Synthesis of pyrazolo[4',3':5,6]pyrano[2,3-d]pyrimidine derivatives for antiviral evaluation

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).