Abstract
4-Imino-1-p-tolyl-1,4-dihydropyrazolo[3,4-d]pyrimidin-5-ylamine (2) and (1-p-tolyl-1H-pyrazolo[3,4-d]pyrimidin-4-yl)-hydrazine (3) were prepared starting from ethyl 4-cyano-1-p-tolyl-1H-pyrazol-5-ylimidoformate (1). The structure of compound 3 was confirmed through preparation of the pyrazole derivatives 4 and 5. Also, the synthesis and structural characterization of pyrazolo[4,3-e][1,2,4]triazolo[4,3-c]pyrimidine derivatives 7 and 9 and their isomerization to pyrazolo[4,3-e][1,2,4]triazolo[1,5-c]pyrimidine derivatives 6 and 8, respectively, under different suitable reaction conditions were reported. Moreover, the syntheses of 2-substituted-pyrazolo[4,3-e][1,2,4]triazolo[1,5-c]pyrimidine derivatives 10 and 11 was described.
Highlights
As part of our ongoing research program on heterocyclic compounds which may serve as leads for designing novel chemotherapeutic agents, we were interested in pyrazoles and fused pyrazolopyrimidines [1,2]
Pyrazolo[3,4-d]pyrimidines and their related fused heterocycles are of considerable significance chemical and pharmaceutical utility as purine analogs [3] and many of their derivatives were reported to possess antiviral [1,4] antimicrobial [2,5] anti-inflammatory [6,7]
The synthesis of fused triazolopyrimidine moieties has been described by many investigators and these compounds have been proved to have pronounced biological activities [2,10,11,12,13]
Summary
As part of our ongoing research program on heterocyclic compounds which may serve as leads for designing novel chemotherapeutic agents, we were interested in pyrazoles and fused pyrazolopyrimidines [1,2]. Previous observations revealed that the [1,2,4]triazolo[4,3-c]pyrimidine derivatives can isomerize under different suitable reaction conditions to the thermodynamically more stable [1,2,4]triazolo[1,5c]pyrimidines [14,15,16]. This isomerization was first reported by Miller and Rose [17,18] when they treated [1,2,4] triazolo[4,3-c]pyrimidine derivatives with an acid, base, or thermally. Based on the above mentioned research results, the goal of this study is to synthesize some novel pyrazolopyrimidine, pyrazolotriazolo[4,3-c]pyrimidines and pyrazolotriazolo[1,5-c]pyrimidines to study their isomerization, and to obtain new compounds which are expected to possess notable pharmacological applications
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