6-Amino-5-imino-pyrazolo[4',3':5,6]pyrano[2,3-d]pyrimidine derivative 4 and pyrazolo-[4',3':5,6]pyrano[2,3-d]pyrimidin-5-ylhydrazine derivative 5 were prepared starting from 6-amino-3-methyl-4-(p-nitrophenyl)-2,4-dihydropyrano[2,3-c]pyrazole-5-carbonitrile 1. The synthesis and structure characterization of 9,11-dihydropyrazolo[4',3':5,6]pyrano[3,2-e][1,2,4]triazolo[4,3-c]pyrimidine derivatives 7 and 9 and their isomerization to 9,11-dihydropyrazolo[4',3':5,6]pyrano[3,2-e] [1,2,4]triazolo[1,5-c]pyrimidine derivatives 6 and 8, respectively, under different suitable reaction conditions are reported. Moreover, the synthesis of 9,11-dihydropyrazolo[4',3':5,6]pyrano[3,2-e] tetrazolo[1,5-c]pyrimidine derivative 14 and N(9)-acyclic nucleoside 15 are described. Some of the prepared products showed potent antimicrobial activity.

Some novel cyclic and acyclic pyridazine and triazolopyridazine nucleoside derivatives were prepared. Some of the prepared products were selected and tested for antiviral activity against herpes simplex virus type‐1 (HSV‐1) and hepatitis‐A virus (HAV, MBB‐cell culture adapted strain). Plaque reduction infectivity assay was used to determine virus count reduction as a result of treatment with test compounds. Compound 15 showed the highest effect on the HAV than the other tested compounds. © 2007 Wiley Periodicals, Inc. Heteroatom Chem 18:274–282, 2007; Published online in Wiley InterScience (http://www.interscience.wiley.com). DOI 10.1002/hc.20296

6-Amino-3-methyl-4-(4-nitrophenyl)-2,4-dihydropyrano[2,3-c]pyrazole-5-carbonitrile (1) was used as a precursor for preparation of some novel 3,7-dimethyl-4-(4-nitrophenyl)-2,4-dihydropyrazolo[4',3':5,6]pyrano[2,3-d]pyrimidine derivatives 3-6, and some of their corresponding N(2)- and C(5)-S-acyclic nucleosides 7 and 8. Furthermore, the preparation of 5-amino-1-[3,7-dimethyl-4-(4-nitrophenyl)-2,4-dihydropyrazolo[4',3':5,6]pyrano[2,3-d]pyrimidin-5-yl]-1H-pyrazole derivatives 10-16 were described. Some of the prepared products were selected and tested for antiviral activity against Herpes Simplex Virus type-1 (HSV-1).

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Reaction of 6‐amino‐2‐methylthiouracil and 6‐amino‐1,3‐dimethyluracil with equimoler amounts of cyclic ketones or cyclic 1,3‐diketones and the appropriate aromatic aldehydes yielded regioselectivity a series of polycyclic pyrimido[4,5‐b]quinoline and pyrido[2,3‐d]pyrimidine derivatives in good yields.