Prodrugs of imidazotriazine and pyrrolotriazine C-nucleosides can increase anti-HCV activity and enhance nucleotide triphosphate concentrations in vitro

A number of prodrugs of HCV-active purine nucleoside analogues 2'-C-methyl 4-aza-9-deaza adenosine 1, 2'-C-methyl 4-aza-7,9-dideaza adenosine 2, 2'-C-methyl 4-aza-9-deaza guanosine 3 and 2'-C-methyl 4-aza-7,9-dideaza guanosine 4 were prepared and evaluated to improve potency, selectivity and liver targeting. Phosphoramidate guanosine prodrugs (3a-3k and 4a, b) showed insufficient cell activity for further profiling. Striking enhancement in replicon activity relative to the parent was observed for phosphoramidate imidazo[2,1-f][1,2,4]triazine-4-amine adenosine prodrugs (1a-1p), but this was accompanied by an increase in cytotoxicity. Improved or similar potency without a concomitant increase in toxicity relative to the parent was demonstrated for phosphoramidate pyrrolo[2,1-f][1,2,4]triazine-4-amine adenosine prodrugs (2a-2k). Carbamate, ester and mixed prodrugs of 2 showed mixed results. Selected prodrugs of 2 were analysed for activation to the triphosphate, with most demonstrating much better activation in hepatocytes over replicon cells. The best activation was observed for a mixed phosphoramidate-3'ester (11) followed by a simple 3'-ester (10).

Derivatives of imidazotriazine and pyrrolotriazine C-nucleosides as potential new anti-HCV agents

Previous investigations identified 2'-C-Me-branched ribo-C-nucleoside adenosine analogues, 1, which contains a pyrrolo[2,1-f][1,2,4]triazin-4-amine heterocyclic base, and 2, which contains an imidazo[2,1-f][1,2,4]triazin-4-amine heterocyclic base as two compounds with promising anti-HCV in vitro activity. This Letter describes the synthesis and evaluation of a series of novel analogues of these compounds substituted at the 2-, 7-, and 8-positions of the heterocyclic bases. A number of active new HCV inhibitors were identified but most compounds also demonstrated unacceptable cytotoxicity. However, the 7-fluoro analogue of 1 displayed good potency with a promising cytotherapeutic margin.

Applying the Structure Correlation Principle to retro Diels Alder Reactions

The early stages of molecular rearrangements are often apparent in the crystal structures of molecules susceptible to that rearrangement. For example, if a particular bond is broken, or if a particular group migrates during the rearrangement, then deviations of bond distances and angles from their `standard values' along the reaction coordinate are often observed. This is the structure correlation principle,1 which holds provided the molecule exists in the ground state, in a geometry, which is similar to the transition state geometry for the reaction. In this geometry the frontier orbitals whose interactions facilitate the reaction, can mix in the ground state. This paper discusses the application of this principle to pericyclic fragmentation reactions related to the retro Diels Alder reaction, using low temperature X-ray structural analysis of a range of model substrates. The substrates can be classified on the basis of this data into three groups: (i) those that undergo a synchronous retro Diels Alder reaction, (2) those that undergo an asynchronous retro Diels Alder reaction, and (3) those that react via a 2-step process. Examples of molecules falling into these three categories are given below.

Discovery and Synthesis of C-Nucleosides as Potential New Anti-HCV Agents

Nucleoside analogues have long been recognized as prospects for the discovery of direct acting antivirals (DAAs) to treat hepatitis C virus because they have generally exhibited cross-genotype activity and a high barrier to resistance. C-Nucleosides have the potential for improved metabolism and pharmacokinetic properties over their N-nucleoside counterparts due to the presence of a strong carbon-carbon glycosidic bond and a non-natural heterocyclic base. Three 2'CMe-C-adenosine analogues and two 2'CMe-guanosine analogues were synthesized and evaluated for their anti-HCV efficacy. The nucleotide triphosphates of four of these analogues were found to inhibit the NS5B polymerase, and adenosine analogue 1 was discovered to have excellent pharmacokinetic properties demonstrating the potential of this drug class.

Batch lot variability in permeation through nitrile gloves

Many factors should be considered in the selection of chemical protective clothing, but the majority of selections are based on manufacturers' permeation data composed of average results for three replicates; usually no information about variability is provided. It was hypothesized that variability across batch lots might be considerable, and that variability may be due to cure factors that may vary from one site to another within the same company. Glass transition temperature (Tg) has been demonstrated to be an indicator of cure, and so its relationship to permeation parameters was examined. Steady state permeation rate, breakthrough detection time (BDT), cumulative permeation at 125 minutes (ASTM F1407), and Tg (ASTM E1356) were measured for two makes of nitrile gloves presumably in four batches. Tg was not related to any of the permeation parameters even though batch-to-batch variability was statistically significant for all parameters except BDT. A comparison with recent ASTM round-robin results indicates that some of the variability may be due to the method; however, manufacturer quality control must be suspected as the major source of variability based on the results of this study.

Alcoholdehydrogenase as an activating enzyme for N-nitrosodiethanolamine (NDELA): in vitro activation of NDELA to a potent mutagen in Salmonella typhimurium

N-Nitrosodiethanolamine (NDELA), a potent carcinogen, has not so far been found to be mutagenic in a wide range of test systems. In particular, mutagenicity testing in Salmonella typhimurium with rat liver S-9 mix or microsomal fraction used for activation has failed to indicate mutagenicity. However, when incubated with alcohol dehydrogenase (ADH) in the presence of NAD, NDELA is converted to a potent mutagen. A possible mechanism of activation comprises the generation of an aldehyde as a primary metabolite formed by NAD/ADH and its subsequent rearrangement into cyclic intermediates. The latter might either be further metabolized or spontaneously decompose into various alkylating agents and glycolaldehyde. Standard test conditions used for the Ames test will not favor the detection of mutagens to be activated by NAD/ADH because they require the presence of NADPH, whereas ADH needs NAD to become an activating enzyme, as shown for NDELA.

Fluoro-substituted N-nitrosamines. 1. Inactivity of N-nitrosobis(2,2,2-trifluoroethyl)amine in carcinogenicity and mutagenicity tests

N-Nitroso-bis(2,2,2-trifluoroethyl)amine (hexafluorodiethylnitrosamine, 6-F-DEN) was synthesized as a derivative of diethylnitrosamine (DEN) with blocked terminal C-atoms to avoid metabolic oxidation at this site. Chronic oral administration of 6-F-DEN in drinking water did not induce tumours in Sprague-Dawley and in Fischer 344 rats. On the other hand, equimolar doses of DEN or even much lower ones are clearly carcinogenic. Mutagenicity tests using Salmonella typhimurium strains TA 1535 and TA 100 and metabolic activation by rat liver S-9 fraction were equally negative with 6-F-DEn. The substitution of fluorine in the beta-position of DEn apparently inhibits the alpha-oxidation considered necessary for carcinogenesis and mutagenesis of dialkylnitrosamines.