Hydrogen‐transfer reactions between methyl radicals and protic solvents, such as water and ethanol, have been studied at the G3(MP2)‐RAD level of theory. The typically high barriers for hydrogen abstraction from the OH group are lowered dramatically on complexation of protic solvents with BMe3. The barrier lowering is found to be a consequence of the unique properties of trialkylboranes, acting as Lewis acids towards the closed‐shell solvent, but as electron donors towards the evolving oxygen‐centered radicals.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Using a combined theoretical and experimental strategy, the heats of hydrogenation of the nucleotide bases uracil, thymine, cytosine, adenine, and guanine have been determined. The most easily hydrogenated base is uracil, followed by thymine and cytosine. Comparison of these hydrogenation enthalpies with those of ketones and aldehydes derived from sugar models indicates the possibility of near-thermoneutral hydrogen transfer between uracil and the sugar phosphate backbone in oligonucleotides.

4-(2-(4-Halophenyl)hydrazinyl)-6-phenylpyridazin-3(2H)-ones 1a,b were prepared and treated with phosphorus oxychloride, phosphorus pentasulphide and ethyl chloroformate to give the corresponding chloropyridazine, pyridazinethione, oxazolopyridazine derivatives 2–4, respectively. Compound 2 reacted with hydrazine hydrate to afford hydrazinylpyridazine 7. The reaction of 4-(2-(4-chlorophenyl)hydrazinyl)-3-hydrazinyl-6-phenylpyridazine (7) with acetic anhydride, p-chlorobenzaldehyde and carbon disulphide gave the corresponding pyridazinotriazine derivatives 8–10. On the other hand, 5-(4-chlorophenylamino)-7-(3,5-dimethoxybenzylidene)-3-phenyl-5H-pyridazino[3,4-b][1,4]thiazin-6(7H)-one (11) was prepared directly from the reaction of compound 3 with chloroacetic acid in presence of p-chlorobenzaldehyde. Compound 11 reacted with nitrogen nucleophiles (hydroxylamine hydrochloride, hydrazine hydrate) and active methylene group-containing reagents (malononitrile, ethyl cyanoacetate) to afford the corresponding fused compounds 12–15, respectively. Pharmacological screening for antiviral activity against hepatitis A virus (HAV) was performed for the new compounds. 4-(4-Chlorophenylamino)-6-phenyl-1,2-dihydropyridazino[4,3-e][1,2,4]triazine-3(4H)-thione (10) showed the highest effect against HAV.

New substituted pyrazole, thiazole, and 1,2,4‐triazole derivatives were synthesized. The sugar hydrazones, their acetylated derivatives as well as their derived acyclic C‐nucleoside analogs, and the thioglycosides of the 1,2,4‐traizole derivatives were also prepared. The antitumor activity of some of the synthesized compounds were studied, and a number of the tested compounds showed significant activities.

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