerated, suggesting that deviations from the nucleotide structure may result in improved utility as pharmacological probes. The N6-methoxy modification eliminated receptor affinity. Pyrimidine nucleoside 3', 5'-bisphosphate derivatives were inactive as agonists or antagonists at P2Y receptor subtypes.

Modulation of apoptosis in human lymphocytes by adenosine analogues

We previously described that 2-chloroadenosine (2CA) and 2-chloro-2'-deoxyadenosine (2CdA) induced apoptosis in human peripheral blood mononuclear cells (PBMC). In this study we tested different adenosine analogues on PBMC and we found that the modifications introduced in the 2CA structure prevented the molecule from exerting its apoptotic effect. On the other hand, substitutions on 2CdA are tolerated, although with a significant decrease in activity.